The Pluto Revolt: Leading Astronomers Want the Plutoid to be Reinstated as a Planet

If you thought Pluto was going quietly and giving up its planetary status without a fight, think again. Leading astronomers have spoken out against the International Astronomical Union (IAU) decision to classify the dwarf planet as a “Plutoid,” described by some critics as a “celestial underclass.” The IAU decision was made after it was deemed that Pluto cannot be called a “planet.” Although the spherical rocky body can tick most attributes of being a “planet,” the IAU pointed out that Pluto is too small to be capable of gravitationally clearing its own orbit (plus it periodically crosses the path of Neptune’s orbit); it should therefore be called a “dwarf planet.” Back in June however, the IAU gloriously announced that Pluto should be now be re-classified as a “Plutoid” and any other Pluto-like planets should follow suit. But on Thursday, at a major conference in Maryland, leading astronomers will refute the Plutoid classification saying the IAU re-naming is confusing and unworkable

It may be the smallest planet in the Solar System a Plutoid, but this little spherical rock is causing a lot of noise down here on Earth. In 2006, the IAU re-classified the definition of a planet to distinguish between the differences between the larger known planets with the smaller rocky bodies (such as the increasing number of observed Kuiper Belt objects). There are three defining characteristics of what a planet should be:

  1. It is in orbit around the Sun.
  2. It has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape.
  3. It has “cleared the neighbourhood” around its orbit.

Pluto fulfils #1 and #2, but fails on #3, it is simply too small to gravitationally clear its own orbit. So Pluto was caught right in the middle of the “planetary classification debate ’06” and incidentally failed on one count. If any object fulfils the first two planetary criteria, but fails on the last, the IAU would classify the celestial body as a “dwarf planet.” To complicate matters, Pluto also travels inside the orbit of the gas giant Neptune periodically, giving it the extra classification of being a Trans-Neptunian Object (TNO). Although Pluto is a “dwarf” by Solar System standards, it is one of the largest Kuiper Belt Objects (KBO) in the outer Solar System; a true King amongst dwarfs.

Pluto has had a hard few months after getting kicked out of the planetary club.
Pluto has had a hard few months after getting kicked out of the planetary club.

So, for two years, Pluto was stuck in no-man’s land. It had been re-classified as a dwarf planet and astronomy teachers had to re-write their teaching material. Websites like had to scrub the 9 and replace it with an 8; but also had the foresight to buy “” Times were a little messy for Pluto. Then, in June this year, the IAU seemed to want Pluto to feel a little better. Not only was it the King of the Kuiper Belt, it would have an entire army of Pluto-like dwarf planets named after it. The IAU created the “Plutoid,” and as if to avoid any more confusion, it gave the classification a no-nonsense definition:

Plutoids are celestial bodies in orbit around the Sun at a semi major axis greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighbourhood around their orbit. Satellites of plutoids are not plutoids themselves. – The IAU definition of a Plutoid (June 11th 2008).

Got that? Good. But not everyone was happy, least of all Pluto. T-shirts have even been printed with the quote: “It’s okay Pluto, I’m not a planet either” (and yes, I have one), for anyone wanting to show their support for the struggling rocky body.

So this Thursday, some very prominent astronomers will take their case to the “The Great Planet Debate: Science as Process” conference at The Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Maryland. To cut a long story short, they want Pluto to be reinstated as a planet, thereby abandoning the term “Plutoid.”

Dr David Morrison, director of the NASA Lunar Science Institute in California, makes the point that if the largest planets in our Solar System can be called Gas “Giants” then it should be fine to call Pluto a “Dwarf” Planet. But in the current IAU classification, Pluto cannot be called a planet.

It has never before been necessary for any organisation to define a word that has been in common every day use so I see no reason why it was necessary on this occasion. Astronomers use adjectives such as giant and dwarf to describe different subclasses of objects like planets, stars and galaxies, so why could Pluto not remain as a dwarf planet just as Jupiter is a giant planet. Also, around 90 per cent of the planets we know now are outside our solar system, but under the International Astronomical Union’s definition, they cannot be classed as planets.” – Dr David Morrison

So it would seem the classification of “planet” will remain a very exclusive club of eight under the IAU rules; only Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune will have this honour unless the scientists at the Great Planet Debate conference can convince the IAU otherwise. Mark Sykes, from the Planetary Science Institute, argues that only #2 of the IAU planet definition need be applied; it is therefore the shape, or roundness, of the object that defines whether it can be called a planet or not. If this definition were applied, the Solar System would expand to include 12 planets. This worries some traditional thinkers at the IAU. As our observational techniques improve, more planet candidates will be discovered, therefore making the Solar System wildly different than what it is now.

