Giant sunspots are giant

By Phil Plait | November 9, 2011 8:40 am

Active Region 1339 — a huge cluster of sunspots which appeared on the Sun a few days ago — is still going strong. "Amateur" astronomer Alan Friedman took a devastating picture of the 100,000 km-wide-grouping:

[Click to embiggen.]

This picture was taken using an Hα filter, which picks out the light from warm hydrogen, and really shows the texture of the solar surface. I added the Earth in there just to give you a taste of how fracking huge this cluster is; the scale should be pretty close. Obviously, several of the individual spots in AR 1339 are as big or bigger than our entire planet, in case you happened to feel too big for your britches today.

… but still. The thing is, we’re starting to understand sunspots, better than any time in human history before us. Heck, a few centuries ago most people didn’t know sunspots even existed, and if you had said they did — violating the Aristotelian perfection of the heavens — they would’ve laughed at you. If you were lucky. Some folks had a really hard time dropping Aristotle’s influence.

And not only that, we can now routinely capture incredible images of these spots and present them on the internet, where an entire planet can see them and gasp at their size and beauty. I posted my own imaging attempts on Google+ last weekend, for that matter.

Chinese curses be damned: we do live in interesting times, and I’m glad. I wouldn’t have it any other way.

Image credit: Alan Friedman, used by permission.


Related posts:

For your viewing pleasure: Active Region 1302
Seriously jaw-dropping picture of the Sun
The boiling, erupting Sun
The birth of a sunspot cluster

Comments (118)

  1. CJSF

    Breathtaking! But, Phil, what the heck is this with “Chinese curses?” I don’t get it.

    CJSF

  2. Awesome, mind boggling stuff.

    “than **out** entire planet”

  3. Bette Noir

    Is it just me, or does the surface of the sun look like guinea pig fur?

    CJSF: There’s an American saying that “May you live in interesting times” is a Chinese curse, as in wars, droughts, famines make for interesting reading in the history books.

  4. Maria

    “May you live in interesting times” is supposedly an English translation/bastardization of an old Chinese curse/proverb.

    /edit *pets the sun* :P

  5. Timmy

    Wow, that overlay of the Earth really puts it into perspective.
    I hope I never lose my keys on the Sun, because I would NEVER find them…

  6. Douglas Troy

    I keep waiting for one of these “Phil modified pictures” to show up on a Blog or Tabloid with the title “Earth Hurdling Toward Sun! Government Hides Truth!”.

  7. For some reason, the Yakko’s Universe song from Animaniacs comes to mind. Yes, it was a kid’s show (and the animation took liberties with scale/distance), but it was quite a fun song for kids to put matters into perspective.

    And we’re part of a vast interplanetary system
    Stretching seven hundred billion miles long.
    With nine planets and a sun; we think the Earth’s the only one
    That has life on it, although we could be wrong.
    Across the interstellar voids are a billion asteroids
    Including meteors and Halley’s Comet too.
    And there’s over fifty moons floating out there like balloons
    In a panoramic trillion-mile view.

    And still it’s all a speck amid a hundred billion stars
    In a galaxy we call the Milky Way.
    It’s sixty thousand trillion miles from one end to the other
    And still that’s just a fraction of the way.
    ‘Cause there’s a hundred billion galaxies that stretch across the sky
    Filled with constellations, planets, moons and stars.
    And still the universe extends to a place that never ends
    Which is maybe just inside a little jar!

    (NOTE: This was written/sung back when Pluto was still considered a planet.)

  8. Crux Australis

    I sing that song to my kids as part of their bedtime routine! With minor modifications to metric units, “eight planets”, etc.

  9. Daniel J. Andrews

    I sing another song to my nephew and niece…the one from Monty Python The Meaning of Life. My sis won’t let me babysit them anymore…apparently, I’m the one that needs being kept an eye on. Sing one song, give them one book (There’s a Hair in my Dirt by Gary Larson), and you’re on probation till the kids are 18.

  10. I wanted to use this as a background, but there’s a pesky earth in the way. Gonna have crack out the photoshop.

  11. I don’t know why, but looking at these clusters with the Earth there for size comparison got a pretty big emotional reaction out of me. I just got for a fraction of a second, an emotional understanding of how huge that is… My eyes are wet. I think some people would call that a religious experience (but not me).

  12. mikie burkhart

    I have see sunspots by using my telescope to project the sun image. (As every Astronomy book says : DON’T LOOK AT THE SUN DIRECTLY THRO A TELESCOPE UNLESS YOU WANT TO LOSE YOUR EYESITE and I would not use Solar filters either, if there are scratches chips or cracks in them the harmfull rays will get thro and damage your eyes the only safe way is to use the telescope to project the sun image on to a pice of paper) The interesting thing about sunspots is that they look dark because there cooler then the rest of the sun but if you could take one off the sun it would outshine a full moon.

  13. Banger

    It is nice to see our young sun hitting puberty. A little astringent should clear those right up.

  14. Ron1

    @1. CJSF Said: “But, Phil, what the heck is this with “Chinese curses?” I don’t get it.”

    I think Phil is thinking along the same lines as Charles Dickin’s who wrote, in A Tale of Two Cities, “It was the best of times, it was the worst of times”.

    This really is a great time to be alive, regardless of all the bad stuff happening in the world.

    Cheers

  15. @Michel, I think we need a new term for experiencing something that gives you a profound sense of wonder/interconnectedness/beauty/etc. Everything that a religious experience entails minus the “god” part. A “scientific experience” just doesn’t cut it. Sounds too dry. Perhaps, in honor of the fact that today would have been Carl Sagan’s 77th birthday, we should call it a Saganistic Experience.

  16. Messier Tidy Upper

    Size is relative.

    As this :

    http://www.youtube.com/watch?v=HEheh1BH34Q

    Youtube clip shows.

    Plus this one :

    http://www.youtube.com/watch?v=2FwCMnyWZDg

    which starts with another great Carl Sagan quote. :-)

    Time – the other component of spacetime is relative too as this :

    http://www.youtube.com/watch?v=yFqbm_94nTM

    youtube clip of Carl Sagan’s Cosmic Calendar thought-provokingly and dramatically illustrates.

  17. Marc

    @12, if I remember correctly, the only types of telescopes that you can project with are refracting telescopes. I think I heard that reflecting telescopes are NOT suitable for projections of the sun. Hence why the solar filters.

  18. CR

    You know, it’s always cool to hear that some sunspots are as big as Earth, and some are even bigger. But WOW, that whole “a picture’s worth a thousand words” thing just kicks right in with pics like this!

    Think of it: everything you know from firsthand experience, every location you’ve ever been to around the globe (or just around your local town), every person you’ve ever met… almost all of our human history… it’s all on that tiny blue, brown and white globe.

    And it all fits into a dark splotch on the face of the sun. Wow. Or yikes. I’m at a loss to describe it…

  19. Messier Tidy Upper

    @ ^ CR : “And it all fits into a dark splotch on the face of the sun. “

    The sun? Which sun? Proxima Centauri? Barnard’s Star? Van Maanen’s Star? Oh wait you mean *our* Sun don’t you? ;-)

    Yeah, very true – and our Earth also fits inside the Great Red Spot on Jupiter (x four, if memory serves) and even into the erstwhile Great Dark Spot on Neptune too. :-)

    @ 7. TechyDad :” NOTE: This was written/sung back when Pluto was still considered a planet.”

    Some of us – me included still consider it one. ;-)

  20. @7. TechyDad : “For some reason, the Yakko’s Universe song from Animaniacs comes to mind.”

    This the one :

    http://www.youtube.com/watch?v=hmlrI74fwa0

    you mean?

    @9. Daniel J. Andrews : “I sing another song to my nephew and niece…the one from Monty Python The Meaning of Life.”

    Ditto for :

    http://www.youtube.com/watch?v=YAlqdunLAL0&feature=related

    WARNING : Mild obscenity warning. Language possibly very slightly Not Safe For Work at the very end of that linked clip.

    Whilst for something completely (well okay not all that completely but rather) different, see :

    http://www.youtube.com/watch?v=SDnM40P5Qx0&feature=results_video&playnext=1&list=PLED5347E948BC4093

    for another installment in this musical astronomical interlude.

    (Featuring guest appearances by plaster Galileo & stone Copernicus. ;-) )

  21. Nigel Depledge

    TechyDad (16) said:

    A “scientific experience” just doesn’t cut it. Sounds too dry.

    Hmm, perhaps.

    To my mind this conjures a memory of scraping my reaction product off the lab ceiling after a little . . . erm . . . injudicious use of phosphorous oxychloride, combined with an inadequacy of thinking.

  22. Nigel Depledge

    MTU (20) said:

    Some of us – me included still consider it one.

    Oh, man, should I bite, or leave it be?

    Sorry everyone, I can’t leave it.

    MTU, please explain, using reason rather than emotional appeals, why you still consider Pluto to be a planet as opposed to merely the largest known KBO.

  23. Infinite123Lifer

    Giant sunspots are giant

    Indeed Phil. I like the title. Sometimes less is more.

  24. Awsome picture! Does anyone know what exactly causes the sun spots?

  25. Chuck P.

    Nigel @24
    You haven’t read many BA comment threads have you?

  26. CR

    Chuck P. @27
    Actually, I think Nigel’s name has popped up a lot in the comments over the past few months/years. That’s why he was debating actually ‘biting or leaving it be’… like the rest of us, he’s seen the floodgates get opened on many occasions!
    I’ll bring the popcorn, you bring the drinks, Nigel can bring some comfy chairs for us to sit on (since he’s the one opening the floodgatges this time, though arguably it’s MTU’s fault for bringing it up in the first place), and we can enjoy the fray!

    Just to be clear, I say all this in good cheer for the spirit of fun, not to pick on anyone.

  27. @24. Nigel Depledge :

    MTU (20) said: “Some of us – me included still consider it [Pluto] one.”
    Oh, man, should I bite, or leave it be? Sorry everyone, I can’t leave it. MTU, please explain, using reason rather than emotional appeals, why you still consider Pluto to be a planet as opposed to merely the largest known KBO.

    I thought I’d already explained this many times here haven’t I?

    For the record, here’s my list of 12 reasons why the IAU decision was wrong :

    * 12 REASONS WHY PLUTO *IS* A PLANET :

    1) The orbital clearing condition which is the reason for eliminating Pluto is fatally flawed because it is itself too hard to define – what is meant by “cleared” & how far from the planet must the orbit be “cleared”? Strictly speaking this eliminates any object in our solar system as all planets (except perhaps Mercury?) have objects – comets and asteroids crossing their orbits, Jupiter has Trojan asteroids, Neptune has Pluto crossing its orbit, Earth has numerous near-earth asteroids such as Eros and so forth. A consistent application of this criterion would technically exclude all the planets of our solar system!

    NB. Coming up with definitions for what is meant by a “cleared orbit” is a superfluous excericise and fails the Occams Razor test.

    2) A reductio ad absurdum examination also reveals that this “orbital clearance” criterion fails because it leads to absurd results ruling out objects we’d clearly consider planets based on their location – a Jupiter or Earth-type planet hypothetically located in the Oort cloud would be excluded yet we’d clearly still call it a planet otherwise! Why then draw the line at smaller objects that would otherwise fit the planetary description ie. rounded by their own gravity and directly orbiting the Sun? (Or their common centre of gravity for “double planets.”)

    Oh & another “orbital clearing absurdity” : an iceball smaller than Pluto (But still gravitatioonally rounded (eg, Ceres or even Vesta mass) captured around an otherwise planetless and diskless O type star could be considered to be a planet whereas a Jupiter mass around a star with a thick disk of material wouldn’t be.

    3) In relation to forming planetary systems including historically our own, planetary orbits cross and interact in unpredictable ways. By the IAU’s “orbital clearance” criterion, these objects – even ones Jupiter sized and above – are NOT strictly planets because their orbits are not yet cleared – again failing the ‘reductio ad absurdum’ test. Eg : The earth before it was hit by the Mars-sized body that became our moon would NOT have been termed a “planet” because it had that Mars-sized object in its orbital path.

    4) From point 3 above, we see that by IAU definitions planets cannot collide because their neighbourhood then isn’t clear – nor can they exist as binaries or “double planets” by the same logic. This appears contrary to common-sense and consistency. It also has potential for creating trouble with exoplanets given the so-far hypothetical but quite probable possibility that some extrasolar planets may exist in this form – even potentially twin Neptunes or Jupiters. Given that some would describe the Earth-Moon system as well as the Pluto-Charon one as such a ‘double planet’ then a strict definition of the IAU rule may rule our Earth out of planetary status again clearly a ridiculous proposition!

    5) Inconsistency and inapplicability in regard to exoplanets – the IAU definition excluded planets of other stars. Yet surely planets orbiting other suns are no less planets for not orbiting our star! Even more tellingly, at least one of the Pulsar planets, PSR B 1257+12 e is tiny – smaller than our Moon and smaller than Pluto raising a glaring inconsistency. Given PSR1257+12 e is counted as an exoplanet then Pluto, equally, should equally count as a planet for the sake of consistency.

    6) The “dwarf planet-dwarf” star analogy – just as dwarf stars are still stars so surely are dwarf planets still planets. Extrapolating the “dwarf planets don’t count” line to stellar astronomy would imply the Sun is not a proper star nor are 99 % of all stars – those 90% on the main-sequence and the 10 % of “stellar corpses” such as white dwarfs and neutron stars. Moreover, as with stars, the smaller the object’s size the greater its numbers! Therefore calling a planet “dwarf” should NOT rule it out of being considered a proper planet.

    7) “Classical” problems with the “classical” planets term : the IAU defined “classical”; planets are restricted to our Earth’s solar system and it is hard to see how they apply to exoplanets or how the term can work usefully as a scientific description. Apart from differing immensely – Earth and Pluto are arguably far more similar worlds than Earth and Jupiter or Mercury or Neptune – they also clash with a previous understanding arguably much more apt of classical planets being those visible to the “classical” age peoples – the five original bright wanderers – Mercury, Venus, Mars, Jupiter, & Saturn. If that ‘classical’ term is retained, it seems best used in this sense as a historical and descriptive sense.

    8) Sentimental, cultural and historical reasons – noting Pluto’s long-established and culturally scientific place as a recognised planet from its discovery in 1930 until its demotion in 2006. This also covers the slight to Clyde Tombaugh’s memory, widow and family plus the perceived political aspect of stripping from planetary status the sole planet discovered by an American.

    9) The undemocratic manner in which the IAU ruling was made. For instance, of the 10,000 IAU members only 2,500 attended the 2006 Prague meeting that demoted Pluto and rejected the other planetary candidates, Eris, Charon and Ceres from planetary status. Furthermore, of those 2,500 only the merest handful – just 424 actually got to vote making therefore a very unrepresentative decision. Among those to excluded from voting and arguing their case in that last minute meeting were some highly relevant and articulate people – notably Pluto expert Alan S. Stern, head of the New Horizons mission. Stern’s summary of the IAU judgement was blunt :

    “ … idiotic. I have nothing but ridicule for this decision.”

    Source : Alan Stern, P.28, ‘Astronomy Now’ magazine, October, 2006.

    10) The decision to demote Pluto has had a generally negative reception from the general public and on public perceptions of astronomers. It has , in short and understandably, broughtastronomy into disrepute and is bad for the science and its practioners.

    11) The first proposed IAU definition of ‘planet’ (that would have included Pluto, Eris and Ceres) was much better in terms of logical consistency and general application as well as being more easily explained, understand and applied – ie. two main criteria for planets are that they are objects circling a star directly which are not themselves stars or brown dwarfs and are rounded by their own gravity.

    12) Pluto is a complex world with the key aspects of planets – it dominates its own satellite system of four moons (Charon, Hydra, Nix and the latest to be found P4 2011), has its own atmosphere, has a complex geology and weather system (of nitrogen frosting based on HST images and theory) and meets all the criteria for planethood with the sole exception of the problematic and, I believe, absurd “orbital clearance” criterion.

    ***

    Hopefully, there won’t be too many more years that pass before the IAU’s decision is reversed and Pluto re-instated as a planet along with Eris and Ceres!

    My preferred definition would be that a planet is an object that :

    1) Is round or rounded by its own gravity thus not a comet or asteroid.

    2) Isn’t and has never been self-luminous by core nuclear fusion thus not a star or brown dwarf

    &

    3) Doesn’t directly orbit another planet thus not a moon.

    Yes, that would mean lots of planets which would then be broken down into categories such as gas giant (eg. Jupiter), rock dwarf (eg. Earth) and ice dwarf (eg. Eris) and our solar system could be divided into the three main zones – the rocky, the gassy and the icy! I think a broader more inclusive definition (pretty much at the animal mineral vegetable level of astronomy where animal =star, mineral =planet and vegetable = smaller bodies) is best esp. given the surprises exoplanets have since delivered us!

    Although I think Ken Croswell’s alternative definition – again at odds with the IAUs bad idea – is another reasonable alternative.

    *****
    “…Marc Buie can very easily imagine what it must be like to walk around on Pluto: with less than 1% of your weight on Earth because of the low gravity, at temperatures of 230 degrees below zero, in the twilight because the Sun is nothing more than a dazzling star in the black sky, across snowfields of methane ice and transparent crystals of frozen nitrogen and with a gigantic moon hanging overhead – at least if you are on the right side of the planet.”
    – Page 61, ‘The Hunt For Planet X’, Govert Schilling, Copernicus Books, 2009.

  28. BTW. Click on my name for Ken Croswell’s definition and perspective on this.

    He (& I) and Alan Stern are far from alone in this matter.

    Its also worth noting that we now know that Pluto may well be larger than Eris after all and no further larger objects have been found in the Edgeworth-Kuiper belt to date.

    It will be interesting to see the reaction when NewHorizons flies past Pluto in 2015 if this silly & widely rejected IAU decree hasn’t already been reversed by then.

    I think future generations will find the temporary demotion of Pluto – and its fellow ice dwarfs – among the more farcical and absurd episodes of astronomy history and wonder how the IAU could ever have been so ludicrously silly as to do such a thing.

  29. A trio of other things to reflect on considering Pluto’s case :

    As Croswell notes here :

    http://kencroswell.com/HD45364.html

    We have gas giant exoplanets in orbits analogous to Pluto & Neptune’s orbital relationship. Would we call these planets “dwarfs” and not proper planets – I don’t think so!

    Pluto is also in some respects remarkably earth-like – arguably next to Mars as one of the more similar worlds to ours :

    http://kencroswell.com/NitrogenInPlutosAtmosphere.html

    It too has a large moon, seasons and a mainly nitrogen atmosphere. Pluto is far more like what most people consider a planet to be than Jupiter is!

    Then there’s the implications raised by this question :

    http://kencroswell.com/PlutoQuestion2.html

    which I’ll let people guess at for themselves if they haven’t seen it before. The earlier Pluto question Croswell asks is also thought provoking.

    As is the article now linked to my name here via ABC online science which again provides another perspective and demonstrates once more that the IAU got it wrong in Prague. The sooner they correct their mistake admit they got it badly wrong and restore Pluto to full planethood the better. The longer the IAU leave it the worse it’ll look for them.

  30. Nigel Depledge

    @ MTU (29) –

    OK, I’ll try to go point by point.

    MTU (29) said:

    I thought I’d already explained this many times here haven’t I?

    No.

    You have accused the IAU of many things, but you have never backed up your assertions with actual facts, and your arguments have more often been emotional rhetoric rather than reason.

    For the record, here’s my list of 12 reasons why the IAU decision was wrong :

    * 12 REASONS WHY PLUTO *IS* A PLANET :

    1) The orbital clearing condition which is the reason for eliminating Pluto is fatally flawed because it is itself too hard to define – what is meant by “cleared” & how far from the planet must the orbit be “cleared”? Strictly speaking this eliminates any object in our solar system as all planets (except perhaps Mercury?) have objects – comets and asteroids crossing their orbits, Jupiter has Trojan asteroids, Neptune has Pluto crossing its orbit, Earth has numerous near-earth asteroids such as Eros and so forth. A consistent application of this criterion would technically exclude all the planets of our solar system!

    Since the definition is applied only to our solar system, this criterion is clear enough. The 8 IAU planets each dominate everything else in the vicinity of their orbit by many orders of magnitude. For instance, you mention trojan asteroids, but Jupiter’s Trojans are less than a ten-thousandth of its mass. You mention orbit-crossing asteroids and comets, but these are all gravitationally dominated by the planet if that planet happens to be anywhere near when that minor object crosses the planet’s orbit.

    Including this criterion means that only major solar system bodies count as planets. It means that future large KBOs that we discover don’t have to count as planets (because the Kuiper Belt is in no way swept clear by the gravity of any one body). And it means that you can see all 8 planets using a modest-sized telescope.

    You have complained on many occasions that this criterion is illogical, but you have never even attempted to demonstrate how it is illogical – you have merely asserted that it is.

    I agree that it may be hard to apply if you demand an unreasonable definition of “clear”; but, at the end of the day, we have a solar system that contains 8 non-stellar objects that are quite clearly gravitationally dominant within the regions of their orbits. Any first-time visitor to our solar system would naturally classify them in one category (or maybe two).

    There is an obvious and natural discontinuity between the 8 IAU planets and all the other objects in the solar system. This criterion is a way of recognising this discontinuity. To argue that the obvious discontinuity should be ignored is illogical if one is trying to classify solar system objects into sensible categories.

    Pluto is not sufficiently different from the other KBOs, nor sufficiently like the 8 IAU planets, to count as a major solar system body in its own right.

    NB. Coming up with definitions for what is meant by a “cleared orbit” is a superfluous excericise and fails the Occams Razor test.

    How so?

    You have previously mentioned that the question “how clear is clear?” is a problem, but you seem to have no issue with the “how round is round?” question. Each will be equally arbitrary, so one should have issue either with both questions or with neither. It seems to me that you raise the “how clear is clear?” question not because of logic or reason, but because it is a means whereby you can argue that Pluto should still count as a planet.

