Breaking News– Pluto not a planet!

By Phil Plait | August 24, 2006 8:31 am

The IAU has voted on a series of resolutions on what a planet is and what a planet isn’t, and the verdict is…

Pluto is not a planet.

At least, not a major one.

This is a big turnaround from the initial resolution, which would have given our solar system at least 12 planets, and potentially many, many more. Here is the first resolution that passed:

The IAU therefore resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way:

(1) A planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A dwarf planet is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

Ignoring for the moment, once again, that it’s silly to try to scientifically define a class of objects that are really only defined culturally, these definitions are still unsatisfying to me. A planet-sized object between stars is not a planet? How round is round? How do you define its "neighborhood"? These are still the same objections I made before in my earlier post about this.

But I suppose what people want to know is how Pluto fits in this. Pluto is round, and orbits the Sun, but has not cleared out its local neighborhood. Smaller objects that orbit the Sun in nearly the same orbit will get absorbed by or ejected by the larger object. As planets form, their gravity either pulls in smaller bits of junk, causing them to impact, making the planet grow, or it slingshots the smaller object away, putting it in a very different orbit. That’s why big objects in the solar system tend not to have anything else near them (except moons).

Pluto fails this. As I understand it (the news is still sketchy from the IAU meeting) there are other objects in similar orbits as Pluto, and therefore Pluto has not cleared out its neighborhood. I’m not sure if Charon, Pluto’s moon, is included in that list of uncleared objects. Now, this is a little confusing: lots of planets have moons, so just having a moon doesn’t mean a planet has not cleared its area (since the moon is bound gravitationally by the planet). But Charon orbits Pluto far enough out that the center-of-mass of the system is outside Pluto’s surface (again, see see my earlier post about this). Ironically, with the original resolution, this made both Pluto and Charon a planet. Now, under the new rules, this may mean neither is.

So: according to the new rules, passed by the IAU, Pluto is no longer a planet. I guess Neil Tyson will have to go on Colbert again.

The IAU made this pretty official with another resolution:

The IAU further resolves:

Pluto is a dwarf planet by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

This sits better with me, actually, than calling Pluto a planet, but a lot of people aren’t gonna like it.

Incidentally, there were two resolutions voted down:

Insert the word “classical” before the word “planet” in Resolution 5A, Section (1)

so that if it had passed we’d call the 8 major planets "classical". The other resolution would have been added to 6A about the dwarf planets:

This category is to be called “plutonian objects.”

Since this last bit was voted down (narrowly, 187 to 183!), the IAU will decide what to call this class of objects at the next meeting, in Rio in 2009. Rio, hmmmm… maybe I’d better go to that one.

Let me once again reiterate that trying to define what a planet is is very, very silly. The very fact that all this is so bizarrely confusing is good evidence of this.

Want another reason this is silly? If the reason Pluto isn’t a planet is because of Charon, then we’re in trouble: as I pointed out in my other post, in a billion years or so the Moon will be far enough away that the Earth-Moon center-of-mass will be outside the Earth. So at that time, if I understand this correctly (and I may not), Earth will no longer be a planet. I need to find out more about all this, but as I said, details about why exactly Pluto isn’t a planet anymore are still a little sketchy. I’ll post more when I find out.

And here’s another point. Pluto crosses Neptune’s orbit. Due to the delicate dance of gravity between the two, they never actually get near each; Pluto is always on the opposite side of the Sun from Neptune when it crosses the bigger planet’s orbit. So, if Pluto’s orbit actually overlaps Neptune’s, doesn’t that mean Neptune hasn’t cleared out its neighborhood? I think you might argue that. So why don’t we have 7 planets?

I’m really torn over this. Scientifically, this whole debate is a tempest in a teapot. It’s ridiculous, and serves no purpose. How is scientific knowledge furthered in any way by debating and resolving this?

On the other hand, it’s gotten a lot of interest by the public, and it’s been positive interest so far. People are talking about what it means to be a planet, and given the abysmal level of science education in the US, it’s great that folks are actually talking about astronomy. Maybe it’ll lead to some of them looking into it more, and that’s a good thing.

And now, finally, just maybe, we can actually get back to studying these objects instead of arguing about what to call them. There’s much to learn about them, real stuff, interesting stuff. The planets — however many you may think there are — are waiting. Let’s get going.

Comments (214)

  1. great shock that is. Now the solar system has 8 planets.

  2. RAF

    That which we call a rose, by any other name…

  3. But without a decent definition how are we supposed to know what anyone’s talking about when they tell us that a new planet has been discovered in some other solar system?

  4. George Greene

    In addition to the several good questions BA has about the defiinition of “planet”, what do we call the thingies that we’ve discovered orbiting other stars? The IAU’s definition says a planet “(a) is in orbit around the Sun”. So there are no other planets in the universe. So much for ET.

    I had the same thought about Neptune too: I’m not sure what other objects there are that Pluto is supposed not to have cleared from its orbit; one would hope that this does not include satellites, or we’re down to Mercury and Venus. But is Pluto supposed to have cleared Neptune from its orbit??? Talk about tail wagging dog. If those two are, despite the difference in inclination, in the same orbit, then Neptune is not a planet.

  5. JIanying ji

    I prefered the 12+ planet proposal far better than this. Just like we have multiple stars, I have no problem with multiple planets. The original proposal also has a better structure, starts general and than creates sub-categories. This new definition is a confused muddle. The idea of clearing a zone is far less scientific than any thing in the original proposal. I think IAU made a major mistake here. I rather have thousands of planet with a easy to remember definition than eight with an unexplainable one.

  6. idlemind

    I dunno. Seems that Neptune has cleared its orbit of everything that it possibly could, leaving the only objects that, due to orbital resonance, just happen to occupy an orbit that avoids any interaction. If not for Neptune, the Kuiper belt might extend closer to the Sun, with hundreds of bodies like Pluto/Charon. As it stands, the latter are just the lucky ones which by their very existence imply just how effective has cleared its orbital neighborhood.

  7. George Greene

    … and even if they change the definition to allow extra-solar planets, the definition is still faulty, since it would appear to make stars in orbit about other, larger stars into planets. Nothing there about being too small to ignite fusion.

    We don’t have that issue as long as we are dealing with the solar system, but hey, we found out that we were not the center of the universe some time ago.

  8. kit

    hehehe. now not only our solar system has 8 plannets, the entire universe has only 8 planets. and all orbit our sun.

    So what are those things orbiting other stars they have found? Whatever they are, they are not planets.

  9. I like this outcome much better. I have always thought of Pluto being anything other than an official planet; its composition being a Kuiper Belt Object that just happens to be large. If the 12 planet proposal was approved, I can see out Solar System growing even larger as larger KBO’s are discovered – and the thought of labelling a large asteroid a planet seems silly to me.

    Why not have different classes of planets: planets, dwarf planets, irregular planets, gasseous planets… Stars have multiple classifications so this is not that far fetched. The benefit is that our Solar System will remain with the (now) 8 planets in the classical sense with the addition of multiple irregular planets and dwarf planets (or plutons if you will – which is a silly name as well in my opinion).

    Do I see and H-R like diagram for planets in the near future?

  10. Walt

    The BA leaves me a little confused. He says that a planet classification system is a cultural definition and silly. So is the solar classification system he often refers to also cultural and silly? His writings would seem to suggest he endorses classifying stars. Why is classifying planets different?

  11. DF

    Good points BA – and what about the Trojans or the many near-Earth asteroids?

    It would have been far more sensible to label the 9 planets that we have (had) the 9 “classical” planets and to call large Kuiper belt objects large Kuiper belt objects with Pluto having a dual designation.

    It seems that planets are like pornography – hard to define but you know it when you see it.

  12. Mike

    Well between having a 100 planet solar system or an 8 planet configuration, I’ll pick the latter.

    Secondly, neighbourhood is not necessarily an unscientific term. We can define it to be a small region of space around an object, but I can see the word’s shortcomings.

  13. Matija

    I don’t see why this definition would exclude the extrasolar planets. The whole controversy was about where do we draw the line between the large and the small planets in our system. All ESPs found so far are large, so it’s a moot point. Later in the future we might define them more carefully, but presently there is no need for that as we don’t know of any extrasolar asteroids.

    Pluto and Neptune don’t really have crossing orbits, they are in a mean-motion resonance and never meet as they go around the Sun. The same is true for Jupiter and its Trojans. Moons, by definition, are bound to planets gravitationally, so they also can’t be kicked out of the system by close encounters (which must be hyperbolic). The eight planets have truly cleared out their environment of almost everything else, and the present small bodies they are encountering (NEAs, comets, Centaurs) are just passing through and were not original inhabitants of those regions.

    For those who are really interested in what “clearing out” exactly means, I recommend Steven Soter’s paper on astro-ph (it’s free, but quite long):

  14. hhEB09'1

    In the BA blog today (Breaking News– Pluto not a planet!), the BA asserts that “as I pointed out in my other post, in a billion years or so the Moon will be far enough away that the Earth-Moon center-of-mass will be outside the Earth.”

    Because the tidal-slowing process is limited, that will not happen.

  15. Christian Burnham

    If we allowed Pluto to have planetary status then it would be a short step to polygamy and people marrying dogs.

  16. tacitus

    I would have been happy with two types of planet–major planets and minor planets–with Pluto becoming a minor planet. But I guess that “planet” and “dwarf planet” is close enough. Fine with me.

    I suspect that if we even come across planet-sized objects that do not orbit a star, we will simply create a new category of planet–either rogue planet or, more likely, wandering planet. No big deal.

    The irony is that it’s pretty easy to see why Pluto doesn’t belong in the list of “classical planets”, but it’s proving darned difficult to come up with a rigorous specification that explains why Pluto is not a classical planet.

  17. kit


    How come you don’t see why the definition excludes the extrasolar objetcs? It says right there – orbit the SUN.
    Who cares how large the ESP is, as long as it does not orbit the SUN it falls out of the definition of the planet. ESPs under this definition are not planets!

  18. “People are talking about what it means to be a planet” – well, I’ve never been one as far as I can remember, although I have a brain the size of one…

    Seriously though, it is a good thing as it is getting people who wouldn’t normally talk about astronomy doing just that – and maybe doing a bit of thinking too.

  19. Martín Pereyra

    Maybe that thing of “cleared the neighbourhood around its orbit” means “to be more massive than all other bodies in the orbit together”. Earth would still qualify as a planet when the Moon finally leaves it. I remember that Neptune is way bigger than Pluto, and still qualifies as a planet…

    Nice work of IAU guys: their clarifying definition confuses things even more.

  20. Matija


    The IAU definition starts with:

    “The IAU therefore resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way…”

    I think this makes clear that the definition says nothing directly about ESPs. However, by analogy, one would expect the same distinction bewteen major and dwarf planets to be made in other systems, once there is a need.

  21. I applaud the new definition of a planet. Let’s remember that the term was coined by our ancestors in reference to star-like objects that appear to wander relative to the so-called fixed stars. Invisible objects due to small size or great distance were understandably not included. In particular, the term did not apply to unseen bodies circling fixed stars. Earth was added to the set following an historic debate regarding heliocentricity. The later discovered Uranus and Neptune unquestionably had the size and orbital characteristics of planets.

    The characteristics and methods of formation of other bodies in the solar system seem to mandate classes of their own. Regarding bodies circling fixed stars, the term extra-solar planets may be sufficient for that set, although a new term could be devised.

    It would have been simplest if the IAU had defined the set of planets as Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus & Neptune. Apparently they feel that defining the set by its properties provides justification. I suspect that very soon the simple naming of the members of the set will be deemed sufficient, especially for fourth grade textbooks.

  22. Kaptain K

    “That which we call a rose, by any other name…”

    Would still have thorns! ;)

  23. I can’t see how it can be claimed that Saturn has cleared the neighborhood around it’s orbit. It may be in the process of doing so, but it hasn’t finished the job just yet. Come to think of it, the other gas planets have rings that demonstrate that they are not quite done clearing their orbits either.

    Eventually we will have 8 planets it seems, but for now there might only be 4 or 5.

  24. Has anybody read to the bottom of the AP reports on the decision? My favorite part of the press coverage is this gem from the latest AP article:

    “It was unclear how Pluto’s demotion might affect the mission of NASA’s New Horizons spacecraft, which earlier this year began a 9 1/2-year journey to the oddball object….”

    It’s a bit late now to cancel the mission, does the AP think New Horizons will get out to Pluto’s orbit and find just empty space (maybe a “Pardon our dust” sign with the IAU logo)?


  25. DF
  26. Ashley Zinyk

    > A planet-sized object between stars is not a planet?

    Science-fiction writers have speculated about “rogue planets” – planets that don’t orbit a star, but is there any evidence that such a thing can exist? We don’t know everything about planet formation, but maybe all planets are around stars. Also, the only thing that makes the moon not a planet is it’s location, so I don’t see what’s wrong with applying the same criteria to interstellar bodies.