But if there are more “planets” out there, why shouldn’t more planets be added to the official eight we currently have? It sounds like the Pluto debate is far from over and it will be interesting to hear what the delegates have to say on Thursday…

Source: Telegraph

81 Replies to “The Pluto Revolt: Leading Astronomers Want the Plutoid to be Reinstated as a Planet”

  1. Thoughts: 1) *Earth* hasn’t cleared *orbit* — look at all the junk in it, from the Moon to artificial satellites to the SSI and the rest of it. 2) Mike Brown is clearly working out his karma, and will be doing so for some time: “Call *Me* a dwarf, will you, you idiot mortal?!” sez Eris . . .3) I wonder what Grandmaster Robert A. Heinlein would have thought and said about this debate — or maybe not, it might not be suitable for a family publication. 4) Hades — the Greek original — is infinitely patient; everything and everyone comes to Him eventually. Including that 4% from the IAU who voted to kick Him out of the club . . . Well, you know what they say about where all the best lawyers go when they die, so maybe Mr. Brown will have good representation there . . . 5) Enough of this debate. Let’s go back to calling Pluto a planet, and also Ceres, and Eris, and Sedna, and other round bodies in the Solar System that happen to orbit the Sun; and find some nice activity for Mr. Brown and friends to immerse themselves in for their next science fair project.

  2. And then again, how about the Lovecraftian Mythos types and their reverence for Yuggoth? Is a platoon of Mythos monsters winging its way toward Earth even as we debate this, rarin’ to do terrible things to whoever downgraded their lovely world? Stay tuned for further exciting developments in All My Dwarf Planets, or, As the Phrase Turns . . .

  3. My suggestion, made in 2000, is the name “microplanet” for objects under 1000km in diameter that orbit a star. After the success of Microsoft the prefix “micro” does not have the stigma of “dwarf”! This suggestion retained Pluto as a planet and gave a group term for asteroids, comets, TNOs and the like.

    I also pointed out that Pluto and Charon form a binary planet because the barycentre (common centre of gravity) is outside the surface of Pluto.


    Of course, as I am not an astronomer and not in the IAU, my suggestions were not taken seriously. But it would be useful if journalists and members of the public took matters into their own hands 🙂

  4. I vote for creating many different classes:

    Mercuroïds, Venusoïds, Earthoïds, Marsoïds, Neptunoïds, Uranusoïds, Jupiteroïds, Saturnjoïds, Plutoïds, Europaïds and Titanoïds.

    We can then continue with Apophisoïd, TU239oïd, schumacher-levytoïd, and keep expanding to Andromedoïd and Zeta Reticuloïd galaxies………

    Should take care of all that darn bickering and maybe give them some time to focus on science 🙂

  5. just call it a dwarf planet, or a micro planet…alter definitons a bit and be done with it. Its only as hard as you want to make it IAU…

    Anything but some wacked out name like Plutoid.

    Maybe the IAU should adopt a two tiered system like biology, where there is a public name for each object, and then a totally unpronounceable and incomprehensible scientific name that only the scientists care about…

  6. The discovery of Pluto came along at a culturally significant time. Its hard to just roll that back because someone decided the rules needed to change for their convenience.

    I would have kept the old definition of planet, and then kept adding planets or defined them as a new subsect that was still under “planet”.

    Much simpler.

  7. Hey Earthlings. Did you ask any of the other inhabitants of the Sol solar system about your Pluto issue? Ya didn’t did you? You don’t even know where they are, do you ya self-centered jackasses.

    We’ll we’ve been talking and guess what, Earth isn’t a planet anymore. The six other inhabited planets voted and you’ve been designated Giant Pain in the Ass.

    So listen here Earthlings, if you don’t want a Extinction sized Kuiper belt object lobbed your way you better watch all of this Plutoid-dwarf-planet crap. You Giant pain in the Ass inhabitants.

    Oh and stop flying those junky little “space-crafts” out here. We don’t need the mess.

  8. Do you think, if you placed Neptune at 100 AU, that it would have much chance of “clearing” its orbit? If it took 600-1000 years to go around the sun once?

  9. Well, I didn’t want it to come to this, but…

    It looks like we’re going to have to destroy Pluto.

  10. Go figure…take into account that this whole thing was not settled anyway in a formal session of the IAU but rather in a bar fight where a lot of the members were hanging out.

  11. btw…j/k nights too quiet here this evening..think I will go try and spot a few stray Perseids

  12. I really felt that coining a neologism like Plutoid was a mistake, and there wasn’t anything particularly wrong with the dwarf planet designation as a reasonable compromise between the two scientific camps involved.

  13. I think the IAU got it right the first time with the term dwarf planet. I think some effort should be made to separate those objects that clear out their orbits and those so small that they get pushed around by the others. I have a really hard time accepting Ceres as a planet when what it really turns out to be is a KBO that got pulled into the asteroid belt. The case of Ceres might be an excellent test of the dwarf planet classification system as in fact it turns out to share a great deal in common with KBOs besides its IAU designation. I think for the same reason using the definition plutoid is artificial and needless.

  14. Ohh for the love of… This!? AGAIN!? I am sure once we have a better understanding of Solar Systems in General we’ll be better able to classify the Planets in our own. I vote we make it something simple like Girth.