    There are plenty of instances in science where definitions become arbitrary, rather than based on fundamental properties of a thing. Previously, you have used biological taxonomy as an analogy, and I will extend that a bit here. What is the difference between a butterfly and a moth? Morphologically, most butterflies have clubbed antennae, while most moths have feathered antennae, but this is not universally the case. Behaviourally, most moths are night-flying, while most butterflies are day-flying, but this is not universally the case. In essence, then, the distinction of butterfly or moth is arbitrary, based more on an organism’s relationships to other lepidopterae than on some fundamental characteristic. If you have no problem with this, why then do you have a problem with the clearance criterion for planethood? Your arguments against the clearance criterion are actually stronger if applied to butterfly / moth distinction.

    After all, the clearance criterion exists, IIUC, to recognise the natural discontinuity that exists in solar system objects.

  31. Nigel Depledge

    MTU (29) said:

    2) A reductio ad absurdum examination also reveals that this “orbital clearance” criterion fails because it leads to absurd results ruling out objects we’d clearly consider planets based on their location – a Jupiter or Earth-type planet hypothetically located in the Oort cloud would be excluded yet we’d clearly still call it a planet otherwise! Why then draw the line at smaller objects that would otherwise fit the planetary description ie. rounded by their own gravity and directly orbiting the Sun? (Or their common centre of gravity for “double planets.”)

    This is not ludicrous. First, if there were a Jupiter-sized object in the Oort cloud, we’d already have detected it. It would, after all, spend all its time bombarding us with comets! Second, the individual size of an object is far less significant than the history of the object and how it came to form. If there were an Earth-size Oort-cloud object, it would not count as a planet, for good reasons (it would just be a whopping big Oort cloud object, not anything like any of the 8 rocky or gas planets).

    Your point here does not recognise that the definition of “planet” applies only to the solar system that we have. Sure, there may be some large objects out there that we have yet to discover, but they will simply be the largest of their kind and unlike the 8 IAU planets. Why are you so hung up on an object’s size as a key component of any classification system?

    Oh & another “orbital clearing absurdity” : an iceball smaller than Pluto (But still gravitatioonally rounded (eg, Ceres or even Vesta mass) captured around an otherwise planetless and diskless O type star could be considered to be a planet whereas a Jupiter mass around a star with a thick disk of material wouldn’t be.

    Yes, and so what? The definition of “planet” applies only and specifically to our solar system.

    Size is not everything, you know.

  32. Nigel Depledge

    MTU (29) said:

    3) In relation to forming planetary systems including historically our own, planetary orbits cross and interact in unpredictable ways. By the IAU’s “orbital clearance” criterion, these objects – even ones Jupiter sized and above – are NOT strictly planets because their orbits are not yet cleared – again failing the ‘reductio ad absurdum’ test. Eg : The earth before it was hit by the Mars-sized body that became our moon would NOT have been termed a “planet” because it had that Mars-sized object in its orbital path.

    Perhaps.

    How is this relevant to a working definition of “planet” that applies to our solar system now and in the future?

    Your reductio ad absurdum examples are indeed absurd, but you do not show that they are relevant.

  33. Nigel Depledge

    MTU (29) said:

    4) From point 3 above, we see that by IAU definitions planets cannot collide because their neighbourhood then isn’t clear – nor can they exist as binaries or “double planets” by the same logic.

    Again, this is true, as far as it goes, but since we know of no examples of such objects in our solar system, it is a purely academic point.

    This appears contrary to common-sense and consistency.

    Not really. The clearance criterion recognises a clear and natural discontinuity in the known solar system objects, while simultaneously allowing us to discover many more objects in the Kuiper Belt and (who knows, maybe one day) the Oort Cloud that won’t count as planets.

    It also has potential for creating trouble with exoplanets given the so-far hypothetical but quite probable possibility that some extrasolar planets may exist in this form – even potentially twin Neptunes or Jupiters.

    Except that, under the new definition, there is a clear distinction between exoplanets and planets. The term “planet” applies only to our solar system – and for good reason, which you may see if you think about it with a bit less hostility.

    Given that some would describe the Earth-Moon system as well as the Pluto-Charon one as such a ‘double planet’ then a strict definition of the IAU rule may rule our Earth out of planetary status again clearly a ridiculous proposition!

    Well, no. First, the barycentre of the Earth-moon system is within the Earth, which is a pretty good indicator of a planet-moon relationship as opposed to a double-planet relationship.

    Second, if Pluto-Charon is counted as a double-planet (or a double-dwarf-planet), this makes no difference to the simple fact that Pluto and Charon are – as far as anyone can tell – the largest known examples of KBOs (and Pluto is only a few km larger in diameter than Eris so it’s a close-run thing). (Well, Charon by itself is not larger than other known KBOs, but if you count the Pluto-Charon system as a single entity, then it is.)

  34. Nigel Depledge

    MTU (29) said:

    5) Inconsistency and inapplicability in regard to exoplanets – the IAU definition excluded planets of other stars. Yet surely planets orbiting other suns are no less planets for not orbiting our star!

    This is applied pragmatism that you seem to be objecting to.

    It may be many decades before we have any detailed information about exoplanets, and in the meantime we need to have a definition of planet that can be used. Maybe in 50 years’ time the definition will be changed again (it is not, after all, set in stone!).

    Exoplanets are distinguished by that prefix. In comparison with the 8 IAU planets, we know very little about any of them.

    Even more tellingly, at least one of the Pulsar planets, PSR B 1257+12 e is tiny – smaller than our Moon and smaller than Pluto raising a glaring inconsistency. Given PSR1257+12 e is counted as an exoplanet then Pluto, equally, should equally count as a planet for the sake of consistency.

    Again, you seem to consider size to be so critical, but you do not explain why this is a key criterion for you.

    It matters not how large or small an exoplanet is to count as an exoplanet. What matters is that we can detect its influence on its parent star. For all we know, some of the exoplanets we detect are merely the largest examples of a group of similar objects. For this reason (and probably for others too), we should not classify exoplanets alongside the 8 planets about which we know so much more.

  35. Nigel Depledge

    MTU (29) said:

    6) The “dwarf planet-dwarf” star analogy – just as dwarf stars are still stars so surely are dwarf planets still planets. Extrapolating the “dwarf planets don’t count” line to stellar astronomy would imply the Sun is not a proper star nor are 99 % of all stars – those 90% on the main-sequence and the 10 % of “stellar corpses” such as white dwarfs and neutron stars. Moreover, as with stars, the smaller the object’s size the greater its numbers! Therefore calling a planet “dwarf” should NOT rule it out of being considered a proper planet.

    You are drawing a parallel that, while it would make sense to have some consistency between the classification systems, demands that consistency exist. Why must there be consistency between the classification of stars and the classification of other solar system objects? With stars, size (mass) is almost everything. With planets, their relationship to other bodies in their system (including the parent star) is far more significant than their size. The IAU definition acknowledges this.

    Why can’t you?

  36. Nigel Depledge

    MTU (29) said:

    7) “Classical” problems with the “classical” planets term : the IAU defined “classical”; planets are restricted to our Earth’s solar system and it is hard to see how they apply to exoplanets or how the term can work usefully as a scientific description. Apart from differing immensely – Earth and Pluto are arguably far more similar worlds than Earth and Jupiter or Mercury or Neptune –

    If you take them out of context, yes (although Jupiter’s core was probably rather more Earthlike before it accumulated its massive atmosphere than you may care to believe). But a substantial point about the IAU definition is that it recognises the importance of context.

    they also clash with a previous understanding arguably much more apt of classical planets being those visible to the “classical” age peoples – the five original bright wanderers – Mercury, Venus, Mars, Jupiter, & Saturn. If that ‘classical’ term is retained, it seems best used in this sense as a historical and descriptive sense.

    I agree that this may cause confusion. I do not agree that the potential confusion trumps a definition of “planet” that recognises the obvious and natural discontinuity between solar system objects. Although, of course, I’d be as happy for the IAU to do away with the “classical planet” term. I do not see it as necessary.

  37. Nigel Depledge

    MTU (29) said:

    [8.]

    Sentimental, cultural and historical reasons

    Erm, yes, I was hoping you’d have something different this time. ;-)

    – noting Pluto’s long-established and culturally scientific place as a recognised planet from its discovery in 1930 until its demotion in 2006. This also covers the slight to Clyde Tombaugh’s memory, widow and family plus the perceived political aspect of stripping from planetary status the sole planet discovered by an American.

    What?

    If anything, recognising Pluto as the first-discovered KBO amplifies the significance of Tombaugh’s discovery. Pluto, being very small and very, very far away, is a difficult object to observe.

    An alteration of terminology does not in any way diminish the significance of Tombaugh’s contribution. IMO, obviously. Maybe you are taking it personally on his behalf because you are so passionately attached to the idea of Pluto being a planet?

  38. Nigel Depledge

    MTU (29) said:

    9) The undemocratic manner in which the IAU ruling was made. For instance, of the 10,000 IAU members only 2,500 attended the 2006 Prague meeting that demoted Pluto and rejected the other planetary candidates, Eris, Charon and Ceres from planetary status. Furthermore, of those 2,500 only the merest handful – just 424 actually got to vote making therefore a very unrepresentative decision. Among those to excluded from voting and arguing their case in that last minute meeting were some highly relevant and articulate people – notably Pluto expert Alan S. Stern, head of the New Horizons mission. Stern’s summary of the IAU judgement was blunt :

    “ … idiotic. I have nothing but ridicule for this decision.”

    Source : Alan Stern, P.28, ‘Astronomy Now’ magazine, October, 2006.

    So, if a definition that you agreed with had been established in a similar manner, would you still argue against the definition because of it?

    I do not know very much about the politics of the IAU meeting at which the decision was made.

    I also do not see it as relevant. The IAU can change the definition at some future meeting if its members collectively choose to do so. That they have thus far not done so indicates to me that more IAU members accept the new definition than reject it, in which case it is appropriate that it stand.

    Issues over the way in which the change was made do not make an argument that the change should not have been made.

  39. Nigel Depledge

    MTU (29) said:

    10) The decision to demote Pluto has had a generally negative reception from the general public and on public perceptions of astronomers. It has , in short and understandably, broughtastronomy into disrepute and is bad for the science and its practioners.

    Utter rubbish!

    The IAU has the right to define terms it uses in its profession, in the same way that I – being a biochemist – support the right of The Biochemical Society to redefine the term “protein” without any input from the general public should its members decide that it is appropriate to do so.

    Most members of the public will never see Pluto, except in pictures transmitted from New Horizons. As an amateur astronomer, I have never seen Pluto. I do not expect ever to be able to buy and site a telescope that has sufficient power to resolve Pluto.

    The public outcry was, I feel, blown out of proportion. Most members of the public will have forgotten about it by now. The way in which the public use the word “planet” does not really have any bearing on the way professional astronomers use the term.

  40. Nigel Depledge

    MTU (29) said:

    11) The first proposed IAU definition of ‘planet’ (that would have included Pluto, Eris and Ceres) was much better in terms of logical consistency and general application as well as being more easily explained, understand and applied – ie. two main criteria for planets are that they are objects circling a star directly which are not themselves stars or brown dwarfs and are rounded by their own gravity.

    Well, you are right if you consider size to be more important than context. There are problems with the “rounded by their own gravity” point, which you tend to gloss over (e.g. how round is round, what about the difference in rocky and icy bodies, etc.). Obviously, it has a pragmatic purpose, to ensure that we do not label as planets every last little speck of dust orbiting our star. By the same token, the “gravitational clearance” criterion to which you so vociferously object has a pragmatic purpose, to recognise the obvious and natural discontinuity that exists between the 8 IAU planets and other gravitationally-rounded bodies such as Pluto, Eris and Ceres.

    It is inconsistent of you to object to the one pragmatic and vague definition while supporting the other pragmatic and vague definition.

    So, I disagree that the definition you describe in this point is more logically consistent than the IAU definition. I would say they are equally logically consistent. You have certainly not shown that the “how round is round” question can be safely brushed under the carpet while at the same time you object to the “gravitational clearance” criterion.

  41. Nigel Depledge

    MTU (29) said:

    12) Pluto is a complex world with the key aspects of planets – it dominates its own satellite system of four moons (Charon, Hydra, Nix and the latest to be found P4 2011),

    Some asteroids also have moons. Dominating a system of moons is not purely a planetary characteristic, and is trivial in comparison with gravitationally dominating the body’s entire orbit.

    has its own atmosphere,

    So does Titan. Hell, if you’re going to count an atmosphere as rarefied as Pluto’s, then so do Triton and our Moon. Possessing an atmosphere is not a purely planetary characteristic.

    has a complex geology and weather system (of nitrogen frosting based on HST images and theory)

    Io also has complex geology. Titan also has complex weather and geology. These are not defining planetary characteristics.

    and meets all the criteria for planethood with the sole exception of the problematic and, I believe, absurd “orbital clearance” criterion.

    You claim that the “orbital clearance” criterion is absurd but you have made no real effort to demonstrate this. You simply assert it over and over again, backed up by nothing more than an argument that has no relevance to our solar system. Yes, if Earth were in the Kuiper Belt it would not count as a planet. But it isn’t in the Kuiper Belt, and that’s why the IAU definition counts it as a planet.

    Your twelfth point really does look like you are clutching at anything at all that might give your position some legitimacy, but as far as I can tell, your entire argument rests on one main point – that you personally disagree with the “orbital clearance” criterion. Furthermore, it seems to me that you only object to this criterion because it changes Pluto from having been considered to be a planet to now no longer being considered to be a planet. If you were objecting on purely logical, rational grounds, then you would have to object also to the “gravitational roundness” criterion, because this has a comparable vagueness to it and exists for comparably pragmatic reasons.

    You have not convinced me that the IAU made a mistake. You have not even addressed the purpose for which the “gravitational clearance” criterion was introduced (i.e. to recognise that a body’s context should be considered when deciding whether or not we treat it as a major solar system body or otherwise).

    Overall, therefore, I do not find any of your points to be compelling in terms of deciding the status of Pluto. Taken collectively, your arguments look progressively more desperate.

  42. Nigel Depledge

    MTU (30) said:

    BTW. Click on my name for Ken Croswell’s definition and perspective on this.

    He (& I) and Alan Stern are far from alone in this matter.

    So what? This does not change the weakness of your argument.

    Its also worth noting that we now know that Pluto may well be larger than Eris after all and no further larger objects have been found in the Edgeworth-Kuiper belt to date.

    True, but presented disingenuously. Pluto is probably only a few km larger in diameter than Eris. And the Kuiper Belt contains a whole lot of space that we have yet to examine in any detail. I would not be in the least surprised if we were, in the next few decades, to find several more objects that are roughly the same size as Pluto and Eris, and maybe one or two that are larger than Pluto.

    You’ve got to admit that the IAU definition at least means that we can guarantee that we aren’t going to be adding new planets every year or two for the next 30 years.

    It will be interesting to see the reaction when NewHorizons flies past Pluto in 2015 if this silly & widely rejected IAU decree hasn’t already been reversed by then.

    Calling it silly is childish. If anything, your attempts to argue against the IAU definition make it look more sensible, because your arguments are so weak.

    You might consider it to be “widely rejected” [sic (should have been hyphenated)] but the IAU have not overturned it since the definition was agreed. This indicates to me (as an outside observer) that more IAU members agree with it than otherwise. That hardly makes it “widely rejected”.

    I think future generations will find the temporary demotion of Pluto

    It hasn’t been “demoted”, it has been reclassified. And, IMO, its new classification recognises a fundamental difference between Pluto and the 8 IAU planets. You use language that seems intended to polarise debate rather than reach accord. Why is this?

    – and its fellow ice dwarfs – among the more farcical and absurd episodes of astronomy history and wonder how the IAU could ever have been so ludicrously silly as to do such a thing.

    Again, your childish name-calling does not strengthen your argument. Instead, it emphasises its fundamental weakness.

  43. Nigel Depledge

    MTU (31) said:

    A trio of other things to reflect on considering Pluto’s case :

    As Croswell notes here :

    [url omitted]
    We have gas giant exoplanets in orbits analogous to Pluto & Neptune’s orbital relationship. Would we call these planets “dwarfs” and not proper planets – I don’t think so!

    Well, it depends.

    Currently, they are rightly known as exoplanets. If it turns out that each object is dominant in its orbital vicinity, then they count as planet-analogues. If not, then they would count as dwarf-planet-analogues. It could also be that finding out more about such systems prompts the IAU to revise or re-word the definition of “planet”. At this stage, who can say? We know too little about such systems and the orbital context of each object.

    Pluto is also in some respects remarkably earth-like – arguably next to Mars as one of the more similar worlds to ours :

    [url omitted]

    It too has a large moon, seasons and a mainly nitrogen atmosphere. Pluto is far more like what most people consider a planet to be than Jupiter is!

    Apart from not being a unique object.

    Pluto is one of hundreds or thousands of KBOs. Yes, it is currently the largest known KBO, but there’s no reason it should remain so as we discover more KBOs (remember that it was the discovery of some large KBOs that prompted the IAU to actually define the term “planet” in the first place).

    Yes, Pluto superficially resembles the Earth, but the atmospheric resemblance is trivial, as is the seasonal one (Pluto’s seasons being largely the result of changing distance to the sun – and therefore global – rather than changes in the angle of incidence of sunlight). Pluto and Earth each have a large moon, but if the mechanism of acquisition of said moon is similar, all that means is that KBOs can get struck by large objects also. And if the mechanism of acquisition was different, then it means that this resemblance also is trivial.

    Then there’s the implications raised by this question :

    [url omitted]
    which I’ll let people guess at for themselves if they haven’t seen it before. The earlier Pluto question Croswell asks is also thought provoking.

    Well that was an interesting bit of trivia, but it is irrelevant. Pluto was not reclassified because it is small or far away – it was reclassified because it is merely one example of a large number of objects that orbit in the same region. The fact remains that Mercury, Venus, Mars, Jupiter, Saturn and Uranus don’t orbit out in the Kuiper Belt. (Neptune’s position is arguable because a KBO – Pluto – crosses its orbit, but Neptune is gravitationally dominant in that relationship.)

    And Pluto does orbit out in the Kuiper Belt, along with many other objects over which Pluto has no dominance.

    As is the article now linked to my name here via ABC online science which again provides another perspective and demonstrates once more that the IAU got it wrong in Prague. The sooner they correct their mistake admit they got it badly wrong and restore Pluto to full planethood the better. The longer the IAU leave it the worse it’ll look for them.

    You have abjectly failed to demonstrate that there is anything wrong with classifying solar system objects in such a way as to recognise that Pluto (being a KBO) is different from the 8 planets.

    Seriously, to return to the biological taxonomy parallel, your hypothetical scenarios (such as “if Earth were in the Kuiper Belt, it wouldn’t count as a planet”) are akin to someone who, on calling a spider an insect and being corrected, cries “but if it had 6 legs, it would be an insect!”.

    Ifs and buts don’t matter – the IAU definition deals with what is.

  44. Nigel Depledge

    MTU (29) said:

    I think a broader more inclusive definition (pretty much at the animal mineral vegetable level of astronomy where animal =star, mineral =planet and vegetable = smaller bodies) is best

    Except that your definition includes a vague and arbitrary boundary between planet and smaller body. Whether or not an object counts as a planet under your system depdnds as much on what it is made of as it does on how massive it is. A rocky body that is massive but irregular might be counted as an asteroid, whereas an icy body with half the mass might count as a planet because of the different plasticity of the body’s material. Why is this vague and arbitrary distinction any different from the vague and arbitrary distinction to which you object so frequently?

    Furthermore, your definition allows our solar system to keep on adding planets indefinitely as new large KBOs are discovered, but you can bet your bottom dollar that the public at large won’t keep up with the changes, so your appeal against the IAU on the grounds of public awareness of the nine “planets” is an equally valid objection to your own preferred definition. I happen to think it’s an irrelevant objection, but you are being inconsistent.

  45. flip

    Late to the game as always….

    I had a reply to MTU’s stuff, but @Nigel, #32, etc.

    As always, thank you for that enlightening explanation and rebuttal. :) Your reply is so much better than mine (that I now won’t bother posting because your points were similar but far more precise), and not just because you’re more informed about the issue than me. I learned a few things I didn’t already know, as well as clarified the stuff I did know, or thought I knew. Thanks!

  46. Nigel Depledge

    @ Flip (47) –
    Thank-you.

    It’s just a shame that MTU seems to post his comments, and then not return to the thread by the time someone has responded.

    Admittedly, it was a couple of days before I noticed that he had posted his comment, and then another day or two before I started pasting in my responses, so he might have checked back a time or two between his latest post and my first response, but at least two people are still checking this thread (thee and me), and I cannot help but wonder if MTU does not want to see a response to his comments about Pluto.

  47. flip

    I think it’s most likely that he just hasn’t returned; he certainly does start the Pluto issue often enough in other threads to see replies. I also think that, among several other issues, this is one of those ones where MTU blocks his ears and says ‘lalalala’. But given he changed his mind over climate change, maybe it just takes a while to get through and perserverance is necessary.

    I also like to read every comment before replying to a thread, so it takes me a while to comb through the backlog of posts and their respective comments. I didn’t expect anyone was still watching this thread :)

  48. @ ^ flip & 48. Nigel Depledge : Okay I hadn’t seen that anyone had replied to my eralier comments here up till now. Thought this thread was finished. If I’d known this was still going earlier then I’d have responded earlier.

    Anyhow here goes.

    @32. Nigel Depledge :

    You have accused the IAU of many things, but you have never backed up your assertions with actual facts, and your arguments have more often been emotional rhetoric rather than reason.

    As I guess you’d expect I disagree with that characterisation of my arguments Pluto~wise entirely. I’d say I’ve provided plenty of facts and logic here.

