Pluto at the top of the key

By Phil Plait | September 22, 2010 10:21 am

Astronomer Mike Brown is a friend of mine. He’s a pretty nice guy, and while he’s not exactly sad that he was instrumental in getting Pluto demoted from its planethood status — his Twitter handle is @PlutoKiller, after all — I don’t think he deserves all the slings and arrows he’s received.

ronartest_gazooAnd he certainly doesn’t deserve an elbow to the nose, as LA Laker Ron Artest recently said. I can understand Mr. Artest’s lament at some level, but physical punishment will only redouble Mike’s efforts, and who knows what will happen then! We might lose Neptune.

So if I had to think of suitable punishments, they’d be

1) a pie to the face,

2) a Benny Hill-style rapid-repeat slap on the top of the head,

3) a dressing down by Goofy, or just possibly

4) more telescope time.

I don’t think he’d disagree with any of these, with the exception of getting a pie to the face before more time on a telescope. Whipped cream is hard to get off a 10-meter mirror.

Tip o’ the nose guard to Jerome Clemente. Image credit: Ball Don’t Lie.

CATEGORIZED UNDER: Astronomy, Humor
MORE ABOUT: Pluto, Ron Artest

Comments (101)

  1. plutosdad

    My dog is named Pluto, and everybody loves him too! He told me he’d bite Mr. Brown in the shin, unless Brown gives him a treat.

  2. Michel

    Kicking out Pluto was dumb. What will aliens think of us.
    “Look they are so picky about their planets that they kick the small ones out”
    And then they take them.
    Nobody makes his territory smaller!
    Nobody!
    If you´ve got it, stick to it.

  3. You forgot the name of his upcoming book: How I Killed Pluto and Why It Had It Coming[emphasis mine]

    Now as a hardened pro-Mike Brown, pro-dwarf planet status for Pluto partisan, I take this news as more evidence of the violent, illiberal, and generally irrational nature of the unwashed “Pluto is a planet” masses. ;)

  4. Chris

    The first link on his twitter feed is pretty funny
    http://tumblr.com/xuwj8e5vb
    Although I think Pluto is now the second biggest member of the Kuiper belt after Eris (It’ll still always be Xena to me!)

  5. Actually, I don’t think Mike Brown had that much to do with it (and Artest doesn’t name him). Pluto was on the skids before ever Eris came along.

    The guy who keeps bugging the police with his ‘confession’ usually isn’t the murderer.

  6. I’m a little surprised that fundamentalist Xians haven’t taken up a ‘not a planet’ crusade. With all the other nonsense they peddle you’d think they’d be big on demoting the object named after the lord of the underworld.

  7. Yeah, I’m sure he would prefer the telescope time.

  8. Pie in the face, bucket of water propped up on a half-open door, and a serious, serious wedgie. Pluto’s a planet. So THERE!

  9. Michael Swanson

    If Pluto is a planet, then so are a half dozen KBOs that we know about the potentially huge number that we don’t. So it’s much, much easier to simply come up with another category than to start arguing about even more borderline icy rocks a few billion miles from the Sun.

    I don’t know why people can’t get over this. (Just wait until it’s again recategorized 75 or 1000 years from now and people start crying, “But It’s a dwarf planet! It’s always been a dwarf planet! You’ve robbed me of my childhood memories!”)

  10. Gus Snarp

    Mike Brown spoke at my local observatory recently and I really wanted to go, but couldn’t get a sitter (4 year olds and infants aren’t known for sitting through astronomy lectures, no matter how interesting), but he was billed in the publicity materials as the “demoter of Pluto”.

  11. Guysmiley777

    If Pluto is a planet, these people freaking out need to start memorizing all the other large Kuiper Belt objects as well.

    Childhood wistfulness be damned, the number of planets WAS going to change from 9, one way or the other. Saying “No! I learned 9 and it will always be 9!” when presented with new evidence is pretty much the opposite of science.

  12. Michel

    @Michael Swanson
    They should also have been put into our solar system. Now they are up for grabs!
    And one of these days some passing aliens will grab them.
    And were would stand then?
    Hey?
    But noooooo, you take the easy way out.
    Simply come up with another category.
    peacemongerer

    [/ ;^) ]

  13. Gus Snarp

    My only problem with Pluto not being a planet is that I don’t know how to finish singing “Interplanet Janet” anymore.

  14. Michael Swanson

    @ 12. Gus Snarp

    “My only problem with Pluto not being a planet is that I don’t know how to finish singing “Interplanet Janet” anymore.”

    Hadn’t thought of that. Pluto needs to be a planet again. Nobody ****s with Schoolhouse Rock.

  15. Adrian Lopez

    @Michael Swanson

    “If Pluto is a planet, then so are a half dozen KBOs that we know about the potentially huge number that we don’t.”

    So you think Pluto should be categorized according to convenience rather than according to how similar Pluto is to the objects we continue to call planets? Do you also have no problem with the notion that dwarf planets aren’t actually planets, or the fact that dwarf planets are defined according to extrinsic criteria such as those which, coupled with a dwarf planet’s own gravitational pull, prevent the dwarf planet from clearing its particular orbit?

  16. Dashukta

    @Adrian Lopes (#16)

    My understanding is that Pluto is more similar to those other KBOs, not the 8 “planets”, anyway.

    So its more Boolean: IF Pluto is a planet with full planetary honors, than so are all those other KBOs, but if those other KBOs are not full-on planets, then by definition neither is Pluto. Call them whatever you like: dwarf planets, planetoids, planet-like objects, but whatever you call them, Pluto is one.

  17. Wait, a professional athlete is acting violently and irrationally . . . this can’t be right.

  18. Justin

    I would think Artest would be comfortable with the reclassification- in the linked article he claims to be 25 when, as some commenters over there pointed out, he’s actually 30. That, or he’s just not a fan of applying accurate labels based on verifiable data.

  19. Michael Swanson

    @ 16. Adrian Lopes

    What Dashukta said.

    It’s not like a classification absolutely defines how we look at an object. At its most fundamental level, a classification is a convenient way of finding a book on the shelf, or specimen in a drawer. If you get too caught up in it arguing about it, then you waste too much time fighting over what to call, for instance, a platypus, rather than simply studying the platypus in an attempt to fully understand it.

    The Pluto reclassification seems simple enough to me. It’s more like the many other KBOs than the eight large bodies closer in, so let’s call it something else. Frankly, if the consensus had been to skip “clears its orbit,” then I’d be perfectly happy waking up one morning and finding out that IAU had decided that we now have 10 or 12 or 15 planets. It wouldn’t change how we study them, it would just make any book called “The Planets” that much thicker.

    I know that I’m 0versimplifying, but really – how has adding the word “dwarf” to Pluto’s description altered your perception of it?

  20. Is an athlete’s response to something he disagrees with always physical violence?

    And keep that whipped cream away from our mirror segments! We just finished re-coating!

  21. mike burkhart

    How about banishment to Pluto . He can live in exile . Now I know things are bad on Pluto : pepuatal darknes (sun only appers as a bright star in the sky of Pluto) surface frozen , in fact Plutos atmosphere is frozen on its surface (Its cold out there) but I’m sure he will adapt.

  22. I don’t remember “Interplanet Janet” (though I do remember “Schoolhouse Rock”).

    My problem is that I’ll never know what my very educated mother just served us.

  23. Gus Snarp

    I’ve tried singing, “Pluto, little Pluto was the farthest planet from our Sun.” instead of, “Pluto, little Pluto is the farthest planet from our Sun.” But then the kids ask, “What happened to Pluto? Was it destroyed?” “Yes, son. Mike Brown, also known as Darth Sidious, and his apprentice Phil Plait, AKA Darth Vader, built a huge space station with a weapon powerful enough to destroy an entire planet. And in spite of Plait constantly moaning about how they shouldn’t have enough mass to have earthlike gravity on the station when it was smaller than the moon, and how it somehow travels faster than the speed of light with no visible means of propulsion and no evidence of any time distortion effects, and that its weapons somehow made noise in the vacuum of space, and it fired a weapon of such destructive power but was unaffected by the force of the weapon or the subsequent explosion, they flew the weapon, called the Death Star, out to Pluto and vaporized the planet for no apparent reason. All that is left of it now is the Kuiper Belt.

  24. Keith Bowden

    Of course Pluto’s a planet; it’s a dwarf planet. (See? “Planet” is in the name.) ;)

    Just because I’m a white man, that doesn’t mean I’m not a man. We’ve got rocky planets, we’ve got giant gas planets, we’ve got failed stars (oops, that is insulting).

    I think people are just looking at “dwarf” as a pejorative.

  25. Michael Swanson

    @24. Gus Snarp

    I find your lack of faith disturbing.

  26. Adrian Lopez

    @Michael Swanson,

    I understand that an object’s classification does not determine the object’s properties, but I do think an object should be classified according to its intrinsic properties using labels which are free of contradictions. A definition in terms of an object clearing its orbit makes sense if the thing you are describing is the object *and* its neighborhood. If you’re only describing the object, however, a definition that includes the object’s neighborhood is problematic. As for labels, calling something a “dwarf planet” makes sense if the thing being described is in fact a planet, but if the object is not a planet then calling it a *dwarf* planet (dwarf being the adjective, planet being the noun) is problematic.

    You offer a platypus as an example of a thing that’s hard to classify. Whether or not that is true, it reminds me of something Richard Dawkins said in one of his books. I can’t remember his exact words, but his point was that out of the many possible taxonomies for living organisms, there is one and only one that is actually correct.