    If a Planet is below X KM it is a Dwarf, if it is above X but below Y it is a Planet, if it exceeds Y it is a Giant. Sort of a Metric System for Planets, it’d be great if we used a Base Ten System to keep things simple.

    I know this is an over simplification but we are busily over thinking an issue that just needs a clear and logical decision. Too much emotion and sentiment going into a question of rationality.

  15. news about pluto’s planethood is more annoying than news about brett favre’s retirement/return.

  16. Dr David Morrison:

    “It has never before been necessary for any organisation to define a word that has been in common every day use so I see no reason why it was necessary on this occasion.”

    You know, that seems a very sensible position. So why are they making the effort of holding a special conference, instead of just going about their business and ignoring the IAU definition?

  17. If pluto is a planet, than we should also include such Kupier belt objects as Eris, Sedna etc. in the planet list. Nobody knows the exact number of such objects. But they may be too populous.
    I think that IAU 2006 classification is a reasonable one.

  18. Why can’t reporters do their research. Pluto is NOT ” the largest Kuiper Belt Object (KBO) in the outer Solar System.” A larger one was discovered years ago. Since it’s not even the larget KBO, how can it be a planet? Besides, if Pluto came too close to the Sun, it would grow a tail! Yeah, like a comet! What kind of behavior is that for a planet?

  19. to Betsy’s comment, yes, it absolutely would. A thousand years is a completely negligible amount of time in astronomical terms. The planets formed Billions of years ago, so Neptune, placed in your hypothetical orbit, would orbit MILLIONS of times! (and Neptune is big)

  20. “more planet candidates will be discovered, therefore making the Solar System wildly different than what it is now”

    you wrote this in jest, I hope… to highlight the pointlessness of this debate?

    Last time I visited my elderly Mom, I brought her some Brussels Pate. It tasted really nice. Then my Dad called it Pork and Liver Pate, therefore making it a wildly different type of cooked meat dish… and suddenly it tasted just plain awful……. 😉

  21. I say that Pluto is NOT a leading contributer to the CO2 content of the solar system and find this ‘cap and trade’ definition of the word “planet” morally reprehensible!!

    You let one scientific field get away with junk science and every other field of science wants to get in on it!! Planet means “planet”, just leave the word alone…

  22. If we have a classification of ‘Plutoid’ then I imagine that Pluto will be the only body ever to be given that status.

    This is because, if we are ever able to identify bodies the size of Pluto orbiting distant stars (something which may be impossible anyway) how will we then be able to determine that it has It has “cleared the neighbourhood” around its orbit so that we can classify it?

    ‘Plutoid’ is, in my opinion, a meaningless classification, and Pluto should be re-instated as a Planet.

  23. Hi All

    I’m all for blowing Pluto up. The rest of the Kuiper Belt is getting a bit thin, so let’s add some debris. How many bombs will we need? Let’s see Pluto’s binding energy is ~ 6 E+27 Joules, some 1.45 trillion megatons of TNT equivalent. To be on the safe side about 3 trillion should do. About 14 billion tons of fusion bombs should do the job…

  24. Without questioning, Pluto belongs to our solar system. It is orientated towards the same disk in sorrounding our sun – like all the other planets. It is round – pheric. So off course it’s a planet.

    As far as I know we allready have devided our solar system in an ‘inner’ and an ‘outer’ solar system – where pluto belongs to the ‘outer solar system of planets. Apparently, a whole lot of new planets are comming in to our knowledge … we could call them exterior planets, belonging to our exterior solar system.

    I do have respects for the IAU’s attempt in defining things according to certain creteria. But, obviously, their third definition is quite vague. And how can this defenition rule out Pluto!!! – Since the very proces of any objects, becoming a planets in its births or creation – involves the very proces of smashing into other objects, within its trajectory.
    By this very process of ‘clearing the neighbourhood’ pluto have achieved becoming a pheric planet. Apparently, it might even grow bigger in this proces – but, it has allready achived its planets status of becoming a pheric objects.

    In other words this third definition is a froud. In comparison it would allmost be the same thing to say a baby isn’t a human – because it is too small, and because it is eating way to much compared to adults.


  25. What IAU needs to define is the ‘Periodic table of Celestial Bodies’. Find and set the properties of the small and large ones, organize those bodies in proper groups and then decide how to classify Solar System objects. For instance where is the border line between large Jupiter type planets and small brown dwarfs? Why one thing is a huge planet while the other is a “nano” failed star? That does not affect Solar system bodies, of course. But one can see different possible types inside our own system. The present classification is still very “solarcentric”. Suppose an erratic thing, ejected from it’s own system, Earth mass or bigger, and orbiting no star. Isn’t that a planet? It fails the third criteria. Inside our system we can see rocky planets and gas planets and a lot of other smaller things, small planets, debris, etc. Classification of those objects should not include criteria that are not a function of their size, composition and properties. The third criteria of IAU for a planet is a bit “out of context”. But I still agree that Pluto is in a different class when compared whit the other traditional 8 planets.