    Since the definition is applied only to our solar system, this criterion is clear enough.

    Which in itself is ridiculuous. Saying that planets are defined as objects only in our own solar system is, well, pretty silly really. Clearly other planets exists around other stars – and around no stars at all for that matter. A decent (ie non-IAU) definition has to acknowledge that and the diversity of forms planets come in surely!?

    The 8 IAU planets each dominate everything else in the vicinity of their orbit by many orders of magnitude.

    So does Pluto – it dominates Charon, Nyx, Hydra and P4. The many orders of magnitude thing only raises additional questions that, I think, violate Occam’s Razor. If your definition raises superflous questions that a betetr definition does not then science & logic says go for the simpler definition.

    For instance, you mention trojan asteroids, but Jupiter’s Trojans are less than a ten-thousandth of its mass. You mention orbit-crossing asteroids and comets, but these are all gravitationally dominated by the planet if that planet happens to be anywhere near when that minor object crosses the planet’s orbit.

    But what if they didn’t? What if an Earth-sized world wandered by and crossed the orbit – and gravitationally interacted with Jupiter or neptuen would that stop them being planets then? What if the trojan asterodis clumped together and formed an Earth sized or Mercury sized world or in other systems gas giants formed in trojan orbits? Would they not be planets?

    See a good definition of planet needs to cover all sorts of possible – so far – hypotethical eventualities that may well be discovered around other stars. A good definition therefore is a broader and more inclusive one that allows some flexibility as I see it anyway.

    Including this criterion means that only major solar system bodies count as planets.

    But that begs the question what *is* a major Solar system body? I’d describe Pluto as one along with Eris and some of the other ice dwarfs. It puts the question back into how do you define what isand isn’t “major” in our solar system – and others.

  49. Continuing :

    It means that future large KBOs that we discover don’t have to count as planets (because the Kuiper Belt is in no way swept clear by the gravity of any one body).

    Which is a silly sitaution in my view because if we find something that’s large as Mars or Earth or Jupiter out there then saying it is merely a “dwarf planet” strikes me as just nonsensical.

    Why shouldn’t a planet orbit inside an asteroid belt – if you count their trojans Jupiter and Neptune actually do just that!

    The whole “clearence criteria” just amounts to discrimination based not on what the planet is but where it orbits and means that if you put Earth further from the Sun where it can’t “clear” it’s orbit then it wouldn’t be a planet or if you put Ceres around a star with no other worlds it would become a planet and that just doesn’t strike me as reasonable at all.

    And it means that you can see all 8 planets using a modest-sized telescope.

    All 8 planets? But haven’t you heard Nigel we’ve found hundreds of them -soon to be thousands – almost all of them orbiting other stars and thus well out of amateur ‘scope viewing range! ;-)

    You’re not seriously saying that planets should be defined as visible in a amatuer astronomers telescope are you? :-o

    If so, why not keep it to those visible to unaided eyesight – the original clasical five planets (Venus, Mercury, Mars, Jupiter and Saturn.)

    You have complained on many occasions that this criterion is illogical, but you have never even attempted to demonstrate how it is illogical – you have merely asserted that it is.

    Really? Really? :roll:

    Haven’t I demonstrated exactly why the IAU definition is illogical a hundred and one times already? Could’ve sworn I had!

    I agree that it may be hard to apply if you demand an unreasonable definition of “clear”; but, at the end of the day, we have a solar system that contains 8 non-stellar objects that are quite clearly gravitationally dominant within the regions of their orbits. Any first-time visitor to our solar system would naturally classify them in one category (or maybe two).

    Not necessarily. I’d say there’s at least three classes of world here – the rocky, the gassy and the icy. We have rocky planets like Mercury, gassy ones like Saturn and icy ones like Pluto.

    The gravitational dominance thing again is dubious given interactions with Saturn and Jupiter have tipped Ouranos on its side and that planetary migration in the past has resulted in all the planets present orbits. It raises questions of how gravitionaly dominant is “gravitationally dominant” enough and where do we draw the line? I say we draw it as a strike-through through the whole notion of “gravitational dominence” being a defining factor or at least unless the object is actually orbiting another planet and thus is a moon.

  50. flip

    #50 MTU

    Saying that planets are defined as objects only in our own solar system is, well, pretty silly really. Clearly other planets exists around other stars – and around no stars at all for that matter. A decent (ie non-IAU) definition has to acknowledge that and the diversity of forms planets come in surely!?

    It’s pretty obvious that definitions are arbitrary. Language changes over time, and so does our meaning of it. For instance, the word ‘google’… is now a verb. Likewise, I’m betting if you look back at the terminology of many science subjects – heck, the word science itself – has changed over time as our understanding of things got better. Why can’t you understand that just as science needs to be tentative, so must our terminology of it? Why does it have to be set in stone? No one is saying that our solar system is cut off terminology-wise from everything else; they’re just saying that for the time being, while we learn more about other planets/galaxies, this version of the definition is what will help keep the community on the same page when using a particular word. Clearly a decent definition first has to be a working one; your expectation of it to include diversity is superfluous.

    So does Pluto – it dominates Charon, Nyx, Hydra and P4. The many orders of magnitude thing only raises additional questions that, I think, violate Occam’s Razor. If your definition raises superflous questions that a betetr definition does not then science & logic says go for the simpler definition.

    In this case, I think Occam’s razor was applied to avoid having thousands of other planets ‘introduced’ to the solar system. As said above, it’s easier to reduce 9 to 8 than go from 9 to thousands. As for ‘better’, surely it’s up to the astronomers to figure that out – which is what they did – because they’re the ones who will be using it and will need to have a consistent use of a word in order to better understand papers, review the science, and follow up on conclusions.

    But what if they didn’t?

    And here we get stuck again. Seriously, if they changed it once, they can change it again. If an Earth sized world came along and crossed the orbit, there would be *new* information which would impact on the definition. This is the whole point you seem to miss and willfully ignore: new information arose about KBOs. This impacted the definition which was found to be inexact. A new definition was created. This can happen time and time again. You seem happy enough to accept that new science changes previously held conclusions and theories, but can’t accept it for the definition of a *word*. MTU’s cognitive dissonance strikes again. Seriously, stop worrying about the “what if’s”. They’ll deal with those if/as they come along.

    See a good definition of planet needs to cover all sorts of possible – so far – hypotethical eventualities that may well be discovered around other stars. A good definition therefore is a broader and more inclusive one that allows some flexibility as I see it anyway.”

    No, a good definition is something that conveys information about a subject in a manner which is concise and understood easily by those who use it. You seem to think language should cover all possibilities. In which case, I now pronounce that ‘messy’ should also include a definition about a guy in Adelaide because there *might* just be someone out there who includes ‘mess’ in his online name. Does this make the word ‘messy’ easily understood and used by someone who just wants to know if a room in his house is ‘messy’ or ‘tidy’? Is that kind of inclusion in a definition really necessary to those who study garbology? Or could it just, maybe, be a little too broad to be useful?

    But that begs the question what *is* a major Solar system body? I’d describe Pluto as one along with Eris and some of the other ice dwarfs. It puts the question back into how do you define what isand isn’t “major” in our solar system – and others.”

    Yes, it does. And maybe that’s something they plan on discussing. But again, it’s arbitrary. Calling a cat a dog doesn’t change the fact that it’s a cat. (I won’t quote Shakespeare) It’s also something that doesn’t necessarily require an answer, so long as astronomers have a working terminology that all in the field can understand. And this is why updating definitions is a good thing, because it allows newer questions to be looked at and thought about.

  51. flip

    #51 MTU

    Which is a silly sitaution in my view because if we find something that’s large as Mars or Earth or Jupiter out there then saying it is merely a “dwarf planet” strikes me as just nonsensical.

    Arggh! Stop lighting strawmen! How hard is it to understand that this wouldn’t happen? First, they’d take each new object on a case-by-case basis I’m betting; second, the definition can change *again*.

    Sigh.. I think this tree looks familiar. We’ve been going around in circles haven’t we?

    Are you willfully ignoring the points that deal with your problems, or are you just not understanding the explanations?

    The whole “clearence criteria” just amounts to discrimination based not on what the planet is but where it orbits and means that if you put Earth further from the Sun where it can’t “clear” it’s orbit then it wouldn’t be a planet or if you put Ceres around a star with no other worlds it would become a planet and that just doesn’t strike me as reasonable at all.

    Anthropormorphism. I love it. Venus is from Venus and Mars is from Jupiter. But seriously, did you not read the above stuff about defining objects based on their *context* in the solar system? Yep, definitely the same tree.

    And you keep coming up with pretty hypotheticals that don’t actually match *our* solar system. Which, as explained to you, is what the definition is about; not hypothetical or actual planets outside of our solar system. Whilst we collect information about exoplanets, we have a working definition of our own system; when we have enough new info about exoplanets, we can then worry about how to include them or create a new/better term. Here’s a hint: if you’re waiting to define something whilst you’re collecting information, but still need to actually talk about the stuff you already know, you’re not going to have a very clear or useful discussion.

    Really? Really? :roll:

    Haven’t I demonstrated exactly why the IAU definition is illogical a hundred and one times already? Could’ve sworn I had!

    If you had, I would have changed my mind already. Or at least not been snarky in response. I know barely anything about the issue and don’t care one way or the other whether Pluto is ‘in or out’. And yet you haven’t convinced me that you’re right. So I’m going to go with, no, you haven’t demonstrated anything.

    If you could answer my question as to why you need terminology to be set in stone, that would help. You could also properly respond to terminology being decided by the people who use it and why they might want it to be concise and have everyone on the same page.

    Working in a particular field in the arts, I know a lot of specialised terminology for it. I’d bet if you came along to the ‘office’, you’d not know what we were talking about most of the time. Is it really your job to tell me if my use of a term is incorrect based on your outside perspective of the job, even though the term is used in a specific manner and aids quick and concise understanding of the activity we’re undertaking? Because if you do, you’d probably end up getting hit in the head with something, as we don’t use the global word “duck” to signal that something is about to fall. We know what our term means, and the usage of it is easy to explain. If we widened the explanation to include all possible uses, then it would end up being a useless word within our industry. Particularly as the word is a common one that has an entirely different use/definition in common parlance.

    Like I said, I don’t get your issue with it.

  52. Messier Tidy Upper

    @ ^ Flip : Well it’s not like I haven’t tried pretty hard to explain it to you! (Shrug) :-(

    Arggh! Stop lighting strawmen! How hard is it to understand that this wouldn’t happen? First, they’d take each new object on a case-by-case basis I’m betting; second, the definition can change *again*.

    So .. what? We wait for something we expect will show the definition is silly turning up and confirming that the IAU definition is silly *then* change the IAU definition because the IAU definition is silly and we already *know* it is silly and inadequate?

    Huh?

    Why not get a step ahead and say we can already tell the IAU definition is inadequate – not covering exoplanets and ice dwarfs, failing to account for sun-less rogue planets et cetera – and thereffore change a poor inadequate definition to a better one now?

    Yes, it does. And maybe that’s something they plan on discussing. But again, it’s arbitrary. Calling a cat a dog doesn’t change the fact that it’s a cat.

    Calling a cat planet a non-planet dog doesn’t change the fact that it’s a cat.

    Too easy – see how that works. ;-)

    Pluto is a planet as is Eris as is Ceres.

    I don’t get your confusion and failure tograsp my points and logic on this on this any more than you seem to get mine. :-(

  53. Messier Tidy Upper

    Continued :

    @32. Nigel Depledge :

    There is an obvious and natural discontinuity between the 8 IAU planets and all the other objects in the solar system. This criterion is a way of recognising this discontinuity. To argue that the obvious discontinuity should be ignored is illogical if one is trying to classify solar system objects into sensible categories.

    There is? I’d argue that that’s not necessarily the case – there is a spectrum of planetary bodies from those as large as Jupiter down to those as large as Ceres.

    Is the discontinuity there really any greater than that between Jupiter and Earth, the gas giants and the rock dwarfs?

    The planets with solid surfaces that youcan walk onand explore versus worlds that are more like semi-stars which are all air and no ground?

    Pluto is not sufficiently different from the other KBOs, nor sufficiently like the 8 IAU planets, to count as a major solar system body in its own right.

    Jupiter is like the other gas giants and unlike Earth and Pluto – by your logic it shouldn’t then by a planet either! ;-)

    Plnets come in a wide range and variety of forms. Jupiter is one extreme form at the high mass end of the planetary spectrum, Pluto is, well actually pretty average given there are far more ice dwarf type planets than gas giant variety worlds!

  54. Messier Tidy Upper

    Back from tea :

    You have previously mentioned that the question “how clear is clear?” is a problem, but you seem to have no issue with the “how round is round?” question. Each will be equally arbitrary, so one should have issue either with both questions or with neither. .

    I don’t think the two qualities are equal – I don’t find roundness is quite as arbitrary as a “cleared orbit” appears. Roundness is tangible, easy to calculate and it’s pretty obvious and immediately apparent. Roundness is the first thing people think of as a defining trait for what is a planet. If it looks round or gravitationally rounded by mass then it pretty much is. It just doesn’t raise as many questions as “orbital clearance” and it is intrinsic to the object rather than depending on the objects spatial and temporal relationships to other objects.

    Although, yes, I guess there’s some scope for arguing over exactly “how round is round” and, yes, there are objects like Haumea (well, actually *just* Haumea that we know of so far!) that are – quite literally – spun out of shape and would be round if their “days” were longer!

    Incidentally, Pluto is almost certainly more round than the rotationally bulging and flattened Jupiter is! ;-)

    It seems to me that you raise the “how clear is clear?” question not because of logic or reason, but because it is a means whereby you can argue that Pluto should still count as a planet.

    Hmm.. the logical fallacy and irrelevance of ascribing motives. The logic and point is there regardless of what my motives are. I make no secret of thinking the IAU definition stinks for a number of very good reasons, making Pluto a non-planet is one of them but not the only one. It is just a plain bad definition for all the reasons I’ve outlined many times before.

    In essence, then, the distinction of butterfly or moth is arbitrary, based more on an organism’s relationships to other lepidopterae than on some fundamental characteristic. If you have no problem with this, why then do you have a problem with the clearance criterion for planethood?

    So are you saying that a bad if much more minor biological definition is a good argument in favour of a bad definition of planet? I don’t think so! ;-)

  55. @33. Nigel Depledge :

    First, if there were a Jupiter-sized object in the Oort cloud, we’d already have detected it.

    Would we have? What about Tyche the one recently theorised to exist as noted in this thread by the BA? (Click on my name or see : ‘No, there’s no proof of a giant planet in the outer solar system’ posted February 14th, 2011 2:30 PM by the BA.) As well as the previous long standing theories about ‘nemeis and planet X existing. Why did we find Eris and other ice dwarfs – in part at least we found them because we were looking for other planets out beyond Pluto’s orbit.

    Second, the individual size of an object is far less significant than the history of the object and how it came to form. If there were an Earth-size Oort-cloud object, it would not count as a planet, for good reasons (it would just be a whopping big Oort cloud object, not anything like any of the 8 rocky or gas planets).

    I think that’s highly debatable actually! I’d certainly class an Earth-sized Oort cloud object as a proper planet just as I class Pluto and even Sedna as planets too.

    Why are you so hung up on an object’s size as a key component of any classification system?

    I’m not. One of my favourite lines on this issue is that a planet’s a planet no matter how small! ;-)

    Pluto is a small planet although it is also larger than many smaller ones – Haumea, Makemake, and Ceres – and equal at least in size to Eris.

    I’m NOT the one arguing that just because ice dwarfs are small and numerous that removes them from counting as proper planets y’know! ;-)

    The definition of “planet” applies only and specifically to our solar system.

    That’s (yet) another flaw in the IAU definition that I’ve already pointed out myself. So, yeah.

  56. @ 34. Nigel Depledge :

    How is this (point 3 of 12 in comment 29 – reductio ad absurdum test of the IAU definition which the IAU def fails bigtime – ed.) relevant to a working definition of “planet” that applies to our solar system now and in the future? Your reductio ad absurdum examples are indeed absurd, but you do not show that they are relevant.

    I thought you knew more about logic than this Nigel? You know what a Reductio ad absurdum’ test is right? No?

    Okay, if an argument / proposition or in this specific case leads to logically absurd consequences as found by applying the Reductio ad absurdum test then the argument / proposition / definition is logically shown to be invalid or illogical. The IAU definion of Planet fails the Reductio logic test and is therefore, QED, illogical and invalid.

    Which is very relevant indeed when the anti-Pluto definition is the whole subject at hand here! ;-)

    @35. Nigel Depledge :

    MTU (29) said: : 4) From point 3 above, we see that by IAU definitions planets cannot collide because their neighbourhood then isn’t clear – nor can they exist as binaries or “double planets” by the same logic.
    Again, this is true, as far as it goes, but since we know of no examples of such objects in our solar system, it is a purely academic point.

    No examples eh? Bzzzt, wrong, sorry. Planets that *may* potentially collide in our solar system include our Earth with Venus or Mars albeit admittedly only a slim chance in the far future because of Mercury’s erratic wanderings as one computer model apparently published in June 11 issue of the journal ‘Nature’ has found.

    Planets that did collide or interact in the past just within our own solar system include once again Earth – this time with a Mars-sized planet sometimes dubbed Theia – that led to the formation of our Moon in the Big Splash impact whilst the Caloris Basin impact on Mercury may be the result of another planetary impact that stripped Mercury’s mantle down to a minimum leaving it with a huge core relative to its size by one theory and Ouranos may have been tipped over onto its side by a huge impact – or even series of impacts according to another theory. Pluto too has probably experienced a similar event forming its moons. Then there’s the theory noted recently here that apparently explains much of our solar systems structure today by a missing fifth gas giant planet. What happened to that world – maybe, just maybe, could it have collided with and been swallowed up early on by Jupiter or one of the other gas giants?

    So, yeah, we can have colliding planets even in our solar system or at least we can if it is not ludicrously ruled out by the IAU’s “idiocy” – as Alan Stern called it.

    How about binary planets? We don’t have any in our solar system? Try Earth-Moon plus Pluto-Charon for the quartet most prominently springing to mind; several ice dwarfs known by numbers not names are also, so I gather, binary planets too.

    Mind you, that’s out of just our solar system which is a very small statistical set to derive conclusions from and one we know is lacking in some types of planet – Hot Jupiter, Eccentric Orbiters and SuperVenus type planets to name three varieties we’re missing. (Fortunately for us!)

    Moving beyond our parochial solar system limit we’ve witnessed collidng exoplanets such as those around HD 172555 and may well eventually find a number of binary planets too I hope – and also expect.

    I’ll post some article links to back this up but don’t know if they’ll get through moderation given the age of this thread. Hopefully they will sooner rather than later.

  57. Colliding planets links :
    http://www.space.com/7116-worlds-collide-deep-space.html

    Two exoplanets orbiting HD 172555 collided as detected by the Spitzer space telescope.
    http://www.space.com/6824-long-shot-planet-hit-earth-distant-future.html

    Mercury unleashes hell and planetary collision risks by going eccentrically long.

    http://www.space.com/724-pluto-hit-twin-create-moon-study-suggests.html

    On how the Pluto-Charon system as it is today resulting probably from a collision of two ice dwarfs.

    Click on my name for the “Missing gas giant” modelled for our solar system or see :

    ‘Did Jupiter toss a giant planet out of the solar system?’

    posted 2011 November 16th at 12:00 PM.

  58. Messier Tidy Upper

    Still @35. Nigel Depledge (lots of ground to cover here) :

    “This appears contrary to common-sense and consistency.”
    Not really. The clearance criterion recognises a clear and natural discontinuity in the known solar system objects, while simultaneously allowing us to discover many more objects in the Kuiper Belt and (who knows, maybe one day) the Oort Cloud that won’t count as planets.

    Even if they’re the size of Earth or Neptune or Jupiter? yeah, that is contrary to common sense and consistency! To say a planet cannot by definition orbit in the Edgeworth-Kuiper Cometary belt or Oort cloud even when by any other way of assessing it just doesn’t add up. There just isn’t a good enough reason to rule that.

    Except that, under the new definition, there is a clear distinction between exoplanets and planets. The term “planet” applies only to our solar system – and for good reason, which you may see if you think about it with a bit less hostility.

    What good reason? Why define planet only to apply to our solar system? It semes not only silly to do but also violates the Copernican principle or principle of mediocrity. In Other Words; why is our solar system special interms of being the only one to have defined planets?

    Surely a definition of planet should be universally – quite literally universally as wellas intergalactically – applicable? No?

    Plus in practice the exoplanet / planet distinction frequently just gets ignored anyhow.

    First, the barycentre of the Earth-moon system is within the Earth, which is a pretty good indicator of a planet-moon relationship as opposed to a double-planet relationship.

    However, the Moon is gradually moving furtheraway and as it does so the baryentre too shifts outwards. Ecventually after enough time has passed (admittedly geologically aeons), the barycentre will be outside the Earth’s crust and indeed our Moon may even escape into independent solar orbit. It is therefore in some sense a planet in the making!

    Second, if Pluto-Charon is counted as a double-planet (or a double-dwarf-planet), this makes no difference to the simple fact that Pluto and Charon are – as far as anyone can tell – the largest known examples of KBOs

    So? I think I’ve already said that just because a planet or double planet orbits in the Edgeworth-Kuiper Cometary belt does NOT by itself mean it isn’t a proper planet. IOW, I’m using my definition of planet here. In any case, Pluto-Charon is probably the closest thing we’ve got to a binary planet in our solar system with the Earth-Moon system the next closest thing. (With the possible exception of some of the other ice dwarf planets.)

  59. Messier Tidy Upper

    @36. Nigel Depledge :

    It may be many decades before we have any detailed information about exoplanets, and in the meantime we need to have a definition of planet that can be used.