    >Pluto is a dwarf planet by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

    I’m happy with “trans-Neptunian object” but “dwarf planet” sticks in my craw a little. It makes it sound like it’s a planet that’s small, but I don’t think it should qualify as even a “dwarf” planet. A SmartCar is a dwarf car, but a Bonneville Triumph with a sidecar is a motorcycle, not a car, even though it’s nearly as big as the SmartCar. I think Pluto should just be considered “the largest of the TNOs”, because there’s a smooth continuum of sizes among TNOs. Still, I’m glad it’s not a full planet any more.

  27. Nutmeg

    I like this decision. Since Pluto and Charon are essentially Kuiper Belt objects, with 100s more bodies just like them, it appears to me that we have either 8 planets, or we have 1,000+. This makes sense to me. In the end, it maintains the cultural importance of the inner planets. And we’ll always remember Pluto. ;)

  28. I think the better definition is the center-of-mass, ok in a billion year or so, like you said the Earth will no longer a planet with this one, but i think we are going to destroy Earth sooner than that.
    (first comment i made :P )

  29. Mike

    I agree with many above comments: the way the decision was formed was pretty ugly, but the end results seems pretty, well, right. I have to call this a victory for the IAU.

  30. Ashley: Yes. Google “planemo”. Or check this article:

    So anyway… Pluto is a “dwarf planet” now. (And presumably so is Ceres, maybe one or two other Asteroids, and then perhaps a number of other Kuiper Belt objects.) I’m not sure about the “cleared its neighborhood” business. How big is the neighborhood? Aren’t there over 1,500 asteroids which share Jupiter’s orbit but just happen to be far enough from the planet and orbitting in sync with it so as to remain unmolested by it? I think they are called “trojans”?

  31. Doodler

    Ah well, at least the fingercounting crowd can still count the planets on their fingers or some ridiculous mnemonic.

    Hukt awn fahniks wirks 4 IAU.

    I truly appreciate the sick irony of a heliocentric definition for planets, the Christians must be drooling over the possibility of restoring Earth’s place as “special” in the universe.

  32. Scott

    The problem is not that they’re trying to define what a planet is. They already have a very good idea what a planet is! The problem is that they’re trying to find a set of criteria that cover all the objects they call planets. And then suddenly they realize that they all have a lot in common with objects they don’t want to call planets. Must be rather frustrating to keep coming up with rules that just don’t fit like they want them to!

  33. Filipe

    If you note the definition states that the dwarf planets are not a subclass of planets but a new class. It doesm’t make sense. Earth and Jupiter are in the same class of objects. Pluto and the Earth are not. All the TNOs and Pluto could fit inside the Earth but then all the other planets could fit inside Jupiter. The only criterion is the “cleaning of the orbit”.

  34. rvr

    Ashley Zinyk: Yes, there exist “free floating objects” of jovian mass, but right now, they form just like stars, by a collapsing cloud. Indeed, some weeks ago a double object was discovered, one just above the brown dwarf limit and one well below (14 and 7 jovian masses).

  35. ♥♥♥♥♥Fender♥♥♥♥♥


    Hey what about Xena? D= Xena should be a planet!

  36. What I think is silly is that this was never defined in the first place.

  37. Michelle Rochon

    You know, I think that I’m more confused now than ever about our system.

    And Fender, “Xena” is UB313 and it is not a planet. It’s now a dwarf planet like Pluto and Ceres

  38. Will. M.

    BA wrote: “…given the abysmal level of science education in the US, it’s great that folks are actually talking about astronomy.”
    But what are the abysmally ignorant talking about? The inability of astronomers to solve a non-poblem, it seems – if the Daily Show take on this is any example.
    So what does this say about a group of the best astronomers in the world failing to arrive at even a partially successful solution which seems could be resolved with the existing science covering bodies which inhabit solar systems? It says to me that they behave just like a group of high school teachers when put on a committee to decide a like problem: the number of solutions (and those who defend them) are directly proportional to the number of teachers on the committee, notwithstanding the nature of the problem or the expertise of the committee participants, and the solution doesn’t satisfy anyone. (And, I’ve seen teenagers get to the heart of the matter and make clearer decisions than such faculty-peopled committees.) Perhaps we can’t ever get clear answers to problems which are (a) not crucial, and (b) which don’t have clearly defined data with which to address them. This jury wasn’t deciding a life or death decision, and the planets/orbiting bodies/objects/etc. will still be there when we do get enough data to finally classify them (should we decide we need to).

  39. “Let me once again reiterate that trying to define what a planet is is very, very silly.”

    How can it be that the definition of a basic term in your field is “silly”? Can you imagine any other field of science where the definition of a basic term would be an exercise in silliness?

    Imagine chemists saying that attempting to define the term “element” is silly. Would anyone take them – or their field of study – seriously?

  40. ♥♥♥♥♥Fender♥♥♥♥♥

    “And Fender, “Xena” is UB313 and it is not a planet. It’s now a dwarf planet like Pluto and Ceres”

    I know what Xena is, I’m not retarded. I just don’t want to waste 3 seconds of my life typing UB313 when insted I could use that time to utter my last important words with my last breath.

  41. If anyone is interested, over at the Jodcast we have edited down the very lengthy IAU session that took place this afternoon to a more reasonable 20 minutes or so (the MP3 is around 10MB). Many of the questions raised in the comments here were also raised by astronomers in the session (we took out some parts just to keep the whole thing brief) such as the status of Neptune being a planet and why Charon is not a dwarf planet. The BA is not going to be happy though, as people kept calling Charon “Sharon”.

  42. Eric

    I find one thing kind of funny, anytime someone mistakenly calls a meteorite a meteor or vise versa, Phil is quick to point out their mistake. Yet he states that coming up with rules that define what is a planet and what isn’t is “silly”.

  43. So far NASA has said this will not affect the NH mission, I just hope this is not used as an excuse to scrub a mission underway so nobody will be there to hear thge NH signal.

    I read one report that most of the astronomers had gone home and the vote was taken by a small number. Any word on that?

    Is there some avenue of appeal?

  44. Aerimus

    I like the new definition.

    Now maybe I’m wrong, but I thought that the objects that pluto failed to clear from its neighborhood was the rest of the Kupier belt Objects, not Neptune.

    Also, concerning the recession of Earth’s moon, unless I’m missing something, the moon does not neccessarily gain planethood, nor do we lose ours, as the moon could still be considered our satellite.

    Finally, I don’t think that they meant that ALL debris was cleared from the neighborhood, just a considerable chunk. So while their are still Near Eart Astroids, the population density is not near that of the asteriod belt. Also, Trojans, Moons, and rings, while they are debris, are under the influence of the planet policing the neighborhood (as opposed to the asteroids and KBO, which have no obital “policing” planet).

  45. Gillianren

    Wow, it’s amazing how many people ignore the “in our Solar System” bit and get all het up over the “orbiting the Sun” bit. Perhaps poor reading comprehension is the reason for the sad state of American education?

    [b]Ed Minchau[/b]: When was the last time you heard a debate about what an “element” is? There is a simple definition, and there are things that clearly do and don’t meet it. Whereas “planet” is clearly not so simple a definition. It’s a lot foggier, and everything that fits it also technically fits the definition “satellite,” so “planet” is, indeed, a human and essentially worthless construct.

    Still, it makes elementary school education easier, I suppose.

  46. Aerimus


    Even if true, those that went home probably did not feel that the vote was important, or they didn’t care. Afterall, we all knew a week ago that a vote on the definition was supposed to be coming today.

  47. Aerimus


    From a technical standpoint, the definition is quite worthless, but setting a good definition is important for the purposes of public outreach. Now we just have to show the public that this is how science works: our way of seeing the universe changes based on observations and does not mere stand still just do to traditions.

  48. Proesterchen

    Pluto’s characterization has bugged me since I was an early teen, today I can finally rejoice at its demotion. I drink to you, Pluto, the planet that never was.

  49. This definition is far more amenable to extra-solar planets than the one first floated by the sub-committee, with its arbitrary 200-year orbital period dividing line. I think it’s a reasonable definition, but there is the issue of what it means to “clear the neighborhood around its orbit”. Pluto’s problem on this front is not Charon or its other moons, but the several other objects (previously dubbed “Plutinos”) that are in the same 3:2 orbital resonance with Neptune that Pluto is in. Or, maybe its problem is that its orbit crosses the orbit of Neptune (although it is stable due to that 3:2 resonance). Or maybe its because its orbit crosses the orbits of other Kuiper Belt Objects. The asteroids are on crossing orbits, but they are also on planet-crossing orbits, so some additional distinction is needed about just how clear the “neighborhood” has to be.

  50. From now on, I’m going to call Earth a “large, wet asteroid.”

  51. Annie

    That is because what is fundamental in this situation is physics. Physically, what we call a meteor and what we call a meteorite are completely different things, completely separate phenomena. With the term ‘planet’, however, you make the definition however you like. As far as physics goes, Pluto is absolutely no different today than it was a month ago, and it is therefore very very silly for a group of scientists to try to change via nomenclature what has not changed via the laws of physics. Historically, the term “planet” has much more to do with Earthbound observers than it has to do with physics, solar system formation theory, or hydrostatics. Earth and Jupiter are physically different places, yet we use the same name – planet – for each. We acknowledge the physical difference when we describe the separate searches for extrasolar “Earths” and extrasolar “Jupiters.” The nomenclature is a cultural and traditional decision, not a description of the physics at play in the body in question.

  52. DJ

    So, why is UB313 not a planet? Because it hasn’t cleared out the Kuiper belt?

  53. owlbear1

    I think of it as the first steps in refining the idea of “Planet Classification”. It is at its earliest and broadest start. As our understanding of the planets and other objects that orbit our Sun advances, so to will the definitions. Yes it has gaps but so does our understanding of our solar system.

  54. Wait, what about Cruithne? It shares an orbit with Earth, so Earth has not cleared out its neighborhood! OMG, Earth is not a planet!!!

  55. DJ: Yes.

    I’m pretty pleased with this, but then again I was pleased with last week’s definition, too. What would make me really, really happy is if we formalised different classes of planets for rocky planets and gas giants. So I would have four classes of object where the IAU has three: gas planets, rocky planets, dwarf planets, and SSBOs. The first two categories fall under the term “classical planets”, and the first three categories fall under the broader umbrella of “planets”. But “planets” plus “dwarf planets” with “SSBOs” hanging around the edges is ok with me.

  56. TJ

    “our way of seeing the universe changes”

    Fundamental Zen error #1: the name is not the thing.

    Fundamental Zen error #2: The name change is not the result of observations, but of “interpretations” of the observations.

    Habits from millenia gone-by still clinging … bad hygiene.

  57. Hinschelwood

    “if Pluto’s orbit actually overlaps Neptune’s, doesn’t that mean Neptune hasn’t cleared out its neighborhood? I think you might argue that. So why don’t we have 7 planets?”

    No. This is obviously intended to mean bodies that have the same orbit. Pluto’s orbit is different to Neptune’s, so it is not in Neptune’s neighbourhood, no more than Halley’s comet is in Earth’s neighbourhood, despite the fact that their orbits cross.

    Personally, I’m quite pleased that this non-planet is no longer considered a planet, for whatever reason. It’s not that contrived, either, although I agree that it’s nonsense to try to give a failsafe definition of a planet.

  58. P. Edward Murray

    So we are saying that 187 elitist professional astronomers voted for this and 183 were against?

    Out of how many members?

    And the next meeting is when?

    In 2009?

    Ok, here is what I think.

    Let’s strip the funding from IAU member Astronomers totally and
    see how they like that!

    Here’s what Johns Hopkins astronomers are saying:


  59. Chip

    Never bothered me if Pluto was a “Planet” or a “Dwarf Planet.”

    BTW, if Pluto were the same size as Mars it would still not be a planet, right? If not, what is the maximum diameter of a “dwarf planet”?

  60. ioresult

    Why not call Pluto a moon of Neptune, since it is gravitationnaly bound to it? (resonance orbit and all…)

  61. @Chip:

    If Pluto were the size of Mars, I’d expect it would have done a better job at clearing its orbit (greater mass, stronger gravitational tugs, etc.). Big planets keep the spaceways tidy.

    I haven’t done the calculations on this, but my first blog-commentor’s guess is that by our current understanding of How Things Work, such a problem isn’t likely to arise.

  62. P. Edward Murray

    And what about this “clearing” business?
    Sounds to me like this definition says that the Earth is not
    a planet because it hasn’t cleared it’s orbit!

    What in heck do we call these NEO’s? Space Dust?
    What about comets such as Halley’s that regularly
    pass through our orbit?

    And what about meteors?

    Clearly, the Earth has not cleared it’s orbit yet either!

    If anyone asks me I will ask them which definition?

  63. drow

    honestly. sol has one planet, three minor planets, and a lot of debris.

  64. david

    As long as the name xena did not stick is the only thing i care about and i feel sorry for anyone who has to teach an intro astromony course or is tour guide at a telescope in about year from hearing the same question over and over ” is pluto a planet what are your thoughts”

  65. Dagger

    Whoa B.A, chill bud. You and many others here have stated this is unscientific and your right. Why get your knickers in a twist over it? All the IAU has done is to define what is and what isn’t a planet for the ordinary layperson. And let’s face it, there are a heck of a lot more of them then there are scientist types.