  26. Whatever the definition of a planet, Pluto should have been grandfathered into the planetary family.

    Pluto as a planet matters to the next generation of scientists. It stimulates the imagination like no other planet.

  27. ‘Plutoid’ is an absurd term but worse is to say that a ‘dwarf’ planet’ is not a ‘planet’. This is like saying that a ‘small cow’ is not a cow! Linguistic nonsense! Are there no literate (and logical!) astronomers out there?

  28. I’m in the adjective camp.

    @Joe – if the Earth came TOO close to the Sun it would grow a tail too. (Ouch)

    @GregM – The club now stands at 3. Eris and MakeMake are miffed at you.

    But Plutoid? Really! Does anyone got a photoshopped pic of a tube of “Preparation H”?

  29. Media wise, “new planets found” would have made a better headline than “astronomers being whiny about definitions”.

    The pluto thing has all the drama of a scrabble game gone bad, and means bumpkiss to the general public.

    I’d rather have new planets… much as the school kids might hate memorizing them all.

  30. I got confused – again. Since Pluto is a TNO; does that mean that Neptune has not cleared out objects in its orbit? Maybe Neptune should be reclasified a Neptoid?

  31. If this is such an issue, I recommend keeping the 2006 definitions with just one tweak.

    Leave the ‘dwarf planet’ definition as is. Change the criteria for ‘planet’ to read ‘major planet.’

    Now both groups are planets. You have two classes: major and dwarf. Major planets clear their orbits (pretty much) while dwarf planets don’t.

    Within the major planets one can still distinguish between gas giants, rocky planets, as you like. People can count planets either way, as they wish: they can talk about the eight major planets, or umpety-ump planets total.

    One more tweak: say planets orbit ‘their suns’ rather than ‘the sun.’ Now you’re all set.

  32. I agree with Kevin F. when he writes:

    “Just call the originals the “Nine traditional planets” and have it done with!”

    Our nine wandering spheres have existed as planets for a long time, now we’re discovering that there are myriad types of objects orbiting our sun – not to mention what we’ll find orbiting OTHER systems. I’m for protecting Pluto and it’s nine siblings by granting them the equivalent of planetary landmark status, move forward from there.

  33. Of course the Pluto debate is far from over. Anyone who expected it to be over with the IAU linguistic nonsense that a dwarf planet is not a planet at all, a decision made by four percent of the IAU and immediately opposed in an official petition of an equal number of professional astronomers, had to have been engaged in wishful thinking.

    Websites, teachers, and textbooks never needed to rewrite their material because of this vote by a tiny minority of astronomers, most of whom are not even planetary scientists. The IAU is not some sort of priesthood that can dictate what something is. In a case like this one, teachers best serve their students when they explain that there is more than one school of thought on the subject, present arguments on both sides, and allow students to draw their own conclusions. It’s the difference between teaching how to think versus teaching what to think.

    The Plutoid designation is a further IAU debacle. Plutoid means “Pluto like.” In Pluto’s case, does that mean Pluto is like itself? Pluto does not even orbit at a semi-major access greater than Neptune all the time. For about 20 years during its 248-year orbit, it actually comes closer to the sun than Neptune. Add to that the term “plutoids” was coined by an even smaller group of the IAU in a closed process. Many leading planetary scientists in the world were unaware of the discussion until the term was announced as a fait accompli.

    There is one easy step the IAU could take to resolve most of this problem. In addition to dropping the term “plutoids,” they should nullify the vote that says dwarf planets are not planets at all. Then we can keep the designation of dwarf planet for small planets that have achieved hydrostatic equilibrium but do not dominate the neighborhood of their orbits (i.e., orbit in a belt of objects). We should keep the overall term “planet” as broad as possible to include the many new and diverse objects being discovered in this and other solar systems. Then we can distinguish these objects by their individual characteristics, including orbital dynamics, through establishing multiple subcategories of planets. These subcategories would include terrestrial planets, gas giants, ice giants, dwarf planets, hot Jupiters, super Earths, etc., with more likely to come.

    It makes absolutely no sense to define an object solely by where it is while ignoring what it is. In fact, we will know more about what Pluto–and Ceres–are in only seven years when New Horizons and Dawn both fly by these objects and give us critical data that will likely change whatever conceptions we currently have.

    I plan to be at the Great Planet Debate and look forward to both a far more open and inclusive process and a better, more encompassing planet definition than what took place at the IAU General Assembly two years ago.

  34. I really hate it how all too often this thing is brought up as if it was Pluto the center of it. It isn’t. The center of it is finding a definition (or a set of definitions) that works and only then should we be trying to fit bodies into categories.

    I’m all for stating that anything massive enough to be significantly round is a planet. It’s simple, it’s universal, it generates only a small amount of ambiguity and much less category shifts with time than the current IAU wording. Not to mention a much lesser probability of extrasolar discoveries able to put it radically in question somewhere in the future.

    Therefore that’s what should be used for the main separation between what’s a planet and what isn’t. Every other classification schemes are good also, but only to define subcategories. It’s one thing to say that over time a given body that changes very little shifts from one category of planet to another, and another quite different to say that this body first isn’t a planet and then becomes one, without any significant change in its physical characteristics.