    Agreed. But having a useable definition is NOT the same as having the IAU definition. A better definition is posisble -in fact many better definitions than the IAU one are possible and not only that, preferable as well! ;-)

    Such better definitions can also have – as a feature – their applicablity to exoplanets and a broader more inclusive sweep.

    Maybe in 50 years’ time the definition will be changed again (it is not, after all, set in stone!)

    Good thing too. Thank the FSM for that! Can’t wait until the IAU do come to their senses and change the definition to a better one. ;-)

    Again, you seem to consider size to be so critical, but you do not explain why this is a key criterion for you.

    Roundness – hydrostatic equilibrium due to mass – not size as I thought I’d made clear before. If it has enough mass to be round its a planet, if not, then not Pluto is round, Ceres is round, Vesta is not quite.

    My point is that people have been happy to call exoplanetary discoveries (eg. PSR 1257+12 e) far smaller than Pluto planets so why then not call Pluto a planet too?

    Thing is Pluto and the other ice dwarfs have been accused of being too small to count as proper planets when, in fact, Pluto is an average sized planet with worlds such as Earth being above the average in size – in much the same way that people often call our Sun an “average star” despite the fact that it is really much brighter and more massive than the real average stars which are red dwarfs. Do you not see the analogy there?

  60. There’s a lot more here to comment on – & I will get to it again – but tomorrow. (My timezone.) I need sleep.

    I have, however, found one more proof – perhaps the most powerful yet that Pluto is indeed a planet. 8)

    Click on my name and pay careful attention at the one minute twenty two second mark. That dog is always right! ;-)

    PS. I believe saying ‘Happy Thanksgiving’ or something is order for those over in the States, yes? Happy Thanksgiving then. :-)

  61. Messier Tidy Upper

    One very last comment for tonight before I turn my lights off :

    It appears to me that under the IAU definition, the universe is short on recognising an awful lot of truly remarkable, wonders-filled, marvels-rich little planets and is very, *very* much the poorer for that.

    (Guess that counts as an emotional argument – but y’know what? It is still true! ;-) )

    *****

    “… (Plutonian specialist scientist) Marc Buie can very easily imagine what it must be like to walk around on Pluto: with less than 1% of your weight on Earth because of the low gravity, at temperatures of 230 degrees below zero, in the twilight because the Sun is nothing more than a dazzling star in the black sky, across snowfields of methane ice and transparent crystals of frozen nitrogen and with a gigantic moon hanging overhead – at least if you are on the right side of the planet.”
    – Page 61, ‘The Hunt For Planet X’, Govert Schilling, Copernicus Books, 2009.

  62. Messier Tidy Upper

    @37. Nigel Depledge :

    You are drawing a parallel that, while it would make sense to have some consistency between the classification systems, demands that consistency exist.

    Um. because having a system that’s consistent is far better (& more memorable and more appealing) than having one that’s inconsistent?

    Why must there be consistency between the classification of stars and the classification of other solar system objects? With stars, size (mass) is almost everything. With planets, their relationship to other bodies in their system (including the parent star) is far more significant than their size. The IAU definition acknowledges this. Why can’t you?

    The IAU definition is clearly badly flawed. You’ve admitted its inconsistent here and its illogicalll and too restrictive and much more to boot – why can’t you acknowledge & accept that?

    @ 38. Nigel Depledge :

    But a substantial point about the IAU definition is that it recognises the importance of context.

    Eh? I think that statement itself needs to be put in context and, FWIW, I’d disagree.

    Although, of course, I’d be as happy for the IAU to do away with the “classical planet” term. I do not see it as necessary.

    Yay! we agree on something! :-)

    If “classical planet” is to mean anything at all then I think it best refers to the original “wandering stars” that were known to the Ancients.

  63. Nigel Depledge

    MTU (50) said:

    As I guess you’d expect I disagree with that characterisation of my arguments Pluto~wise entirely. I’d say I’ve provided plenty of facts and logic here.

    I disagree.

    You have presented facts, but failed to show that they are relevant. And your logic has huge gaps in it. You accused the IAU “gravitational dominance” criterion of being illogical, but you have not shown this, and your attempts to do so rely on ifs and buts that don’t apply to our solar system.

  64. Nigel Depledge

    MTU (50) said:

    Which in itself is ridiculuous. Saying that planets are defined as objects only in our own solar system is, well, pretty silly really. Clearly other planets exists around other stars – and around no stars at all for that matter. A decent (ie non-IAU) definition has to acknowledge that and the diversity of forms planets come in surely!?

    No.

    Because, while we know a great deal about the planetary objects in our solar system, we know almost nothing about such objects in general.

    Therefore, for any definition not to be silly, it must accommodate both our knowledge of our solar system and our ignorance of others.

    I grant you that the definition may need to change as we learn more about exoplanets over the next few decades, but that is no use for here and now, is it?

  65. Messier Tidy Upper

    @ ^ Expansion for clarity :

    Eh? What do you mean by context here? I think that statement itself needs to be put in context and, FWIW, I’d disagree.

    I’d say in context that our solar system has three main types of planets :

    four large gaseous giants, four more much smaller (medium sized?) rocky worlds and a whole host of icy little worlds with each planetary type occupying their own region. Inner zone – rock dwarfs, middle zone – gas giants and outer zone – ice dwarfs.

    That, to me, seems a good sentence or so summary picture of our solar system. But the lousy IAU definition (“context” or no) would warp that view by removing the whole ice dwarf category seemingly on the manifestly insufficent ground of their small size and considerable numbers.

    To use another analogy, its like saying insects aren’t animals simply because they too are exceedingly numerous and relatively small – note that excluding them would mean missing out on most of the planet’s biomass and some of the most important ecological links in the food chain. It would, IOW, give a very misleading and incorrect view of animal life.

    Ditto methinks for excluding the ice dwarfs from the planet count. Or, for that matter, the red dwarf stars – let alone all the dwarf (main-sequence) stars of which our Sun is one of the 90% – from the star count.

  66. Messier Tidy Upper

    It’s going to take a while but there’s the next installment FWIW :

    @65. Nigel Depledge : November 25th, 2011 at 5:57 am

    You have presented facts, but failed to show that they are relevant. And your logic has huge gaps in it. You accused the IAU “gravitational dominance” criterion of being illogical, but you have not shown this, and your attempts to do so rely on ifs and buts that don’t apply to our solar system.

    ER .. didn’t you see the examples which were specific to our solar system in comments #58 & #60 with links in #59?

    Colliding planet examples from our solar system :

    1. Earth & “Theia” leading to our Moon’s formation.

    2. Pluto & another ice dwarf explaining Charon’s origin plus more.

    3. Merury’s Caloris basin & explainationfor its core :matntle ratio

    4. Ouranos being tipped on its side -one well-known theory anyhow &

    5. A huge collison is also theorised as explaining tehdisparity between Mars two hemisphere -the flater northern with the Vastitas Borealis ex-ocean and the older heavily cratered Southern hemisphere.

    Binary planets in our solar system :

    I. Pluto & Charon

    II. Earth & Moon.

    III. Various ice dwarf examples – incidentally a twin planet situation may be required to explain how Neptune captured Triton with Triton’s companion escaping and Trition being left in its unusual retrograde orbit typical of captured moons.

    You are actually reading what I’m saying here right?

    Also you accuse me of having gaps in my logic – but I’ve yet to see any examples to back your claim there. What gaps exactly -examples please? How and where is my logic flawed in your view?

  67. Messier Tidy Upper

    @39. Nigel Depledge :

    If anything, recognising Pluto as the first-discovered KBO amplifies the significance of Tombaugh’s discovery. Pluto, being very small and very, very far away, is a difficult object planet to observe.

    Fixed it for you! ;-)

    An alteration of terminology does not in any way diminish the significance of Tombaugh’s contribution. IMO, obviously. Maybe you are taking it personally on his behalf because you are so passionately attached to the idea of Pluto being a planet?

    It seems pretty obvious to me that by wrongly demoting Pluto from planetary status the IAU is also demoting Tombaugh from having the honour of discovering a planet.

    Clyde Tombaugh being the only American to do so. Well apart from Mike Brown who discovered Eris, Haumea, Sedna and more.

    It does occur to my cynical side that the IAU dominated by non-Americans might have been affected by politics and anti-Americanism here because the demotion of Pluto and the ice dwarf type planets – as I’ve explained – makes no good logical sense. Seeing as there are no good logical or scientific reasons to demote Pluto and reject ice dwraf planets from the planet count; explanations that are not science based but politically based instead are left as the non-eliminated plausible explanations for why the IAu has done something so silly. This is, of course, suspicion on my part and I’ve no proof but I don’t think it is unreasonable.

    @40. Nigel Depledge :

    So, if a definition that you agreed with had been established in a similar manner, would you still argue against the definition because of it?

    Well, I am only human so perhaps not to the same extent but even if I agreed with a definition arrived at in such an anti-democratic fashion I’d certainly have misgivings about the method it was arrived at.

    Don’t *you* have any misgivings over the undemocratic, unfair way this Prague IAU definition was imposed yourself?

    Turning this question around if this had been a decidsion /definition you were unhappy with would you not point out the poor procedure and flaws that occurred in making it yourself?

  68. Messier Tidy Upper

    Continuing :

    I do not know very much about the politics of the IAU meeting at which the decision was made. I also do not see it as relevant.

    Why not? Why wouldn’t it be relevant?

    If a decision is NOT scientifically valid but seems to have been made more for unsound politicial reasons than valid logical ones – as I think the anti-ice dwarf Prague IAU decision was – then how isn’t that relevant?

    Appealing to the IAU as some sort of infallible authority here runs slap-bang into the “appeal to authority” logical fallacy.

    Just because the International Astronomical Union is supposedly in charge doesn’t mean they can’t and don’t make some grave mistakes and silly rulings. The IAU are not and should never be beyond question and rational criticism.

    An analogy to explain for y’all : If the “Mobility Aid Association Of the World” decreed (for whatever warped reasons of their own) that henceforth pogo sticks were to be called “wheelchairs” and wheelchairs called “pogosticks” would that really make a pogostick into a ‘wheelchair’ and vice-versa? Would that be reasonable and justified or utterly confusing and downright silly? Wouldn’t people in that situation be entirely justified in saying “have you lost your flippin’ minds? No way!” and rejecting the decision to call pogosticks ‘wheelchairs’ just as I and other reasonable astronomers totally reject the nonsense of saying that Pluto isn’t a planet when it clearly is?

    The IAU can change the definition at some future meeting if its members collectively choose to do so.

    Hopefully that will be exactly what happens – preferably with an apology from the IAU for getting their definition so absurdly wrong in the first place.

    That they have thus far not done so indicates to me that more IAU members accept the new definition than reject it, in which case it is appropriate that it stand.

    Well to me, it indicates simply that the current IAU bosses are too stubborn and pig headed to admit they got it wrong and correct their dreadful mistake. Hopefully that will change when the current IAU leadership does – which, frankly, can’t come too soon.

    Issues over the way in which the change was made do not make an argument that the change should not have been made.

    If the way a change came about was illegitimate then it actually *does* indicate that the change should NOT have been made.

    For instance, if a military coup replaced the US government with a military dictator wouldn’t you say the way they took power was illegitimate and so was the new dictator and the changed system of running the nation by military decree?

    If a textbook was changed from teaching evolution to Creationism by a School board packed with Creationist appointees would’nt you say that change was illegitimate based at least in part on the *way* it happened and that the change from educating kids about evolution to misinforming them with Creationist propaganda was utterly wrong?

    Or to refer back to my earlier anology – if the MAAOW decided to call pogosticks “wheelchairs” and vice versa wouldn’t you say the way they did that was wrong and the change unacceptable? ;-)

    Just because you are an organisation of experts in a particular field does NOT mean that there are no limits on your power and does NOT mean that you can change everybody’s language in a way that is plain silly.

    The Geologists Association can’t change the word “rock” to mean air.
    The Zoological Institute cannot change the word animal to exclude birds from being animals.
    The IAU cannot change the word “planet” to exclude Pluto.

  69. @41. Nigel Depledge : November 15th, 2011 at 6:47 am

    MTU (29) said: 10) The decision to demote Pluto has had a generally negative reception from the general public and on public perceptions of astronomers. It has, in short and understandably, brought astronomy into disrepute and is bad for the science and its practioners.
    Utter rubbish!</i.

    I don’t think so.

    From the article ‘Demote Pluto, or demote “planet”?’ by Jeff Foust published on the 28th August 2006 in The Space Review :

    From newspaper columns to the blogosphere to late-night television, it was hard to escape the news about the IAU’s decision, and the debate about whether it had made the right call. … (snip) … The reaction to the IAU’s decision has been surprisingly strong and deep. The Bakersfield Californian reported on how students at one elementary school voted overwhelmingly to keep Pluto a planet. A spokesperson for the Chabot Space and Science Center in Oakland, California, told a reporter that there has been a “sadness” among visitors after the IAU decision. In Boston, commuters at a suburban train station that is home to a scale model of Pluto (part of a spawling solar system model based at the Museum of Science downtown) passed judgment on the decision, with one calling it “bizarre”.

    & another article ‘Demotion of Pluto from Planetary Status’ by an unnamed author on Knol observed :

    Distant Pluto’s demotion from the status of a planet came as a disappointment to people all over the world. The well known and much loved planet was dropped from its glorious position, ending its reign as one of the celebrated planets in our solar system. This very decision has given birth to animosity in the minds of the people towards astronomers.

    Then there’s this excellent and informative article on Laurel’s Pluto Blog – which is linked to my name in this comment – which notes :

    All these developments (noted in the article- ed.) have served to strengthen support for Pluto’s planet status and for the planet status of all dwarf planets. Online discussions clearly show a tide turning in small planets’ favor. Arguments such as the claim that we cannot have too many planets because it would be too hard for kids to memorize all of them, or that the term “planet” is devalued by having a large number, or that “the experts have spoken, and it’s over,” or that support for keeping small round objects as a subclass of planets is based on sentiment and emotion are more and more frequently falling flat on their faces.
    Scientific principles rise and fall over time, not through a vote. For more than 100 years, people have failed in attempts to prove Einstein’s theory of relativity false. In just five years, the IAU planet definition has not only failed to take hold, but has lost ground and continues to do so as new evidence shows just how premature the decision was. Of Pluto and the IAU’s increasing irrelevance in the discussion, Alan Stern recently said, “I believe that most planetary scientists know it’s a planet, and we don’t need the IAU to tell us it is.” Neither, for that matter, does the general public need that.

    So that evidence seems to contradict your rather rude “rubbish” assertion and that’s just for starters.

    The IAU has the right to define terms it uses in its profession, in the same way that I – being a biochemist – support the right of The Biochemical Society to redefine the term “protein” without any input from the general public should its members decide that it is appropriate to do so.

    Really? Having the *right* to do something doesn’t necessarily make doing that thing the “right” thing to do.

    If the Biochemical Society was to decide that ‘proteins’ now meant viruses instead would you really be happy to go along with such stupidity? Honestly?

    Most members of the public will never see Pluto, except in pictures transmitted from New Horizons. As an amateur astronomer, I have never seen Pluto. I do not expect ever to be able to buy and site a telescope that has sufficient power to resolve Pluto.

    So? This is relevant how precisely?

    Peopel know about Pluto, they see images of Pluto – and its 4 moons – from Hubble and Keck and artists impressions and books and novels and TV shows like Dr Who in the popular culture.

    Physically seeing Pluto is a neat thing to accomplish but not physically seeing Pluto with one’s own eyes doesn’t mean you can’t know or care about it. For the record, I’ve yet to see Pluto through a telescope myself and yet Pluto is still my favourite planet! ;-)

    The public outcry was, I feel, blown out of proportion. Most members of the public will have forgotten about it by now.

    Nope. That’s just not true, Nigel Depledge. See the article linked to my name here.

    The way in which the public use the word “planet” does not really have any bearing on the way professional astronomers use the term.

    Or does it?

    Astronomers need to communictae with the public if they are to get funding and be understood and appreciated. Astronomers are also members of the public living as part of the rest of society. There is enough failure to communicate already and making it worse by making unnecessary decisions that many find bizarre or silly or wrong isn’t helping our cause with everybody else in the world. The decison to demote Pluto hurts us with the general public and why would we inflict that limiting, narrowing, overly strict definition on ourselves when better definitions exist that keep Pluto and allow more people the chance to discover more planets of the ice dwarf type?

    I think a “planet” definition that includes ice dwarfs as proper planets would increase public excitement and inspire more people to learn astronomy because people can dream of finding planets. It would mean there a lot more worlds in the solar system and we’re still finding more all the time and I think that would be a very positive thing.

  70. Messier Tidy Upper

    Other links for the sources quoted above :

    http://www.thespacereview.com/article/692/1

    For ‘Demote Pluto, or demote “planet”?’ by Jeff Foust published on the 28th August 2006 in The Space Review online.

    See :

    http://knol.google.com/k/demotion-of-pluto-from-planetary-status#
    For ‘Demotion of Pluto from Planetary Status’ by an unnamed author on Knol. NB. Apparently Knol will be discontinued on May 1, 2012.

    Plus see :

    http://laurele.livejournal.com/27415.html

    Which notes that many schools as wellas several democratic state govts reject the IAU’s anti-Pluto decree and retain it as a planet in various ways such as solar system scale models.

  71. Messier Tidy Upper

    @42. Nigel Depledge :

    There are problems with the “rounded by their own gravity” point, which you tend to gloss over … [snip] .. It is inconsistent of you to object to the one pragmatic and vague definition while supporting the other pragmatic and vague definition.

    So, I disagree that the definition you describe in this point is more logically consistent than the IAU definition. I would say they are equally logically consistent. You have certainly not shown that the “how round is round” question can be safely brushed under the carpet while at the same time you object to the “gravitational clearance” criterion.

    I’ve dealt with that already in comment #56 here :

    I don’t think the two qualities are equal – I don’t find roundness is quite as arbitrary as a “cleared orbit” appears. Roundness is tangible, easy to calculate and it’s pretty obvious and immediately apparent. Roundness is the first thing people think of as a defining trait for what is a planet. If it looks round or gravitationally rounded by mass then it pretty much is. It just doesn’t raise as many questions as “orbital clearance” and it is intrinsic to the object rather than depending on the objects spatial and temporal relationships to other objects.

    I stand by that – again. Roundness is a lot clearer and raises less issues than “orbital clearing does.

    @43. Nigel Depledge : November 15th, 2011 at 6:49 am

    Some asteroids also have moons. Dominating a system of moons is not purely a planetary characteristic, and is trivial in comparison with gravitationally dominating the body’s entire orbit.

    But doesn’t Pluto pretty much gravitationally domiate its moons orbits? ;-)

    Okay, some asteroids also have moons – although I don’t think w eknow ofany asterodis with as many as four moons – and, okay that doesn’t make them planets but that was just part of why Pluto is a lot more than just an asteroid.

    So does Titan. Hell, if you’re going to count an atmosphere as rarefied as Pluto’s, then so do Triton and our Moon. Possessing an atmosphere is not a purely planetary characteristic.
    [&]
    .. Io also has complex geology. Titan also has complex weather and geology. These are not defining planetary characteristics.

    Not defining, no, but certainly I’d say indicative. Certainly indicative of being something more than an asteroid or comet.

  72. Messier Tidy Upper

    Not defining, no, but certainly I’d say indicative.

    To elaborate on this, think of seeing an object floating in space and trying to work out whether its a planet or not. What features do you look for? What things suggest that it is or isn’t a planet? What items are on the checklist as making it more or less likely to be a planet as opposed to a star, brown or asteroid or moon?

    Well, first thing is is it round or gravitationally in hydrostatic equilibrium. Check that off first because if not its clearly an asteroid or something else. Next is it shining self-luminosuly from soem kind of nuclear fusion or internal heat source? If so, then it’s got to be a star or ex-star -although actually Jupiter and some gas giants come close to failing that test since they produce more energy than they recieve! Okay, so we have something that’s round, that’s notself-luminous by its own core fusion what next? What else do we expect from planets that we can quickly see and use as criteria from classifying what it is? Moons, atmosphere, differentiated geology or internal strcuture? Now okay, it’s not impossible to have one of these things and not be a planet – you can have asteroids with smaller moonlets around them, you can have moons with atmospheres and geological activity and so on but if it ticks a lot of the boxes then, yeah, it indicates its more likely than not to be a planet, same way as if it quacks like a duck and walks like a duck, odds are good that yeah, its a duck. It might not be but it probably is.

    My point is Pluto has the features and items you’d expect many planets to have. Moons – its got a quartet of them. Atmosphere – yep. Seasons and weather, yep. Rings? Maybe. Pluto then passes the duck test having many of the traits you’d expect to find make a planet. So if you are to disqualify it fromplanethood then you’re going to need something truly significant -and I don’t think a clear orbit is significant enough.

    You claim that the “orbital clearance” criterion is absurd but you have made no real effort to demonstrate this. You simply assert it over and over again, backed up by nothing more than an argument that has no relevance to our solar system.

    Oh for pity’s sake! I’ve made plenty of effort at demonstrating this for everyone and I’m baffled as to how you can possibly argue otherwise. What else do I have to do, Nigel Depledge? What would satisfy you on that score?

    Yes, if Earth were in the Kuiper Belt it would not count as a planet. But it isn’t in the Kuiper Belt, and that’s why the IAU definition counts it as a planet.

    But how do we know there isn’t an earth-mass or even larger planet orbiting out there in the Edgeworth-Kuiper Cometary belt and how does it make sense to call it a dwarf planet based solely on the region of space it happens to be orbiting in? If you have two worlds the same size and one is a dwarf but the other is a full planet only because of the region each inhabits then, sorry, but that’s just daft. Its logically inconsistent and does NOT make a good defining trait.

    That, for the umpteenth time, is why the whole “orbital clearence” rubbish fails the logic test.