  27. Annalee Flower Horne

    Oh, he can just wait. The King of the Kuiper Belt Will Have His Vengeance!

    The reason the “it’s more like a KBO than it’s like the eight planets in our system” argument doesn’t work for me is that I don’t understand why it wouldn’t work equally well to say that Mercury, Venus, Earth and Mars are more similar to belt objects than they are similar to the four planets in our system. (I don’t mean that rhetorically–I actually don’t understand, and would be happy to have it explained to me).

    But I also don’t think anyone should mistake my arguments for legitimate scientific discourse. Pluto’s a planet because “My Very Educated Mother Just Served Us Nectarines” sounds silly. And I’m an American, which means that the scientific community is required to yield to my emotional and aesthetic sensibilities. True story. It’s in the rules.

  28. Jamey

    You know, a Jupiter-massed object in the deeps of the Kuiper Belt probably wouldn’t have had time to have cleared its orbital track – and really, how well has Jupiter cleared *its* track? See all those Trojan asteroids lately? Nah – I say if its self-gravitates to an oblate shape consistent with its spin, then it’s a planet. Yeah, that lets in Ceres. I’m cool with that.

    Maybe I’m just an inclusive instead of exclusive kinda person.

  29. Cindy

    Ken B #23:

    Easy, change it to “My Very Educated Mother Just Served Us Nachos”. (or noodles …)

    Not only that, but you don’t have to worry about changing the lineup during the times when Pluto is closer to the Sun than Neptune.

  30. Aron Elvis

    I think he should just listen to Jonathan Coulton’s “I’m your moon” song about 5 times. It’ll tear him up inside.

  31. I’m sorry, but the other KBOs and “dwarf planet” objects were never considered planets for 70-plus years. Pluto was/is. FOR 70-PLUS YEARS! So the argument we should complain/memorize/bemoan-the-fate-of all other KBOs or DPs doesn’t hold any water. No kid of mine will ever have cause to feel they were “robbed of a childhood memory” when sanity is restored and Pluto is once again called what it is and always has been since 1930… a PLANET!

  32. Georg

    Strange!
    Why all this fuss about Plutos status in US?
    There is nothing to be compared to this in Europe.
    Is Pluto in American possession?
    Georg

  33. rob

    o, be some other name!
    what’s in a name? that which we call pluto
    by any other planetary classification convention would orbit as sweet;

  34. Michael Swanson

    I just don’t get the argument is so emotional. I keep wondering when someone’s going to throw a chair at Neil deGrasse Tyson on Jerry Springer.

  35. Michel

    Adding dwarf to anything might be seen as politically incorrect.

  36. Nemo

    Is Pluto in American possession?

    It was discovered by an American, which some have proposed as an explanation for the misplaced passion. But I don’t buy it — for that to be the issue, it would imply that people actually knew something about Pluto, beyond “it’s a planet!!!1!”.

    Seriously, although there are some exceptions, I think the level of knowledge about Pluto tends to be inversely proportional to the degree of caring about its classification. After all, if all you know about it is “it’s a planet” or even “it’s the ninth planet”, and then someone comes along and says “no it’s not”, they’ve robbed you of the only thing you thought you knew about it. If you know more, then its planetary status means less.

    I can’t wait for New Horizons!

  37. Georg

    Have/had American children to learn the planets names by heart?
    If one changes something like that, reaction can be very irrational.
    Its like altering the words of the Lord’s Prayer or omitting out the
    10th commandment .
    Georg

  38. amphiox

    I can’t remember his exact words, but his point was that out of the many possible taxonomies for living organisms, there is one and only one that is actually correct.

    Read that whole section carefully. Dawkins is pointing out that living organisms have only one correct taxonomy because of common descent, and only because of common descent. For all other cases (Dawkins gives many examples), this is not true, and neither is it true for planets. Planets do not derive from common descent. Classification systems of physical objects like planets are always arbitrary, and multiple systems are equally valid. Where we may compare them for “correctness”, the only criteria that can reasonably be used is usefulness, and that of course brings up the question “useful for what?” which will vary from application to application.

  39. amphiox

    I’m sorry, but the other KBOs and “dwarf planet” objects were never considered planets for 70-plus years. Pluto was/is. FOR 70-PLUS YEARS!

    And how is that relevant? Ceres was considered a planet for about 1 year, and then was demoted for the exact same reason Pluto was. The parallels are almost absolute. Astronomers even invented an entirely new classification of objects (they called them ‘asteroids’) into which Ceres and its fellows were placed. In fact, the only difference between Ceres and Pluto is that at the time of its demotion, Ceres was still (and still is!) the largest known object of its type. Unlike Pluto.

    Is there something qualitatively different between 1 year and 70 years? Is there a statute of limitation on error, such that if you are wrong for longer than that you suddenly become right?

  40. amphiox

    The reason the “it’s more like a KBO than it’s like the eight planets in our system” argument doesn’t work for me is that I don’t understand why it wouldn’t work equally well to say that Mercury, Venus, Earth and Mars are more similar to belt objects than they are similar to the four planets in our system. (I don’t mean that rhetorically–I actually don’t understand, and would be happy to have it explained to me).

    Mercury, Venus, Earth and Mars aren’t more similar to the belt objects than the other four planets in the solar system. All of them (that is all the planets, all the asteroids, and all the KBOs as well) are gravitationally acreted collections of the same combination of starting materials, the ratios of which depend on the distance from the sun. At the core of a planet like Jupiter is a rocky ball several times bigger than earth, so for all intents and purposes the only difference between earth and Jupiter is the thickness of the atmosphere that surrounds the rocky core.

  41. amphiox

    You know, a Jupiter-massed object in the deeps of the Kuiper Belt probably wouldn’t have had time to have cleared its orbital track – and really, how well has Jupiter cleared *its* track?

    What is the ratio of Jupiter’s mass to the total mass of all objects in its orbital track? For Jupiter, and all the 8 planets, it’s >99%. In fact I think Mars is the only one that is less that 99.9%. For Pluto it is <1%.

    The orbits of ALL the objects in the vicinity of Jupiter's orbital tract are controlled by Jupiter's gravity – they are in Lagrange points, or in resonance, etc, with Jupiter. The orbits of pretty much NONE of the known KBOs is in any way shape or form affected even the slightest by Pluto's gravity.

    Using such numbers as a cut-off is of course arbitrary, but the difference between Pluto and the other eight planets is clear and obvious no matter how you slice it.

  42. amphiox

    Can we do model simulations to see if a given planetary mass will clear out its orbit in a given period of time in a given configuration of other large objects? The question of whether a Jupiter sized object could clear out the Kuiper belt could be settled that way.

    I’m guessing that the answer will be easily yes. If I recall, we already have observations of very young protoplanetary disks with debris belts analogous to the Kuiper belt that have gaps in them where known or suspected Jupiter-sized planets have cleared them.

  43. Adrian Lopez

    @amphiox

    “Classification systems of physical objects like planets are always arbitrary, and multiple systems are equally valid.”

    They are not, however, *completely* arbitrary. Whatever flexibility exists is still constrained by reality and logic. It makes little sense to refer to something that is not a planet as a “dwarf planet”, and the notion that a planet is not a planet if you change its orbit is at least problematic.

  44. Messier Tidy Upper

    I blame the IAU not Mike Brown and I hope their current absurd and I think very wrong definition is reviewed and scrapped and replaced by a better definition that includes Pluto, Eris, Ceres and the other dwarf planets.

    If Earth or even Jupiter orbited out in the Edgeworth-Kuiper cometary belt then Erath or Jupiter would cease to be planets and become dwarf planets instead. That’s IAU definition FAIL right there.

    If Pluto orbited inside the orbit of Mars it would be a planet and a bright one at that.

    If a dwarf star is still a star – and our Sun and 90% of all stars *are* dwarf (main-sequence) stars then why the blazes don’t we count dwarfs planets as planets in the same consistent way?

    Nope the IAU definition fails the tests of logic, science and linguistic convention. It is absurd and downright stupid.

    Besides it is ignored in practice anyhway – who here has ever used the terms “classical planet” for those from Mercury to Neptune or the clunky long-winded “small solar system bodies” for asteroids and comets?

    Plus the IAU definition excludes exoplanets and anyhow are their rules even legally binding or just a matter of convention? Not to mention the fact that the decision making in Prague was highly dubious and only a tiny areguably unrepresentative minority of astronomers. We need a reveiw and a re-examination of the Planet definition that comes to a reasonable decision methinks.

    We do need a good definition and there is a contiuuum of object sizes and fuzziness at the boundaries.

    I would suggest a three part definition similar to thecurrent one but dropping the silly “orbital clearing” criterion. An object is a planet to my way of thinking if :

    1. Its orbits a primary star or brown dwarf directly or a barycentre inthecase of double planets. If it orbits aplanet rather than a star it is a moon instead.

    2. It is large enough to be round or elliptical for rapidly spinning objects like Haumea via its own gravity.

    but ..

    3. It is not so round that shines via nuclera fusion of any kind such objects being brown dwarfs or stars.

    Simple. Workable, easy to tell. What’s wrong with using that instead?

    We cna then break planets down into categories eg. rocky, gas giants , ice dwarfs etc ..

  45. Messier Tidy Upper

    Nor am I alone in thinking this – Ken Croswell is among many great astronomers and science writers who have spoken out against the unfair, illogical and undemocratic demotion of Pluto by the rubbish IAU definition -see :

    http://kencroswell.com/NinthRockFromTheSun.html

    and it is also interesting to check out the questions Croswell asks here :

    http://kencroswell.com/PlutoQuestion.html

    & here :

    http://kencroswell.com/PlutoQuestion2.html

    I’d also recomend folks read Croswell’s article ‘Extrasolar Neptune-Pluto Analogue Discovered’ (February 18, 2009) on a set of two jovian exoplanets orbiting the star HD 45364 the same orbital relationship as Neptune and Pluto have. Yet no-one would say that doesn’t make the smaller of the two jovians a dwarf – it would be silly to say so!