    Furthermore, the only real objection I see to this is that we might end up with a large number of planets in the Solar System. Sometimes poeple try to disguise it, but in the end that’s what it comes to. The problem, of course, is that deciding first how many members of a category we want and then tayloring a categorization scheme to make it so is a bit like deciding first who should win an election and then frauding it up to get the desired “result”.

    Most definitely not the kind of thing I’m willing to accept.

  35. The Plutoid controversy is part of a larger conspiracy to further the cause of Project Lucifer. If they call it a Plutoid, the reasoning will follow that NASA can destroy it (since it’s not really a planet), thus perturbing the orbits of untold millions of Plutoid objects and catapulting them toward Jupiter, thus setting into motion its ignition as a second star. I’m willing to bet there’s already a conspiracy theorist working overtime…

  36. On a more serious note, I don’t get all the attention that this thing is getting. If “Plutoid” helps talented, gifted people study astronomy more fully, I’m all for it. If “planet” fits the bill, then so be it. I only hope the fixation with classifying objects doesn’t become a distraction from other pressing questions…like what is the surface like of these objects, do they have a measurable atmosphere, what is their relationship to the solar system, etc etc.

  37. It seems to me that Neptune does not fit rule 3 either.
    If a planet has one or more moons then it hasn’t really
    cleared its neighborhood either. Therefore there are
    only two planets left.

  38. all definitions are arbitary and subjective. Pluto will be oblivious to what we define it as, and it’s ‘behaviour’ will not be affected, whether we call it planet, TNO, plutiod, dwarf, or dog.
    Making a distinction based on girth of 1000km would not work cos (a) how would you measure exactly? (b) if 1 object was 999.999km and another was 1000.0001km you’d have to class them differently.
    How do we know when an object has ‘cleared ther area’ of it’s orbit? What if it’s clear except for 1 tiny rock? 2 tiny rocks? 3 big rocks? 300 big rocks? etc.
    What if it’s cleared the area, but then 2 comets collide in it’s orbital path, scattering more debris to be cleared, would we demote it from planetary status?.
    No 2 objects in the universe are alike, be they stars, planets, galaxies, potatoes, snowflakes or grains of sand.
    We may see certain similarities from our limited human perspective, and it may help our comprehension if we group certain things we observe together under a collective term, but those terms aren’t ‘reality’.

    This is Philosophy Today, isn’t it?

  39. When they called Pluto a planet and part of the nine, we were all happy about it. As far as I am concerned it still is a planet, and here’s why.

    The largest body in a Bode orbital area should be the planet. The fact that Pluto’s orbit is excentric and some of it is inside Neptune’s more regular orbit, I feel, should not effect it’s status.

    Seven of our planets have moons, so the big one is a planet and the small one is a moon. Of course moons may be required to orbit their planet in order to be entitled to the name. So far so good and that all makes sense to me anyway.

    If we find objects orbiting Pluto, and we have Pluto the major object in what could be agreed upon as ‘being within a Bode orbital path’, what then?

    And as for a classification criteria being ‘able to keep its orbital zone clear of rubbish’, or words to that effect, and knowing that Pluto has the largest orbital area to sweep, I think that is grossly unfair.
    So if our beloved planet earth was suddenly placed in Pluto’s position, would we then have to demote it to an ‘earthitide, or, ‘teratoid; just because she too wouldn’t have the gravity mass to keep that vast area tidy? Oooooooooooh!


  40. To me, it seems some people had a need to be known so they figured up this little scheme to remove Pluto’s status as a planet.
    Seriously, it appears the pre-requisites of a planet were made up or changed (depending on your point of view) in order to remove Pluto based on the views of the minority. Not scientific at all.

    Each of the planets are different. In fact, if you include Pluto as a planet, the biggest odd ball orb circling the sun is Earth. No other planet is remotely close to it outside of size and basic structure.

    Point is, you can come up with a list of 3 items to exclude any of the planets from their current status.

    You can come up with a list of items to create something new. Why not a Jupitoid? Something huge, gaseous, and having so many natural satellites can’t be a planet… it has to be a Jupitoid!

    So IAU, admit your foolishness and include Pluto as a planet, as it should be. Come up with something you actually have to work at in order to make your name. Pluto was a planet for years; nobody was hurt by it, and it didn’t screw up science one little bit.

    Sometimes the status quo is just fine.

  41. So much ado about nothing from supposedly intelligent minds. What about “Dinosaurs” or “Terrible Lizards”? A term first coined by British paleontologist Sir Richard Owen in 1842. Birds today are considered descendants of Sauropods, a so called “Dinosaur” species. So by extension of this terminology we spend every third Thursday in November with family and friends dinning on “Terrible Lizards”!