    So which aspect of you is balking Pluto not being a planet? The scientist or the regular everyday joe with a wife and 2.1 kids? (i’m counting the dogs too :) )

    Until you scientists get together and get a scientific definition of what a planet is, including ours, then the rest of us will just have to deal with the fact that Pluto has been demoted to “dwarf” status. No big deal.

  66. Apocalipsys

    The planet definition should be named only to its size and mass.
    Maybe adding the category of ice, rocky, and gas planets depending of the main sustance they are from.
    Planets should not be tied to its orbit. One day we may find a solar system with a planet the size of jupiter with an orbit like the comets. But it would be called a comet or a planet???.
    Other posibility that we may find a rock of the size of Jupiter but not orbiting a star but only static on a gas cloud. Still this would be called a rock or a planet. In our minds there are constraints from our learning past, althought they are great we should not be tied to that. We can learn a new definition. On the past a man could only walk or swin, now we can fly to outer space. Free from the clasical view and evolve to a more scientific model. Keep it scientific not semantical.

    Again sorry for my English.
    Thank you for your time.

  67. Steve

    What about the asteroid belt. Wouldn’t that be in the neighbourhood of both Mars and Jupiter? Would they be therefore declassified as pplanets, becuase they haven’t cleaned up that part of their neighbourhood?

    I think we now need a decent definition of neighbourhood to stop these sorts of silly questions about what is or is not part of a planet’s neighbourhood.

  68. Jianying

    As I stated before this definition is far worse the previous proposal that was floated. In stead of defining planet and then creating sub-categories, it clutter the definition itself with pointless things like this clearing its neighborhood.

    The previous proposal is simply: A planet is a round object that orbits the sun, and may co-orbit another planet.

    This new proposal that now has being made official is: planet is a round object orbiting the sun that cleared its neighborhood.

    The amount of NEOS is an indication that earth has not cleared its neighborhood. I would venture to wager that the number of NEOS-like objects within certain fixed volume arounod pluto is less than around earth. Certainly not a fair comparison but within the vaguery of the definition. I cannot think any way clearing the neighborhood can be made precise the way co-orbit and round can be made precise.

  69. P. Edward Murray


    They haven’t defined it at all they have only muddied the whole discussion.
    They didn’t even talk about a planet having an atmosphere or setting a definite limit in size.

    They left it to the very last.

    Thank God I don’t let these folks do my taxes or make any life or death decisions for me!

  70. cachalachi

    Using the word “neighborhood” to to describe astronomical distances is just [i]weird[/i]. Could we not have some formulas, or numbers, or something?

  71. Dagger

    P. Edward Murray,

    No argument with the tax assessment, but as to muddled, we’ll have to agree to disagree. I don’t believe it’s muddled at all. They really didn’t get into proper definitions and certainly didn’t apply any sort of science to it at all. I prefer to think of it as the precursor to when the scientists do develop a valid system of defining a planet. But we’ll have to be careful with that. Until now, we’ve only been good a defining what we can see. With 190 or so extrasolar planets now in the catalogue, it’s a daunting task to find a robust enough system to be able to catagorize them all. Scientifically.

  72. I found the following comment on the BBC “Have your say” web page. I hope Mr. Slawson doesn’t mind me reprinting it here. He’s summed it all up succinctly thus:

    “If Pluto is a planet then I’m the Ravenous Bug Blatter Beast of Traal. It is quite clearly a lump of irrelevant rubble left over after the Solar System coalesced out of the primordial gloop. It doesnt have a propper orbit and worst of all I cant find it in my telescope. I’m happy to have it described as a Pluton along with all the other garbage in the Oort cloud. Propper planets have tunes written for them by Gustav Holst and thats the end of it.”

    jeremy slawson, plymouth, United Kingdom

  73. HERE HERE to Phil’s suggestion to study the planets. I think, however, that the category of “planet” can still be retained, and the idea retain its coherency, without getting in the way of science.

    Why not just give the name of “planet” to any body that is sufficiently round but has not achieved nuclear fusion? Then we’ll have billions of stars, billions of planets, and billions of smaller objects (everything from irregularly shaped asteroids to dust particles), and we can start sub-classifying planets the way we do with stars. We can have terrestrial-type, comet-type, gas giant, etc.

    Leave the question of orbit out. Phil just demonstrated how it makes things too complicated — and I’m beginning to think myself that defining a body according to its relationship to another body is complicating things too much. We could indicate whether something is a satellite of something else, or not, and leave it at that. Best to study the planets according to their properties: size, atmosphere, chemistry (biology?).

    That would make scientists happy and it would still give the public something like the old definition: we can still say that we have 8 large planets (not including satellites) in the inner reaches of the solar system (our “neighborhood”), half of them terrestrial and half of them gas giants.

  74. Alan

    I frankly think that the IAU’s decision was HORRIBLE — not because of any scientific reasons, but because it was a Public Relations disaster. Let me explain….

    As we know the public’s interest in Astronomy and science in general is at best iffy and short term. In general, only an important first or discovery tends to attract any meaningful attention from the average person. That is why the idea of having new “Planets” discovered would be such a boon to public relations. All people are drawn to the new and unknown if they realize its significance. What better possibility as far as Astronomy is concerned other than finding a new Planet in our own solar system?

    Don’t bother to complain that science shouldn’t bow to public opinion — the two are hardly mutually exclusive! It is all about the presentation. If, for instance, the IAU had listed the first eight planets as “classical” it would have allowed for the discovery of more “planets” while keeping the more scientific definition that there is difference between “Classical” and “Dwarf” planets. It is a compromise with great PR potential — there would be many “planets” to be found, just of different types. To the general public the discovery/reclassification would represent something new, an addition to their understanding of the universe that made it more expansive and interesting.

    By comparison, by not qualifying the classic Eight planets as just a subset of the larger term “planet” what you get — and the reaction from the public and media already reflects this — is the widespread understanding that a “dwarf planet” really isn’t a “planet” at all, but something LESS interesting. By not only taking away part of the public understanding of the “universe”, but by effectively stating that no more planets will ever be found (in our solar system, which is the only planets most people are likely to care about) you turn this whole question into a serious NEGATIVE.

    It’s the sort of thing that will just leave a bad taste in people’s mouths — the IAU “took away” Pluto, not to mention other potential candidates. In short, psychologically speaking for the average person the universe just became a less mysterious, less relevant place. Sure, those of us interested in Astronomy know better, but that is far less likely to be the case for the average person.

    Worse, the IAU may very well have added fuel to the anti-intellectual bias that is such an evident thing in our society (especially in the U.S.). It will only strengthen the perception (partially because of all the arguing that has already gone on over this subject) that scientists are just remote ivory tower intellectuals who obsess over trivia that has little or no importance to “real life”. Given how this decision was made by just a tiny percentage of all Astronomers it will also encourage the other common negative impression that scientists are merely a bunch of self-serving elitists making decisions for everyone else.

    That is why this decision — and the handling of the matter in general — is turning into such a negative. It makes the scientific community seem petty and elitist. Yet, it didn’t have to be this way. With some common sense and savvy salesmanship this could have been a great PR triumph, yet without harming the basic science at all.

  75. P. Edward Murray


    I think you’ve just hit the proverbial nail on the head.
    Yes, it is a PR disaster and yes it flows right into this Anti-Intellectual bent
    that we seem to be stuck in here in the States.

    To me, it “seems” that they were hell bent on determining that Pluto was not a planet. I might be wrong but it smells of an “Elitist” mentality as in
    Non-Professional Astronomers don’t or shouldn’t make major discoveries.

    And that’s the attitude that we don’t need in the sciences today, rather we need a welcoming attitude to those who want to contribute and those who just want to learn. Because if we don’t foster that attitude who will?

    Science & Technology after all are the engines of change and the engines that create. If we, in the United States don’t DO others in other nations WILL and leave us behind and then our standard of living will be left behind.

    I think the IAU has outlived it’s usefulness.

    All of us Astronomers, Pro’s and Ams need to create a new organization.
    An organization that is vibrant and full of life.

  76. Grand Lunar

    I do prefer this resolution with 8 classical planets, and the rest as “dwarf planets”.

    One must wonder if they can really come up with a satifying answer. I suppose they won’t.

    Perhaps the IAU should have set up a classification system. You have major planets like the classical eight, which themselves are either terrestrial or gas giants, and then you have dwarf planets, with Pluto as the prototype. And add that a dwarf planet is one that fits neither into the gas giant or terrestrial planet catagories.
    Then we could drop the ’roundness’ and ‘clearing the neighborhood’ issues.

    Oh yes, perhaps this would also be a start; define a planet as a celestial object that is not a star. And then you have the classification mentioned above.

    Maybe the IAU will think of that for their next meeting. Think they’ll take suggestions?

  77. Chris

    “Neighborhood” is actually a well-defined mathematical term, but it requires a parameter. The neighborhood of size epsilon around a point P is the set of all points whose distance from P is less than epsilon.

    This can be pretty easily extended to: the neighborhood of size epsilon around a set of points S (such as an orbit) is the union of the neighborhoods of size epsilon around each point of S.

    So the orbit of Pluto or any other body has not just one well-defined neighborhood, but infinitely many of them (of different sizes). Do they mean the 1-km neighborhood, or the 1,000-km neighborhood, or the 1,000,000-km neighborhood, or the 1,000,000,000-km neighborhood?

    Furthermore, unless the neighborhood size is set *really* small, Pluto and Charon are in Neptune’s neighborhood and thus Neptune is a dwarf planet. The absurdity of a gas giant being classified as a “dwarf” planet is patent.

    And what does “cleared” mean with respect to double planets (double dwarf planets?), moons, rings, Trojans and miscellaneous small objects and dust? What if some body of substantial size *enters* the neighborhood of a planet? Does it lose planet status until it gets rid of the intruder?

    Any definition is going to be arbitrary, but this one is *vague*, too. Ick.

    P.S. Charon is still a dwarf planet, right? The not-a-satellite criterion reduces to the center-of-mass criterion from the previous definition?

  78. Daniel Burton

    I say math is fundamental to all science. Lewis Carroll demonstated a basic mathmatical principle when he wrote, ‘”When I use a word,”Humpty Dumpty said, in rather a scornful tone, “it means just what I choose it to mean — neither more nor less.”‘ I think math trumps the IAU.

    Spread the word, Pluto is a planet whether the IAU likes it or not. In fact I now know there are 12 planets, Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Neptune, Uranus, Pluto, Charon, and 2003 UB313.

  79. But think of all the ping-pong balls that will be saved.

  80. Katherine

    Huh. Well, THIS is some surprising news. I suppose there were enough 11th-hour objections for the initial resolution to get voted down. While I am somewhat glad that the initial terms weren’t set in stone, I am a bit uneasy about the ones that just were. I can definitely see some controversy over this for a long time to come.

    Now, here’s a thought I had as how one would go about making a definition for a “planet” if they absolutely had to: I was looking through my college astro textbook last night (from ~2003, so not so old), and I noticed that, while the outer “planets” (Jupiter, Saturn, Uranus, Neptune) were different from the inner ones in several ways, a) they all follow the general “rule” of what major planets should be like based on distance from the parent star; and b) they all have differentiated (i.e. layered) structures. I suspect that a) may have something remotely to do with the “clearing the neighborhood” rule in one way or another, but b) really got me thinking. From what I understand, differentiated structures are the exception rather than the rule in terms of non-solar objects, and differentiation suggests processes such as tectonic activity, etc. that don’t happen on just any or every object around. Objects such as asteroids, KBOs, etc. are for the most part NOT differentiated the way that the “classic” 8 planets are. AFAIK, Pluto is not. Other large KBOs are not. Most asteroids are not, although there has been some research to suggest that Ceres has a differentiated structure. So, could this be a possible criterion by which objects could be called “planets” or not? Incidentally, I’d actually have less of a problem with Ceres being called a “planet”, since it lives out amongst the failed planets of ages long past…

  81. ScottM

    To me Pluto is still a planet. Xena is also a planet to me. Maybe there hasn’t been a scientific definition of planet until now, but it has been popularly accepted that Pluto is a planet. According to that, Xena, which is larger than Pluto would also be a planet.

    I find it quite ironic that it has been the questions of the public, in large part, that has lead to this: a public that has always accepted Pluto as a planet, and certainly would have accepted Pluto also.

    Also, some astronomers believe we may eventually find objects as large as Mars in the Kuiper Belt. The IAU will have a difficult time justifying those objects’ not being planets. After all, they would be larger than one accepted planet (Mercury) and at least as large as another (Mars). Yet, according to the IAU definition, they more than likely could not be planets, since they would not be the dominant body in their neighborhood.

    I’d really be interested on your thoughts of how that scenario would be handled. Would such an object be a planet in your opinion? What would the IAU do?