    Just as its silly to suggest a definition which would make Earth or Jupiter or Pluto not a planet just for orbiting a lot further out as opposed to further in. A planet’s a planet wherever it orbits and however small it might be!

    Moreover, while for a long time Pluto has been seen as odd for having an extremely tilted and elliptical (eccentric) orbit, today we know this is not uncommon for other planets. After all, there is a whole class of eccentrically orbiting exoplanets incl. one of those orbiting Upsilon Andromedae which is tilted wa-aay out of the ecliptic plane for that system. We know – and the BA has posted here of Jupiter-sized exoplanets that have orbits like comets (eg. HD 80606b) and of Hot Jupiters (eg. HD 209458 b) that have comet-like tails being stripped away by their star’s intense radiation.

    Planets can be stranger and make up a far broader category than we used to imagine. In this context the IAU’s narrow and overly exclusive definition makes little if any sense.

  46. Messier Tidy Upper

    In any case, Pluto does indeed gravitationally dominate its local region otherwise it wouldn’t boast three moons incl. one very large one.

    Another thing to remember here too is that if we look at the continuum of objects in our solar system and the majority of the planets and dwarf planets making it up then Pluto really isn’t, actually, relatively all that small. It may be smaller than the gas giants, the rocky planets and Eris but Pluto is larger than Makemake, Haumea, Sedna, Quaoar, Varuna, Ceres, Ixion, Huya, Orcus, “Buffy” (2004 XR190), Vesta, “Dracula” (2008 KV 42), et cetera..

    If we use the reasonable definition of planet like that I’ve suggested or another reasonable definition that includes dwarf planets as one type of planet then, far from being the smallest planet, Pluto is about medium or even larger than most – and the majority of planets are ice dwarfs.

    We’d then have three major divisions of planet in our solar system – the gassy, the rocky and the icy with most planets belonging to the icy category and Pluto being among the largest of that class.

    To me, that makes a hell of a lot more sense in every way of looking at things than the IAU’s definition.

    Adopting this idea in place of the IAU’s ludicrous definition also restores Mike Brown’s honour as a discover of a planet (or more) and clears him of the odius charge of committing “planetcide”. :-)

    I really hope something like this happens one day and the IAU eventually see reason here.

  47. Tribeca Mike

    Not being a basketball fan, at least since the great Kareem Abdul-Jabbar retired, I have no idea who Ron Artest is. But he does sound like someone my beloved Red Sox could use next season.

  48. Nigel Depledge

    Michel (3) said:

    Kicking out Pluto was dumb. What will aliens think of us.

    What, so you think trying to make the word “planet” mean something was dumb, do you?

  49. Nigel Depledge

    Mark (9) said:

    Pluto’s a planet. So THERE!

    So, two questions for you:

    1) How many planets are there in the solar system?
    2) What does the word “planet” mean?

  50. Nigel Depledge

    Adrian Lopez (16) said:

    So you think Pluto should be categorized according to convenience rather than according to how similar Pluto is to the objects we continue to call planets?

    Actually, I think the commenter was saying the opposite of this.

    I.e., if you categorise Pluto as a planet, you must also include a bunch of other KBOs that are also large enough to be made round by their own gravity. This is not convenience – this is systematism.

    Do you also have no problem with the notion that dwarf planets aren’t actually planets,

    Do you have a problem with the notion that dwarf planets are a distinct category of objects in our solar system?

    or the fact that dwarf planets are defined according to extrinsic criteria such as those which, coupled with a dwarf planet’s own gravitational pull, prevent the dwarf planet from clearing its particular orbit?

    If you have a problem with a “planet” needing to gravitationally dominate its orbital path, tell me how many planets there are in the solar system please.

  51. Nigel Depledge

    Michael Swanson (20) said:

    Frankly, if the consensus had been to skip “clears its orbit,” then I’d be perfectly happy waking up one morning and finding out that IAU had decided that we now have 10 or 12 or 15 planets.

    Me too.

    But it might have been closer to 25 or 30, since it would have included Ceres and a handful of other Asteroid Belt objects (can I call them ABOs?).

  52. Nigel Depledge

    Mike Burkhart (22) said:

    . . .Plutos atmosphere is frozen on its surface . . .

    Only for about 1/3 to 1/2 of its year.

    The rest of the time, Pluto’s atmosphere is an atmosphere.

    Otherwise we’d call it, y’know, the surface.

  53. hevach

    @27. Adrian Lopez Says

    The “clears its orbit” definition doesn’t define the neighborhood as part of the planet. It defines a planet, in part, by the influence it has on its neighborhood.

    And ultimately, in a system defined by gravitational interactions, everything’s status in that system is based on the influence it has on the rest of the system. A planet is of high status, having a strong local influence on the system, gas giants are a class apart from rocky planets because they have a much greater influence still (I’d even say Jupiter has a higher influence on the solar system than the sun – the sun sits in the middle while things happen around it, but Jupiter moves relative to the system, throwing all kinds of stuff everywhere like a giant gravitational snow plow).

    An asteroid is of very low status, having minimal influence on anything it doesn’t actually collide with. A dwarf planet is somewhere in between, not enough influence to quality as a planet but enough to set it apart from other minor objects.

  54. Nigel Depledge

    Adrian Lopez (27) said:

    I understand that an object’s classification does not determine the object’s properties, but I do think an object should be classified according to its intrinsic properties using labels which are free of contradictions. A definition in terms of an object clearing its orbit makes sense if the thing you are describing is the object *and* its neighborhood. If you’re only describing the object, however, a definition that includes the object’s neighborhood is problematic. As for labels, calling something a “dwarf planet” makes sense if the thing being described is in fact a planet, but if the object is not a planet then calling it a *dwarf* planet (dwarf being the adjective, planet being the noun) is problematic.

    OK, how would you define the term “planet”?

    And how many planets would that give our solar system?

    I realise that the ability to gravitationally dominate its orbital path is not an intrinsic property of an object, but why is that a problem? Do you have a problem with the IAU’s distinction between “planet” and “exoplanet”? Surely that is even more arbitrary – and extrinsic – than the requirement that it gravitationally dominate its orbital path.

    So, if a “planet” must be defined purely by intrinsic properties, there are about 400 known planets (by a rough guesstimate).

    Do you find this more satisfying than Pluto’s status as a dwarf planet?

    You offer a platypus as an example of a thing that’s hard to classify. Whether or not that is true, it reminds me of something Richard Dawkins said in one of his books. I can’t remember his exact words, but his point was that out of the many possible taxonomies for living organisms, there is one and only one that is actually correct.

    This is a false analogy. In biology, all life is related genealogically. Thus, we are closely related to the great apes, less closely related to monkeys and lemurs, related less closely still with dogs and bears, more distantly related to the platypus, related more distantly still to eagles, related more distantly still to marlin, and so on.

    Thus, a correct biological taxonomy must reflect the genealogical relationships between species.

    Planets do not share such a nested set of relationships. They all formed at about the same time and have (in gross terms) changed little since their formation. Thus, any classification of planets is purely arbitrary. It must, however, be consistent.

    Pluto is problematic because, if we insist on defining it as a planet, there are at least a dozen other objects in the solar system that would therefore also count as planets. I have no problem with calling all of these things planets, but the IAU voted to call those that gravitationally dominate their orbital paths “planets” and those that do not “dwarf plaents”. I don’t see any problem with this either.

    What I would have a problem with is if the term “planet” meant only “members of this list of nine objects”, because then the term itself would be a meaningless label. Just because Pluto was the first KBO to be discovered does not make it special.

  55. Nigel Depledge

    Annalee Flower Horne (28) said:

    The reason the “it’s more like a KBO than it’s like the eight planets in our system” argument doesn’t work for me is that I don’t understand why it wouldn’t work equally well to say that Mercury, Venus, Earth and Mars are more similar to belt objects than they are similar to the four planets in our system. (I don’t mean that rhetorically–I actually don’t understand, and would be happy to have it explained to me).

    Well, Mercury is rather similar to the largest asteroid-belt objects (albeit, IIUC, more dense than any of them for which a density is known), but Mercury gravitationally dominates its orbital path. IOW, Mercury isn’t just one of a collection of similar objects in the same part of the solar system – it stands alone, so it meets the definition of “planet”. Venus, Earth and Mars are all the gravitationally-dominant bodies within their orbital paths, i.e. any other objects that follow the same path are gravitationally bound to one of these.

  56. Nigel Depledge

    Jamey (29) said:

    You know, a Jupiter-massed object in the deeps of the Kuiper Belt probably wouldn’t have had time to have cleared its orbital track – and really, how well has Jupiter cleared *its* track? See all those Trojan asteroids lately? Nah – I say if its self-gravitates to an oblate shape consistent with its spin, then it’s a planet. Yeah, that lets in Ceres. I’m cool with that.

    The Trojans are gravitationally dominated by Jupiter. The orbital path doesn’t have to be swept clear of other objects (otherwise, duh, any planet with moons wouldn’t be a planet!) – for an object to qualify as a planet, it must be gravitationally dominant within its orbital path.

    That aside, however, your definition would not let merely Ceres in, it would let in at least a dozen other objects too. But that’s not a problem, as long as the word “planet” has a consistent meaning.