  42. Not to be argumentative, but…
    Pluto’s classification as a trans-Netptunian object (TNO) has nothing to do with the fact that its orbit sometimes brings it closer to the Sun than Neptune. Most Kuiper Belt objects do not come closer to the Sun than Neptune, yet they are still classified as TNOs.
    What I’d like to know is what happened to the classification “Plutino.” For years, Pluto and all other KBOs in 3:2 resonance with Neptune were classified as “plutinos.” Now we have Plutoids, but if I understand it correctly, not all Plutoids are in the 3:2 resonance.
    So does that mean that Pluto is a “dwarf plutino, plutoid, planet?” Or maybe it should be “binary, dwarf, plutino, plutoid, planet.” Or perhaps “binary, dwarf, KBO, plutino, TNO, plutoid planet.”
    By the way, if a human being is classified as a “dwarf,” isn’t he still considered human?

  43. Indeed it should be much ado about nothing, but unfortunately it isn’t. I very much doubt we’d have New Horizons right now hadn’t Pluto been considered a planet for all those years. And, conversely, I very much doubt that the first mission to Ceres were Dawn if it had remained a planet instead of an asteroid.

    What we call the astronomical objects shouldn’t really matter, but it does.

  44. I think I’ll swap to German in future and just refer to Pluto and its ilk with “Planetschen”.

  45. Just to highlight the incompetence at the IAU, it is worth noting that under the revised definition f “planet”, neither Jupiter or Earth are longer classifiable as “planets” either. Jupiter shares its orbit with the Trojans, and therefore it is not “c;eared”, while Earth has not “cleared” its own orbital “neighborhood” of Cruithne (yet). Thus, there are but 6 “planets” proper in the Sol system, and we no longer live on one of them…

    Here’s a freebie to help the IAU along —


    1. large enough to assume a roughly spherical shape, but not so large that hot fusion processes begin with in it, and

    2. does not orbit another planet (i.e., own orbital barycenter not within the surface of another planet).

    That’ll do you. And it promotes Ceres, Pluto, Eris immediately, with Sedna, Quaoar, and Makemake to follow shortly.

    I’m sorry that many members of the IAU will now have to take their shoes off to remember all the names of the planets, but science is about *facts*, not aesthetics…

  46. What we call astronomical objects shouldn’t matter and doesn’t matter. Research and funding is based on more than names. How many times has the classification for the sun changed in the last 10,000 years…yet how much attention has it received (including research and funding)? We’re getting into the realm of linguistics and semantics. Names change. In science, they change in part because of developments in research, classification and distinction. The point isn’t the name. It’s the advancements in our understanding!

  47. Oh, and now that I stop to look at it, Neptune is no longer a “planet” either under the IAU’s definition, since apparently it has not “cleared” its own orbital “neighborhood” of high-eccentricity-Pluto.

    So, I suppose if the IAU definition stands we’re actually down to a mere 5 planets now… Mercury, Venus, Mars, Saturn, and Uranus, with the “dwarf planet” Ceres, and the “plutoids” Pluto, Eris, Sedna, Quaoar, and Makemake, the “terroid” Earth, and the “jupitoids” Jupiter and Neptune?

    Oh yeah, that’s *much* clearer and simpler… easy to teach to primary schoolers, you bet…

  48. Ha, Ya’ll gotta love this…

    On one level this sounds like a trivial exercise, but it really isn’t.

    What we call things defnitely influences what and how we think of them. It may well influence what research is done on them. I am a scientist and educator in another discipline – one well overendowed with jargon terms (Invertebrate Zoology) – and it is painfully – and ridiculously – obvious in that discipline how much a difference in a category can mean with regard to studying something.

    What is being done here is, in effect, digitizing a continuum of sizes (from micrometer-sized dust to Jupiter). Why not recognize that it is a a continuum and go from there?

    Pluto should be a planet – as should the larger Kuiper belt objects. Adjectives such giant, dwarf, ellipsoidal, pink and such can be applied to these structures.

    On the other hand, doing that would take the fun out of these trivial arguments, and would remove the very useful aspect of providing a glorious way to waste time. Hey, it’s better than listening to politicians…

  49. Pluto is a Kuiper Belt Object. Period.

    It must be a REALLY slow day on the global warming, (AHEM!) climate change front.

    I personally like the story. ‘Ian’ (get it right, where did you go to school anyway, California?) and the rest of the UT staff do a great job of getting us excellent articles on astronomy.

  50. Pluto is a Kuiper Belt Object AND a planet–as are Eris, MakeMake, and Sedna. There is no reason that objects in the Kuiper Belt that are in a state of hydrostatic equilibrium cannot simultaneously belong to both categories. These objects are unlike the other KBOs because objects in hydrostatic equilibrium have geophysical processes unlike inert asteroids, which do not.

    Yes, classifying, reclassifying, and subclassifying objects in science is a normal and essential process–IF that reclassifying, etc. is based on sound reasoning and makes actual sense. The IAU reclassification does not do either. Resorting to derogatory personal attacks against those who, for solid logical reasons, reject the IAU decision, is nothing more than an ad hominem attack and does nothing to promote your position.