  82. hotjupiter

    The debate rages and is fascinating for folks like me, who are learning immense amounts from it. I thought you, BA, and the rest of the commenters would be amused by a link my friend send me:

  83. Doug

    Its too bad there that no one at this conference decided to develop a classification system like the one that is used in Star Trek. Granted, we are talking about sci-fi, but what is fantasy now can be fact later on. It just needs a thoughtful approach. Something like:

    Location: Hot Zone, Eco Zone, Cold Zone… based on our current understanding about water being a prerequisite for life.
    Size: Asteroidal or Spheroidal… depending on whether gravity can shape it into a round body.
    Geological Activity: Is the body geologically active or inactive? Can it evolve from being active to inactive like the planet Mars is?
    Atmosphere: Is it transitory or largely permanent? What is it composed of?

    So and so on… and eventually a pattern will emerge that could satisfy almost everybody. I mean come on, it was reasoning like this that gave us our stellar classification system and its familiar refrain ‘Oh Be A Fine Girl, Kiss Me’. Right now, its too simplistic, vague, and more about showmanship. Is Pluto a planet? Its such a non-issue. Its a Class C Planet.

  84. Bad Reader Eric

    Ok, these new rules still do not fit. they are no better than the ones before.

    Ok here are a few contridictions:

    1. the largest asteroid we have found (I forget the name.. is it ceres?) is round, and HAS cleared its neighborhood. Just because it crosses the orbits of other planets, still means that it has “cleared its neighborhood”

    2. If the “cleared the neighborhood” rule were followed, then Jupiter IS NOT A PLANET because there are at least 2 groups of asteroids that currently share jupiter’s orbit.

    3. if the above said rule was followed, then that would also mean that plants with satilites do not qualify as planets as sattilites are objects in their “neighborhood” Then there would only be 2 “planets” which comprise of Venus and Mecury.

    4. If a sattilite, say titan, was somehow ejected, and assumes a stationary orbit around the sun between saturn and uranus. Would titan be reclassified as a planet if this happens?? Probably not.

    5. What about sedna, quoar, and the other elipical orbiting “planetoids” that were found?? Since we do not know of where the objects in the Oort cloud are or how many are near the orbits of Sedna, Quoar and the other recently discovered planetoids, then it would be inappreopriate to classify them at all as they can possibly fit those rules.

    6. Then would mercury be classified as a dwarf planet? (not following these rules, but looking at the size and mass of mercury, it would be “appropriate” to classify mercury as a dwarf planet.

  85. Stogoe

    too many of the posters here need to take a deep breath and chill out. Hydrostaticicity is probably the best limiter of planetdom. As for neighborhood, man, it can be narrowed down later. Pluto/Charon, Ceres, and Xena pretty obviously haven’t cleared their neighborhood, and the 8 by definition have. Therefore, their epsilon is somewhere between the two.

    I also don’t understand why BA thinks this is silly, starting a definition of the most important (to laypeople) astronomical object.

    I think planet-likes that don’t orbit stars shouldn’t qualify, and should get their own name, because there’s a qualitative difference – namely, the orbit of a star. Nyah.

    When they start to work on an extrasolar definition of planet, then we can add ‘not big enough to start fusion’.

  86. Bobberto De La Te Da Pluto

    It’s One Flew Over The Kuiper’s Nest for sure. I wants me Pluto, and anybody denying me my Pluto can kiss my ice. All them other planets are on aSteroids and that’s why they became so biggie sized.

    If Wendy’s (can’t say that) can finally sell a vanilla Frosty (it’s for a pun, yes I can) which one might enjoy Charon with their friends, then Pluto can be a planet because it’s still a shake even if it can melt. If in doubt, ask William Orbit, I’m sure he has a Neptune to cover it. Discrimination against ellipses such as this shall not stand!

    World up ; talk to the hand!

    Begin Hyperbola: Pluto Sez: Foci your momma, and your daddy and the IAU rode end upon end on. Uranus ain’t the only thing stinking sideways about this decision, and if you think otherwise I have a parabolas I can sell you on ebay. End Hyperbola.

    What’s next, if you have an atmosphere or not? I loathe that. So, now we have a case of atmosphere and loathing, and in the least, beer and loafing. I’m Ceres. Stop laughing. I need a Sednative now. Somebody help open the bottle here, who Titan’ed this lid? I never Xena one so tight.

    Punography aside, the original definition was better, with the Round and In Orbit and Party of 12. Made Sense. This makes only Specialist Sense. And thus, no sense. So I’m further incensed. Pooey. Somebody tell New Horizons it’s flying to one that no longer exists.

  87. The universe is so huge with uncountable stars and planets in it, and somewhere in the depths there is an unimportant planet named earth where unimportant people discussing/deciding whether pluto is a planet or not. I mean, who cares? If people on earth call it a planet of their system or not … Pluto is still what it was before.

  88. P. Edward Murray

    Check this out:

    For those of us who think Pluto is a Planet..
    there will be a rematch!

  89. Kevin Conod

    Actually I’m beginning to like this definition of a planet a bit better. I think one reason why people aren’t taking to it, because the science behind it hasn’t been explained too well.

    The “cleared neighborhood” criteria is really a backdoor statement on formation and probably more important than equilibrium. If you compare an object’s mass and period (mass squared divided by period) and compare the traditional 9 planets to the new KBOs and asteroids, there’s a big “gap” bewtween the planets and non-planets. Pluto and UB313 fall dramatically on the wrong side of the gap in the non-planet category.

  90. Prime

    Earth & Jupiter don’t meet the criteria set out in clause (c). From:

    “I’m embarrassed for astronomy. Less than 5 percent of the world’s astronomers voted,” said Alan Stern, leader of NASA’s New Horizons mission to Pluto and a scientist at the Southwest Research Institute.

    “This definition stinks, for technical reasons,” Stern told He expects the astronomy community to overturn the decision. Other astronomers criticized the definition as ambiguous….Stern, in charge of the robotic probe on its way to Pluto, said the language of the resolution is flawed. It requires that a planet “has cleared the neighborhood around its orbit.” But Earth, Mars, Jupiter and Neptune all have asteroids as neighbors.

    “It’s patently clear that Earth’s zone is not cleared,” Stern told “Jupiter has 50,000 Trojan asteroids,” which orbit in lockstep with the planet.

    Also, Saturn doesn’t fit into the “nearly round” criteria of clause (b). It’s an oblate spheroid, that’s flat at it’s poles.

  91. P. Edward Murray

    Yeah Kevin 424 people vote out of 10,000 some odd professional astronomers worldwide.

    This decision won’t stand.

  92. david

    When Ceres was found they called it a planet for a while then they found a lot of other objects were found in same orbit. The same with pluto and other obects that are in kuiper belt or a trans neptune objects, in about a hundred years nobody will think of pluto as a planet.

  93. Ms. Hauptmanova

    So is this new resolution truly a “Cosmic Demotion,” or in the words of Frank Zappa, “Kosmik Debris”? I got sarcastic with some friends and some rather pointed remarks about Pluto’s “demotion” were made. For example:

    Does this mean that Pluto will have to take a cut in pay? What about “his” benefits, such as medical, dental, vision and retirement? What about Pluto’s mortgage, alimony and child support payments?

    “Failed to clear the neighborhood,” does this mean that Pluto was too lazy to mow the yard or participate in a neighborhood watch program? This demotion seems a little harsh for some long grass and blackberry bushes.

    Pluto is NOT a “Dwarf” Planet, “he” is merely “size challenged.”

    It seems that Pluto is being discriminated against – who’s going to call the IAASCP? [The Interplanetary Association for the Advancement of Size Challenged Planets].

    “I am NOT a Trans-Neptunian “object,” I am a PLANET BEING!”

    This is your brain on drugs, this is a bunch of supposedly “professional” astronomers trying to act like linguists. Any questions?

    Why, oh, WHY wasn’t Phil Plait of Bad Astronomy allowed to sit in and tell it like it is?

  94. Bob

    Not the first time the definition of “planet” has changed. Anybody read any Shakespeare lately? In the Bard’s day, the sun and moon were also considered “planets,” the operative definition (from astrology) being any object that appeared to move across the sky (instead of appearing “fixed” in the sky, like the stars). Of course, this definition came from the today much laughed-at “discipline” (word loosely used) of astrology (and, indeed, modern astrologers still refer to sun and moon as “planets”).

    Before you baste me in lamb for mentioning astrology in this forum, consider that, as kooky as it seems in comparison to the modern science of astronomy, astrology was the stargazer’s primary outlet back in those daze, from which astronomy later developed as the paradigm shift occurred (from religion/superstition to science). Certain lauded historical astronomers (for instance, Galileo) were actually astrologers.

    Also, regarding the moon thing, I remember hearing Michio Kaku say on the radio a while back that in a couple zillion years or so, we would actually loose the moon, which would effectively end life on Earth as we know it, for, without the moon’s gravity, the Earth would begin to tumble, causing our weather to go haywire. If this is actually the case, how come having a proportionately sized moon isn’t included in the Drake equation (because Drake didn’t think of it?)? Just wondering…

  95. Bob

    From the 5th grade point of view (my son’s, to be precise), it’s much better to demote Pluto and have only 8 planets than to promote dozens, if not hundreds, of somewhat big objects to “planetary” status. He told me he didn’t think he could enjoy astronomy anymore if he had to remember the names (and orbits) of a couple dozen (not to mention a couple hundred) “planets.”

  96. Russ

    The time it takes to change books in this country, we’ll be lucky if our great-great-great grand kids find out about this change.

  97. Apparently Pluto itself is somewhat ticked off; read the tirade here:

  98. Charles C.

    Until reading through some of the comments here, most of my thinking on this debate has been about what the news headlines say the issue is – Pluto’s status as a planet. But I realized after reading some of these comments that despite the headlines, the demotion of Pluto, and all the interesting technical points raised in criticism of the new definition, the debate was never about anything besides one particular, near-term problem.

    It was about Sedna, 2003 UB313 and other big trans-Neptunian iceballs to be discovered in the next few years, and the new defintion, however unsaisfactory from the general point of view, does exactly what it was designed to do: it disposes of 2003 UB313 in particular as a dwarf planet and not as a “classic” planet.

    Pluto’s demotion was collateral damage of this short term-fix. The other issues don’t really matter, as none of them raise near-term definitional and discovery-credit issues. To cite one example, whatever “clearing the neighborhood around an orbit” means, since the IAU certainly did not intend to raise questions about any of the “inner eight” planets, we can assume as a practical matter that it includes whatever those eight are doing. And whatever those things are, 2003 UB313 and its to-be-discovered siblings don’t have what it takes to do them. Over the next few years, the orbital clearing criterion will be dissected to shavings, but by the time it becomes wholly unsatisfactory, 2003 UB313′s status as something other than a “classic” planet will have become set. (We saw what happened when the original proposal included reviving Ceres as a planet. Thwack!)

    Once the dust settles, “planet” will be reasserted as a common-sense notion as extrasolar planet discoverers continue to discover what they discover and continue to call them extrasolar planets, and as the recent-historical idea of terrestrial planets and gas giant planets continues to be used whether or not, for instance, Earth can be said to have cleared its orbit with that pesky lump of debris out there at 239,000 miles. And I’ll bet the IAU revises the definition of “planet” before the Earth-Moon barycenter emerges from the earth’s crust to endanger Earth’s planetary status.

    Bottom line: 2003 UB313 and like trans-Neptunians (including Pluto) didn’t make the cut as planets; everything else will sort itself out in time.

  99. The moment I heard the news I knew there’d be a nice discussion going on here.

    My thoughts: on the bright side, Pluto and Ceres are unremarkable as planets, but awesome as smaller objects.

  100. Dead Boy

    Well I for one am pretty pleased with this decision. Not only have I never really be all the happy about calling Pluto a “planet” due to it’s orbit being off the solar system’s natural plane, but its proximity to the Kuiper Belt seems to make it more belonging to that formation that that of the inner planets’.

    But the other reason why I’m content with this call is it may take the name of 2003UB313′s fate out of the IAU’s hands. If it’s no longer a planet but now considered one of possibly millions of similar objects yet to be discovered like asteroids and comets, then it would fall to is discoverer to name it, as it should have been all along. Dr. Michael Brown decided to name his find “Xena” and it’s moon (or whatever it’s going to be cataloged as now) “Gabriele”. And though a tad geeky, I feel that should stand.

  101. Shock Horror! Never mind in the great scheme of things it matters not.

  102. Annie

    Dead Boy — while I am a fan of the tradition wherein discoverers of such objects get to name them, I am very very opposed to “Xena” and “Gabrielle,” and how it makes the astronomical community look to the general public. As in, we’re all guys who think Xena is hot and the idea of Xena and Gabrielle together is so exciting as to be worthy of this honor.

  103. P. Edward Murray


    Xena & Gabrielle are just nicknames and not the Official names, the IAU will have to meet or the committee on naming objects, at a later date.

  104. David A. Bruni

    I think IAU are covering themselves with ridiculous with this Pluto downgrading.
    Did they feel the need to change the definition of moons? In fact, planets have two types of moons: the ones which formed together with the planet (I think about Earth’s moon or the largest Jupiter moons), and the ones which were captured later by the planet’s gravity (I think about smaller moons of Jupiter, maybe Phobos and Deimos). No one in the IAU never thought about changing the definition for these object, afaik. Maybe because the claim “I discovered a new moon of Saturn” is not so strong as “I discovered a new solar system’s planet” ?