  57. Nigel Depledge

    Mark (32) said:

    I’m sorry, but the other KBOs and “dwarf planet” objects were never considered planets for 70-plus years. Pluto was/is. FOR 70-PLUS YEARS! So the argument we should complain/memorize/bemoan-the-fate-of all other KBOs or DPs doesn’t hold any water. No kid of mine will ever have cause to feel they were “robbed of a childhood memory” when sanity is restored and Pluto is once again called what it is and always has been since 1930… a PLANET!

    This argument is almost compelling, but it has one substantial counter with which it cannot cope:

    So what?

    Why is Pluto special just because it was discovered decades before any other KBO?

    Mercury, Venus, Mars, Jupiter and Saturn were known for millenia before any other planetary bodies were discovered – does this make them special? If I follow your argument, it makes them more special than any subsequently-discovered object.

    So, following your reasoning to its logical end, we should actually exclude Pluto, Neptune and Ouranos because they don’t belong to the “we were noticed by humans first” club.

    And we’d still end up with a definition of “planet” that is simply “members of this list”.

  58. Nigel Depledge

    Adrian Lopez (44) said:

    @amphiox

    “Classification systems of physical objects like planets are always arbitrary, and multiple systems are equally valid.”

    They are not, however, *completely* arbitrary.

    Actually, the “nine planets” calssification was completely arbitrary. It depended entirely on historical accidents and bore no relation to the objects themselves.

    Whatever flexibility exists is still constrained by reality and logic. It makes little sense to refer to something that is not a planet as a “dwarf planet”, and the notion that a planet is not a planet if you change its orbit is at least problematic.

    Would you be less bothered if the dwarf planets were called something without “planet” in the name? If so, why?

    Here in Europe there is a small brown bird called the Dunnock. It has another name, the Hedge Sparrow. But it isn’t a sparrow at all, it’s an accentor. Does that make your head explode too?

    At least calling all of the gravitationally-spheroidal sun-orbiting objects “dwarf planets” gives them a category that has some meaning. I.e., they’re a bit like planets in some respects (2 out of 3 ain’t bad), but they do not gravitationally dominate the regions in which they orbit, so they don’t count as planets.

    What is so wrong about defining an object with reference to the context in which it is found? It’s not as if we can move planets from one orbit to another is it?

  59. Messier Tidy Upper

    @12. Guysmiley777 Says:

    If Pluto is a planet, these people freaking out need to start memorizing all the other large Kuiper Belt objects as well. Childhood wistfulness be damned, the number of planets WAS going to change from 9, one way or the other. Saying “No! I learned 9 and it will always be 9!” when presented with new evidence is pretty much the opposite of science.

    The number should go up though – not down. Just because there are a lot of ice dwarf planets doesn’t make them less planet-like.

    If it looks like a planet and acts like a planet in most respects then why not just admit it *is* a planet?

    Pluto has moons like other planets,
    Pluto has a geologically differentiated geological structure like other planets,
    Pluto has an atmosphere with complex weather and seasons like other planets,
    Pluto might well also have rings as well like many other planets do!

    That’s way more than the 2/3 mark suggested by (#59.) Nigel Depledge.

    Now, ok, it can’t claim to have shifted everything out of its huge orbit space but then it could if it was orbiting closer in.

    In contrast, Mercury which even the IAU does call a planet doesn’t have moons, rings or an atmosphere, Venus doesn’t have any moons or rings either – does that mean they get less than full marks planet-wise?

    If you tick off a list of features typical of planets then Pluto is arguably far more qualified to be a planet than Mercury is! ;-)

    Why should orbital clearance be so important? Answer – it really shouldnt be! Besides how far and how thorough the clearnmace needs to be is problematic too. Who says when an orbit is clear enough or cleared far out enough – its just silly.

    One of the great discoveries of our age is that there is a third zone of our solar system beyond Neptune where there are a number of ice dwarf planets.

    I wouldn’t make kids necessarily memorise all of these worlds but I would suggest that we teach them that a modern understanding holds that the solar system ha sthree zones – a close inner zone with rocky planets like Earth, a middle zone where the planets are gas giants like Jupiter and an outer zone where the planets are ice dwarfs like Pluto.

    Not only is this reasonable but we can also add that we are still discovering planets inside our own solar system just as we are still discovering exoplanets orbiting other stars.

    We know of a lot more than 9 planets – there are neraly 500 or so exoplanets outside our solar system and perhaps twenty or fifty or who knows how many inside our own. Really, what’s wrong with that approach?

  60. Nigel Depledge

    Messier Tidy Upper (45) said:

    I blame the IAU not Mike Brown and I hope their current absurd and I think very wrong definition is reviewed and scrapped and replaced by a better definition that includes Pluto, Eris, Ceres and the other dwarf planets.

    Well, I’d be equally happy with a definition along the lines of “orbits the sun and has sufficient gravity to make itself spheroidal”. We’d then have about 25 or 30 planets in the solar system.

    But what is wrong with a definition that excludes the asteroids and KBOs?

    If Earth or even Jupiter orbited out in the Edgeworth-Kuiper cometary belt then Erath or Jupiter would cease to be planets and become dwarf planets instead. That’s IAU definition FAIL right there.

    Well, (a) there’s every chance that Jupiter would clean up the Kuiper belt, and (b) Earth and Jupiter don’t orbit in the Kuiper belt, so this is just speculation.

    The IAU decided that the definition of a planet would include the context in which the object is found.

    If Pluto orbited inside the orbit of Mars it would be a planet and a bright one at that.

    Actually, there’s every likelihood that Pluto would have evaporated if it had moved to an orbit inside that of Mars. All the other KBOs that travel to the inner solar system end up as not much more than trails of dust and a few rocks.

    So, would it then still count as a planet in your book?

    Ultimately, though, Pluto doesn’t orbit inside the orbit of Mars. It is a KBO.

    What is your problem with a contextual definition?

  61. Nigel Depledge

    Messier Tidy Upper (45) said:

    Nope the IAU definition fails the tests of logic, science and linguistic convention. It is absurd and downright stupid.

    At least the word now actually has a definition, rather than simply being “a member of this list of objects”.

    Would you prefer a definition of “planet” that means something at least (even if that “something” is absurd, as you put it), or would you prefer a definition that is meaningless except in a historical sense?

  62. PeteC

    There’s a perfectly good reason for the “Pluto is definitely a planet” crowd.
    Faith. Straightforward, true believer faith.

    Pluto has always been a planet. My priest told me it was a planet. Or maybe teacher. Whoever. Anyway, it’s a planet because that’s what I believe.

    This “evidence” and “data” and “standards” nonsense is for sceptics and rationalists!

    … or maybe we just need to take a definition and stick with it. Whatever that definition is – so we either have dozens of planets or just eight. But that would be logical and sensible, so I understand there’s a lot of opposition. Personally, I’m happy with eight planets.

  63. Nigel Depledge

    MTU (45) said:

    I would suggest a three part definition similar to thecurrent one but dropping the silly “orbital clearing” criterion. An object is a planet to my way of thinking if :

    1. Its orbits a primary star or brown dwarf directly or a barycentre inthecase of double planets. If it orbits aplanet rather than a star it is a moon instead.

    2. It is large enough to be round or elliptical for rapidly spinning objects like Haumea via its own gravity.

    but ..

    3. It is not so round that shines via nuclera fusion of any kind such objects being brown dwarfs or stars.

    Simple. Workable, easy to tell. What’s wrong with using that instead?

    How do you define the boundary between a brown dwarf and a planet?

    If it is purely by the criterion of nuclear fusion, then surely you will have brown dwarfs becoming planets on a regular basis. And therefore you will have planets becoming moons at the same time.

    No, I think it best to leave brown dwarfs out of it. They’re weird.

    The rest of it would probably work, though. Now you just need to lobby enough IAU members to get the next vote in your favour.

  64. Nigel Depledge

    MTU (46) said:

    A planet’s a planet wherever it orbits and however small it might be!

    Oh goody. You just promoted all the moons in the solar system to “Planet” status. ;-)

    Does that include all the particles in Saturn’s ring systems…?

  65. Nigel Depledge

    MTU (46) said:

    Moreover, while for a long time Pluto has been seen as odd for having an extremely tilted and elliptical (eccentric) orbit, today we know this is not uncommon for other planets.

    Pretty much irrelevant, since no-one is suggesting we include orbital inclination in the definition of “planet”.

    No, Pluto is odd because it is just like several other bodies we know about in the Kuiper Belt, and there may well be dozens more that are fairly similar to it. None of the eight planets has that distinction (or, really, I should say “that lack of distinction”).

  66. Nigel Depledge

    MTU (46) said:

    Planets can be stranger and make up a far broader category than we used to imagine. In this context the IAU’s narrow and overly exclusive definition makes little if any sense.

    I think you mean “Objects that orbit stars can be stranger . . .”

    The IAU’s definition makes sense if you consider that it:
    A) systematically defines what the word “planet” actually means;
    B) does not permit the uncontrolled expansion of objects that meet the criteria for this status; and
    C) replaced a convention that amounted to “planets are members of this list”.

  67. Annalee Flower Horne

    Nigel@56, amphiox@41, thanks for the explanation. My next question is (and again, I’m not trying to be snarky–I actually want to know), how do you define gravitational dominance? My understanding is that Saturn’s relationship with its moons doesn’t look like our relationship with ours. Which is to say Saturn is definitely, clearly, unequivocally the boss in that relationship, whereas we look more like a binary planet than we do like a planet with a moon (keeping in mind that my knowledge of astronomy is pretty much limited to exhibits at the Air and Space Museum, so I could be on crack about what a double planet is).