  51. Granted, this is my “modern jackass” moment, but it seems to me that one reason for including round objects like Pluto and Ceres as part of the same bestiary as the major planets, is that so far, the round bodies we’ve observed have been shaped by similar mechanisms of stratification, compression, and internal heat. I suspect this debate won’t be settled until New Horizons either finds signs of a surprisingly dynamic history on Pluto, or signs that its had a rather placid history.

  52. Still with this Plutoid crap?

    We are now sending one Extinction level KBO EXPRESS to your gravity well.

    Adios Earthlings.

  53. Let’s not forget HD 69830 d which is has 10 times Earth’s mass, is 7 billion years old, and lies in a very thick asteroid belt. If it cannot meet the definition, than how can Pluto?

  54. In a rare display of primal screaming, 12 angry scientists took to the lower frequency airwaves defending Pluto. They refused to acknowledge anything other than a planet named Pluto and said the “Plutoid word was nothing more than excrement from pitiable, wanna-be researchers who don’t know a freaking thing about the universe. We fart in your general direction and shall never tire of taunting you.” Next time: conspiracy theorists link the plutoid debate with black helicopters and Project Lucifer…stay tuned.

  55. The article is clearly biased. Where are the “leading astronomers”? Who are the “very prominent astronomers”? The only name you could dig up was Mark Sykes who opposes reclassifying Pluto a plutoid.

    This is no news article. It is simply a rehashing of old whiners who can’t let go of their baby blankets.

    Classifying and reclassifying and subclassifying not only planets but ALL objects found and studied in science is a normal and essential process if science is to progress and advance.

    If you can’t seem to handle that fact because of abnormal psychological reasons, then perhaps science isn’t your bag.

    Try a subject where everything always stays the same like…..NOTHING.

  56. Ion O Neil, try coming up with a real news story. The information that someone is selling Pluto t-shirts so they have something to dry their eyes on doesn’t cut it as news bud.

  57. How can we gauge what is and what isn’t a planet by it’s size – how lumpy it is – what it’s made of – if it keeps its pathways clean or not – or what? That stuff is simply fudge because there are no clearly defined boundaries. The questions will remain as to how much is enough or not enough. (Maybe that’s what Science wants).

    On the other hand, if we can locate Pluto as existing within a Bode’s Law orbital zone, mainly beyond and therefore larger than Neptune’s, and are sure that it is the largest body in that zone, I feel that it has the right to be a planet – because

    The largest body should be the dominant collector of dust and rocks etc. in that zone. That being so, as it collects, it will grow and that means that eventually it could qualify as a planet under to-days thoughtless, shortsighted, meaningless criteria.


  58. Scientist are to occupied by the need to categorize everything. I refer to this as BSology and I’d like to write a book about it if I live long enough. This is an ongoing problem in other branches of science. As man discovers something new he realizes that his existing categories are insufficient to define all of the discoveries. Then we have a big meeting and invite all the world members of our professional organization that we joined to feel self important. By a vote of members, we exercise our power over everything that you know. We create a new class, order or whatever. Because we said it, it is so. Change the books because we have voted. Redefine right and wrong because we have voted and our vote makes you wrong.

    I still support the notion that only one thing qualifies what is a planet. “2. It has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape“. Moon and Titan and many others are planets.

  59. Wouldn’t that make every other American a planet, except in Beverly hill of course.

  60. From a philosophical point of view.

    A planet – is a planet, that – nobody can change.

    In this respect I will say, things are what they looks like.

    I enjoy to define things for my own sake, and believe it’s a good things in order to keep a certain order in my head – and thereby understanding.

    I prefer to view IAU’s decision as a positiv thing – allthough I disagree with their decision – simply because it has created a debate … and coursed me to get a better definition on the ‘planet’ term.

    My final decision in defining the term planet is: ”A spheric object free in space”.

    ”Free in space”: If a spheric objekt is in permanent contact to another object – I will call it a ball.

    ”Spheric object”: It has just come clear to me that a ‘spherical object’ is the very first visible sign of ‘order’ in the univers … of natures marvellous ability to create order in kaos.

    And yes, if an electron/proton/neotron or any other subatomic particles is believed og known to be spherical they are also planets – atomical planets.

    Consequently I view:

    ‘Stars’ as planets – lightplanets or ‘Galaxy planets’.

    The next in the order … please notice the allready used term of astronomers ”extrasolar planets”. For me I would call them starplanets or in our case – sunplanets. Subtitles could be as allready used ”giant plantets” – ”dwarfplanet”, and other terms refering to their substance.

    For planets not circling around a particular object, is for me ”wild planets”

    If an object clearly have obtained a spherical shape, but then by colision have lost this spherical shape, it is a ”damaged planet”.

    Then Moons: ”Moonplanets”.

    ‘None spherical’ objects cirkling another object, is for me a satelite, regardless its size.

    I realise that the basic foundation for my planet definition, is the ”spherical shape”, whitch I consider no more or less than marvellous. And, in reallity sufficient for me, in the defining characteristic of a planet – provided it is ‘free in space’.