  73. Messier Tidy Upper

    @44. Nigel Depledge : November 16th, 2011 at 3:21 am

    True, but presented disingenuously. Pluto is probably only a few km larger in diameter than Eris. And the Kuiper Belt contains a whole lot of space that we have yet to examine in any detail. I would not be in the least surprised if we were, in the next few decades, to find several more objects that are roughly the same size as Pluto and Eris, and maybe one or two that are larger than Pluto.

    I wouldn’t be surprised either but so far in many years of searching we’ve discovered nothing larger than Pluto – since it now turns out Eris is almost exactly the same size. There may be something, after all, to Ken Croswell’s suggestion of making Pluto’s size the arbitrary (“mountain-hill” style) cut off point which would add only Eris to the planetary tally while restoring Pluto.

    Mind you, I’m sure why smaller but still otherwise planetary bodies such as Makemake, Quaoar and Sedna shouldn’t count either. The only reason seems to be that people dislike adding to the number of planets counted as such which doesn’t seem to be a sufficiently valid reason to justify their exclusion to me.

    You’ve got to admit that the IAU definition at least means that we can guarantee that we aren’t going to be adding new planets every year or two for the next 30 years.

    Except for exoplanets – oh wait, you don’t consider them ‘proper’ planets either for some reason! How very snobby of you! ;-)

    Seriously now, you seem to be saying that like its a good thing. I disagree. I think its better if we do add new ice dwarf planets, if people can hope to discover new planets out there in that distant new found zone of our own solar system.

    Calling it [the IAU definition] silly is childish accurate & if anything an understatement

    FixedItForYou. ;-)

    If anything, your attempts to argue against the IAU definition make it look more sensible, because your arguments are so weak.

    As you might expect I totally disagree with that asessment of my arguments strength. You merely calling them “weak” doesn’t make them so. I’ve backed up what I’ve said with numerous examples, real as well as hypothetical and pointed out how my logic works and is consistent. Not sure that you’ve done the same for your side at all.

  74. Typo correction :

    Mind you, I’m NOT sure why smaller but still otherwise planetary bodies such as Makemake, Quaoar and Sedna shouldn’t count either.

    Moving on now still deconstructing #44. Nigel Depledge (November 16th, 2011 at 3:21 am) :

    It [Pluto] hasn’t been “demoted”, it has been reclassified.

    Come on. You mean “reclassified ” in a way that demotes it from counting as a full proper planet into a mere dwarf planet instead. The iAU is saying Pluto is nolonger a planet – which is, indeed, a demotion.

    Again, your childish name-calling does not strengthen your argument. Instead, it emphasises its fundamental weakness.

    You think that’s “name-calling” I think that’s an accurate description of the situation. (Shrugs.)

    @ 45. Nigel Depledge : November 16th, 2011 at 6:04 am

    Currently, they [the Neptune-Pluto analogue gas giants of HD 45364 -ed.] are rightly known as exoplanets. If it turns out that each object is dominant in its orbital vicinity, then they count as planet-analogues. If not, then they would count as dwarf-planet-analogues. It could also be that finding out more about such systems prompts the IAU to revise or re-word the definition of “planet”. At this stage, who can say? We know too little about such systems and the orbital context of each object.

    Really? From what we do know it seems perfectly reasonable to call both these worlds planets and unreasonable to suggets that they are dwraf exoplanets. Note that the inner planet has at least 3.5 times the mass of Neptune and the outer planet has at least 2.2 times the mass of Saturn so calling them “dwarfs” when they’d bracket Saturn in size listings if put in our solar system hardly makes any sense at all! :-o

    (Source : ‘Extrasolar Neptune-Pluto Analogue Discovered’ is linked to my name for this comment.)

    “Pluto is far more like what most people consider a planet to be than Jupiter is!” [MTU]
    Apart from not being a unique object. Pluto is one of hundreds or thousands of KBOs.

    And Jupiter is one of hundreds of thousands of gas giants – four in our solar system alone. Your point is what exactly?

    Yes, Pluto superficially resembles the Earth, but the atmospheric resemblance is trivial, as is the seasonal one.

    You cliam those factors are trivial, I think they are interesting, significant and worth consideration. Guess “triviality” is in the eye of the beholder. Fact is that Earth and Pluto have more in common than Earth and Jupiter do. Pluto is thus worth studying and ranking seriously and doesn’t deserve to be demeaned and relegated.

    Pluto was not reclassified because it is small or far away – it was reclassified because it is merely one example of a large number of objects that orbit in the same region.

    Although if Pluto was larger or orbited closer to the Sun it would unquestionably be considered a planet still today justas if Mercury was found in the Edgeworth-Kuipercometary belt then we would be questioning its planetary status so in a sense it clearly *is* part of the problem.

    The fact remains that Mercury, Venus, Mars, Jupiter, Saturn and Uranus don’t orbit out in the Kuiper Belt.

    No, they orbit crammed in together with other similar rocky worlds and thus can be considered part of the inner rocky dwarf planet belt instead of in long proper orbits with the majority of icy planets! They’re strange, there’s quite a few of them tucked into a small corner of the solar system so they shouldn’t really count as planets like the rest of us ice dwarfs! Or so Pluto could argue from its perspective! ;-)

    A planets, a planet no matter how small – and no matter where it orbits too.

  75. Final installment of The Great Planetary Definition Debate here for tonight before I turn across to watching NASA TV and the hopefully the launch of the Curiousity rover. (T-minus 53 minutes, 23 seconds as of submitting this.)

    ***

    @45. Nigel Depledge (still.)

    ..along with many other objects over which Pluto has no dominance.

    But wait on a second, Earth doesn’t gravitationally dominate Venus or Mars and it still counts as a planet and Jupiter doesn’t gravitationally dominate Saturn and Neptune so why should Pluto have to dominate Eris or Makemake?

    We need to keep the criteria consistent and the IAU definition stinks at consistency in this regard. It also completely ignores the fact that it is, of course, far easier to keep a smaller orbit “clear” than a longer one thus making the criteria vastly easier from equal mass planets in close orbits to their stars versus those in longer orbits to meet which doesn’t really work.

    .. to return to the biological taxonomy parallel, your hypothetical scenarios (such as “if Earth were in the Kuiper Belt, it wouldn’t count as a planet”) are akin to someone who, on calling a spider an insect and being corrected, cries “but if it had 6 legs, it would be an insect!”.

    No, in that metaphor I’m saying if its got six legs its a spider even if its one of thousands of small spiders living on a tree versus the IAU equivalent of saying “it s only a spider if it dominates all the other spiders keeping them fromcrossing its path, is found almost entirely alone all the time and only lives inside your house not out further away in the woodland! ;-)

    @46. Nigel Depledge : November 16th, 2011 at 6:13 am

    Except that your definition includes a vague and arbitrary boundary between planet and smaller body. Whether or not an object counts as a planet under your system depdnds as much on what it is made of as it does on how massive it is.

    Roundness or hydrostaic equilibrium though isn’t as arbitrary and is much clearer to tell at a glance than orbital clearence. Yes, if a body is icier its easier than if its rocky in composition but I don’t think that makes too much of a real difference or is going to unjustly disqualify too many boarderline objects.

    Remember that Pluto is made of rock and ice not just ice alone. Also that we can have stars smaller than Pluto & / or equal to Earth and their not planets either based on their composition if they’re neutron stars or white dwarfs.

  76. Okay, just got time – 33 minutes and all going well Curiosity countdown~wise – so here’s one final one for now :

    @46. Nigel Depledge :

    Furthermore, your definition allows our solar system to keep on adding planets indefinitely as new large KBOs are discovered, but you can bet your bottom dollar that the public at large won’t keep up with the changes,

    True enough, I don’t think the public keep up with the ever rising number of exoplanets and ice dwarfs being discovered either. Even I find it hard to do so sometimes given the pace of discovery and this new found worlds area is one I follow fairly closely and with great interest but I don’t think that really matters.

    I think what matters is that we *do* include new planets for what they are and we do allow for the possibility – probability even – of finding more full fledged planets. Rather than, say, downgrading them and pretending the solar system isn’t a fully richer realm with us finding more about it that we didn’t know was out there all the time.

    so your appeal against the IAU on the grounds of public awareness of the nine “planets” is an equally valid objection to your own preferred definition. I happen to think it’s an irrelevant objection, but you are being inconsistent.

    Er, no. You are misinterpreting what I’m saying to make it sound inconsistent. I’m not arguing – and never have been – for keeping the solar system’s planet tally to nine planets and only restoring Pluto’s status. I’m in favour of an inclusive definition that also adds Eris, Ceres, Sedna and more* as well. If I win this argument and the definition changes we won’t go back to having just nine planets. We’ll have somewhere in the vicinty of twenty or so* and rising – and I’m happy to live with that and a definition of planet that makes sense.

    (Looks down the the thread checks .. Phew .. Is this where I came in? Have I now finally caught up & responded to all the previous comments I’d missed before? Seems so?)

    PS. To quote Pink Floyd – Is There Anybody Out (T)here still? You still reading this thread Nigel?

    ——-

    * These worlds at least would almost certainly be added under my definition Pluto, Eris, Ceres, Haumea, Makemake, Quaoar, Varuna, Orcus, Sedna, “Buffy” (2004 XR190) and Ixion plus more. That’s at least eleven extra planets for a total of twenty in our solar system with more no doubt to add as we find them! 8)

  77. Nigel Depledge

    MTU (50) said:

    So does Pluto – it dominates Charon, Nyx, Hydra and P4. The many orders of magnitude thing only raises additional questions that, I think, violate Occam’s Razor. If your definition raises superflous questions that a betetr definition does not then science & logic says go for the simpler definition.

    But Pluto dominates nothing else in its orbital region. Its influence over Neptune, for example, is practically undetectable. Its influence over other KBOs is trivial.

    So, sure, Pluto gravitationally dominates its own satellites, but it orbits in a region that contains other wandering stuff over which Pluto exerts only a little influence.

    The many orders of magnitude thing is not really a key criterion, it is merely there for emphasis. The key point is that our solar system has 8 planets that each dominate the whole region in which they orbit. Pluto is different. As are Eris and Ceres. They get a category of their own to recognise this difference.

  78. Nigel Depledge

    MTU (50) said:

    But what if they didn’t? What if an Earth-sized world wandered by and crossed the orbit – and gravitationally interacted with Jupiter or neptuen would that stop them being planets then?

    Who cares?

    What if spiders had 6 legs instead of 8? Would that make them insects?

    Ifs and buts don’t matter. The IAU definition deals with the solar system as it is, not as it might have been. As I pointed out, the IAU is free to change the definition as new knowledge is accrued. But for now, the definition recognises the very clear and obvious distinctions in our solar system. No defintion that you have proposed would do likewise.

    What if the trojan asterodis clumped together and formed an Earth sized or Mercury sized world or in other systems gas giants formed in trojan orbits? Would they not be planets?

    Again, who cares? They have not done this (AFAIK, they cannot do this).

    See a good definition of planet needs to cover all sorts of possible – so far – hypotethical eventualities that may well be discovered around other stars.

    No. Quite the contrary, in fact.

    A good definition of “planet” needs to be useful. It should not have to consider hypotheticals, nor should it have to accommodate what we might possibly one day discover orbiting around other stars.

    It needs to be useful in our solar system, and it needs to be useful now.

    A good definition therefore is a broader and more inclusive one that allows some flexibility as I see it anyway.

    I notice that you now seem to be shying away from the biological taxonomy analogy, but let’s play with it some more.

    Biological taxonomy is based only on what is known. The IAU planet definition is also based only on what is known. Biological taxonomy is subject to extension or revision as required. The IAU definition could be extended or revised as required, as new knowledge comes to light. Biological taxonomy is pragmatic. The IAU planet definition is pragmatic. There are plenty of parallels, in fact.

    There is absolutely no requirement for the IAU to define “planet” in such a way as to accommodate new knowledge that we might not acquire for 50 years. It has no need to be intrinsically flexible, because it can be changed if needed.

    The criterion that a planet must orbit our Sun shows us that the IAU is considering a definition only for the one solar system about which we have a good deal of detailed knowledge.

  79. Nigel Depledge

    MTU (51) said:

    Which is a silly sitaution in my view because if we find something that’s large as Mars or Earth or Jupiter out there then saying it is merely a “dwarf planet” strikes me as just nonsensical.

    So maybe the term should be changed. Whatever. If it doesn’t clearly dominate the region in which it orbits, then it is self-evidently not in the same category as the 8 planets we know now.

    Why shouldn’t a planet orbit inside an asteroid belt – if you count their trojans Jupiter and Neptune actually do just that!

    You’ve had this point before. Jupiter and Neptune dictate the behaviour of their trojans. Pluto does not dictate the bahviour of any other KBO apart from its satellites.

    The whole “clearence criteria” just amounts to discrimination based not on what the planet is but where it orbits and means that if you put Earth further from the Sun where it can’t “clear” it’s orbit then it wouldn’t be a planet or if you put Ceres around a star with no other worlds it would become a planet and that just doesn’t strike me as reasonable at all.

    You’ve said this before, and you have yet to make any rational argument at all that considering a planet’s context is unreasonable. The only argument you have attempted – and you keep coming back to it no matter how often its flaws are pointed out – is that of hypothetical situations that have no relevance to the solar system that we know and love.

    That it “doesn’t strike [you] as reasonable” is nothing more than an appeal to emotion. It is as empty as an argument against evolution based on a person’s desire to have no relation with other great apes.

    The fact remains – and I have yet to see you even address this fact – that our solar system contains 8 bodies that are clearly different from everything else. Each of these 8 bodies is the dominant force within the region of its orbit, i.e. nothing else orbits in the same region without its behaviour being dictated by the dominant body.

  80. Nigel Depledge

    MTU (51) said:

    All 8 planets? But haven’t you heard Nigel we’ve found hundreds of them -soon to be thousands – almost all of them orbiting other stars and thus well out of amateur ‘scope viewing range!

    Those are exoplanets.

    You’re not seriously saying that planets should be defined as visible in a amatuer astronomers telescope are you?

    No, of course not, but it’s quite a nice thing to have, isn’t it?

    If so, why not keep it to those visible to unaided eyesight – the original clasical five planets (Venus, Mercury, Mars, Jupiter and Saturn.)

    Because Ouranos and Neptune are both visible through a reasonably-priced ‘scope, and don’t require unusually dark skies to be observable. Anyhow, this sentence was just my bit of whimsy.

  81. Nigel Depledge

    MTU (51) said:

    Really? Really?

    Haven’t I demonstrated exactly why the IAU definition is illogical a hundred and one times already? Could’ve sworn I had!

    Nope.

    Your argument rests entirely on hypothetical scenarios that you have not shown are relevant to our solar system. The IAU definition doesn’t concern itself with what might become known in the future. It concerns itself with what is known now.

    By parallel to biological taxonomy, that seems pretty logical to me.

  82. Nigel Depledge

    MTU (51) said:

    Not necessarily. I’d say there’s at least three classes of world here – the rocky, the gassy and the icy. We have rocky planets like Mercury, gassy ones like Saturn and icy ones like Pluto.

    Again you ignore the glaring fact that the 8 IAU planets each dominate their orbital region. And Pluto does not.

    I say again, any first-time visitor to our solar system would classify the 8 IAU planets as things different from the KBOs. I agree that you may get the rocky / gassy planet distinction, but Pluto would most naturally be classified alongside all the other lumps of ice in the Kuiper Belt.

    The gravitational dominance thing again is dubious given interactions with Saturn and Jupiter have tipped Ouranos on its side and that planetary migration in the past has resulted in all the planets present orbits. It raises questions of how gravitionaly dominant is “gravitationally dominant” enough and where do we draw the line? I say we draw it as a strike-through through the whole notion of “gravitational dominence” being a defining factor or at least unless the object is actually orbiting another planet and thus is a moon.

    You are constructing a strawman. A planet only has to gravitationally dominate its orbital region to count as a planet (assuming it meets the other two criteria against which you have no objection). It does not have to resist influences from other planets to still count as a planet.

    You again question where the line should be drawn on “how clear is clear” but it doesn’t matter – you only have to take an objective look at our solar system to see that 8 of the bodies orbiting the sun are the dominant objects in their orbital region and nothing else is anywhere.

    And, if you want to get stuck into the “how clear is clear” question, then you must also face the “how round is round” question for the sake of consistency.

    Oh, but you don’t object to the gravitational roundness criterion, because that allows Pluto to count as a major object. No, if you wish to be logical (and you have claimed that the IAU definition defies logic so one is forced to assume that you do), then you must face the latter question with the same vigour as you face the former.

  83. Nigel Depledge

    Flip (52) said:

    And here we get stuck again. Seriously, if they changed it once, they can change it again. If an Earth sized world came along and crossed the orbit, there would be *new* information which would impact on the definition. This is the whole point you seem to miss and willfully ignore: new information arose about KBOs. This impacted the definition which was found to be inexact. A new definition was created. This can happen time and time again. You seem happy enough to accept that new science changes previously held conclusions and theories, but can’t accept it for the definition of a *word*. MTU’s cognitive dissonance strikes again. Seriously, stop worrying about the “what if’s”. They’ll deal with those if/as they come along.

    Yes, this!

  84. Nigel Depledge

    MTU (54) said:

    Flip : Well it’s not like I haven’t tried pretty hard to explain it to you! (Shrug)

    You don’t seem to have tried at all to be objective.

    You have uttered plenty of emotional rhetoric, and you have speculated about hypotheical exceptions to the IAU definition, but you have persistently refused to consider the IAU defintion based only on what is known now.

    It feels like at least half of your arguments start with “what if…”, and the rest are peppered with accusations such as “silly” and “illogical”, but you have not found one piece of evidence to show that the gravitational clearance criterion is illogical. All you have is speculative hypotheticals.

  85. Messier Tidy Upper

    @ ^ Nigel Depledge : Really? :roll:

    After all the examples I’ve given? Our Moon is hypothetical then? As are Pluto’s moons? As are the exolanets detected around HD 45364? Purely speculative? Ie. the carefulobservations that discovered those worlds weren’t made or somehow unacceptably wrong? You know I think you owe the astronomers who found it an apology for that. :-(

    I’ve produced plenty of evidence and backed up everything I’ve said. Your contuinually denying all the evidence and accusing me of vague logic flaws without actually specifically giving any specific examples of supposed “illogic” or fallacies here is getting *really* tedious and exasperating. :-(

    @79. Nigel Depledge :

    But Pluto dominates nothing else in its orbital region. Its influence over Neptune, for example, is practically undetectable.

    Mars has virtually no gravitational influence over Earth, its only half an AU away – pretty much inthe same orbit especuially as seen from Pluto’s vast realm. By your logic there Mars wouldn’t count as a planet either – yet w edo call Mars a planet – so Pluto in a similar situation should also be called a planet too.

    Its influence over other KBOs is trivial.

    Bzzt. Wrong. Have you not heard of Orcus which has been dubbed the “anti-Pluto” for its orbital relationship or the whole ‘Plutino’ class of ice dwarfs generally?

    So, sure, Pluto gravitationally dominates its own satellites, but it orbits in a region that contains other wandering stuff over which Pluto exerts only a little influence.

    Earth orbits in a region with other stuff that it doesn’t influence too much – see my first paragraph, so do the other gas giant planets – which is fortunate becase if they did interact more gravitationally we’d be in trouble.

    Pluto also has to cover a lot more space. This means its harder for it to affect things than it is for, say, Mercury as I’ve already explained. This means the “orbital clearence” criteria unfairly categories planets differently based on the region they’re found in and the amount of other objects in their local zone. This doesn’t make much sense as I’ve explained already.

    The many orders of magnitude thing is not really a key criterion, it is merely there for emphasis. The key point is that our solar system has 8 planets that each dominate the whole region in which they orbit. Pluto is different.

    Being different shouldn’t stop it being counted as a planet and repeating the erronoeus assertion that it isn’t doesn’t make it become true. Just as the IAU can’t make a planet become a comet just by calling it one.

  86. Messier Tidy Upper

    @80. Nigel Depledge :

    MTU (50) said: “But what if they didn’t? What if an Earth-sized world wandered by and crossed the orbit – and gravitationally interacted with Jupiter or Neptune would that stop them being planets then?”
    Who cares? What if spiders had 6 legs instead of 8? Would that make them insects?

    Please don’t be deiberately obtuse here, Nigel, it really doesn’t suit you & I find it hard to imagine you really fail to grasp this reality and the implications this argument has for the IAU’s rubbish definition.

    What that shows and why we should care about it is that the orbital clearence criterion simply fails. We wouldn’t apply it to Earth or Jupiter or Neptune – so we shouldn’t apply it to Pluto either. It shows that the IAU got it wrong. It shows that orbital clearence as a qualifying criterion for defining what is a planet isn’t a workable or tenable notion. Period.

    Ifs and buts don’t matter. The IAU definition deals with the solar system as it is, not as it might have been. [Emphasis added. -ed.]

    So are you actually denying the whole Big Splash theory then? The currently accepted scientific consensus on how the Pluto-Charon system formed? The Nice model of how our solar system became as it is today and much more? Honestly? :-o

    As I pointed out, the IAU is free to change the definition as new knowledge is accrued.

    And as I’ve pointed out they are not only “free to” but they really need to do so because their current definition is fatally flawed. ;-)

    But for now, the definition recognises the very clear and obvious distinctions in our solar system.

    What “clear and obvious” distinction would that be? The distinction between gas giants and the smaller planets – rock and ice dwrafs alike? But the IAU says nothing about that one! ;-)

    How about the distinction between “inferior planets” Mercury and Venus that orbit inside the Earth’s orbit and the rest of the “superior” planets that orbit outside our globe’s orbit? No, the IAU definition ignores that “clear and ovious distinction” between worlds too.

    What is clear and obvious is a matter of opinion. The planets of the solar system are clearly and distinctly different in various ways – Venus spins backwards, Ouranos on its side, Jupiter has vastly more mass than all the other worlds put together, Saturn its shiny distinctive rings et cetera.
    Which raise steh question of whats so special about “orbital clearence” that means that’s be the one “clear and obvious” disntinction that most matters? The clearand obvious answer to that is : It shouldn’t be!