  105. TheProbe

    We need a plan of action!

    First, we have to recall New Horizon’s since it is a terrible expenditure of money to investigate a dwarf planet.

    Second, we should file suit as this ruling clearly discriminates against dwarves.

    Third, I am buying stock in any company that publishes science textbooks.

    Fourth, we should be prepared to meet some really upset Plutoniums in a few years.

  106. Pandabear

    don’t we have a certain probe out there with a certain disc on it saying our solar system has 9 planets to recall before any aliens find it and laugh at us for not being able to count properly?

  107. Annie

    P. Edward Murray — I know that, as my post indicates (and I was referring to a preceding post which stated that Dr. Brown should be able to name UB313 whatever he chooses), but the point still stands as far as the mainstream press and public are concerned.

  108. sirjonsnow

    They still need to rename it back to Yuggoth.

  109. Kym

    Well, even if Pluto can’t make up its mind if it wants ‘in’ on the planet thing or not at least it’s keeping us all entertained! It also seems Pluto has two more moons, Nyx and Hydra! Here’s the link to the NASA article about the moons. Pluto has been very busy for a small whatever it is!

  110. MaDeR

    Uh, looks like “cleared his neighbourhood” was nof fortunate choosing of words. I propose “gravitationally dominant”. Why?
    1. Sounds cool. Like SF. Or something.
    2. Clears his neighbourhood, too.
    3… and anything that survive clearing (or joins later) is UNDOUBTEDLY gravitationally dominated by body in question.

    This is why Pluto is not a planet, but Neptun is. In addition to gigantic difference in mass, Pluto is controlled gravitationally (by resonance). Same for solar system moons, asteroids in L4 and L5, and many other deribs.

    Only one problem: what the hell is neighbourhood? Maybe epsilon in mathematical definition of neighbourhood should be proportional to mass of body in question, creating virtual torus (in center lies orbit).

  111. David A. Bruni

    Just wild thoughts… Mercury actually did “clean his neighborhoods” or maybe was the Sun the responsible in cleaning its (of Mercury) orbit from other objects?

  112. Irishman

    I think the new definition is stupid. I don’t really care whether Pluto is a planet or not, but I find the definitions vague and unscientific.

    Look linguistically, we have already been saying that anything that orbits a star is a planet. We even had a word for those asteroids and comets and things: “Minor Planets”. Yes, that means that Ceres already was a Planet, it just wasn’t a Major Planet.

    Now the IAU has generated a new term, “Dwarf Planet”. This is to set Pluto and Ceres and the others off from “real planets”. But they’re already set off by composition and orbit and such, just like Earth is set off from Jupiter by being terrestrial and inhabited, and Mercury is set off from Earth by being so toasty hot.

    Culturally a planet is something that primarily orbits a star and is not just a small rock. I like the definitions offered for “planemo” and fusors and such.

    Something that fuses = star
    Something that does not fuse but is in hydrostatic equilibrium = planemo
    A planemo orbiting a star = planet
    A planemo orbiting a planet = moon
    A body not in hydrostatic equilibrium = small solar system body (need better term, or abbreviation – SSSB? SS debris?)

    The clearing it’s neighborhood is poorly defined and a general mess.

    I don’t think we should worry about keeping “planet” somehow special. We discovered that the Sun is just a run of the mill star, but that doesn’t mean we don’t think it’s special. We have 9 classical planets (8 big ones and Pluto for cultural reasons), we have 8 major planets. But Ceres and 2003 UB313 and Sedna and Quoaor all count as planets. There are probably others out there in the Kuiper Belt. Wheee!

    That still leaves the question of “double planets” to be solved. What is the best means to determine it? Ratio of diameters? Location of barycenter? Primary gravitational influence?

  113. Pluto IS a planet it’s just not a regular planet. It’s a dwarf planet.

  114. P. Edward Murray


    Quite possibly you are misunderstanding me. We are talking about Astronomical Nomenclature here…how objects get named.

    For example, if you discover an asteroid you can name it however you want to. If you discover a comet and you are the 1st or 2nd discoverer (it used to be 3) your last name is tacked onto it as in Hyakutake or Hale-Bopp. And there are other scientific designations too.

    If you discover a planet…officially it will go by a numerical name until it is named by a committee of the IAU.

    The good Doctors nickname is just HIS nickname for it not the official name which will probably be some greek or Roman god or goddess or
    some other culture’s. It will have something to do with Pluto or the local facsimile of god of the dead.

  115. Insight

    A few observations, comments and questions:

    “…a hydrostatic equilibrium (nearly round) shape…”

    Round? Do they mean like a circle? Are they allowing for some kind of disk or donut? Seems like these smart scientists should have used “(nearly spherical)”. Even “(nearly a ball)” would have been better – so as to not scare off people with a big technical term like “spherical.”

    Regarding objections to “in orbit around the Sun”, this has nothing to do with planets outside our Solar System because the IAU definition only applies to “planets and other bodies in our Solar System.”

    But I’m wondering about: “defined into three distinct categories in the following way:
    “(1) A planet is …
    “(2) A dwarf planet is …”

    So where’s number (3) in this scheme? The term “satellite” appears in the definition but I don’t see where it’s defined. Did I miss something?

    Lots of things have been scientifically defined and then redefined over the years as part of the scientific process. Now the IAU (or a tiny fraction of it) has provided a new opportunity for redefinition.

  116. BA: Don’t you think the fact that the Pluto and Neptune are never actually near means that while the orbit is in Neptune’s neighborhood the two are not in anywhere near the same neighborhood?

    Doesn’t Pluto belong to the Kuiper Belt? And UB313 too. Ceres the asteroid belt, right. Isn’t that what is meant by neighborhood, objects that are relatively near each other. I mean, there are Earth-crossing asteroids, yet Earth is a planet. Some asteroids practically share our orbit. Nothing can really, truly clear its neighborhood.

    What do you think?

  117. Annie

    P. Edward Murray — No, I’m understanding you perfectly. It’s the poster to whom I was originally responding, Dead Boy, who was speaking about the possibility of Xena becoming UB313′s official name. I was responding to his idea that this Pluto ‘kerfluffle’ could lead to UB313 being classified as an object that would be named by is discoverer. I am fully aware that Xena is not its official name. I am fully aware that it is unlikely to *become* its official name. My concern is that this has become its popular name; it is referred to in the press and by the public as Xena. And as far as that press and the public is concerned, by fear — which has specifically to do *with the press and the public* — still stands.

  118. SpikeNut

    Are there any restrictions or requirements about future [major] planets orbiting *in the plane* of the solar system or *not* crossing the orbit of any of our great eight? Those seem like pretty reasonable aspects to put into the definition as it sits right now — it would certainly keep the classical feel that it seems the IAU wants.

  119. Zadillo

    In some sense though, doesn’t astronomy have an inherent capacity to deal with incorrect names, etc.? The example that comes to mind for me is “planetary nebula”. We still use the term even though we now know that it doesn’t have anything to do with planets. I would think that it wouldn’t be such a big deal in terms of how and when we use the term “planet”.

  120. P. Edward Murray


    In the case of “planetary nebula” planetary means large as in a planet.

  121. Annie

    P. Edward Murray — No, I understood you perfectly; I think you’re misunderstanding what I’m discussing, which is not official names but with the use of the name Xena in the press and in the public. Again, I was not the one who said that Xena could be the official name of UB313. Additionally, if you read the post to which I was responding, that poster was speculating on the possibility of UB313 being classified as an object which Dr. Brown would have be able to name (ie, if UB313 had been classified as a planet, the IAU would name it, but if UB313 had been classified as a mere asteroid, Dr. Brown could name it as he preferred to) and on the possibility that Dr. Brown might indeed continue to prefer Xena. I absolutely know how astronomical nomenclature is decided, I know that “Xena” is not the official name of UB313, I know that it is very unlikely such a name would stick, and as I said, I am merely concerned with the media attention it has gotten under its “colloquial” name; this concern is valid, as I said before, despite the fact that this name is not official.

  122. Craig Dorrance

    JUPITER BITES THE DUST ( Jupiter no longer a planet official )

    Yes its official ( According to the IAU anyway ) we now have only 6 Planets

    Pluto X ( Fails criteria c ) has not cleared Neptune from its Neighbourhood
    Neptune X ( Fails criteria c ) has not cleared Pluto from its Neighbourhood
    Jupiter ( Fails criteria c ) has not cleared its Neighbourhood of thousands of asteroids
    The Trojan Groups are made up of thousands of asteroids that follow a similar orbit to Jupiter as far a I understand it
    60 Degrees to either side ?? of the X Planet. Please correct me if I am wrong.

    But we can go further

    Do we also scratch Saturn ( It has rings , not cleared ) no mention of these
    Do we also have to scratch Uranus ( No pun intended ) it has rings also ( might wanna get that looked at )

    Do we scratch Earth and Mars too they have satellites ( not cleared ).

    So really if we apply rule c strictly we only have Mercury and Venus left.

    The purpose of a definition is that it leaves no ambiguity – without a definition of term (c) and specifically what “cleared” means, it is worthless.

    In the rush to determine that Pluto is no longer a planet the IAU has failed to apply there own definition equally to Pluto / Neptune / Jupiter
    I’m sure they would say Neptune / Jupiter are huge objects, they are definitely planets ( But that is criteria (b) and Pluto satisfies that also )
    and the real problem will come if a large Mercury+ sized object is found floating out there in the oort cloud, how in the heavens will astronomers be able to ascertain whether its neighbourhood is clear or not in order to properly categorise it ?

    Lets face it the reason Pluto has been demoted by the IAU ( and not Neptune or Jupiter ) is due to size pure and simple and has nothing to do with the convoluted rules with which they have tried to obscure the issue.

    If they are going to redefine terms of LANGUAGE and CULTURE not merely astonomy, then they should do so in a way that is clear to everyone.

    Pro Pluto or Anti Pluto
    we need a classification system based on mass that gives us an absolute criteria that can be applied simply to any object orbiting the sun or any other star.


  123. Craig Dorrance


  124. Craig Dorrance

    Apologies for the multiple post I keep losing parts

    0 – 1Kg Rock
    1e3 Kg – 1e18 Kg Asteroid
    1e18Kg – 1e22 Kg Planetoid
    1e22Kg – 1e28 Kg Planet
    1e28Kg + Brown Dwarf

    0 – 1Kg Rock
    1e3 Kg – 1e18 Kg Asteroid
    1e18Kg – 1e22 Kg Planetoid
    1e23Kg – 1e28 Kg Planet
    1e28Kg + Brown Dwarf

    Argue over the numbers Guys and Girls and come to a decision that isn’t so obscure.

    I know it
    You know it
    Everyone else knows it
    at the end of the day,
    the only thing that really matters is SIZE.

  125. Walter

    In the 17th century the atom was the smallest thing in the universe. At the beginning of the 20th century, there were 8 planets and the smallest thing in the universe was an electron. The nucleus was made of proton(s) and neutron(s). As our telescopes and microscopes improved we discovered smaller bodies and smaller particles. Now comes the string theory (re: subnuclear physics) and detection of extra-solar planets. Why shouldn’t adjustments be made to our classification systems based on our most recent discoveries. I’m sure there’ll be more adjustments to come within the next century.

  126. P. Edward Murray


    Oh, I see now. I don’t really worry about it because if a reporter is smart enough he will say that or if a regular guy just reads enough he will get the idea too.

    There are just so many problems with the definition, it really looks like it was hobbled together in 5 seconds:(

  127. Filipe

    Clearing its neighbourhood means it contains most of the mass. Ceres only has about 1/3 of the mass in the asteroid belt. Xena contains only a small fraction of the mass in Kuiper Belt. The problem is that Xena’s neighbourhood is a volume orders of magnitude higher than Mercury’s or Earth’s neighbourhood. This thing was put there on purpose to remove Ceres and Pluto.

    But the name “dwarf planet” really bothers me. What if something bigger than Mercury (unlikely but…) was pushed to the edge of the solar system? Can we have a dwarf planet bigger than a regular planet?

  128. So? Now Pluto “the dog” has been renamed Pluto “the puppy”. The general public is not that interested in the study of astronomy. With this latest professional peer group approved change in the definition of the Solar System the public is going to be LESS interested in our awesome solar system. Mabey when the pictures from Pluto Express are returned to Earth Pluto may get the last laugh—or should I say—bark.

  129. Don C

    By the new definition of what a planet is, then as far as I am concern, Neptune is not a planet. It is a really, really, big, dwarf planet because under the new definition it has not cleared Pluto from its orbit.

  130. cvj

    Did you see the objection form within the community that is circulating in the form of a petition? Their points are interesting. Ive got a post about it here:

    Basically they are objecting to the definition being more in terms of the location than the intrinsic properties of the object itself (along the lines of a number of thoughts expressed in this comment thread already), and they make the point that this is very different than what happens in so much of the rest of astronomy….