    Are binary planets excluded from planet status under this definition, and if so, are we excluded? Or are binary planets just counted as one object for the purposes of determining gravitational dominance?

    The plus side of Pluto getting demoted, according to my classical music-loving friends, is that Gustav Holst’s suite “The Planets” is no longer short a movement.

  68. Nigel Depledge

    MTU (47) said:

    In any case, Pluto does indeed gravitationally dominate its local region otherwise it wouldn’t boast three moons incl. one very large one.

    It may have moons but it doesn’t gravitationally dominate its orbital path. There are other KBOs in that vicinity IIUC.

    In fact, the Pluto-Charon system has often been described as a double planet because Charon is not all that much smaller than Pluto, and sometimes their barycentre is outside Pluto (again IIUC).

    Another thing to remember here too is that if we look at the continuum of objects in our solar system and the majority of the planets and dwarf planets making it up then Pluto really isn’t, actually, relatively all that small. It may be smaller than the gas giants, the rocky planets and Eris but Pluto is larger than Makemake, Haumea, Sedna, Quaoar, Varuna, Ceres, Ixion, Huya, Orcus, “Buffy” (2004 XR190), Vesta, “Dracula” (2008 KV 42), et cetera..

    So, obviously Pluto and Eris are quantitatively different from those other objects, but is there a qualitative difference? What significance is there to the fact that Pluto is larger than most of the other KBOs we know about? That would be akin to saying that Ganymede ought to be a planet.

  69. Messier Tidy Upper

    @59. Nigel Depledge :

    It’s not as if we can move planets from one orbit to another is it?

    Not yet .. one day though! ;-)

    but they do not gravitationally dominate the regions in which they orbit, so they don’t count as planets.

    But Pluto does gravitationally dominate its region – what do you call Charon, Nix and Hydra? Moons! Moons that are gravitationally dominated by and have their orbital path’s controlled by the gravity of their primary planet. Its just a matter of how far a given planet’s domination (Hill) sphere of influence extends.

    Large planets have larger influence than smaller ones sure and when a planet has a large orbit it also makes it much harder for that planet to have its orbit cleared than if the planet has a small orbit.

    It’s like giving a pygmy a toothbrush and expecting her to keep an entire state clear of leaves and dust versus getting an all-star national basketballer to rake one small area of lawn clean! ;-)

    But you wouldn’t deny a pygmy her human rights or status as a person because of that just like you shouldn’t deny Pluto its status as a planet. It is, quite frankly, unethical. :-(

    Also note that Jupiter’s orbit isn’t clear – it has trojan asteroids. Sun-grazing comets have orbits that cross all planetary paths. A strict adherence to the IAU definition would thus deny there are any planets in our solar systems at all! It is just that silly.

    The IAU definition as I’ve noted several times before is simply NOT logical. It fails the reductio ad absurdum test and it also fails Occams razor by adding many layers of unnecessary, superflous complication. The IAU’s definition is a poor definition that was chosen in a very dubious and malodourous fashion – and so, unsurprisingly, it stinks. It should be corrected and replaced by a reasonable definition that counts dwarf planets as planets and does not have all the problems the woeful “orbital clearing” criteria creates.

    Here in Europe there is a small brown bird called the Dunnock. It has another name, the Hedge Sparrow. But it isn’t a sparrow at all, it’s an accentor. Does that make your head explode too?

    No. Why? Because I think everybody would agree that the species in question there is a bird or even an animal. Its finer classification is another story but we’re talking the equivalent of kingdom level here not the species one. Star, planet, asteroid here is equivalent to animal, vegetable, mineral. Once we narrow your Dunnock here down to the “animal” kingdom which it clearly is – as it equally clearly isn’t a bacteria or a fungus or a plant then we can go to the next step down the taxonomic order which is that its a bird not a reptile or an insect or a mammal.

    In just the same way, Pluto fits in the very broad “planet” kingdom; it isn’t a star, it isn’t an asteroid, it isn’t a moon. Then we can then go into more precise “planet” genera – ice dwarf, gas giant, rocky planet, Superjovian, SuperEarth, Hot Jupiter, Hot Earth, etc .. Pluto is in this taxonomic classification first a planet then an ice dwarf variety of planet with possible further categorisation eg. Trans-Neptunean large and reflective class ice dwarf planet. Easy! ;-)

  70. Gus Snarp

    @Georg #38 – Yes, American school kids have to memorize the names of the planets in order. At least I did. It’s pretty standard. That’s why you see references to mnemonic tricks to aid memorization above, like: “Mary’s Very Educated Mother Just Sat Upon New Pillows”, indicating the first letter of each planet’s name (though apparently they all learned some heretical version where Mary’s mother was serving something instead), as well as the song “Interplanet Janet” from the “Schoolhouse Rock” educational TV program, which goes:

    “Mercury was near the Sun so Janet stopped by,
    but the mercury on Mercury was much too high.
    So Janet split for Venus but on Venus she found,
    She couldn’t see a thing for all the clouds around.

    Earth looked exciting,
    Kind of green and inviting,
    So Janet thought she’d give it a go.
    But the creatures on that planet seemed so very weird to Janet,
    She didn’t even dare to say ‘Hello’.

    Mars is red and Jupiter’s big and Saturn shows off its rings.
    Uranus is built on a funny tilt,
    And Neptune is its twin.

    And Pluto, little Pluto, is the farthest planet from our sun.”

    (that’s from memory, no Googling involved. Geek Dad!)

    So yes, all of that has created a very emotional attachment for some of us, you’re right. I’m a little sad about it myself, but it doesn’t bother me that much, given the good reasons for the demotion. My wife, however, is much less forgiving. Maybe it was a good thing we didn’t make it to the Mike Brown lecture, I think she might have brought a pie.

  71. Messier Tidy Upper

    @69. Nigel Depledge :

    That would be akin to saying that Ganymede ought to be a planet.

    Ganymede orbits Jupiter making it a moon.
    Pluto orbits our Sun making it a planet.
    If Ganymede orbited our Sun (or another star) directly then I’d have no issue at all callig it a planet.

    If Pluto orbited Jupiter or even Earth (imagine the view if we had Pluto as our moon as well as, well, our Moon!) instead of being in independent solar orbit as it is then I’d have no problem calling it a moon.

    So, obviously Pluto and Eris are quantitatively different from those other objects, but is there a qualitative difference? What significance is there to the fact that Pluto is larger than most of the other KBOs we know about?

    It has enough mass to be round through its own gravity, not enough mass to shine via nuclear fusion – I have no trouble using that as the main test of planethood along with orbiting a star.

    Whether there are other similar bodies is irrelevant to that just as the fact that Jupiter has Saturn and Neptune relatively nearby and of a relatively similar nature and Earth has Venus and Mars that are near and like it doesn’t rule them out of planethood either. ;-)

    In fact, the Pluto-Charon system has often been described as a double planet because Charon is not all that much smaller than Pluto, and sometimes their barycentre is outside Pluto (again IIUC).

    So? What do you have against double planets? Our Earth-Moon system is similar if not quite as extreme. I kinda like the thought of double planets and expect we will probably find a few examples in the universe.

    There are other KBOs in that vicinity IIUC.

    Again, so what? How far does “vicinity” extend for? How do you define “vicnity” in this regard? Just because we’ve got Venus and Mars and Mercury relatively near us in our vicinity does that rule Earth out of planethood? It makes no difference if there are other planets nearby – unless Pluto is orbiting one of them and becomes a moon then as far as I’m concerned if it meets the other reasonable criteria* – and it does – then its a planet.

    —-

    * For the logical reasons I’ve already noted I don’t count the undefinable “orbital clearence” part as such – it is unreasonable instead.

  72. Messier Tidy Upper

    @62. Nigel Depledge Says:

    Would you prefer a definition of “planet” that means something at least (even if that “something” is absurd, as you put it), or would you prefer a definition that is meaningless except in a historical sense?

    I’ve given my preferred definition already in comment #45 but once more :

    A planet is defined best as an astronomical object that is :

    a) Never self luminous by nuclear fusion thus not a star or brown dwarf,

    b) not directly orbiting another planet thus not a moon,

    &

    c) large enough to be round or if rapidly spinning oblate spheroidal rounded through its own gravity thus not a comet or asteroid.

    Historically, the planets were originally defined based on the criteria of showing apparent moving across the sky. They were the “wanderers” or wandering stars as opposed to fixed stars – and they included our Sun and Moon! I agree that that definition needed updating. ;-)

    Incidentally I think the “classical planets” term is best reserved for those orginal five unaided eye wandering stars – Mercury, Venus, Mars, Jupiter & Saturn.

    @65. Nigel Depledge Says:

    MTU (46) said: “A planet’s a planet wherever it orbits and however small it might be!” Oh goody. You just promoted all the moons in the solar system to “Planet” status. Does that include all the particles in Saturn’s ring systems…?

    Yeah, well, I’m a generous bloke! ;-)

    Clearly the missing unstated assumption there was that a planet is a planet as defined with enough gravity to be round but not so much that it fuses nuclear~wise and is orbiting a star not another planet. Those conditions met then however small (provided its enough to be round) and wherever it orbits (provided its around a star) it counts as a planet.

    @66. Nigel Depledge Says:

    Pretty much irrelevant, since no-one is suggesting we include orbital inclination in the definition of “planet”.

    Yet Pluto’s oddball orbit was one argument I’ve seen used against it by Pluto-bashers. It doesn’t orbit neatly like the rest of the planets so is it really a planet? Well now we realise a lot of exoplanets do have eccentric orbits so that isn’t an issue.