    No definition that you have proposed would do likewise.

    Becaus I don’t think orbital clearing matters as the defining trait and I’ve justified why about a hundred times now. I’ll just add that defining an object as a ‘planet’ is like defining an object as a star – its just the starting point and covers objects that vary over a very wide range. The next step – defining what type of star (red supergiant, Luminous Blue Variable, red dwarf) or planet (gas giant, ice dwarf, pulsar planet) is actually more important and tells us much more just as the whole “animal-mineral-vegetable” division is very much a basic level of classification that then needs to be narrowed much further to know what specific level of object we’re talking about.

    Again, who cares? They [Trojan asteroids clumping together into planets -ed.]have not done this. (AFAIK, they cannot do this).

    Its called a thought experiment and the conclusions of these thought experiments, its the imagination stage of science that often leads to its best ideas being uncovered and such hypothesis’es (plural form?) can turn out to be very valid and usefully informative. Remember that Einstein’s relativity was a thought experiment before it was verified too.

    Again, we should care about this particular thought-experiment because it illustrates that that the IAU definition of planet is fatally flawed. The IAU definition rules out such co-orbital planetary systems -if they exist even if they could exist – it refutes their definition and shows it up as the ludicrous nonsnese it is.

  87. Messier Tidy Upper

    Continuing :

    A good definition of “planet” needs to be useful. ..

    I agree with that.

    .. It should not have to consider hypotheticals, nor should it have to accommodate what we might possibly one day discover orbiting around other stars.

    I totally disagree with that though. I think definition such as ‘planets’ or even ‘life’ to use another example should consider hypothetical possibilities.

    Of course, as several of the examples I’ve already given show we’re beyond the stage of “hypotheticals” anyhow. We know of planets that collide and binary planets and exoplanets in orbital relationships analogous to Pluto and Neptune. These aren’t just hypothetical or speculative concepts anymore.

    Our langauge should be flexible enough that we don’t have to redefine words when they clash with observed reality. For instance, the definition of planet should cover the possiblity – indeed since apparenty confirmed – of planets drifting through space instead of orbiting around stars. Similarly, we shouldn’t – and in science fiction and even science essay papers do not define life to mean only the kinds of life we know about and are familiar with.

    It needs to be useful in our solar system, and it needs to be useful now.

    So what use is it to deny ice dwarf planets like Pluto and Eris and Haumea their planetary status? How is it useful to take a variety of planet – the most common type of planet – and diminish their importance by denying they are even proper planets at all? Where is the good in rejecting Pluto and its fellow ice dwarfs their planetary nature?

    The IAU definition could be extended or revised as required, as new knowledge comes to light.

    Yeah well, as I’ve said already – it already needs to be changed. We’re already learning more all the time and the more we learn the sillier the IAU definition seems.

    Biological taxonomy is pragmatic. The IAU planet definition is pragmatic. …

    Is it? How is the IAU definition pragmatic. Are you really saying the fact that it cuts the number of planets in our solar system down to a mere eight supercedes all other considerations of ‘pragmatism’ like, say, having a definition that is logically and scientifically and linguistically consistent?

    There are plenty of parallels, in fact.

    Are there then? Okay here’s a challenge when have biologists ever done the equivalent of demoting a whole numerous class out of a fundamental kingdom – when have they ever, for instance, suggested that insects shouldn’t be considered animals because they’re tooo numerous and small to matter like the IAU has analogously done here to the ice dwarfs?

    The criterion that a planet must orbit our Sun shows us that the IAU is considering a definition only for the one solar system about which we have a good deal of detailed knowledge.

    Actually that shows us that their definition of planet is already unworkable and dated because it ignores exoplanets which we knew hundreds of even back then. We’re getting increasingly detailed knowledge of planets orbiting other stars and are just starting to discover evidence of planets orbiting no suns at all. That “our Sun” criterion itself shows the IAU definition for ‘planet’ is totally inadequate and doomed.

  88. Nigel Depledge

    MTU (87) said:

    After all the examples I’ve given? Our Moon is hypothetical then?

    Obviously not, but you have not shown it to be relevant.

    As are Pluto’s moons?

    Ditto.

    As are the exolanets detected around HD 45364? Purely speculative?

    Exoplanets are completely irrelevant, for very good reasons.

    You keep bringing exoplanets into the discussion, but you do not address the reasons why they are irrelevant, and you have made no attempt (that I have seen thus far) to show them to be relevant to a definition that was clearly intended to apply only to our solar system.

    Ie. the carefulobservations that discovered those worlds weren’t made or somehow unacceptably wrong? You know I think you owe the astronomers who found it an apology for that.

    You are being deliberately obtuse here. Stop it.

    I’ve produced plenty of evidence and backed up everything I’ve said.

    No, you have not.

    You have claimed that the “orbital clearance” criterion is illogical and you reject it utterly.

    The only arguments you make against it involve hypothetically moving a planet from one place to another, or some nonsense about moons that you fail to show has any relevance, and the “how clear is clear” question.

    Your hypothetical cases simply don’t matter, because they are not what is currently known to be. As Flip has pointed out to you, the IAU are very likely to change the definition of “planet” in the light of any dramatic new information that pertains to the topic. You hypotheticals are irrelevant.

    Moons are irrelevant because – despite your claim that they support the case for Pluto being a planet – they are not an exclusively planetary characteristic. Dominating a system of moons is trivial beside dominating an entire orbital region. You have also mentioned trojan asteroids, but if anything they weaken your argument, because they exemplify the gravitational dominance of the major body (be it Jupiter, Neptune or Earth).

    Thirdly, you complain about the vagueness of the “how clear is clear” question. You are right insofar as it is vague. You ignore the fact that, in our solar system, it does not need to be precise. You also ignore the fact that the “how round is round” question – to which you have no apparent objections – is equally vague. If you object to the gravitaional clearance criterion on the basis of its vagueness and ambiguity, then you must also reject the gravitational roundness criterion, because it, too, is vague and ambiguous.

    In short, all of the physical evidence to which you have referred thus far simply does not support your argument.

    Your contuinually denying all the evidence and accusing me of vague logic flaws without actually specifically giving any specific examples of supposed “illogic” or fallacies here is getting *really* tedious and exasperating.

    Your repeated failure to even attempt to show the relevance of the examples you bring up is also exasperating.

    Here’s a clear example of you being illogical. You cite vagueness and ambiguity as reasons to reject the gravitational clearance criterion, yet you accept the gravitational roundness criterion without a qualm.

  89. Nigel Depledge

    MTU (87) said:

    Mars has virtually no gravitational influence over Earth,

    Their orbits do not cross as do Neptune’s and Pluto’s so there is no parallel.

    its only half an AU away – pretty much inthe same orbit especuially as seen from Pluto’s vast realm.

    But half an AU for Mars is 50% farther from the sun than is the Earth. Again, you ignore the significance of context. Half an AU for Pluto is almost nothing (IIUC, the difference between Pluto’s perihelion and aphelion is larger than half an AU).

    Earth and Mars have distinct orbital regions. Each is the dominant body within its orbital region.

    By your logic there Mars wouldn’t count as a planet either – yet w edo call Mars a planet – so Pluto in a similar situation should also be called a planet too.

    Again, your illogic is astonishing.

    You have failed to show any analogy between the Earth-Mars relationship and the Neptune-Pluto relationship, yet you still conclude that it supports your case.

    By my logic, to borrow your phrase, context is an important factor to consider alongside the other factors. And this is what you repeatedly ignore.

    Do you honestly think that ignoring the significance of the context in which a body is found strengthens your argument?

  90. Nigel Depledge

    MTU (87) said:

    Earth orbits in a region with other stuff that it doesn’t influence too much – see my first paragraph,

    Earth is the dominant body within the region of its orbit. Mars and Venus are not in the region of Earth’s orbit. The Moon, Earth’s recently-discovered Trojan, objects such as Cruithne and so on, are in the region of Earth’s orbit and are gravitationally dominated by Earth. Earth-orbit-crossing asteroids are gravitationally dominated by Earth if the Earth happens to be anywhere near at the time those objects cross Earth’s orbit.

    Yes, there is vagueness and ambiguity here, but there is also pragmatism.

    so do the other gas giant planets – which is fortunate becase if they did interact more gravitationally we’d be in trouble.

    Each of the gas planets orbits in a distinct region. While it is likely that they were close enough together in the past to influence opne another significantly, the orbits they now occupy are stable (as far as anyone can tell). Each gas planet is the dominant body within the region of its orbit.

    Pluto also has to cover a lot more space. This means its harder for it to affect things than it is for, say, Mercury as I’ve already explained. This means the “orbital clearence” criteria unfairly categories planets differently based on the region they’re found in and the amount of other objects in their local zone.

    This is the entire point of that criterion. The context in which a body orbits is a significant factor that deserves to be considered. This means that planets close to the sun have an easier time of clearing their orbit than would a similar-sized body farther out. I have no idea what you mean by “unfair” – after all, Pluto cares not how we humans classify it. It’s not as if Pluto is getting any more or less of any resource by being classified as a dwarf planet instead of a planet. Your cry of “unfair” smacks of animism.

    A key factor is that whether or not we count an object in the category “planet” does depend on how far out from the sun it is, and on what other stuff orbits in the same region. And it is right to do this. This is simply a recognition of a natural discontinuity that exists in our solar system.

    This doesn’t make much sense as I’ve explained already.

    No, you have claimed that it doesn’t make sense, but you refrain from addressing the obvious and natural discontinuity that exists – that is that each of the 8 IAU planets is quite obviously the dominant body within its orbital region. And Pluto is not.

    Pluto is simply the largest known example of a collection of objects that contains many members (hundreds at least, and more probably thousands).

  91. Messier Tidy Upper

    @90. Nigel Depledge :

    Obviously not, but you have not shown it to be relevant.

    Yes I have. See comments #68, #58 & point (4) in the original ccomment #29.

    Whilst on with the older stuff pleaes could you answer the question Iasked in comments # 60

    I) Why define planet only to apply to our solar system? It semes not only silly to do but also violates the Copernican principle or principle of mediocrity. In Other Words; why is our solar system special in terms of being the only one to have defined planets? Surely a definition of planet should be universally – quite literally universally as well as intergalactically – applicable? No? You claim there’s a good reason for that – so what is it?

    & #71 :

    II) If the Biochemical Society was to decide that ‘proteins’ now meant viruses instead would you really be happy to go along with such stupidity? Honestly?

    & #74

    III.) What else do I have to do, Nigel Depledge? What would satisfy you on that score?

    Note from 75. Messier Tidy Upper : November 26th, 2011 at 5:55 am

    As you might expect I [MTU-ed.] totally disagree with that asessment of my arguments strength. You [Nigel Depledge] merely calling them “weak” doesn’t make them so. I’ve backed up what I’ve said with numerous examples, real as well as hypothetical and pointed out how my logic works and is consistent. Not sure that you’ve done the same for your side at all.

    You seme to keep repeating yourself as if you haven’t even read or understood my words. Immensely frustrating and I expected much better from you. :-(

  92. Nigel Depledge

    MTU (87) said:

    Being different shouldn’t stop it being counted as a planet

    Eh?

    Why should it not?

    Surely the whole point of defining a term is that the term should collect similar objects together and distinguish them from different things?

    and repeating the erronoeus assertion that it isn’t doesn’t make it become true.

    Erm, well, I agree that repeating an assertion does not make it true, but that is what you are doing.

    Pluto is distinctly different from any of the 8 IAU planets because it is one member of a large collection of objects that orbit in the same region. It only makes sense that Pluto should be classed in a different category from those 8 planets.

    Just as the IAU can’t make a planet become a comet just by calling it one.

    Well, no, but this is not relevant, because they have not done this. What they have done, which you might see if you detach yourself from your emotional attachment to Pluto, is recognise a natural difference that exists in our solar system by categorising Pluto alongside similar objects, and not leaving it in a category of objects to which it bears only the most superficial resemblance.

  93. Nigel Depledge

    MTU (88) said:

    Please don’t be deiberately obtuse here, Nigel, it really doesn’t suit you & I find it hard to imagine you really fail to grasp this reality and the implications this argument has for the IAU’s rubbish definition.

    The implication of the argument is clear enough – that if your hypothetical scenario comes to pass, then the IAU definition breaks down.

    So what? As has already been pointed out to you, the IAU is free to change the definition in light of new evidence, just as it was a sequence of new discoveries (especially Eris, IIUC) that prompted them to institute a precise definition in the first place.

    Do you honestly believe that the IAU would refuse to change the definition if new discoveries were to render it unworkable?

    My point is that it works for our solar system as it exists now – to the best of our knowledge.

    What that shows and why we should care about it is that the orbital clearence criterion simply fails. We wouldn’t apply it to Earth or Jupiter or Neptune – so we shouldn’t apply it to Pluto either.

    No, the orbital clearance criterion, complete with its intrinsic vagueness, works at a pragmatic level, in the same way that the gravitational roundness criterion – complete with its intrinsic vagueness – works. The orbital clearance criterion only fails in your hypothetical scenarios – and it is obvious that this is your intent in constructing them. None of these scenarios is relevant to the solar system as it exists with our present knowledge, and you seem to be tacitly assuming that the IAU would never change the definition in the light of new discoveries, which is unsupportable.

    When a discovery is made that matches one of your scenarios, then I am sure the IAU will change the definition to match the level of knowledge that pertains at that time.

    Therefore, your hypothetical scenarios do not constitute a rational criticism of the IAU definition in today’s solar system.

    It shows that the IAU got it wrong.

    Only if you insist on any definition being universally applicable for all time, which even you might agree is unreasonable. After all, we humans don’t have any other system of classification that is expected to be universally applicable for all time (although possibly the Periodic Table is the closest we have to such a thing).

    It shows that orbital clearence as a qualifying criterion for defining what is a planet isn’t a workable or tenable notion. Period.

    No, it does not. It shows that the orbital clearance criterion might not be workable as new discoveries are made in the depths of the Kuiper Belt, but it does not show that the definition fails now, unless you consider the gravitational roundness criterion to be equally faulty (i.e. they both contain a certain amount of vagueness and ambiguity and exist for the sake of pragmatism).

  94. Messier Tidy Upper

    @90. Nigel Depledge :

    Exoplanets are completely irrelevant, for very good reasons. You keep bringing exoplanets into the discussion, but you do not address the reasons why they are irrelevant, and you have made no attempt (that I have seen thus far) to show them to be relevant to a definition that was clearly intended to apply only to our solar system.

    How many times now have I pointed out to you that the very fact that the IAU’s miserable excuse for a definition of planet is limited to our own solar system only is a terminal flaw in the definition on its own? :roll:

    How about galaxies, Nigel Depledge, shall we make our Milky Way the only galaxy that exists in the cosmos by an equally silly act of linguistic idiocy? Why don’t you get this!?

    A planet is a planet regardless of whether it orbits our sun – in common parlence and imagination and reality – if not in the IAU technical terminology (non)sense of the word.

    It is as silly as saying only our pet cat can be a cat or only the fish in our fishpond are actually defined as fish. To say that only our solar system has “definable planets” is just so ridiculous I cannot believe you type the words with a straight face.

    If the word ‘planet’ has any meaning at all it MUST include exoplanets and planets of stars other than our Sun as well as those that happen to orbit our daytime star.

    @94. Nigel Depledge :

    Why should it not? Surely the whole point of defining a term is that the term should collect similar objects together and distinguish them from different things?

    Indeed. Pluto is a planet because :

    a) It is round because of its own gravity thus not an asteroid.
    b) It is not & never has been self-luminous from nuclear fusion thus not a star

    &

    c) It does not directly orbit another planet and hence is not a moon.

    It is thus defined by its simarities to other bodies that also fulfill those three criteria (eg. Earth, Jupiter, Gliese 581 b) and its differences from bodies (eg. stars, moons,& comets) that do not.

    Orbital clearance is NOT a good defining criteria for the logical, scientific and semantic reasons that I have pointed out here already repeatedly.

  95. Nigel Depledge

    MTU (88) said:

    Ifs and buts don’t matter. The IAU definition deals with the solar system as it is, not as it might have been.

    So are you actually denying the whole Big Splash theory then? The currently accepted scientific consensus on how the Pluto-Charon system formed? The Nice model of how our solar system became as it is today and much more? Honestly?

    Erm . . . what?

    How does emphasising that the IAU definition works with what is, as opposed to what might have been – or, indeed, what was likely to have been aeons ago – deny any theory about the formation of any solar system objects?

    To be frank, I am not up to date on the current accepted theory for the formation of the Pluto-Charon system. In what way is it relevant? Pluto is still the biggest of many chunks of icy stuff, rather than a unique entity.

  96. Nigel Depledge

    MTU (88) said:

    And as I’ve pointed out they are not only “free to” but they really need to do so because their current definition is fatally flawed.

    You have yet to point out any flaw and demonstrate that it is “fatal”.

    Your strongest objection to the gravitational clearance criterion (at least, I see this as the only real objection you have raised), that it is vague and ambiguous, is equally an objection to the gravitational roundness criterion, that you accept without question.

    So, although you have claimed they need to change the definition now, you still have not come up with a serious rational argument for why they should do so. As I have explained over and over again. The arguments you make do not hold water, except for the one about the vagueness of the gravitational clearance criterion. But if this objection is upheld, then we lose the gravitational roundness criterion also, and then where would we be?

  97. Messier Tidy Upper

    @ ^ Nigel Depledge :

    You have yet to point out any flaw and demonstrate that it is “fatal”.

    On the contrary I have done so repeatedly and at great length and depth. That you are not satisified as to that is a mystery that Icannot fathom or it seems cure.

    Your strongest objection to the gravitational clearance criterion (at least, I see this as the only real objection you have raised),

    Actually, I’ve raised 12 points in my original as-requested comment here. All of them are real and valid. The lack of counting exoplanets, teh fialure to permit planets to collide or exist inbinary or trojan form and the failure of the IAU definitionto pass tehreductioo ad absurdum tets are I’d say amongst the strongest points I make.

    .. that it is vague and ambiguous, is equally an objection to the gravitational roundness criterion, that you accept without question.

    This again after beingdebunked already? Sigh. No it isn’t equal at all. Roundness is easy to deteremine, and a logical obvious intrinisc and consistent aspect that enables us to define ‘planet’ as I have explained for everyone in comments # 77 & 87 & 73 & #56 :

    I [MTU} don’t think the two qualities are equal – I don’t find roundness is quite as arbitrary as a “cleared orbit” appears. Roundness is tangible, easy to calculate and it’s pretty obvious and immediately apparent. Roundness is the first thing people think of as a defining trait for what is a planet. If it looks round or gravitationally rounded by mass then it pretty much is. It just doesn’t raise as many questions as “orbital clearance” and it is intrinsic to the object rather than depending on the objects spatial and temporal relationships to other objects. I stand by that – again. Roundness is a lot clearer and raises less issues than “orbital clearing does.

    Have you taken nothing that I’ve said in?

    @94. Nigel Depledge :

    Pluto is distinctly different from any of the 8 IAU planets because it is one member of a large collection of objects that orbit in the same region. It only makes sense that Pluto should be classed in a different category from those 8 planets.

    The rocky planets inhabit the same region – from roughly 0 to 2 AU where they are all crammed in together.

    Similarly the gas giants inhabit their own “gas giant belt” from 5 AU out to 30 AU.

    Its true that there are far fewer of these larger objects but theprinciple remains the same – the fact that there’s more than one Pluto type planet out there should NOT disqualify it from being a planet any more than teh fact that Saturn exists should disqualify Jupiter or tehfact taht Mars exists should disqualify Earth from planethood.

    Pluto – and Eris and Sedna have more in common with the other planets than they do with stars, asteroids and so on. See comment # 74 where I noted indicative features that you would expect a planet may have – and sure enough Pluto does :

    My point is Pluto has the features and items you’d expect many planets to have. Moons – its got a quartet of them. Atmosphere – yep. Seasons and weather, yep. Rings? Maybe. Pluto then passes the duck test having many of the traits you’d expect to find make a planet. So if you are to disqualify it from planethood then you’re going to need something truly significant – and I don’t think a clear orbit is significant enough.

    This also applies to varying extents to other ice dwarf type planets such as Haumea, Quaoar and Eris which, again, either have or almostcertanly have the sort of features – eg. moons, geologically differentiated internal strcutures (core-mantle-crust) you’d expect planets to have.

    @ 95. Nigel Depledge :

    As has already been pointed out to you, the IAU is free to change the definition in light of new evidence, ..

    And, as I have already responded, there is already more than enough reason to state that the IAU definition should be changed rightnow and , infact should never have been adopted inthe first place.

    The orbital clearance criterion only fails in your hypothetical scenarios – and it is obvious that this is your intent in constructing them. None of these scenarios is relevant to the solar system as it exists with our present knowledge, ..

    Oh for pity’s sake! Didn’t you read all the real examples from our solar system that I provided in comment #68 :

    ..didn’t you see the examples which were specific to our solar system in comments #58 & #60 with links in #59?

    Colliding planet examples from our solar system :

    1. Earth & “Theia” leading to our Moon’s formation.

    2. Pluto & another ice dwarf explaining Charon’s origin plus more.

    3. Mercury’s Caloris basin & explainationfor its core:mantle ratio

    4. Ouranos being tipped on its side -one well-known theory anyhow &

    5. A huge collison is also theorised as explaining the disparity between Mars two hemisphere -the flater northern with the Vastitas Borealis ex-ocean and the older heavily cratered Southern hemisphere.

    Binary planets in our solar system :

    I. Pluto & Charon

    II. Earth & Moon.

    III. Various ice dwarf examples – incidentally a twin planet situation may be required to explain how Neptune captured Triton with Triton’s companion escaping and Trition being left in its unusual retrograde orbit typical of captured moons.