  131. Dan Lyon

    I hail from LaSalle County in Illinois, where Streator, the birthplace of Clyde Tombaugh–discoverer of Pluto–can be found. It feels like someone has taken away some of the little bit of thunder we had. Personally I don’t see why they even needed to get into this debate. It feels like some of the astronomers out there just needed to stroke their egos, so they brought this up to make some headlines. Why can’t Pluto just be a planet? It has 3 moons, its own gravity, plenty of mass, a round shape, all that stuff. Why can’t a spade be a spade? Is it because we’re discovering new planet-like bodies in our solar system, and soms astronomers are jealous they didn’t see them first?

  132. P. Edward Murray

    Phil & fellow Bad Astronomy Blog posters,

    I am a member of the JPL/NASA Night Sky Network which is a community of amateur astronomical clubs that do a lot of educational outreach.

    I’ve just sent and e-mail to Dawn Bair the Night Sky Network Coordinator asking if we could start a petition supporting Dr. Alan Stern’s quest to ask the IAU to re-name Pluto as a Planet. I have also contacted Ted A. Nichols of the Astronomical Society of Harrisburg…the young man who started the quest to send New Horizons to Pluto.

    It is my hope that we could start with individual members of the Night Sky Network and extend it to other amateurs and then to schools and students across the United States.

    If you are interested in helping please contact Dawn Bair at



    P. Edward Murray
    Past President,
    Bucks-Mont. Astronomical Assoc., Inc.

  133. Personally, I think that all spherical bodies not obviously stars, quasars, or whatever other type of glowing body, etc. should probably be labeled planets.

    All planetary satellites are Moons (even if spherical)

    Then we can fudge the categories by using phrases like Atmospheric Planets or Atmospheric Moons. Just like we now say rocky vs gaseous planets. We can also say non-atmospheric planets. Titan is an atmospheric moon, for example.

    Atmospheric means you need a heat shield to descend and land, or else you burn up.

    We get away from the dwarf designation.

    We can still have the Nine Historic planets. or the nine planets of the 20th century, etc.

    Once you get out into the Keiper Belt, you will likely have dozens if not hundreds or thousands of new non-atmospheric planets. School kids will not memorize them all.

    But the nine traditional or histroical planets is fine.

    Of course, we will need a naming schema suitable for such quantities. Maybe borrowing from the page of the hurricane watchers, with a rotating list of names selected and preapproved in advance at each international meeting.

  134. kvs

    As with any technical field, the terminology that goes with it will evolve with time. It seems to me that we know a lot more about star formation and the lifecycle of stars than we do about that of planets. Just because they’re easier to observe. So we get more satisfying definitions for all of the flavous of stars which exist. Given the small easily observable sample we have at the moment, we get a dissatisfying scientific definition for planets.

    I guess over time, we’ll come to know more about planet formation, and be better able to articulate the differences and relationships between big ones, small ones, gasseous ones, rocky ones, icy ones, round ones, blue ones, orange ones, ringed ones, ones with highly elliptical orbits, ones without orbits, ones that rotate backwards or on their side, ones which are unformed debris and so on. Then we’ll be able to come up with a more precise, and satisfying, definition of what’s what.

    In the meantime, my unscientific preference is the definition that gives us 8 planets – Yay IAU! ;)

  135. MarsHill2001

    Here is the real news flash! Pluto is still a planet! I really don’t care what the IAU thinks. They are just a bunch of letters that mean nothing to the commen people. If they keep going this route their status will not change any time soon. Quite frankly I think that Clyde Thombaugh’s estate should sue the IAU for defaiming his legacy. Dwarf planet indeed! I don’t swing through here much anymore because, well, I have a life and I have had better debates with my cats. But I do stop by every now and then for entertainment purposes only. It is most amusing to read how you all get so wound up over mostly trivial things. Then you sulk and wonder why most of the country dosen’t take you seriously. Well, this has made for another good laugh, but I am going back to my life now. Please, do keep carring on though; because you are a good cure for a little down time or other such patches of bordom.

  136. Mike

    Congratulations to the IAU for replacing one vague non-scientific definition with yet another vague non-scientific one. The very fact we have astonomers unsure of what “cleared the neighbourhood around its orbit” even means suggests the definition is flawed to start with. This is supposed to clear up the debate? The first proposal’s definition was far more precise and I quite liked it. Far too much emphasis has been placed on whether or not Pluto is a planet and the definition of planet was obviously worded precisely to demote it, at the expense of clarity and flexibility the other proposal had. I don’t see the big deal about Pluto anyway…all the arguments against it run somethig like: “Pluto is a Kuiper belt object, and there are maybe hundreds more just like it. If Pluto is a planet then we will soon have hundreds!” My response is “So what?” Who said there need to be 8, or 9 planets anyway?
    I really don’t understand astronomers’ reluctance to label large KBO’s planets…perhaps if I heard a quanitative statement suggesting why they aren’t…but I doubt there really is such a statement, as evidenced by the circuitous definition of planet we are stuck with. The same goes for Ceres. I hear people saying “A large asteroid is not a planet.” But the first time I saw a picture of Ceres I thought someone had mistakenly shown a picture of a moon or some other body, as it was ROUND! In my mind, an asteroid couldn’t be round…because that would make it a planet. I was shocked I never knew this before. The common sense definition (at least to me) then suggests that Ceres is a planet. So what if it is small and there are other large rocks in it’s orbit.
    Overall, I found the first proposal’s definition far more elegant, less ‘engineered’ and more flexible. The double planet thing bothered some people, but it makes perfect sense. Under the new definition, it seems double planets aren’t even possible…yet I can imagine a pair of Mars-sized objects orbiting a central point, which in turn orbits a central star. Apparently these would be ‘big rocks’ under the new definition.

  137. tabitha

    i am very mad and sad i wuv PLUTO he is so cute for a planet he is a planet and all ways will be people are stupid if they dont think PLUTO is a planet he will become a planet again anouther day he will when people fine out that there stupid and say “well is it round and has a moon so it is a planet i guess we where wrong” then i will be happy again and how can a moon have a moon answer that well i will leave you there to think about it that he really is a planet and always will be! GO PLUTO PLUTO ROCKS YAY PLUTO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

  138. Kevin Conod

    I think y’all are missing some of the science behind the definition…don’t get hung up on the wording. It’s the science behind that’s important and unfortunately the IAU has not done a good job of communicating this to the media or public.

    If you plot and compare the masses and orbital periods of the objects in question, the planets and non-planets seperate themselves out nicely. In fact there’s a big gap between the two groups and Pluto, Ceres, UB313, et al, all fall on the wrong side of the tracks.

    For those of you who are dissapointed or even angry…Rather than mourning Pluto, we should be celebrating the fact that the Solar System is “larger”: we have 8 planets and now 3 dwarf planets (plus a dozen more waiting in the wings). We have whole new class of object to study and marvel over!

  139. Kevin Conod

    PS Remember that Pluto is not gone! Astronomers didn’t blow it up or kill it.

    It is still an important part of our solar system and was the first of its kind to be discovered. And will be the first to be explored by a spacecraft!

    As far as Clyde Tombaugh – he was, is and always will be the discoverer of Pluto. No one can ever take that away. He will always be respected and remembered fondly by the astronomical community.

  140. Mike

    Unlike most people (it seems) I don’t actually care whether Pluto is considered a planet or a large sno-cone. I’d just like to see a nice clean definition that can be useful. The first one seemed to be just that, the second one is not. It seems like it was rushed to produce a single effect…classify objects to fit a specific desired result.

    Kevin, as you said “If you plot and compare the masses and orbital periods of the objects in question, the planets and non-planets seperate themselves out nicely. In fact there’s a big gap between the two groups and Pluto, Ceres, UB313, et al, all fall on the wrong side of the tracks.”
    If that is so true, then perhaps someone knows why none of that is involved in the definition? Would a Neptune sized world with an orbit 300 times greater than pluto not be a planet then? Perhaps because we don’t know enough about planetary formation to know if such an object is even possible, let alone categorize it?

  141. Chris Hecker


    In fairness to the IAU, the resolution did limit the definition to our solar system. They didn’t even attempt to create a definition that would stand up for planets in general.

    But it gets worse. As Phil pointed out, Neptune has not “cleared” its orbit.

    Let me take this one step further. There is a huge collection of assorted asteroids, comets, and other assorted junk out there, that clutters the orbits of every planet. This applies not only within our solar system, but to every large round (non-fusor) body in the universe, that orbits a star. Given the absence of a scientific definition of “cleared” in the resolution, we’re justified in interpreting “cleared” at face value. I.e. the orbit must be free of debris.

    No body in any solar system has “cleared” its orbit. By the internal logic of the IAU definition, there are no longer ANY planets (except perhaps for “dwarf planets”).

    What the IAU has done, is effectively defined planets out of existence.

    (Note that there is a footnote to the definition, which defines the planets in our solar system by fiat, and contradicts the logic of their own definition. I choose to ignore this, since the definition must provide logic by which any or all planets in the solar system can be classified.)

    Watch for another debate at next year’s IAU meeting….

  142. Did you happen to see the “Pluto needs rocks” display at WorldCon today, complete with a cardboard collection box?

  143. Kevin Conod

    >I’d just like to see a nice clean definition that can be useful.

    Actually IMHO it was a complete mess with odd binary planets and awful terminology (“plutons” eecchh!). If it had passed we would’ve ended up with a real mess of 30 or 40 planets in our solar system.

    It also had some very unscientific elements such as the contradictory criteria of equilibrium. It stated that a planet had to be in equilibrium and then slapped on an arbitrary size limit. Equlibrium is different for bodies made of rock, gas or ice. You can’t just slap an arbitrary size limit on it. That is very attractive because its simple but unfortunately its wrong.

    >If that is so true, then perhaps someone knows why none of that is involved in the >definition?

    That I do not know as I was not present at the meeting in Prague. I definetly think the wording could be greatly improved. That’s why I wrote above that you can’t get hung up on the wording – look instead at the science behind it.

    >Would a Neptune sized world with an orbit 300 times greater than pluto not be a >planet then?

    I’m not sure at this late hour, but if you plot it and compare to the other planets the answer should be clear.

  144. Poor Pluto….
    Now he’s not even a Mickey Mouse Planet…

    Whether Pluto remains a ‘planet’ or not, I look forward hopefully to either a better definition of “planet” being determined, or astronomers ditching the attempt for a time when they know enought to actually make a better one.

    I agree with several of the posters here…. Especially Alan.. about halfway up the page from here…
    Alan Says:
    August 24th, 2006 at 5:24 pm
    ‘I frankly think that the IAU’s decision was HORRIBLE — not because of any scientific reasons, but because it was a Public Relations disaster. ‘
    I also agree with the Star Trek Reference above.. (I forgot the name, and have no quote)
    A much looser definition of “planet” with the subcategories which enable you to visualize what SORT of planet a planet is would be much better.
    (Class M Planet, ETC.)

    Sure, Kids might end up having to learn a longer list of planets in school… but most of them only remember that list long enough to pass the test even nowadays!

    This is such an explosive topic, that still seems kind of silly, I couldn’t help making some T-Shirt designs at Cafe Press. :)
    I have more Ideas that I want to take more time to produce, but I’m still getting my planetary say using T-Shirt Media.. :)
    I’ll make requests too, if anyone wants to see their point on view on Tee!!
    See my humor page for my currently published Pluto designs.

  145. Hear my pluto demotion song at…

    …last song on the short list.

    Jim :-)

  146. Greg

    So What About the New Horizons probe?

  147. Henrik, Sweden

    Why not simply call all planets, asteroids, comets and the rest celestial objects that are bound gravitationally to the sun?

  148. P. Edward Murray


    New Horizons Pluto Probe is up there,slogging the miles away.
    Like someone here did post, Dr. Alan Stern, Principle Investigator for the mission doesn’t like the demotion.

    I agree 100%

    I’m guessing at this but I kind of doubt if those folks who voted down Pluto have really anything to do with the mission.

  149. Irishman

    Insight said:
    > But I’m wondering about: “defined into three distinct categories in the following way:
    “(1) A planet is …
    “(2) A dwarf planet is …”

    >So where’s number (3) in this scheme?

    (3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as “Small Solar-System Bodies”.

    You have to go to the IAU results page linked at the top. Phil didn’t bother to quote that part.

    Craig Dorrance said:
    > Pluto X ( Fails criteria c ) has not cleared Neptune from its Neighbourhood

    I’m tired of seeing this. This was never part of the IAU’s justification for demoting Pluto. Nothing about Pluto bore any relationship to Neptune in that decision. Pluto failed category (c) by failing to clear the Kuiper Belt from it’s orbit. Similarly, Ceres failed to clear the Asteroid Belt.

    I’m tired of people mocking the IAU for stupid words they didn’t say. They have plenty of culpability for the stupidity that was theirs to take responsibility for stupidity that wasn’t.