    Pluto is odd because it is just like several other bodies we know about in the Kuiper Belt, and there may well be dozens more that are fairly similar to it. None of the eight planets has that distinction.

    So by that logic if we know of more objects like Jupiter somewhere or Earth that would makes *them* less “planet-ly” to coin a phrase? Que?!?

    To me, the existence of other planets like Pluto confirms it as a type of planet rather than refuting its planetary nature. When we didn’t know of others like it there was a hypothesis that it was merely an escaped Neptunean moon. Now we know that Pluto is instead among the largest and brightest of its planetary class – and you want to kick it out for that?

    @67. Nigel Depledge Says:

    MTU (46) said: “Planets can be stranger and make up a far broader category than we used to imagine. In this context the IAU’s narrow and overly exclusive definition makes little if any sense.”

    I think you mean “Objects that orbit stars can be stranger . . .”

    No, I meant planets just like I wrote.

    Okay, technically exoplanets but then exoplanets are also a class of planets. Although, oddly enough, the IAU definition excluded them too rather unreasonably IMHON. According to the IAU our Sun is the only star that can have planets as they define them – how very quaintly Copernican of them that was. ;-)

    The IAU’s definition makes sense if you consider that it:
    A) systematically defines what the word “planet” actually means;

    But their definition is badly flawed for the logical and consistency reasons I’ve pointed out already.

    A definition that stops Jupiter from becoming a planet if it is moved to the Edgeworth-Kuiper belt FAILS.

    A definition that makes dwarf stars still stars but dwarf planets NOT planets FAILS.

    A definition that excludes Pluto for no good reason FAILS. (No I don’t think there was a good or sufficent reason given to demote Pluto.What you guessed .. ? ;-) )

    B) does not permit the uncontrolled expansion of objects that meet the criteria for this status;

    You say that like its a good thing. Don’t we want the possibility of expansion and adding to the list of planets?

    and C) replaced a convention that amounted to “planets are members of this list”.

    Not quite true. Planets were defined before as “wandering stars” as noted. They did share certain known characteristics even if the definition was somewhat less formal.

    @68. Annalee Flower Horne Says:

    .. how do you define gravitational dominance?

    Good question. :-)

    I think that is a problem for the IAU definition as it adds another unnecessary layer of complication – therefore I think “gravitational dominance” or “orbital clearance” should be scrapped as a defining characteristic. It violates the KISS principle & Occams razor. We are well advised to keep basic definitions like “planet” as simple & broad as possible.

    @71. Gus Snarp : Nice song – I’ve never heard of it before. Would there be a Youtube clip of it somewhere by any chance? :-)

    I woudn’t have brought a pie to that talk by Mike Brown but I would have asked a few tough questions. He might’ve preferred a pie to that! ;-)

    @63.PeteC Says:

    There’s a perfectly good reason for the “Pluto is definitely a planet” crowd. Faith. Straightforward, true believer faith. …Pluto has always been a planet. My priest told me it was a planet. Or maybe teacher. Whoever. Anyway, it’s a planet because that’s what I believe. This “evidence” and “data” and “standards” nonsense is for sceptics and rationalists! …[Shift] … But that would be logical and sensible, so I understand there’s a lot of opposition.

    Not true. Have I been less than logical or sensible here? Am I just using faith? I’m not religious but am agnostic verging on athiest. Nor am I American but an Aussie FWIW.

    My beef with the IAU definition is based on its illogic & I am not trying to stick with just 9 worlds but am open to however many might be out there. I consider the number of known planets to be well over 500 and counting

    … or maybe we just need to take a definition and stick with it. Whatever that definition is – so we either have dozens of planets or just eight.

    Yes, but let’s make sure we have a good & useful definition that makes sense before we then stick with it. The IAU one in my view is not. No point having or sticking to a silly definition that really doesn’t work methinks.

  73. Gus Snarp

    @Messier Tidy Upper: Did your Googling for you: http://www.youtube.com/watch?v=rDre36ZW14I

  74. Gus Snarp

    @Messier Tidy Upper: In case you don’t want to wait for link moderation:
    youtube dot com slash watch?v=rDre36ZW14I

  75. Adrian Lopez

    @Nigel Depledge,

    Actually, the ‘nine planets’ calssification was completely arbitrary. It depended entirely on historical accidents and bore no relation to the objects themselves.

    At no point have I suggested there can only be nine planets. I’m simply saying the definition of planet is not completely arbitrary. Originally, planets had to be large enough to be seen by a naked-eye observer on Earth and, unlike stars, required orbits that could be discerned by just such an observer. The concept of a planet was tied to very real properties of the objects we continue to call planets, even if the model wasn’t exactly correct.

    Would you be less bothered if the dwarf planets were called something without ‘planet’ in the name? If so, why?

    Yes, as it avoids the logical contradiction in the notion that an object that is not a planet can still be called a planet provided the qualifier “dwarf” is placed in front of it.

    Here in Europe there is a small brown bird called the Dunnock. It has another name, the Hedge Sparrow. But it isn’t a sparrow at all, it’s an accentor. Does that make your head explode too?

    People will call it whatever they will. I would hope, however, that scientists wouldn’t call it a “Hedge Sparrow” in those contexts where the distinction between sparrow and non-sparrow actually matters.

    What is so wrong about defining an object with reference to the context in which it is found? It’s not as if we can move planets from one orbit to another is it?

    I’ve been thinking about this, and perhaps it isn’t so bad after all. Most people who think of a moon think of it as an object orbiting around a planet. In that case, the use of the word “moon” is similar to the way we use “husband” to refer to a man who is married. A husband can cease to be a husband without himself becoming something fundamentally different, and so may a moon cease to be a moon without becoming something fundamentally different. The question, then, is whether “planet” refers to the object itself or whether it’s more akin to an attribute of the object such as with the word “husband” or the word “satellite”.

  76. People, people, people. This debate has become sidetracked. The real question is: what would I prefer? Answer: possibly the pie, as long as the pie is predominantly chocolate. And, well, OK, telescope time. But only if I can have pie, too.

  77. Give him controlling interest in Planet Hollywood

  78. Messier Tidy Upper

    @ Gus Snarp 74 & 75 : Thanks. :-)

    @64. Nigel Depledge :

    How do you define the boundary between a brown dwarf and a planet? If it is purely by the criterion of nuclear fusion, then surely you will have brown dwarfs becoming planets on a regular basis. And therefore you will have planets becoming moons at the same time. No, I think it best to leave brown dwarfs out of it. They’re weird.

    True enough I guess. Brown dwarfs would be defined by being able to fuse of deuterium in my book.

    The rest of it would probably work, though. Now you just need to lobby enough IAU members to get the next vote in your favour.

    Thanks I’m trying. :-)

    I hope this happens.

  79. Patteroast

    A couple arguments I saw made that seemed a bit silly:

    “Pluto has moons like other planets,
    Pluto has a geologically differentiated geological structure like other planets,
    Pluto has an atmosphere with complex weather and seasons like other planets,
    Pluto might well also have rings as well like many other planets do!”

    Mercury and Venus do not have moons. There are asteroids as small as 120 meters across that have moons.
    The asteroid Vesta also is differentiated and geologically interesting.
    Saturn’s moon Titan has an atmosphere. Mercury (for the most part) does not.
    It’s possible that Saturn’s moon Rhea has rings. Mercury, Venus, Earth, and Mars do not.

    “But Pluto does gravitationally dominate its region – what do you call Charon, Nix and Hydra?”

    Again… there are asteroids under a kilometer in diameter with moons. That doesn’t make them planets. Having moons has nothing to do with being a planet.

    The one thing I do agree with? It is rather odd that dwarf planets are not considered a kind of planet, just from a linguistic point of view… I think it’d be more logical to consider them a sub-category of planets. But that’s just my personal opinion… the eight-planet system IS scientifically justifiable. So is the ‘everything in hydrostatic equilibrium’ system. (I would not be totally opposed to a system that made gravitationally rounded moons planets, but that’s just me… the major moons get no respect. :( ) The nine-planet system is not scientifically justified.

  80. Nigel Depledge

    Annalee Flower Horne (68) said:

    My next question is (and again, I’m not trying to be snarky–I actually want to know), how do you define gravitational dominance?

    Good question, to which the short answer is: I don’t know. What I mean is, I don’t know how the IAU define it (since there are several plausible ways in which it could be defined). But you’ve made me think about something that I had not previously given much thought, so thanks!

    I hope an astronomer here can answer that for you (or both of us!).

  81. Nigel Depledge

    MTU (70) said:

    But Pluto does gravitationally dominate its region – what do you call Charon, Nix and Hydra? Moons! Moons that are gravitationally dominated by and have their orbital path’s controlled by the gravity of their primary planet. Its just a matter of how far a given planet’s domination (Hill) sphere of influence extends.

    Pluto does not gravitationally dominate its orbital path. It dominates a small portion of it.

  82. Nigel Depledge

    MTU (70) said:

    But you wouldn’t deny a pygmy her human rights or status as a person because of that just like you shouldn’t deny Pluto its status as a planet. It is, quite frankly, unethical.

    What, so you reckon Pluto has some fundamental right to be defined in a category with Mercury, Venus ….. Neptune, instead of with all the other KBOs?

    How do you work that out?

    And, if you call Pluto a planet, but don’t call any other KBOs planets, then you render the meaning of the word planet “a member of this list” which is pretty much useless.

    As I said further up, I’d be equally happy with a definition that included all the gravitationally-spheroidal bodies that orbit the sun, but the definition of planet must mean something about the things it’s describing.