    How many more times do I have to point this out to you?

    No these examples are NOT purely hypothetical any mor ethan our Moon is and they are based on our present scientific understanding of how our Moon got there, how Charon, Nix, Hydra and P4 got there, why Mercury and Mars are as we see them today, etc .. Blink twice and nod your head if you can hear me, Nigel? Nigel? Can you hear me? Are you conscious?! (Sigh) ;-)

    When a discovery is made that matches one of your scenarios, then I am sure the IAU will change the definition to match the level of knowledge that pertains at that time.

    We’re already at that point – and I don’t assume the IAU won’t change their presently untenable definition; quite the reverse as that is exactly what I’m asking them to do!

    Oh & is that a tacit admission on your part that the IAU definition will be changed to become better and, if so, why keep defending a definition you know is in need of replacement?

    After all, we humans don’t have any other system of classification that is expected to be universally applicable for all time (although possibly the Periodic Table is the closest we have to such a thing).

    How about the times tables – & other mathematical ones? How about teh broadest divisions of animal-mineral-vegetable

  98. @97. Nigel Depledge : November 30th, 2011 at 5:55 am

    MTU (88) said : So are you actually denying the whole Big Splash theory then? The currently accepted scientific consensus on how the Pluto-Charon system formed? The Nice model of how our solar system became as it is today and much more? Honestly? Erm . . . what? How does emphasising that the IAU definition works with what is, as opposed to what might have been – or, indeed, what was likely to have been aeons ago – deny any theory about the formation of any solar system objects?

    Because the Moon formed when a mars-sized planet and the Earth collided which in the IAU definition makes them both non-planets at least at the time they were on collision course. Which is plain silly. It is inconsistent and fails the Reductio ad absurdum test of logic to have a world stop being a planet when it is on collision course then become one again when it isn’t. Which was my point (4) on that original list of reasons.

    Just as it fails the same Reductio Test of logic to have a world whether it is Pluto or Jupiter or Earth be a planet when it orbits close to the Sun having only a small area of space to clear but then cease to be a proper planet when it orbits further out and thus has more space to clear.

    To be frank, I am not up to date on the current accepted theory for the formation of the Pluto-Charon system. In what way is it relevant?.

    The exact same way as Earth’s Moon being formed in the Big Splash is. It is an example of colliding planets – and also presents an example of a binary planet as well. Both things I’ve already noted for you and have linked at comment #59. I’ve linked it to my name again here as well.

    Really are trying to wind me up by ignoring everything I’ve said already or something? :-(

    Pluto is still the biggest of many chunks of icy stuff, rather than a unique entity.

    But then Pluto doesn’t *have* to be unique to be a planet. Uniqueness isn’t demanded as a *defining* trait of planets any more than a planet’s exact temperature is. Pluto isn’t unique -agreed but then nor is Jupiter nor is Mars nor is 51 Pegasi b. Jupiter is just one of many Jupiter-like worlds out there in our cosmos. Ditto Mars for mars-like worlds. Ditto Pluto for Pluto-like ones. It just so happens we already know of the existence of many more worlds like Pluto – and even more Jupiter-like ones than we do than we know of worlds like Mars which I’m sure are out there to discover.

    @98. Nigel Depledge:

    The arguments you make do not hold water,

    Well they’re not intended to hold fluid of any type whether dihydrogen oxide or otherwise but rather to prove my case on this logical proposition that ice dwarfs including Pluto are indeed planets and this I still believe they do. ;-)

    Your failure to recognise that is your issue not mine.

    I’ve raised 12 points in my original as-requested comment here. All of them are real and valid. The lack of counting exoplanets, the failure to permit planets to collide or exist in binary or trojan form and the failure of the IAU definition to pass the Reductio ad absurdum test are, I’d say, amongst the strongest points I make. :-)

  99. Nigel Depledge

    MTU (96) said:

    How many times now have I pointe dout to you that the very fact that the IAU’s miserable excuse for a definition of planet is limited to our own solar system only is a terminal flaw in the definition on its own?

    So, you would ignore the vast difference between the amount we know about our solar system, and the paucity of our knowledge about any other solar system?

    This is significant. How can one come up with a useful defintion of a thing if you have 8 examples about which you know a great deal, and 600-odd examples about which you know
    next to nothing? I hesitate to speculate about what kind of situation you might end up with, but it seems crazy to me to try to produce a precise defintion of something where knowledge is so limited. Thus, we have a definition that applies only to our solar system.

    I am sure that, at some later point, the IAU will come up with a definition that might encompass exoplanets, but it would be folly to attempt this without quite a bit more knowledge about these things.

    How about galaxies, Nigel Depledge,

    ‘S okay, you can call me Nigel.

    shall we make our Milky Way the only galaxy that exists in the cosmos by an equally silly act of linguistic idiocy?

    If our galaxy were the only one about which we had any detailed knowledge, then maybe. As it happens, we know as much about some of our near neighbours as we do about our own galaxy because a substantial portion of our galaxy is hard to see. Also as it happens, galaxies are classified mainly by morphology, so your point is purely academic. Also as it happens, there is no precise dividing line between a star cluster and a galaxy, so an official definition of “galaxy” might not be too far away.

    Why don’t you get this!?

    Why do you think it makes sense to try and precisely define objects about which we know next to nothing?

    It seems to me perfectly reasonable to leave exoplanets until we know a lot more about them, and to restrict the definition of “planet” to cover the only solar system about which we have detailed knowledge.

    A planet is a planet regardless of whether it orbits our sun – in common parlence and imagination and reality – if not in the IAU technical terminology (non)sense of the word.

    And here we come to a key point.

    Public perception does not really bear on the matter. If it did, your preferred definition would be just as unsatisfactory as you perceive the IAU definition to be (because your preferred definiton would include objects that most members of the public have never heard of and might never be able to pronounce – yes, Quaoar, I’m looking at you).

    The IAU have arrived at a technical definition of planet for use in discussions of astronomical research. Do you for a moment expect the general public (by which I exclude amateur astronomers) to give two hoots what the IAU definition is? Similarly, if the IAU had used your preferred definition, such that Eris, Ceres, Makemake and several other objects would suddenly count as planets, do you think that the general public would suddenly feel any urge to learn about “the 14 planets” (or however many it might be)?

    So, rather like many other words in science, “planet” now has a specific and precise definition for use in science, and some other, looser definitions for use in everyday speech.

    I do not see this as an issue. It seems to me that you do.

    Your comments make it seem that you believe the IAU should bow to popular public – non-technical – opinion. Yet you must recognise that, alongside terms like energy, power, radiation, theory, berry, nut and probably many others, technical scientific useage is different from uninformed public useage. I have said it before, and I’ll say it again – it is fitting that the IAU defines the terms they need to use in their profession. I’ve never claimed that the general public must use said terms, but it seems that you are insisting that the IAU use the public terms and not use precise definitions.

    It is as silly as saying only our pet cat can be a cat or only the fish in our fishpond are actually defined as fish.

    It would be if your analogy were valid, but it is not. Rather, cats are only cats if they are cats we know something about (such as, foe example, their possession of catlike characteristics). An animal that is probably rather like a cat, but about which we have no precise information, needs a different term. The same goes for fish. If you saw a pod of dolphins from a distance, and that rather distant and hazy view was all you had, would you call them fish, or would you conclude that you don’t know enough about them to define what they are that precisely?

    To say that only our solar system has “definable planets” is just so ridiculous I cannot believe you type the words with a straight face.

    Why?

    What is ridiculous about confining a precise definition to stuff you know something about?

    If the word ‘planet’ has any meaning at all it MUST include exoplanets and planets of stars other than our Sun as well as those that happen to orbit our daytime star.

    Again, why? You have blustered a great deal, but you have not really made a case. We know that our solar system contains several different types of object. Some of these objects are merely examples of collections of similar objects, while others appear to be unique. To arrive at a useful definition, it seems that the IAU has chosen a particular path, i.e. to exclude objects about which we have too little knowledge, and to ensure that a “planet” is a significant object within the context in which it is found.

    I am sure that, to the general public, your insistence is accurate enough, but why must the IAU use a definition that includes exoplanets?

    What makes you thik you have any right to dictate to professional astronomers the language with which they work?

  100. Messier Tidy Upper

    @101. Nigel Depledge :

    How can one come up with a useful defintion of a thing if you have 8 examples about which you know a great deal, and 600-odd examples about which you know
    next to nothing?

    I think its unfair and, indeed, wrong to say we know “next to nothing” about exoplanets. In fact we know a remarkably large amount even though we haven’t yet sent spaceprobes to them – which will, natch take centuries or aeons unless we find a way around the lightspeed limit someday.

    Also as it happens, there is no precise dividing line between a star cluster and a galaxy, so an official definition of “galaxy” might not be too far away.

    If so, then let’s hope they do a much better job than they did with defining planet! ;-)

    My point there was that it is silly to define any astronomical category in a way that limits it only to our own solar system. Defining “planets” in a way that limits them to our solar system is equally silly as defining Galaxy to mean only our Milky Way. Other stars will have a range of objects orbiting them – asteroids and comets and planets. There’s more than enough evidence showing that. Saying that we can’t call the planets of other stars – and planets belonging to no stars – “planets” by definition is just beyond dumb.

    Public perception does not really bear on the matter. If it did, your preferred definition would be just as unsatisfactory as you perceive the IAU definition to be (because your preferred definiton would include objects that most members of the public have never heard of and might never be able to pronounce – yes, Quaoar, I’m looking at you).

    But pronouncing Quaoar is half the fun! “Kwah-wah” is I believe the correct way. ;-)

    Why aren’t the public hearing about these things? Part of it is the media being lousy and having the wrong priorities sure but I also think that maybe we’d hear more and have more interest if it was anounced that astronomers are discovering new planets in our solar system which many of these Trans-Neptunian Objects I think rightly are. I think downgrading them to mere dwarfs, saying in essence these things aren’t planets when they’re in fact members of a class of small planets is not helping astronomy’s cause with the general public.

    It would be if your analogy were valid, but it is not.

    Well, you don’t think its valid but I do.

    What is ridiculous about confining a precise definition to stuff you know something about?

    Thing is, again, I think we do know enough about planets. Certainly enough to say that exoplanets should count – and so should ice dwarfs like Pluto. Yes we know more about some planets than others but I think we do know what mass range and what characteristics generally make something a planet or not.

    Some of these objects are merely examples of collections of similar objects, while others appear to be unique.

    Unique in what sense though? Jupiter and Saturn are not unique in terms of being big gassy planets with much in common and also their own unique features. Same applies to Earth, Mars and, yes, Pluto too. Uniqueness is NOT part of the IAU definition or anybody elses far as I know anyhow.

    the IAU has chosen a particular path, i.e. to exclude objects about which we have too little knowledge, and to ensure that a “planet” is a significant object within the context in which it is found.

    Significance and context is in the eye of the beholder. How significant is significant? Where do we draw the line?

    Earth is found in a region containing a number of similar rocky planets, ditto Jupiter in a regional context containing gas giants and Pluto in a region with similar icy and rocky worlds. You seem to think the number of similar worlds is important, that because Pluto-type planets are more numerous this should rule them out of being planets at all but I don’t.

    Pluto has significant features in common with other planets – moons, an atmosphere, core-mantle-crust internal structure, weather, perhaps rings, etc .. You don’t think these indicate that it should be considered a planet but I do.

    We can keep going around here but I don’t think we’re going to agree.

  101. Messier Tidy Upper

    Continued :

    What makes you think you have any right to dictate to professional astronomers the language with which they work?

    Well for starters, professional astronomers disagree about this themselves. It isn’t just me who thinks the IAU definition is idiotic – it is also Alan Stern and a number of others.

    Secondly, I’m passionate about astronomy, its an area I’ve followed and particpated in for most of my life and so I think I *do* have some idea what I’m talking about here.

    Thirdly, there’s just plain common sense that a decision as silly as the IAU’s anti-Pluto one is NOT immune from criticism however authoritative the group making it may be. As I put it in comment #70 :

    ..to refer back to my earlier anology – if the MAAOW decided to call pogosticks “wheelchairs” and vice versa wouldn’t you say the way they did that was wrong and the change unacceptable?
    Just because you are an organisation of experts in a particular field does NOT mean that there are no limits on your power and does NOT mean that you can change everybody’s language in a way that is plain silly.
    The Geologists Association can’t change the word “rock” to mean air.
    The Zoological Institute cannot change the word animal to exclude birds from being animals.
    Similarly, the IAU cannot change the word “planet” to exclude Pluto.

    Incidentally, I don’t think you ever did answer my earlier questions to you & would appreciate you doing so :

    1) Don’t *you* have any misgivings over the undemocratic, unfair way this Prague IAU definition was imposed ?

    2) If this had been a decision / definition that you were unhappy with would you not point out the poor procedure and flaws that occurred in making it yourself?

    &

    3) If the Biochemical Society was to decide that ‘proteins’ now meant viruses instead would you really be happy to go along with such stupidity? Honestly?

    Plus I’ll ask you again to answer my final question from comment #93 :

    What would it take to convince you that Pluto – and the other ice dwarfs – should be counted as planets?

    Remember too, please that all this started with you asking in comment # 24 here :

    MTU, please explain, using reason rather than emotional appeals, why you still consider Pluto to be a planet as opposed to merely the largest known KBO.

    I really think I’ve done that in the planet~loads of comments I’ve written here since. I’ve explained what I think & why. I’m not sure what more you want or what I need to explain further on this. Clearly we still disagree but I don’t think you can say I haven’t tried or given my reasons!

  102. Nigel Depledge

    MTU (102) said:

    We can keep going around here but I don’t think we’re going to agree.

    It seems that way.

    You contend that the IAU definition is silly (etc.) but your arguments do not sway me.

    You seem to feel it necessary for the technical definition of “planet” to be universally applicable, whereas I see a need for the application of pragmatism (i.e. accommodating what we do and don’t know about such objects).

    You seem wedded to the idea that whatever definition is used, Pluto must remain a planet. I have no idea why you are so wedded to definitions that include Pluto as a planet. AFAICT, it is merely the biggest known KBO of many. And we can’t even be sure that it really is the biggest, because there are bound to be many more KBOs that we have yet to detect. Sure, Pluto bears some superficial resemblances to some of the other planets, but it is nowhere near as significant an object in terms of the influence it exerts within its own region of space. (And, yes, you can quibble about the terminology and about the subjectiveness of such factors, but that ignores the point).

    I have no idea why you even refuse to address one of my main points, that the IAU definition recognises that Mercury, Venus, Earth, Mars, Jupiter, Saturn, Ouranos and Neptune are each unique in a variety of ways, but that Pluto isn’t. Pluto’s only uniqueness stems from its position as the largest known KBO and that it has the largest moon (proportionally) of any known object, and these are trivial things.

    While I might not have chosen to restrict the definition of “planet” to our solar system, I can see a perfectly good reason for doing so, and I can see that the definition is almost certain to change as new information comes in and new discoveries are made, be they in our Kuiper Belt or in other planetary systems around other stars. This factor by itself neutralises one of the main points you have raised, yet you do not acknowledge this.

  103. Nigel Depledge

    MTU (103) said:

    Incidentally, I don’t think you ever did answer my earlier questions to you & would appreciate you doing so :

    No, I had too little time available. And you started answering my responses to your early-fifties comments before I had even got as far as the late fifties, never mind getting through the 60s.

    1) Don’t *you* have any misgivings over the undemocratic, unfair way this Prague IAU definition was imposed ?

    Irrelevant.

    The way a change has been made is a separate issue from whether the change is beneficial or not.

    To be frank, I have not investigated to my satisfaction whether the accusations hold water, so I don’t feel sufficiently well informed on that point to comment. But I do know that I don’t need to know it to comment on whether or not the change is for the better or for the worse.

    If anything, your rants against the IAU over Pluto have convinced me that the IAU definition is reasonable. I won’t say it’s perfect, and it has obvious limitations – but those limitations could easily have been deliberately incorporated – but it is useful and workable, despite your protestations to the contrary.

    2) If this had been a decision / definition that you were unhappy with would you not point out the poor procedure and flaws that occurred in making it yourself?

    I don’t know. Maybe. I would like to think that I can separate in my mind the changes themselves from the way in which they were made.

    &

    3) If the Biochemical Society was to decide that ‘proteins’ now meant viruses instead would you really be happy to go along with such stupidity? Honestly?

    This is not a parallel. The IAU has not defined “planet” as “something that sustains nuclear fusion in its core”, they have merely introduced precision where previously none existed.

    As it happens, “protein” already has a reasonably precise definition, but it could be more precise. For example, if my colleagues in the Biochemical Society were to collectively decide that a protein needed a minimum of 100 amino-acid residues (condensed in linear sequence) to count as a protein and that a linear polymer of 99 amino acids was a mere polypeptide, I’m sure there would be some arguments against the move, but I would at least try to recognise the reasons for the change. The IAU’s definition of “planet” is much more along these lines than the example you give.

    So, to answer your question – if the IAU defined “planet” in such a way as to render all 8 of the existing planets not planets any more, I would indeed oppose such stupidity, in the same way that I would oppose a move to redefine “protein” as “virus”. However, if the Biochemical Society were to attempt to make the term “protein” more precise, then I would probably support such a move.

  104. Nigel Depledge

    MTU (103) said:

    I really think I’ve done that in the planet~loads of comments I’ve written here since. I’ve explained what I think & why.

    Yes, you have, mostly.

    What you have not addressed – or have ignored – is that most of your reasons do not withstand scrutiny.

    You have claimed that the gravitational clearance criterion is silly or illogical, and you cite hypothetical scenarios to illustrate your point (“If Earth were in the Kuiper Belt . . . ” or “If Ceres orbited a different star by itself . . . ” etc.) but you have failed to demonstrate the relevance of those scenarios. You have claimed that any definition of planet must include exoplanets but you don’t really have a rational case – you simply claim it is ridiculous for it not to include exoplanets. Bear in mind, of course, that the IAU has no intention of imposing their definition on common useage – the new definition is a precise definition for technical use.

    You have objected to the gravitational clearance criterion on the grounds that it is vague (how clear is clear, and what volume does a body’s orbital region encompass), but you ignore that the gravitational roundness criterion is similarly vague – so, being logical, one must either object equally to both for this reason or object to neither. To object to one on the basis of its vagueness and not the other is illogical.

    You cite public recognition as a criticism of the IAU definition, but you ignore that any precise definition of “planet” would either include objects of which the public at large is not cognisant, or exclude at least one object that has been considered to be a planet for several decades. Unless the definition is simply “a member of this group of nine objects”, which really would be pointless (although probably workable).

    You seem deliberately to ignore the hefty dose of pragmatism that is – to me – obvious in the IAU definition (it is clearly imperfect, and it contains aspects that are adequate when applied to our solar system but easily shown inadequate by hypotheticals – but it was not devised to include other solar systems) . You also ignore the natural and obvious discontinuity that exists among objects that orbit our sun (and which the IAU definition recognises).

    You have cited the way in which the change was introduced as an argument against the change, but do not acknowledge that this is a separate issue from the change itself.

    You have cited Pluto’s superficial resemblance to some of the planets (atmosphere, weather, seasons, possession of moons, likelihood of active geology) with no acknowledgement that these characteristics are not exclusively planetary. An analogous claim would be that anything with 2 eyes, 2 legs and 2 wings is a bird, when such characteristics also encompass bats.

    And so on. See most of my posts above for why I object to the arguments you propose.

    I’m not sure what more you want or what I need to explain further on this. Clearly we still disagree but I don’t think you can say I haven’t tried or given my reasons!

    Well, this is true enough, but you are moving the goalposts.

    Your objections seem to me to be fundamentally emotional in nature. You certainly have used a fair amount of rhetoric in expounding them (such as your unjustified derisive references to the IAU definition). What I have not seen you make is an objective, rational case.

    The closest you get to a rational objection is that the gravitational clearance criterion is vague, and I have already explained why this is not a good argument against the IAU definition.

  105. Messier Tidy Upper

    @ 104. Nigel Depledge :

    Pluto’s only uniqueness stems from its position as the largest known KBO and that it has the largest moon (proportionally) of any known object, and these are trivial things.

    Are they really? I’ve already answered the “uniqueness issue by saying that uniqueness isn’t a criterion and that there’s almost certainly nothing ‘unique’ to any planet in our solar system. We already know of many worlds analogous to Jupiter and Neptune – albiet most Neptunes found lie much closer to their sun than ours does. Now, okay, we havern’t foudn another Earth or Mars analogue yet but we fully expect to do so one day and have no good reason to rule such exoplanets out.

    While I might not have chosen to restrict the definition of “planet” to our solar system, I can see a perfectly good reason for doing so, and I can see that the definition is almost certain to change as new information comes in and new discoveries are made, be they in our Kuiper Belt or in other planetary systems around other stars. This factor by itself neutralises one of the main points you have raised, yet you do not acknowledge this.

    Acknowledge what? If the IAU definition is so inevitably going to change – and Ithink italready needs changing – then as I’ve already said , let’s make it better right now. Let’s have a better definition that applies to exoplanets and one that inlcudes ice dwarf type planets justas it includes gas giant, gas dwarf and rock dwarf type ones. “This factor” as you call it seems to argue more for my side of this issue than yours!

    @105. Nigel Depledge :

    1) Don’t *you* have any misgivings over the undemocratic, unfair way this Prague IAU definition was imposed ?
    Irrelevant.

    Really? I think it is very relevant and I think you’re trying to evade an answer. You even admit you haven’t looked into this. I think the way this definition was arrived at casts a very big shadow of doubt over its validity.

    You keep saying the IAU has the right to define planet as it chooses, that theprocess is entirely separate fromthe result but, to use an analogy, a dictator may have a legal right under his nations laws to execute politiical dissidents, violate human rights and even destroy cities in his own nation but that isn’t considered valid ethically or reasonable conduct by anyone outside of the dictator and his most blinkered followers.