    I do find your mass-based definition interesting. It does have the advantage of being clear and measurable, if a bit arbitrary. It does manage to overlook “comets” and the confusing gray question of comets vs. asteroids that hasn’t yet surfaced in this debate, mostly because both fall below the line that this debate is centered on. But if you’re defining all categories down the scale, then they need to be accounted for.

    Dan Lyon said:
    > I hail from LaSalle County in Illinois, where Streator, the birthplace of Clyde Tombaugh–discoverer of Pluto–can be found. It feels like someone has taken away some of the little bit of thunder we had. Personally I don’t see why they even needed to get into this debate. It feels like some of the astronomers out there just needed to stroke their egos, so they brought this up to make some headlines. Why can’t Pluto just be a planet? It has 3 moons, its own gravity, plenty of mass, a round shape, all that stuff. Why can’t a spade be a spade? Is it because we’re discovering new planet-like bodies in our solar system, and soms astronomers are jealous they didn’t see them first?

    No. The truth is from the astronomers’ standpoint, the issue is not really about Pluto at all. Pluto is just a casualty of war, as it were, an innocent bystander getting hammered because of it’s unusual precedent of location and historical heritage. The real issue is what to do about the Kuiper Belt. We know it’s there, we’re now finding new objects and by size they fit the old definition of planet as well as Pluto did. So do we want to open up the Solar System to a barrage of new planets or not? That is the real debate.

    Unfortunately, Pluto is a rallying point precisely because of it’s historical heritage. Pluto is a special case that defies easy description. The cultural question is intruding on the scientific one. But I think the real issue is not a scientific one to begin with. Scientifically, what does it matter if the Solar System has 8, 9, 12, or 32,000 planets? Not a whim. The urge to keep the number of “planets” limited is purely cultural – the desire to keep the Earth special and to keep “the big 8″ important. That is ultimately what this debate is about. Witness the people lining up into camps over whether Ceres is a real planet or just an asteroid, or even a “dwarf” planet. Ceres is in the mix for a similar reason to Pluto – it defies easy classification.

    The Solar System does not wish to conform to simple categories to match are linguistic and hubristic needs. I already alluded to asteroids vs. comets. Sure, an asteroid is a big rock whereas a comet is ice (of some sort). Comets have tails. But we have already discovered asteroids that suddenly grew tails when they got closer to the sun. (A buddy of mine has one of the first photographs of an object just prior to growing a tail.) So guess what, the defining line just got fuzzy. Similarly, and has been expressed elsewhere, this definition doesn’t really do anything to address Brown Dwarfs and the defining line between planets and stars. That line is also fuzzy, with some bodies that begin to fuse hydrogen and then stop. They remain large, multi-Jupiter mass gaseous bodies. Are they planets or stars?

    Look at moons – moons are any object that orbit a planet. Composition doesn’t matter – icy, rocky, metallic, carbonaceous. Size doesn’t matter – Titan is larger than Mercury. Oops. Number doesn’t matter – Saturn has 40 something, Earth has 1 big one. Origin doesn’t matter – some coalesced in place, others were captured asteroids or comets, others still are thought to be formed from collisions (i.e. the Moon). Moon is a description of what it does more than what it is.

    I think “planet” is similar. It orbits the Sun primarily (not secondarily), it’s a planet. We put size limitations on it for convenience, to separate it from dust and rocks. How about a lower limit of spherical, anything smaller is “debris”, and an upper limit of fusing, above which is a star? Any objects that used to fuse but no longer do are now planets but were stars, just like any object that has a tail is a comet, but if it doesn’t have a tail it’s an icy asteroid. Works for me.

    Kevin Conod said:
    > If you plot and compare the masses and orbital periods of the objects in question, the planets and non-planets seperate themselves out nicely. In fact there’s a big gap between the two groups and Pluto, Ceres, UB313, et al, all fall on the wrong side of the tracks.

    Why don’t you show us the plots so we can see?

    >Actually IMHO it was a complete mess with odd binary planets and awful terminology (”plutons” eecchh!). If it had passed we would’ve ended up with a real mess of 30 or 40 planets in our solar system.

    1. Binary planets are a case that make sense. The proposed definition was murky on how to make the determination, but an example would be two Mar-sized objects in mutual orbit. They are clearly planets by size, they are the same size so neither is a satellite of the other. Now make one slighly (>100Mg) smaller than the other. Is that suddenly a moon? Clearly there’s the potential for a double planet. But there should be a better criteria for evaluation, and I’m not sure it’s necessary to address now, though by including it the proposers showed forethought into potential future issues.

    2. “Plutons” was a horrible word choice. Trying to make Pluto the namesake is messy, especially since it is already used that way for a couple other categories.

    3. What is wrong with 30 or 40 or an unknown quantity of planets? Why is that inherently bad? Sure, it makes memorizing all the names a trick no longer suited for First graders, but other than that, I fail to see why people so object to it.

    >It also had some very unscientific elements such as the contradictory criteria of equilibrium. It stated that a planet had to be in equilibrium and then slapped on an arbitrary size limit. Equlibrium is different for bodies made of rock, gas or ice. You can’t just slap an arbitrary size limit on it. That is very attractive because its simple but unfortunately its wrong.

    No! The arbitrary size limit is not a binding criterion. For crying out loud, it’s even in a stinking footnote!

    1 This generally applies to objects with mass above 5 x 1020 kg and diameter greater than 800 km. An IAU process will be established to evaluate planet candidates near this boundary.

    Read the disclaimer they happily include in that very same footnote. That in itself says it all, but apparently you (and some other people) are having trouble, so I’ll reiterate. The 5 X 10^20 kg and 800 km limits are approximations – guidelines. The fact that a process must be established to evaluate candidates near the boundary is a direct declaration that the line is not solid on those numbers. The important condition is the main one in the main body of the definition – hydrostatic equilibrium. The “arbitrary size limits” are not binding limits, but clarification of nominal conditions that meet the criteria. I am astounded that there is any confusion on this matter.

    Cheryl said:
    A much looser definition of “planet” with the subcategories which enable you to visualize what SORT of planet a planet is would be much better.
    (Class M Planet, ETC.)

    You still have to clear up the definition of “planet”. Just like stars. Yes, we categorize them and talk about their class, but they’re still all “stars”. Planets are the same way. We can talk about terrestrial and gas giant and icy and dwarf and ugly-step-sister planets, but those are all descriptors for the word “planet”, implying that there is some general class of things called planets. Yet that general class doesn’t currently have neat dividing lines, so it’s hard to know whether we need a category for “too small to be a real planet but does what a planet does” and a category for “too big to be just a planet, but isn’t quite a star” and maybe even “I won’t call that a planet no matter what you say, nyah nyah nyah”.

  150. P. Edward Murray


    Puleez quit apologizing for lame PhD’s who have had 76 years to work out a good, succint definition.

    This is what I most hate about this, they had all the time in the world, any and all resources and yet…

    When push came to shove they just could not do it.

    A really lame excuse for what these folks should be doing..

    No excuses!

    I guess we live in a time when even folks who should know don’t and don’t care much about it even.

    I say it’s time to send govt money away from IAU chaps who can’t seem to even see straight about common sense things.

    Let the Amateurs in because you have proven you can’t cut the mustard!

  151. Kevin Conod

    Mike asked:
    >Would a Neptune sized world with an orbit 300 times greater than pluto not be a >planet then?

    I haven’t had to time to think that one out, but off the top of my head that scenario seems pretty unlikely – at 300 times Pluto’s distance it would be 12,000 AU! That’s well beyond the heliopause – it seems quite unlikley that a gas giant would be found that far out.

    Think about this: an object the size of Mercury would still be massive enough to dominate its orbit out to about 100 AU.

  152. Kevin Conod

    >Why don’t you show us the plots so we can see?

    The plots belong to Steven Soter of AMNH/Hayden Planetarium. I’m not sure why that info hasn’t been posted…I don’t really have a way distributing that nor is it really my place.

    >No! The arbitrary size limit is not a binding criterion. For crying out loud, it’s even >in a stinking footnote!

    Well I missed it. Maybe if they didn’t put it in a footnote maybe more people would’ve “gotten it”. But that’s moot now and the equilibrium criteria is part of the definition of a planet. I think we can both agree that’s a good thing.

  153. Kevin Conod

    Ed — your divisive and desparaging comments are really not helpful to this discussion. Astronomers, both professional and amateur, on the whole are a pretty good lot. As the BA himself can attest.

  154. Kevin Conod

    Ah wonderful – Steven’s paper actually is online…you have to scroll all the way down to the bottom of the article to see the plots, but here it is:

  155. Dave Kary

    Okay, it let me take a crack at this “clearing the neighborhood” question. I think I understand what the IAU was trying to do with this, and really the just need to clarify what that phrase means. Let me through out a couple of suggestions that might alleviate some of the questions:

    To me, clearing the neighborhood suggests that the only smaller bodies that are still in a crossing orbit are either in dynamically short lived orbits (like the NEO’s that will be ejected from the area or will hit something in the next million years) or are stuck in a mean-motion resonance (like the Trojans in the 1:1 resonance with Jupiter). With this approach, Earth still is a planet, Jupiter still is a planet, Neptune still is a planet. The only things they share orbits with are either in resonance or doomed in a cosmically short time. On the other hand, Pluto, UB313, Ceres, etc. all have plenty of other bodies around them that are not likely to be removed on a multi-billion year timescale.

    I am also not so sure about the “public relations disaster” that several people have been talking about. While I suppose that the dedicated Pluto fans within the community might try to make it a disaster by turning this into some sort of nasty fight, but I’ve been finding that the reaction from my students is far more accepting than I expected. Frankly, most of them seem to have recognized that we’ve learned new things and we’ve had to revise our picture of the outer solar system – that’s how science works. It may be that after several years of talking about the idea people are just a lot more willing to accept it than they were a few years ago.


  156. Janet Roberts

    There has long been speculation about a large planet in an elongated orbit that reaches its perigee in the vicinity of the astroid belt and its appogee 3 times the distance from the sun as Pluto. This planet takes 3600 years to complete one orbit. When it reaches its perigee it crosses the orbits of all the other planets in our solar system, swings around the sun in the astroid belt, and on its way back to its apogee it crosses them all again. It is speculated that the planet is almost the size of Jupiter. When it comes this way, what will these astronomers call it?

  157. Wilson Kuhn

    Its been Pluto since it was discovered, and it should be left that way.

  158. Kevin Conod

    >There has long been speculation about a large planet in an elongated orbit that >reaches its perigee in the vicinity of the astroid belt and its appogee 3 times the >distance from the sun as Pluto.

    You’re probably thinking of “Nemisis” but really there isn’t much real evidence for it…

    But that aside if if it did exist, the crossing of orbits has nothing to do with the new definition – that’s not what “clearing ones orbit” means if you read some of the comments above.

  159. Kevin Conod

    Dave –

    I think the kids will adjust just fine. No one died when Ceres was demoted to asteroid back in the 19th century. Its the grups – the adults – that are the problem. They get set in their ways and refuse to change.

  160. Radio

    I’m a teenager. Just because i am a teen does not mean that I shouldn’t be taken seriously. Why did people make it such a big deal to make it not a planet? So it might interfer with another orbit, big deal that will never change, does it make it less of a planet? I think not, i grew up with 9 planets i will teach my future kids that there is 9 planets.
    Why leave pluto out of the planet catergory? Is it because of politics, because some say it is. Is there another reason, because i would really like to hear about it.

    I like Pluto and i think its a planet.

  161. Irishman

    Kevin, thanks for the link. The paper starts out pretty reasonable. However,

    Attempts to define “planet” in terms of upper and lower mass limits have not been satisfactory. An upper mass limit corresponding to the onset of deuterium fusion is complicated by the existence of some brown dwarfs in close orbits around stars (see Section 6).

    A brown dwarf is technically considered a type of star, not planet, because it fuses deuterium. But the ones near stars are apparently formed by different processes than the ones far from stars, and in fact by the same processes that explain the traditional planets. So he wants to classify some deuterium fusers as planets and others as stars. That’s the fuzzy line.

    The bigger problem to my mind is this:

    Brown (2004) proposed a related definition of “planet” based on the natural division of objects into solitary bodies and members of populations. A planet is “any body in the solar system that is more massive than the total mass of all of the other bodies in a similar orbit.” For example, the planet Neptune has 8600 times the mass of Pluto, the largest body that crosses its orbit. Likewise, the planet Earth has 2 x 108 times the mass of the asteroid (1036) Ganymed, the largest body that
    crosses its orbit.
    In contrast, the asteroids and KBOs are members of populations with a shared orbital space, in which no member so dominates the others by mass. The two largest asteroids, Ceres and Pallas, differ in mass by a factor of about 4 (Kovacevic & Kuzmanoski 2005, Goffin 2001), and the largest known KBO (UB313) has only about twice the mass of Pluto. Our solar system has no intermediate cases between solitary bodies (planets) and members of populations, defined in this way.

    Later he states:

    Any body that orbits a star or substar and contains more than about 100 times the mass of all other bodies in its orbital zone is a planet.

    But he is deliberately omitting the Moon from his calculations. The Earth is only about 81 times as massive as the Moon. So by his definition, the Earth is not a planet!