    I certainly don’t see anything about Pluto that merits special treatment.

  83. Nigel Depledge

    MTU (70) said:

    Also note that Jupiter’s orbit isn’t clear – it has trojan asteroids. Sun-grazing comets have orbits that cross all planetary paths.

    Jupiter’s trojans only follow that orbit because of Jupiter’s influence. Therefore, they are gravitationally dominated by Jupiter.

    Asteroids that cross planetary orbits do indeed have their orbits altered by the planets whose paths they cross. Whereas those asteroids don’t alter the orbits of these planets by more than a tiny, tiny fraction. Which is the gravitationally dominant body?

  84. Nigel Depledge

    MTU (70) said:

    Star, planet, asteroid here is equivalent to animal, vegetable, mineral.

    No.

    Stars are qualitatively different from everything else out there, because they carry out sustainable nuclear fusion in their cores.

    Planets and asteroids are the same kind of things. Or do you call Mercury an asteroid because it has no atmosphere and no moons? There is no qualitative difference between planets and asteroids. Classification – at least in biology – is all about identifying qualitative differences between organisms, not merely quantitative differences.

    Similarly, any classification of solar system bodies should operate on qualitative, not quantitative, differences. The only thing that distinguishes Pluto from other KBOs is that it was discovered several decades before any others. But as I (and at least one other commenter) have noted before, the “history” argument doesn’t work either.

  85. shoblock

    Doc Brown helped my daughter with her homework (she had to do a report on him, and he emailed back answering all her questions), so I’m on his side no matter what. In fact, I used to be against Pluto’s demotion, but after he helped with the homework I became a convert. Pluto is dead to me! It’s not a planet, and never should have been.

  86. Nigel Depledge

    MTU (70) said:

    Once we narrow your Dunnock here down to the “animal” kingdom which it clearly is – as it equally clearly isn’t a bacteria or a fungus or a plant then we can go to the next step down the taxonomic order which is that its a bird not a reptile or an insect or a mammal.

    Actually, the next step down from Kingdom (at least, in the simplest classification schemes) is Phylum. In the case of the Dunnock, it is in phylum Chordata. Notice that birds, retiles and mammals (all chordates) are all qualitatively different from insects (all arthropods) – they have an internal skeleton, whereas all insects have an exoskeleton (in at least some stages of their life cycle).

    The next step down from that would be to decide in which class of phylum Chordata it belongs. That’s the stage at which you would distinguish reptiles, birds, fish, mammals and so on from one another.

  87. Nigel Depledge

    MTU (72) said:

    @69. Nigel Depledge :

    That would be akin to saying that Ganymede ought to be a planet.

    Ganymede orbits Jupiter making it a moon.
    Pluto orbits our Sun making it a planet.
    If Ganymede orbited our Sun (or another star) directly then I’d have no issue at all callig it a planet.

    I think you missed my point.

    I was trying to emphasise that we need to focus on qualitative differences for classification, not on merely quantitative ones.

    As you rightly point out, Ganymede has the qualitative distinction of not orbiting the Sun directly. I was emphasising that singling out Pluto as distinct from other KBOs shifts the focus to quantitative differences (whether that quantity is size, number of years since discovery or whatever).

    I think we are agreed that we would both be happy with calling any sun-orbiting gravitationally-spheroidal object a planet.

    It seems to me that where we disagree is on whether the change made by the IAU is an improvement or not. I think it is, and you seem to disagree (correct me if I’m wrong). I’m not saying it couldn’t be better, but I still think it’s an improvement. Now, at least, planets are defined by qualitative distinctions from other solar system bodies, whereas, before, a “planet” was merely a member of a list of nine objects.

  88. Nigel Depledge

    MTU (72) said:

    Again, so what? How far does “vicinity” extend for? How do you define “vicnity” in this regard?

    I don’t, but I’m sure the IAU does.

    Just because we’ve got Venus and Mars and Mercury relatively near us in our vicinity does that rule Earth out of planethood?

    No, of course not – because the inner planets are all gravitationally dominant within their orbital paths. Pluto does not share that distinction.

    You may consider it an illogical distinction, but you cannot ignore the fact that it is a part of the current IAU definition of a planet. As far as I am concerned, the IAU could choose to define planets by colour if they so wish – the point is that there must be some systematic way of rendering a meaning unto the word “planet”, and anything that is systematic is better than what we had before. And the IAU is the body that should make the definition.

    It makes no difference if there are other planets nearby – unless Pluto is orbiting one of them and becomes a moon then as far as I’m concerned if it meets the other reasonable criteria* – and it does – then its a planet.

    —-

    * For the logical reasons I’ve already noted I don’t count the undefinable “orbital clearence” part as such – it is unreasonable instead.

    OK, well I don’t know if you’re a professional astronomer or a more-than-usually informed amateur. You seem to be disputing the IAU’s right to make the rules. Don’t hassle me over that one. I don’t consider myself to be in a position to judge the validity of the IAU rules (although, clearly, you do so consider yourself) – but I do know that having a clear and precise (or as precise as is possible) defintion of the word “planet” is better than having it meaning nothing more significant than “a member of this list”.

  89. Nigel Depledge

    MTU (73) said:

    I’ve given my preferred definition already in comment #45 but once more :

    A planet is defined best as an astronomical object that is :

    a) Never self luminous by nuclear fusion thus not a star or brown dwarf,

    b) not directly orbiting another planet thus not a moon,

    &

    c) large enough to be round or if rapidly spinning oblate spheroidal rounded through its own gravity thus not a comet or asteroid.

    Historically, the planets were originally defined based on the criteria of showing apparent moving across the sky. They were the “wanderers” or wandering stars as opposed to fixed stars – and they included our Sun and Moon! I agree that that definition needed updating.

    Unfortunately, your preferred definition has never been the defintion of a planet.

    So, although you disagree with the new definition, why do you seem to think it is worse that what we had before the IAU issued the definition?

  90. Nigel Depledge

    MTU (73) said:

    Pluto is odd because it is just like several other bodies we know about in the Kuiper Belt, and there may well be dozens more that are fairly similar to it. None of the eight planets has that distinction.

    So by that logic if we know of more objects like Jupiter somewhere or Earth that would makes *them* less “planet-ly” to coin a phrase? Que?!?

    The fact that the KBOs have orbits that often cross one another is a consideration. If we had a solar system with – say – half a dozen Earth-sized objects occupying the same or similar orbital paths, I’m sure that would be a consideration when defining what to call these things. But this is mere speculation. We have the solar system that we have, and it contains 8 objects that are qualitatively different from all of the other objects.

    If a future session of the IAU adopts a definition of “planet” along the lines of your preference, what would you suggest that we call these 8 objects to distinguish them from all the other sun-orbiting gravitationally-spheroidal stuff drifting around?

  91. Nigel Depledge

    MTU (73) said:

    @67. Nigel Depledge Says:

    MTU (46) said: “Planets can be stranger and make up a far broader category than we used to imagine. In this context the IAU’s narrow and overly exclusive definition makes little if any sense.”

    I think you mean “Objects that orbit stars can be stranger . . .”

    No, I meant planets just like I wrote.

    But you are not the IAU. You do not make the rules. They do. And the definition of “planet” is what it is according to the existing IAU rules. So you truly didn’t mean “planet” – what you instead meant was “objects that orbit stars”. However, you have made it abundantly clear that you want “planet” to mean what you choose it to mean, just like Tweedledum (or is that Tweedledee?).

  92. Markle

    #92 Nigel

    But you are not the IAU. You do not make the rules. They do.

    Well, not really. All they have is moral suasion to back up their definition.

    Similarly, you make a lot of assertions that are no more than that. At the meeting there were 3 or 4 options available. One of which was substantially equivalent to what MTU proposes. The main argument for the current definition wasn’t some rigorous objective idea. It was strictly, “well, if we keep Pluto in the club, we’re going to have to admit all these others and probably Ceres as well”. It was simply a numbers game. There was also some mumbling about a bit of “stick it to the Americans” as well. Iraq and all that, y’know.

    I was actually kind of surprised by this notion that there wasn’t a definition of planet. Back before Voyager 2 took it’s close-ups of Neptune, I took Astronomy 10. Our textbook and the instructor (An actual astronomer with a PhD, albeit a Solar astronomer) defined 3 non-stellar objects: Comets, Planets and Minor Planets(asteroids and moons). Basically, what you’re arguing about is whether to slice the pizza evenly or between the pepperoni slices.

    Personally, I think Mike Brown gets a kick out of the notoriety. I seem to remember him saying recently that he is not now nor has he ever been a member of the IAU. So ,he didn’t actually play any direct part in demoting Pluto. He wins either way. He’s either discovered several new planets (something nobody has ever done) or played a part in discovering and defining a whole new class of solar system object. Win. Win. And with a new book out on the subject, this basketball player just opened him up to a whole new audience.

    The best argument I’ve heard against Pluto was Neil Tyson’s “If you moved Pluto into the inner solar system, it would grow a tail. That’s no way for a planet to behave.” But I think he said that before the hot jupiter was discovered. I like the idea of 3 classes of solar planets, myself. Rocky, Gassy and Icy. Ceres excluded because if it got any bigger, Jupiter would tear it apart again.

  93. Messier Tidy Upper

    @ 92. Nigel Depledge :

    But you are not the IAU. You do not make the rules. They do.

    Appeal to authority is a logical fallacy. Just because the IAU are an authority doesn’t automatically make them – or their definition right.