    In reallity, I do not care that much about what the IAU decide, as long as it works for them as a working model – or means of communication. Yet, it disturbes me somehow, since it has such a greath impact to a whole lot of human comprehensions – including the world of writings – symbolism etc. Yet, I really would welcome this new way of defining our solar system, if it made som sense to me – but it doesn’t, it seems only to add confusion in our common comprehension of our solarsystem, not to mention our definition of universal objects.

    Also – remember: It only takes an idiot to confuse and complicate – about anything. But a genious, to make complicated things clear and understandable.

    In general, I beleive that in the mass of astronomers, there are a whole bunch of genious people – do I or we have hope for a better and revised definition of the term planet?


  61. So what if more planets are discovered thus making the Solar System radically different to the way it appears now? I don’t recall a fuss being made when Uranus and Neptune were discovered and disturbed the ‘classical’ view of the system. We’re not at a special time when 8, and 8, only is THE number to have. What happens when we travel out there and find bodies similar in size to Mars or Mercury?? Let the Solar System have 9, 20, 100 planets. Future generations will howl with laughter at this debate. There are at least 12 planets – move on, next scientific discovery please.

  62. To get a good idea at how to compromise over this one should look at how the continent and islands are defined on Earth. I think we can all agree that the continents are North America, South America, Europe, Asia, Africa, Australia, and Antarctica. But how are they defined? We could come up with a three point system: (1) on their own continental plate, (2) have a culturally distinct population, (3) surrounded by oceans on all sides. However Europe would fail since its not surrounded by water and (arguably) not on its own plate (Europe collided with Asia 270 million years ago and the two former plates fused into one Eurasian plate – no new mountain building in the Urals). If we dropped the water requirement (3) then we’d have to promote India from a sub-continent to a continent since certainly on its own plate (the Himalayas are still growing!) and has a culturally distinct population. If we drop the plate requirement (1) then Greenland, Madagascar, and New Guinea could argue for continental status. We could define a continent by size using a nice round base 10 number – i.e. over 10 million – but then Australia gets demoted to an island of 7.6 million

    The continents were named in antiquity as really big chunks of land defined by natural barriers (oceans and/or mountains) with culturally distinct populations resulting in an exclusive club regardless of the advancement of scientific knowledge.

    Maybe its time to say “yup” and define Pluto (Europe) as a planet (continent) because this is an exclusive club defined by history. Then Ceres (India) is dwarf planet/big asteroid (sub-continent) again for traditional reasons. And finally Sedna, Eris, (et al.) out in the Kupier Belt and the asteroids in the Asteroid Belt (Greenland, Madagascar, New Guinea, New Zealand, Newfoundland and Britain) are KBOs/Plutoids or asteroids (islands).

  63. Ah, yes, Watchful Stone Guardian – but does Pluto gain a semblence of respect if other objects are termed Plutoids in its honour? Perhaps they will all have to be smaller, or otherwise inferior in every way. And we who feel the shame in this debate can only pray that Pluto will some day clear its rocky domain and gather those detached particles to its bosom, and grow, and grow, and grow; and may the doubters and scorners and other nasty people, join that growing mass.

    How sad and simply ironic
    Our views are far from platonic
    As milk becomes curds
    The meaning of words
    May well be described as Plutonic


  64. tl;dr

    Seriously, this is not science. Astronomers should stop wasting their time on the issue as I guess most of them already did.

  65. Can’t the IAU think tank come up with something better to do with their time? These guys are an embarrassment.

  66. As I remember this contoversy. It wasn’t that Pluto didn’t meet the definition of a planet.

    What I recall is the definition of a planet was changed to displace Pluto

    Am I mistaken??

  67. Hello there Guys,, i think we should leave the guys in the IAU as in their ass.. Theres nothing we can do in what are their empressions about this 9th planet called pluto as in tradition.. They know more than we are about this. so, please lets try to be an audience. and as a human, we cant force ourselves to be believed, because only God knows about all things we can see..
    So!!! As on your ass Morons

  68. Hello there Guys,, i think we should leave the guys in the IAU as in their ass.. Theres nothing we can do in what are their empressions about this 9th planet called pluto as in tradition.. They know more than we are about this. so, please lets try to be an audience. and as a human, we cant force ourselves to be believed, because only God knows about all things we can see..
    So!!! As on your ass Morons

  69. Maybe it will help to put a little perspective on this. These KBOs were planetoids on their way to becoming larger planets when Neptune wandered out and spewed them about like balls on a billard table after the break. Neptune captured one of the larger ones which is its moon Triton, A big one named Ceres got pulled into the Asteroid belt. Pluto and the rest all had their orbits disturbed and their development stunted as a result of being thrown out of their orbits. Thus the term dwarf planet is wholly appropriate. This debate may come up again however when we find Mars size objects or bigger that Jupiter likely threw into much more distant chaotic orbits when it migrated towards to sun. Will they be called planets or Trans-Jovian Objects or both? Certainly such objects cant be classified as dwarfs. I probably just thwarted my own argument, but as you can see none if this is simple.

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