  162. P. Edward Murray


    As I’ve said before, I am not the ONLY person on the face of this Earth that thinks this is just so much baloney!

    At 49, I call ‘em as I see ‘em and when you reach my ripe old age and older then yo can call ‘em as you see ‘em too!:)

    And as to being devisive…tooo terribly bad.
    Usually, such verbiage is thrown at “New Ideas” not an idea that’s been around for 76 years.

    Hell yes, it’s politics….it’s the politics of a minority view or as our founding fathers said more than 200 years ago “The Tyranny of the Minority”.

  163. DJ

    Seems to me that what’s happened is that the years of talk about Pluto perhaps not being a “planet” have finally been supported by a redefinition of “planet” which excludes it. In other words, it was a foregone conclusion, and was reached basically because many astronomers were squeamish about calling Pluto a “planet.” Now they’ve come up with a definition of “planet” which locks us in at exactly 8, since the only other objects going around our sun will either be in the Kuiper Belt or the Oort Cloud, and the “cleared neighborhood” requirement will never pass muster in either case; and the definition doesn’t allow for any “planets” outside our solar system. I know there was a lot of discussion about this, but ultimately I don’t see how “scientific” this change really is.

  164. In honour of the IAU I have created my own mnemonic to help remember the new order of planets: Many Very Eccentric Men Just Sacked Unwanted Nonentity.

    Perhaps the best new definition for planets should now read: Great balls up in space.


  165. Furkan

    Well making pluto a non planet i do have some question and if thier is some one to answer back to this email:

    I need to know that What was the logic behind this?

    I do understand but i need to know what are the logic behind this dwarf planet. Thank you.


  166. P. Edward Murray

    One last idea here…

    Ok, so they decided Pluto is not a planet and “Zena” won’t be either when they get around to it.

    Well, I have a different idea….

    Let’s keep calling it a planet and it becomes a planet!:)

  167. P. Edward Murray

    300 Professional Astronomers don’t like it either:

  168. Pluto Not a Real Planet

    This makes perfect sense to me. If Pluto remains a planet, then we would have to add thousands of other little bodies to the list of planets. Mercury, Venus, Earth, and Mars are the rocky planets… Jupiter, Saturn, Uranus, and Neptune are the gas planets. Pluto and the other little craps that float around out there are just rocks and “stuff”. Heck, Pluto’s orbit is not even in the plane of the other planets’ orbits, so that alone should tell you that it is not a real planet! If we had the technology in the 1930′s that we have today, then Pluto never would’ve been designated as a planet anyway, so we have learned things over the years and we are correcting a mistake that was made in 1930. Some of you guys are just old farts that are resistant to change. PLUTO IS NOT A REAL PLANET; GET THAT IN YOUR HARD HEADS!

  169. Surprisingly, in the 1930′s, even the lay person knew that Pluto should not be considered a planet. Many people were very vocal about their opinions, staging demonstrations similar to, but in reverse the ones being staged by Pluto-lovers today.

    Pluto Protests

  170. juju

    I think its stupid to take away something that has been made for us to discover we discovered it so we cant make it dissepear. it will always be a planet that cant be moved if you se a round object through a telescope you can’t make it turn into thin air and youll always say its not a planet but it is and its there.

  171. Abby

    Hey ppl i wana tell u all THAT U R DUFFERS… only one got the rite ans…

    1. Pluto is STILL a drawf planet..
    2. PLUTO clused into Neptunne…
    3.Pluto is not a planet.. cuz its orbit is other than the orbits of the other 8 plantes..i.e Mercury – Neptune more .. E-W and Pluto moves N-S

  172. Irishman

    Christopher, I’m skeptical of that Pluto Protests page.

    I note the picture at the bottom left shows reference to Charon and Pluto as a Binary Planet. According to Wikipedia, Charon was not discovered until 1978 – far after the date of the supposed protests.

  173. robin

    SIMPLY: 9-1+3=11+x

    9-1 (planet) +3 (dwarf planets) =11 (planets) + x (whatever others they find and name)

  174. Tavia

    Just wondering… Is it possible that there are new planets? and are they qualifyy?

  175. Angelica

    If pluto is not a planet, What is the status of pluto as of now? Can we consider pluto as a moon or as an asteroid?


  177. Alyce Brannen

    Dear people,
    Pluto is a planet.

  178. Yisrael Asper

    Ironically the 12 planet proposal won out more than would have been thought. The IAU confused respected scientific sources so much that the term “classical planets” previously reserved for the old “naked eye” ones now refers to the IAU’s 8 planets for them and Charon is for them a Dwarf Planet. So vote or no vote the Public has spoken. Ironically Bode’s law as far out as Pluto and if I am not mistaken even farther seems eerily not coincidental (Ceres and Pluto may not dominate their Bodian neighborhoods but lie nicely where Bode’s Law says they should and we have in the place of their dominance asteroids in the case of Ceres and Pluto and oddball Neptune dominates the Bodian neighborhood that Pluto should.) The clearing the neighborhood clause is arbitrary as how big is the neighborhood? and Pluto never intersects into Pluto’s orbit strictly speaking but rather dares to be above the “airspace” of Neptune’s orbit. The IAU’s definition goes like this without them realizing it “A planet is a body that gravitationally dominates a Bodian area.” Ironically too by calling Pluto a Dwarf Planet it gets the recognition its detractors wanted to avoid. Pluto doesn’t revolve around the Sun in the classical sense anymore than Charon does. They are binaries if not more. So far amongst objects that some of us dare still to call a Planet (Pluto has moons that were never officially demoted as major ie. planetary moons! The IAU doesn’t even officially use the term) and those of lesser mass, it is the only multiple system of objects at their levels of mass. What is Pluto really? Pluto, by convention a Planet by convention a Dwarf Planet and by convention a Plutonian-type object (respected scientific sources got confused with what is to be the nameless name and called it Plutonian anyway). I learned some from the debate including that the real push for an 8 Planet system is more emotional than the push for an X Planet system. To me round by the way is when gravity dominates the shape of an object. Lets hope the Prague War of August 2006 doesn’t repeat itself. Except maybe to have some fun in August 2009 wearing Viking gear and holding plastic swords and rooting for Pluto so loudly they’ll vote yes just to shut us up before they kick us out of the building.

  179. Paul VerNooy

    Here’s a little poem I wrote about Pluto’s lost planethood:

    Twinkle, Twinkle, Planetoid

    Twinkle, twinkle, planetoid
    Out so far in inky void
    Rocky core with ice encloaked
    Your planethood has been revoked
    The I.A.U. struck a blow
    To the cosmic status quo
    They’re not quite sure of your fate
    But it leaves us only eight
    Was it that your orbit’s tilted
    Why you were so rudely jilted?
    Could it be your little tryst
    With Neptune that’s got them pissed?
    Despite the fact you have a moon
    Your reputation they impugn.
    But take some comfort in their crime–
    They’ll all be dead in one year’s time!*
    Twinkle, twinkle, far from sun
    So long for now, it’s been fun

    *One year on Pluto is 248 Earth years

  180. tan yuji

    The solar system consists of the Sun; the eight official planets, at least three “dwarf planets”, more than 130 satellites of the planets, a large number of small bodies (the comets and asteroids), and the interplanetary medium. (There are probably also many more planetary satellites that have not yet been discovered.)

    The inner solar system contains the Sun, Mercury, Venus, Earth and Mars:

    The main asteroid belt (not shown) lies between the orbits of Mars and Jupiter. The planets of the outer solar system are Jupiter, Saturn, Uranus, and Neptune (Pluto is now classified as a dwarf planet):

    The first thing to notice is that the solar system is mostly empty space. The planets are very small compared to the space between them. Even the dots on the diagrams above are too big to be in proper scale with respect to the sizes of the orbits.

    The orbits of the planets are ellipses with the Sun at one focus, though all except Mercury are very nearly circular. The orbits of the planets are all more or less in the same plane (called the ecliptic and defined by the plane of the Earth’s orbit). The ecliptic is inclined only 7 degrees from the plane of the Sun’s equator. The above diagrams show the relative sizes of the orbits of the eight planets (plus Pluto) from a perspective somewhat above the ecliptic (hence their non-circular appearance). They all orbit in the same direction (counter-clockwise looking down from above the Sun’s north pole); all but Venus, Uranus and Pluto also rotate in that same sense.

  181. tan yuji

    Here’s a little poem I wrote about Pluto’s lost planethood:

    Twinkle, Twinkle, Planetoid

    Twinkle, twinkle, planetoid
    Out so far in inky void
    Rocky core with ice encloaked
    Your planethood has been revoked
    The I.A.U. struck a blow
    To the cosmic status quo
    They’re not quite sure of your fate
    But it leaves us only eight
    Was it that your orbit’s tilted
    Why you were so rudely jilted?
    Could it be your little tryst
    With Neptune that’s got them pissed?
    Despite the fact you have a moon
    Your reputation they impugn.
    But take some comfort in their crime–
    They’ll all be dead in one year’s time!*
    Twinkle, twinkle, far from sun
    So long for now, it’s been fun

    *One year on Pluto is 248 Earth years

  182. hello everyone, i don’t believe tht pluto is not a planet, is the physical features of a rocky body determined to tell whether its is a planet or not
    wht if pluto has some life in it , we can’t say tht, does our earth has rings around it, so tht we tell earth is not a planet……………………..

  183. Maddie jones


  184. Nebula

    My $0.02:
    I find that the original point at the beginning of this page stating that this is a silly argument is, above all, absolutely correct. It’s silly because of what he says later on; that the reclassification of pluto [or indeed anything else we already have a common name for] has no real scientific usefulness; it’s just plain splitting hairs. Clearly, useful scientific classification would be finding classifications for things which we don’t have names for yet, thus providing a common reference term that enables deeper discussion and comparison among specialists.

    A redefinition of this kind, as arbitrary and uninsightful as it is, has the aire of procrastination or otherwise uninspired thumb-twiddling on the part of the IAU. If science is the process of testing a hypothesis through experiment to gain knowledge about the operations of the universe, then the I.A.U. seems to have been sucked into a perceptual black-hole, focusing its eyepiece not one the heavens, but on their own words; their own internal model of the heavens in the name of clarification.

    Using that line of scientific method, we should next question whether humans are really mammals, since we obviously differ from all other mammals in so many ways. But in reality, this redefinition of humans would have absolutely no practical value, scientific or otherwise. We know what we know about something, regardless of what we call it; renaming something tells us nothing new about what it is and how it behaves. In conclusion, what is being passed for scientific contribution is actually nothing but an inward-looking language game pageanted by pedantic so-called observers, and a completely silly one at that.

  185. cuRious_crEatuRe

    Do they have some other reasons why they demoted Pluto from the solar system? You know I’ve got an assignment about why Pluto was not included anymore out there… Does also the size and its mass matter? And its location there? Please… I need answers for my homework!!! help!!

  186. Ken

    Earth has been unanimously striped of its planet status.

  187. jessica white

    okay here is the deal..i dont know why yall people want to see here and take away something that has been with us for years and years..and i thought trillions of years to come…but yall changed that..i mean just because pluto might not be as big as all the other planets or it might not have the right orbit or whatever yall think is wrong with it..doesnt mean it gives yall the right to take it away..its stupid and not cant just one day up and decide that its not a planet anymore and then say yall found another planet..oh but no…thats just dumb..yall mine as well just keep pluto a planet..i have a whole lot of people who would agree with me..its dumb and i think the planets need to go back to the way they were..thats how i was taught the planets and thats how i want my kids taught..

  188. Hey guys, I feel for Pluto so much, I made a music video with my buddy commemorating it’s loss.

  189. I have no clue what you guys are talking about!!!!!

  190. Anonymous

    my last comment was “hi” and i am doing a debate on pluto and this info was greatly appreciated.

  191. plut0l0v3r

    pluto is definitely a real planet. not dwarf. thats just stupid. pluto has moons that circle around it. in fact it has more moons than the earth does. so does that make the earth a dwarf planet? no. no it doesn’t. pluto is a planet as much as Mars or Jupiter is.

  192. Desire

    I don’t know what they were thinking, but I don’t really agree with the not calling Pluto a planet part. I mean I understand what they are trying to say here, but it just doesn’t feel right calling poor Pluto a satellite. He’s just like all the rest : it has a moon, it orbits the sun, and it’s round. Iknow he is small,but can’t he at least be called something with the word “planet” in it?

  193. yujie

    if dwarf planets aernt planets then midgets aernt people

  194. that is so mean what if i was a midget :( :) :)

  195. Neil

    Personally, I think “Planet” should be a purely astrological title, not an astronomical one. There were only five planets in classical antiquity, and perhaps we should leave it at that. Find a new term for what we consider planets! Since we’d have no semantic attachment to that term, it could cover dwarf planets as well. I’d go with “Peregrine,” the Latin word for wanderer or foreigner.

    No matter what you call it, the whole uproar over the definition of a planet was caused by scientists being afraid there could be potentially more planets than one could remember. However, with the discovery of over a thousand planets orbiting other stars, this reason has become a moot point.


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