    A flawed process that isn’t representative, that doesn’t hear equally from the various sides is just NOT going to result in a fair and reasonable definition and does need to be reviewed properly as opposed to unquestioningly defended.

    This is not a parallel.

    Yes it is. It is an analogy of an organistation making a definition that is ridiculous and the IAU definition is in my view and many others ridiculous. It is saying that an object that clearly is a planet – Pluto – is something else. Just as saying that something that is clearly a protein is something else would be ridiculous.

    So, to answer your question – if the IAU defined “planet” in such a way as to render all 8 of the existing planets not planets any more, I would indeed oppose such stupidity, in the same way that I would oppose a move to redefine “protein” as “virus”.

    Actually if you apply the IAU criteria strictly and fairly that is exactly what it does. No planets orbit is clear as comets and asteroids cross all worlds paths from Pluto’s to Mercury’s even tody, our planets probably swapped orbits in the past and a rogue planet entering our solarsystem from deep space could theoretically cross our paths and make all our planets ludicrously into dwarfs by its mere presence. In addition the ability to clear an orbit depends pretty much entirely on where a planet orbits – a world close in on asmall orbit can clear that easily even if its smaller than Ceres whereas even Jupiter couldn’t clear out the Ooort cloud if it happened to wander out there.

    Far from making the definition “more precise” as you suggest, what the orbital clearence (OC) criteria really does is make it much*less so* and raise a tonne of questions over what is meant by “clear” and so on as I’ve already mentioned right from the start. A precise definition is one thing but Occam’s razor says a definition that requires a answering a whole new set of questions more precisely as the OC criterion does is just NOT logically acceptable and must be rejected. Roundness can be easily determined – literally at a glance – and depends only on the object itself whilst this is not the case for OC which depends on location, the amount of material in as planetary system, the orbital trajectories of other bodies, et cetera.

    @106. Nigel Depledge :

    Yes, you have, mostly. What you have not addressed – or have ignored – is that most of your reasons do not withstand scrutiny.

    You make that claim but cannot supported. Everything you claim I’ve not addressed or ignored I have already countered and answered for you. I have pointed out multiple times here where My reasons here *do* withstand scrutiny whether you accept that personally or not.

    You have claimed that the gravitational clearance criterion is silly or illogical, and you cite hypothetical scenarios to illustrate your point but you have failed to demonstrate the relevance of those scenarios.

    See comment # 100 – & # 99 & #68 and, well, think about it. I have indeed shown how the OC is illogical and sillyand how it fials teh Rcutio test and backed that up with many relevant examples. Your refusal to acknowledge this, Nigel, does no credit. :-(

    Your objections seem to me to be fundamentally emotional in nature.

    Yes, because using logic methodology such as Occam’s Razor, Reductio ad absurdum and calling for consistency in matching how we use the term “dwarf star” with how we use the term “dwarf planet” is fundamentally just emotional. Yeah ri-ight. :roll:

    Why may I ask Nigel do you seem so emotionally attached to defending the IAU’s absurd and terminally logically flawed definition?

    What do you have against Pluto and the other ice dwarf planets that you wish to regard them as less than proper planets in their own right?

  106. Nigel Depledge

    MTU (107) said:

    Are they really? I’ve already answered the “uniqueness issue by saying that uniqueness isn’t a criterion and that there’s almost certainly nothing ‘unique’ to any planet in our solar system.

    Obviously, there are plenty of similarities to point out, but each of the 8 main planets is unique in several ways. Certainly, each of these 8 objects is unique within the region of its orbit. And perhaps this is enough.

    We already know of many worlds analogous to Jupiter and Neptune – albiet most Neptunes found lie much closer to their sun than ours does.

    Well, we assume from their masses that they are anaolgous, but we don’t know.

    That is part of why exoplanets should not yet be included in a definition.

    Now, okay, we havern’t foudn another Earth or Mars analogue yet but we fully expect to do so one day and have no good reason to rule such exoplanets out.

    And what do we do in the meantime?

    I can quite easily see that the IAU definition is a good, workable stop-gap to cover the period in which we know that many exoplanets exist but we have very little definitie information abotu them.

  107. Nigel Depledge

    MTU (107) said:

    Acknowledge what? If the IAU definition is so inevitably going to change – and Ithink italready needs changing – then as I’ve already said , let’s make it better right now.

    How?

    Your preferred definition has at least as many flaws as the IAU one, and perhaps one of those flaws is so immense that it would render the system unworkable – that you insist on including exoplanets about which we know almost nothing be included in the definition.

    What is wrong with waiting until we actually know what we’re talking about?

    Let’s have a better definition that applies to exoplanets and one that inlcudes ice dwarf type planets justas it includes gas giant, gas dwarf and rock dwarf type ones. “This factor” as you call it seems to argue more for my side of this issue than yours!

    No. Just because you refuse to acknowledge that our ignorance about exoplanets matters does not change the fact that it does.

  108. Nigel Depledge

    MTU (107) said:

    @105. Nigel Depledge :

    1) Don’t *you* have any misgivings over the undemocratic, unfair way this Prague IAU definition was imposed ?

    Irrelevant.

    Really? I think it is very relevant and I think you’re trying to evade an answer. You even admit you haven’t looked into this. I think the way this definition was arrived at casts a very big shadow of doubt over its validity.

    No, it doesn’t. It’s a completely separate issue.

    I believe that the only reason you cite the way in which the change was introduced as an argument against that change is because you disagree with the change, not because you have some fundamental objection to a change that is introduced in such a way. Turn it around – if they had used the same approach and tactics to introduce a change that you favour, would you as vehemently argue against it? I very much doubt it.

    The present definition has been in place for nearly 6 years now. I am convinced that if enough IAU members disagreed with it, they would have moved to change it.

    You keep saying the IAU has the right to define planet as it chooses,

    For technical uise among professional astronomers, yes.

    that theprocess is entirely separate fromthe result but, to use an analogy, a dictator may have a legal right under his nations laws to execute politiical dissidents, violate human rights and even destroy cities in his own nation but that isn’t considered valid ethically or reasonable conduct by anyone outside of the dictator and his most blinkered followers.

    This is not an analogy.

    The IAU is not a dictator – it is a collection of professionals. Collectively, they have the right to define the terms they use in their profession (with no implication that the general public must also use such terms).

    If a dictator has given himself the “legal” right to do all sorts of unethical things, this would be analogous to a body of professinals giving themselves the right to do some similarly unethical things. You have not made any kind of case that the IAU’s decision to define the term “planet” is unethical. Instead you have suggested that the way in which the definition was introduced was unethical.

    A flawed process that isn’t representative, that doesn’t hear equally from the various sides is just NOT going to result in a fair and reasonable definition and does need to be reviewed properly as opposed to unquestioningly defended.

    You don’t know this.

    It might result in a definition that is fair and reasonable. Or, at least, as fair and reasonable a definition as it is possible to achieve with our present level of knowledge.

    Not especially that the IAU definition is not set in stone, and that no subsequent meeting (to my knowledge) has moved to change the defintion. This implies that those IAU members who feel that they were not adequately consulted either accept the definition and are just getting on with their work, or are a small enough minority that they themselves are not representative of the IAU as a whole (otherwise, they could have got the definition changed subsequently).

    The definition does indeed need to be reviewed rationally, and not unquestioningly attacked.

    You have claimed it is illogical in several ways, but your arguments fail. Your argumentation is illogical, and it has convinced me that the IAU have done the best job that anyone could, given the axioms that:
    1. We have an obvious and natural discontinuity in our solar system;
    2. We know of many exoplanets, but know very little about any of them;
    3. We have no idea when we might accrue detailed information about a representative cross-section of exoplanets (remember that our current knowledge of exoplanets is dramatically skewed towards those that are easiest to detect);
    4. We know of several KBOs that are almost as large as Pluto;
    5. We have no idea what else we might find in the Kuiper Belt;
    6. It is reasonable to suppose that any undetected objects orbiting the sun (in near-circular orbits) closer than the Kuiper Belt must be pretty small.

  109. Nigel Depledge

    MTU (107) said:

    Yes it is. It is an analogy of an organistation making a definition that is ridiculous

    You *still* have not shown this. Stop using childish name-calling in place of argumentation.

    and the IAU definition is in my view

    But you don’t matter, do you? Why should professional astronomers listen to your whining?

    and many others ridiculous.

    No. Not many. A few.

    If “many” professional astronomers objected to the definition, it would have been changed.

    It is saying that an object that clearly is a planet

    No, it is not “clearly” a planet. What Pluto “clearly” is is the largest known KBO.

    Stop assuming your goal can be used as a part of your argument.

    – Pluto – is something else. Just as saying that something that is clearly a protein is something else would be ridiculous.

    But what is “clearly” a protein?

    We loosely classify phosphorylated proteins, glycosylated proteins and myristoylated proteins as proteins, in the same category as proteins that undergo no post-translational modification. Nothing is “clearly” a protein, except under common useage of the term, which is actually pretty vague. There is no exact boundary between a “mere” polypeptide and a protein. Insulin, for instance, has 52 amino-acid residues. Sometimes it is considered to be a very small protein, and others it is considered to be a peptide. There is no clear boundary.

    We don’t have the same issue in our solar system. We have a clear boundary, and Pluto quite naturally falls into the “other stuff” category.

  110. @ ^ Nigel Depledge : ‘We have a clear boundary, and Pluto quite naturally falls into the “other stuff” category.”

    I totally disagree – if Pluto *clearly* fell into the “Other Stuff” category then it would’nt have ever been considered a planet – but it has been, correctly, considered one since its discovery in 1930 up to today when many people still , correctly, reject the IAU’s ruling and we wouldn’t be having this debate at all.

    You keep saying that the boundary between dwarf planets and classical planets is clear but your repeating this assertion doesn’t make it true and I’ve already pointed out how it is in fact NOT at all clear.

    If Pluto orbited closer to the Sun – say where Mars is – and thus had a clear orbit it would unquestionably be considered a full planet.

    If Mercury, Earth or even Jupiter orbited out in the Cometary Cloud they couldn’t clear their orbits and so would be labelled mere dwarfs.

    Clearly then the difference between dwarf planets and IAU-classical ones is merely what part of the solar system they inhabit and this is NOT good or reasonable grounds for distinguishing them.

    I am baffled by the fact that you appear unable to grasp this basic truth.

    If “many” professional astronomers objected to the definition, it would have been changed

    Change takes time and especually when the current old guard have impose dit wrongfullyand thus have a vested interest inmaintaining it. It may well happen that it is changed to restore Pluto and add the other ice dwarfs- the sooner the better! Indeed aren’t you the one arguing that the IAU definition will indeed eventually have to be changed to allow for exoplanets?

    ,You *still* have not shown this. Stop using childish name-calling in place of argumentation.

    It isn’t name-calling it is an accurate analogy. Calling something that is ridiculous “ridiculous” is entirely justified by the facts. Calling a definition that is bad “bad” and explaining how it is bad is NOT name-calling. I have made my case to you here as best I can – if you refuse to accept my logic as has been presented repeatedly for you here then that is your problem not mine. You calling me a “name-caller” and “childish” for pointing out the metaphorical emperors nudity is wrong and a false allegation. I expect better from you.

    Why should professional astronomers listen to your whining?

    Because I’m right. ;-) :p

    Also it isn’t “whining” but legitimate criticism and there’s no law or reason to exempt the IAU or indeed any scientific body from legitimite rational criticism.

  111. @110. Nigel Depledge :

    No, it doesn’t. It’s [the undemocratic , flawed process – ed.] a completely separate issue.

    No its not a separate issue and I’ll note that again you dodged the question and refused to give a straight answer.

    I believe that the only reason you cite the way in which the change was introduced as an argument against that change is because you disagree with the change, not because you have some fundamental objection to a change that is introduced in such a way.

    The fallacy of attributing motivations and strawmanning on your part. I asked before and you refused to answer so I’ll ask again for you to look at it from the other angle:

    If the IAU had (correctly) defined Pluto – and Eris, Ceres, Sedna etc .. as proper planets would *you* be arguing against that now?

    Turn it around – if they had used the same approach and tactics to introduce a change that you favour, would you as vehemently argue against it? I very much doubt it.

    If I thought the process at arriving at a even a good definition was flawed – unfair and undemocratic – then I’d certainly admit that I thought the process, the *method*, of arriving at the definition was flawed and undemocratic.

    Wouldn’t you agree that is the case here; that the way the decision was arrived at – at the last minute with many of the key actors such as Alan Stern absent and with a minority of a minority making a decision that effects everybody – at the very least is dubious and raises a lot of questions over its validity?

    Look again at and mull over more, please, the facts as noted in point (9) comment #29 :

    For instance, of the 10,000 IAU members only 2,500 attended the 2006 Prague meeting that demoted Pluto and rejected the other planetary candidates, Eris, Charon and Ceres from planetary status. Furthermore, of those 2,500 only the merest handful – just 424 actually got to vote making therefore a very unrepresentative decision. Among those to excluded from voting and arguing their case in that last minute meeting were some highly relevant and articulate people – notably Pluto expert Alan S. Stern.

    Would a debating team be considered legitimate winners of a debate if they maliciously prevented the other side from showing up and participating at all?

    The present definition has been in place for nearly 6 years now. I am convinced that if enough IAU members disagreed with it, they would have moved to change it.

    Slavery and various forms of racial, sexual and other discrimination were in place for many decades indeed centuries too. Did that at any stage make those things right?

    Same applies here – the length of time a bad idea or definition lasts doesn’t make it any less bad.

    The IAU’s refusal to change their bad definition shows that they are too proud and not willing to accept the reality and because they are the self-appointed authorities here doesn’t make them right in this case.

    ****

    PS. Have to head off now. I’ll return to this again once home.

  112. @110. Nigel Depledge :

    For technical uise among professional astronomers, yes.

    So, what about everyone else? Or are we to have two definitions of planet one strict and absurd one for the IAU and another for the public that is broader and actually makes more logical sense? Hmm ..

    You have not made any kind of case that the IAU’s decision to define the term “planet” is unethical. Instead you have suggested that the way in which the definition was introduced was unethical.

    See the above comment and point (9) comment #29. If something is as undemocratic, unfair and generally dubious as the IAU definition was then trying to foist this controversial and unpopular definition upon everyone else is surely verging on unethical – okay not major league physically hurting people unethical but unethical nevertheless.

    Picking on the smallest planets and denying they even *are* planets also strikes me as unethical. In the same way that you don’t discriminate against dwarf people and deny them their personhood and humanity it seems to me you also should avoid discriminating against small planets and denying them their planethood and full planetary status.

  113. Continued :

    This is not an analogy.

    It is an analogy. You may not consider it an apt one perhaps – but I do.

    The IAU is not a dictator – it is a collection of professionals.

    A collection of professionals that is, in my view, in this instance behaving badly and dictatorially in trying to impose a ridiculously bad definition on everyone else. Collections of professionals can act badly and be wrong too y’know.

    “A flawed process that isn’t representative, that doesn’t hear equally from the various sides is just NOT going to result in a fair and reasonable definition and does need to be reviewed properly as opposed to unquestioningly defended.” -MTU
    You don’t know this. It might result in a definition that is fair and reasonable. Or, at least, as fair and reasonable a definition as it is possible to achieve with our present level of knowledge.

    Is that a possibilty? Perhaps it is. But is it *likely* – I doubt it. Is the way of arriving at such a definition dubious and in need of reviewing including setting aside the definition reached that way and reassessing it in a proper debate where all sides get a fair go? Too right it is!

    That’s why there are retrials on dodgy court cases y’know! If the judges are biased and certain key evidence and witnesses and even defence lawyers get omitted or prevented from making their case then a convicted criminal can rightly appeakl for teh original verdict to be quashed and a retrial or pardon ordered. That’s analogous to the Pluto case here.

    This implies that those IAU members who feel that they were not adequately consulted either accept the definition and are just getting on with their work, or are a small enough minority that they themselves are not representative of the IAU as a whole (otherwise, they could have got the definition changed subsequently).

    .. Or just that those with power in the IAU have a vested interest in trying to maintain the status quo and are simply unwilling to admit they made a mistake even when it is very obvious to many that they have.

    You have claimed it is illogical in several ways, but your arguments fail. Your argumentation is illogical,

    On the contrary my argumentation is very logical and my arguments are good ones whether you are willing to accept that or not.

    .. and it has convinced me that the IAU have done the best job that anyone could,

    Well that saddens and baffles me because I fail to see how you can have reached that erroneous conclusion.

    given the axioms that:

    That word ‘axiom” I do not think it means what you think it means! ;-)

  114. Final part for tonight before I collapse of sleep exhaustion :

    given the axioms that:

    So what’s an axiom – lets check with that fount of allknowlegde wikipedia (click on my name for link to source.) :

    In traditional logic, an axiom or postulate is a proposition that is not proven or demonstrated but considered either to be self-evident or to define and delimit the realm of analysis. In other words, an axiom is a logical statement that is assumed to be true. .. (snip) .. Logical axioms are usually statements that are taken to be universally true..

    Now then lets see if these are really axioms :

    1. We have an obvious and natural discontinuity in our solar system;

    Really?

    Well, we do have the Sun and then the planets but I don’t think that’s what you mean is it?

    We have Jupiter and that contains most of the solars ystems mass and then we have all the rest of the planets from Saturn to Ceres which, uh, don’t.

    We have gas giant type planets, ice giant planets, rock dwarf planets and ice dwarf planets which have various similarities and differences.

    We have planets close to the Star and further out and in the middle dividing roughly into rocky, gassy and icy (ice -rock mixes technically) categories but all being round by gravity, non-self luminous from nuclear fusion and not moons.

    You have inner planets – Mercury and Venus without any moons and outer planets from there onwards with moons (except for Ceres or so we now think! ;-) )

    So you have a whole range of possible “obvious and natural discontinuities” to choose from.

    Which is important and relevant? Which is worth choosing as a defining feature? This is far from axiomatically clear!

    Choosing that as an axiom would be to making a false assumption and creating a false axiom that does not stand up to scrutiny and questioning. You would say, I guess that the divide between the realm of ice dwarf planets and others is all important and most relevant – but I totally disagree and say the common features the ice dwarf planets have is more important than their differences just as the very large differences between the rock dwarfs and gas giants does not lead to the conclusion that Earth or Jupiter are other than planets.

    2. We know of many exoplanets, but know very little about any of them;

    That rather belittles the huge amount of study and knowledge that exoplanet hunters like Sara Seager, Debra Fischer and Geoff Marcy have obtained for us through their intellectual sweat and hard laour doesn’t it? :-(

    Its also wrong – we do indeed know quite a lot about exoplanets and our knowledge is improving all the time.

    That “axiom” of yours too falls into the false assumption – and far from axiomatically obvious – category.

    3. We have no idea when we might accrue detailed information about a representative cross-section of exoplanets (remember that our current knowledge of exoplanets is dramatically skewed towards those that are easiest to detect);

    See above. Look at teh kepler, Corot and other sites exoplanet~wise. We’re getting a lot of results and information really rather quickly and, in any case, that isn’t axiomatically relevant to the question of how to define planet.

  115. D’oh! Okay call this the Epilogue part – because editing time ran out before I could quite finish :

    @110. Nigel Depledge :

    4. We know of several KBOs that are almost as large as Pluto;

    So what? We know of several rock dwarfs that are almost as large as Earth but that doesn’t stop Earth being a planet and we know of several gas giants in around the same region of space whose diameter approaches Jupiter’s but we’re not saying that axiomatically makes Jove a dwarf planet are we!? ;-)

    That fails the qualifying for axiom on two groudns – it is, in fact, an irrelevant non-sequiteur and it is far from self evident as a logical starting assumption.

    5. We have no idea what else we might find in the Kuiper Belt;

    Same applies as above. Again so what, again an irrelevant non-sequiteur and not a self-evident logical assumption.

    We may or may not find other larger planets in the Edgeworth Kuiper cometary belt. If we do they deserve to join the list of known planets. But then maybe we won’t. Either way that isnt self-evidently relevant to defining “planet.”

    6. It is reasonable to suppose that any undetected objects orbiting the sun (in near-circular orbits) closer than the Kuiper Belt must be pretty small.

    Again, so .. ? Also what if we find a Hot Jupiter in a very short circular orbit that never or very rarelytransist the Sun.

    Now this is unlikely I’ll grant you – but its not impossible or unreasonable in the sense that it is not a reasonable concept.

    Such a hypothetical solar Hot Jupiter could be in such a tight orbit that it never strays far enough from our Sun to be detected but is just far enough away that it isn’t noticed in SOHO or SDO images. It could have formed from another protoplanetary disk* at another angle that formed around our daytime star much earlier then migrated all the way into its just out-of sight orbit whilst the rest of that disk disappeared or fell into the one that formed our ecliptic planets – Sedna and “Buffy” could even be outer survivors of this second rightangle sprotoplanetary disk! ;-)

    Highly, improbale and amazing that we wouldn’t have unambigously detected sucha world. Indeed but it isn’t impossible or unreasonable. Improbable and unreasonable are not entirely identical notions remember! ;-)

    * Stars with more than one protoplanetary disk have in fact been found although perhaps none yet quite as extreme as that hypothetical Solar hot Jove forming scenario! 8)

  116. Cheyenne

    Just a test is all

    and this too

    He says

    but i think it should be whatever blah blah

    yes i agree

NEW ON DISCOVER
OPEN
CITIZEN SCIENCE
ADVERTISEMENT

Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

ADVERTISEMENT

See More

ADVERTISEMENT
Collapse bottom bar
+

Login to your Account

X
E-mail address:
Password:
Remember me
Forgot your password?
No problem. Click here to have it e-mailed to you.

Not Registered Yet?

Register now for FREE. Registration only takes a few minutes to complete. Register now »