    Imagine the IAU does as you suggest in comment #89 :

    As far as I am concerned, the IAU could choose to define planets by colour if they so wish

    Thus removing the planetary status from all worlds bar Earth & Neptune.

    That would clearly be silly and wrong no matter he authority. If those in authority are making bad decisions then they should be called on it & made to correct them. That is, in my view, the situation here.

    It seems to me that where we disagree is on whether the change made by the IAU is an improvement or not. I think it is, and you seem to disagree (correct me if I’m wrong). I’m not saying it couldn’t be better, but I still think it’s an improvement. Now, at least, planets are defined by qualitative distinctions from other solar system bodies, whereas, before, a “planet” was merely a member of a list of nine objects.

    I don’t think that last sentence is accurate – the planets were more than just members of this list and we did have an idea of what they were. The definition may not have been a formal one but we did have a working idea.

    I do indeed disagree with the IAU definition – it might perhaps be considered an improvement but it isn’t a good logical definition and it doe shave problems that mena we should, in my view – & many others opinions too – reject it and replace it with something better.

  94. Messier Tidy Upper

    CORRECTED BIT from my ^ comment :

    As far as I am concerned, the IAU could choose to define planets by colour if they so wish

    Thus removing the planetary status from all worlds, bar only Earth & Neptune.

    That would clearly be silly and wrong no matter their authority. Would you expect people to say “oh well, they’re the IAU so we must agree with that definition however absurd it might be” or would they say instead, “hang on that’s just not right!?”

    If those in authority are making bad decisions then they should be called on it & made to correct them. If they refuse to do so then they are showing that they shouldn’t be in charge and, if it becomes bad enough to be necessary they get replaced by other more reasonable people. That is, in my view, the situation here.

  95. Messier Tidy Upper

    @83. Nigel Depledge :

    if you call Pluto a planet, but don’t call any other KBOs planets, then you render the meaning of the word planet “a member of this list” which is pretty much useless.

    Not what I’m calling for. I agree here – I want all dwarf planets considered planets, incl, Eris, Sedna, Ceres, etc .. as well.

    I think the first definition they came up with at the Prague conference -which is similar if not identical to the one I’ve given – is superior to the revised anti-Pluto current def’n. I am not alone in this opinion. (Yes, I am an amateur astronomer not a professional one.)

    why do you seem to think it is worse that what we had before the IAU issued the definition?

    See my comment #70 here.

    Pluto does not gravitationally dominate its orbital path. It dominates a small portion of it.

    Okay, allow me a thought experiment here. Imagine a rogue Superjovian planet wanders into our solar system and disrupts the orbits of the outer planets. It swings Neptune off course and draws Jupiter outwards so that the four gas giants are thrown into chaotic orbits they no longer dominate. Would this in your view mean they were no longer “planets”? I don’t think it would. Now if this rogue Superjovian captured, say, Neptune into orbit around itself it would make Neptune a moon & not a planet – but if Neptune was just disturbed and shifted into a region it couldn’t gravitationally dominate – like frex the Oort Cloud – would it stop being a planet in your eyes?

    Methinks orbital dominance is vastly over-rated!

    @86. shoblock : Neat story. I’d call you on your bias there but I hardly have to, you’ve pretty much done so yourself! ;-)

    I hold no ill will at all towards Mike Brown, I’m sure he’s a great bloke. I do disagree with him on Pluto’s status though.

  96. Messier Tidy Upper

    @1. plutosdad Says:

    My dog is named Pluto, and everybody loves him too! He told me he’d bite Mr. Brown in the shin, unless Brown gives him a treat.

    LOL. :-)

    That reminds me of my brother’s dog named Cerberus after the three-headed dog guarding the Greek underworld – ruled by Pluto. I’m puzzled as to why when Pluto’s smaller moons* were discovered one of them wasn’t named Cereberus after that – would ‘ve been apt. Guess there must already have been an asteroid or something with that name?

    @74 & 75. Gus Snarp : Thanks.

    —-

    * Now named Nix and Hydra found by the HST in I think 2005.

  97. Nigel Depledge

    OK, so let me see if I understand the gist of the “IAU definition is wrong” argument…

    The main beef seems to be with the “gravitationally dominates” aspect, although I can’t quite see, from the arguments above, why this is a problem.

    It feels to me as if the main reason that people object to the new definition is not so much in the technical detail as in the fact that it demotes Pluto from planet status. Thus, getting into the technical details of what volume of space any particular planet dominates, and what is meant by “gravitationally dominant” are not ends in themselves, but means to get Pluto back into the club.

    If Pluto brings its entire family with it, that seems to be OK.

    @ MTU (too many comments to numerate) –
    Your defintion may or may not be “better” than the present one. Either way, I fully support the right of the IAU, as the leading international organisation of professional astronomers, to define what the terms used in their science mean.

    If you tried to redefine for me (I’m a biochemist) what may be meant by the term “nucleic acid”, I’d probably tell you to take a running jump. Or just ignore you.

    We, as amateur astronomers, do not “own” the terms used in astronomy. If professional astronomers (as represented by the IAU) feel that the term “planet” needs to be defined in a certain way, then that is their perogative.

    You made reference to a “numbers game” – well, perhaps the majority of IAU members felt that having 25 or 30 planets (with the prospect of discovering many more in the Kuiper Belt in the coming decades) rendered the term useless.

    Ultimately, what we have now is an improvement over what went before, because this is at least an attempt at a systematic defintion of the term. A lot of people don’t like it – but the reasons for this dislike seem to me more emotionally-based than to do with the utility of the term. You claim that the IAU defintion is illogical, but you have not shown this.

    I grow weary of the sheer quantity of text you have put in this thread, so I’ll leave you to have the last word.

  98. Hi, Phil, I’m an astronomer too and also your friend, at least on Facebook. And my Twitter handle is @plutosavior. I have been actively working for the last four years to get Pluto’s planet status reinstated and/or to get the IAU demotion ignored. Only four percent of the IAU voted on the demotion, and most are not planetary scientists. Their decision was immediately opposed in a formal petition by hundreds of planetary scientists led by New Horizons Principal Investigator Dr. Alan Stern. Saying we have to arbitrarily limit the number of planets in the solar system to a small number has no scientific basis. And the claim that those who oppose the demotion base our decision on sentiment is a straw man meant to discredit anyone who disagrees with the IAU decision. There are plenty of sound scientific reasons for keeping Pluto and all dwarf planets as a subclass of planets, objects large enough to be in hydrostatic equilibrium but not large enough to gravitationally dominate their orbits. If that means our solar system has several hundred planets, so be it.

    I’m a liberal, so I’m not for punishments; the closest I come is my Pluto Blog at http://laurele.livejournal.com, my own public presentations, and my upcoming book “The Little Planet That Would Not Die: Pluto’s Story.” I will not leave this Earth before I see that demotion go the way of the dinosaurs.

  99. Shoblock, email me at laurelkornfeld@netzero.net and I will answer any question your daughter has. She deserves to hear both sides fully, as do you, before making a decision just because you like somebody.

    Ceres’ demotion turns out to have been wrong. The telescopes of 19th century astronomers could not resolve it into a disk, so they demoted it along with the other asteroids. In the 1990s, the Hubble telescope imaged Ceres and confirmed it to be spherical, meaning it has reached the threshold where it is pulled into a round shape by its own gravity, a state known as hydrostatic equilibrium. This is what distinguishes small planets from shapeless asteroids and KBOs. Any KBOs that are large enough to be in hydrostatic equilibrium are both KBOs and small planets. One does not preclude the other.

    There have been proposals from the 19th century to today to classify the spherical moons of planets as “satellite planets” or “secondary planets.” These objects are geologically differentiated and have all the characteristics of planets except that they orbit other planets instead of stars directly.

    Brown dwarfs are classed at the lowest end of star categories (actually, a new class of star was created to accommodate them) because the key point is that they once conducted hydrogen fusion even if they are not doing it now. According to Dr. Alan Stern, a planet should be an object that never underwent fusion.

    Memorizing planet names makes little sense. Once upon a time, we knew little more about the planets than their names, so memorizing made sense. Today, we have a wealth of knowledge from 50 years of planetary exploration, and teaching that is much more valuable than having kids memorize names. We don’t ask kids to memorize the names of all the rivers or mountains on Earth; what we do ask is that they know what rivers and mountains are and the characteristics of different types of each.

    I strongly second the statement that argument from authority is a logical fallacy. The IAU has authority only if enough people believe it does. Since several hundred professional astronomers signed a formal petition rejecting the IAU demotion, it is clear that the IAU represents not the “gospel truth” but one side in an ongoing debate. Significantly, even Dr. Tyson has come to admit that this is still an open debate. Unfortunately, when the astronomers who signed the petition formally requested a reopening of this issue at the 2009 General Assembly, the IAU leadership adamantly refused, leading these astronomers to boycott. Shutting off debate itself shows an underlying insecurity on the part of the IAU leadership with their position.

    And amateur astronomers should have a say in the definition of astronomical terms. An incredibly large number of discoveries, including recent impacts on Jupiter and numerous comets, have been made by amateurs. In fact, amateurs usually have a broader knowledge of astronomy whereas professionals specialize in one field. The majority of the 424 (out of a total membership of 10,000) IAU members who voted on the demotion are not even planetary scientists but other types of astronomers.

  100. Laurel, you’re obviously passionate about this. I suggest you read Mike Brown’s book, “How I Killed Pluto and Why It Had It Coming” which should be out soon. I won’t go into details since the book’s not out yet, but Mike makes an excellent point in the last chapter about the difference between the definition of “planet” versus the concept of a planet. I think his point is very well taken.

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