IAU Throws Pluto a Bone: “Plutoid”

Almost two years after the International Astronomical Union (IAU) General Assembly demoted Pluto from a “real” planet to the new category of dwarf planets, the IAU, as promised, has decided on a name for trans-Neptunian dwarf planets similar to Pluto. The name “Plutoid” was proposed and accepted by the IAU at its recent meeting in Oslo, Norway. Here’s the definition of a Plutoid: “Celestial bodies in orbit around the Sun at a distance 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 neighborhood around their orbit.” The two known and named Plutoids are Pluto and Eris. It is expected that more Plutoids will be named as science progresses and new discoveries are made, for example, when the New Horizons mission arrives at the Kuiper Belt region in 2015.

Ceres, however, although a dwarf planet, is not a Plutoid, as it is located in the asteroid belt between Mars and Jupiter. Astronomers believe that Ceres is the only object of its kind. Therefore, a separate category of Ceres-like dwarf planets may be defined and named at a later date.

The IAU has been responsible for naming planetary bodies and their satellites since the early 1900s, and oversees the assignment of names to surface features on bodies in the Solar System.

The IAU confirmed that in French plutoid is “plutoïde,” and in Spanish “plutoide.”

Sources: PhysOrg, International Astronomical Union

29 Replies to “IAU Throws Pluto a Bone: “Plutoid””

  1. No, a plutino always meant something different: an object in resonance with Neptune such that it that orbits the Sun twice in the time it takes Neptune to go round three times.

  2. Just when it seems the IAU cannot get any more ridiculous, they prove us wrong. Plutoids? Come on! How many members took part in this decision? It had to be less than the 424 or four percent who voted in Prague because this was not even done at a General Assembly. As Alan Stern accurately described, it’s just another backroom deal that reveals how out of touch the IAU really is. When you have to create categories like “ceroids” and “plutoids,” it’s clear the focus has been lost in ridiculous minutia. The correct solution is to simply assign ice dwarfs as a subcategory of planets for small icy bodies that don’t clear their orbits. These astronomers may be smart, but they don’t understand the first thing about language, and they are bungling all their attempts to communicate astronomy with the public. I hope Stern goes ahead with forming a rival organization.

  3. Plutoid?




    When are people going to learn that astronomers are lousy when it comes to naming objects in space?

    They see a huge “wall” of galaxies across the Universe and what do they name it?

    The Great Wall.

    Wow, what imaginations.

    They see a big red spot on Jupiter and guess what they call it?

    The Great Red Spot.

    They figure out how the whole entire wide Universe began and what do they call it?

    The Big Bang.

    And now we have Plutoid.

    Sounds like something you would not want to catch.

  4. Doesn’t this term just completely defeat the purpose of the whole IAU meeting 2 years ago when it was decided Pluto, Ceres and Eris were dwarf planets.

    Its hard to take the industry seriously when they make hypocritical decisions like this.

  5. I can’t agree more with Steve & Zifferman. The naming of this and it’s given description is ridiculous. It limits Plutoids to only our solar system. What if we find something similar in another system? We would be forced again to find another inane (and insane) naming and description meeting.

    Come on IAU, get with it and make the names and descriptions something that will work in at least most circumstances.

  6. terrible terrible name. i’d rather these “plutoids” be named “Patricks” or “Little Guys” or something.

    rubbish name

  7. heh – I like the pun.

    And please. We can barely find plutoids in *this* solar system. You’re not gonna make believe we’ll ever find them elsewhere – short of going there in person/robot/satellite.

    If need be it’s easy to extend the definition to “those big lumps of ice outside of the last gas giant.”

    I liked “plutino” better, but “plutoid” isn’t bad.

  8. heh,
    I don’t really find the name all that bad,
    its just the simple fact that all of these definitions apply to our solar system only, and the fact that the term plutoid is the exact definition of a dwarf planet, only with the asterisk added at the bottom with “beyond” the orbit of neptune.

    So out of curiousity, when Pluto crosses the orbit of neptune and becomes closer again, is it back to strictly a dwarf planet :p

  9. Much ado about nothing. Plutoid today, Semi Heliospheric Idiopathic Trans-rotational object tomorrow.

  10. A bit (ha) silly to get a name for *all* dwarf planets except Ceres, but then again everything in this name game has been getting sillier and sillier. Smart people can be pretty obtuse on occasion.

    But silliest of all is the fact that everything in these definitions applies to the Solar System and the Solar System alone. That is way beyond silly, especially in the moment when we’re discovering extrasolar substellar objects by the hundreds.

    And, Sili, direct detections of extrasolar dwarf planets may be centuries ahead, but the if the instrumental sensitivity and refinement of methods continues to increase at today’s rates, their presence will be inferred relatively soon, rest assured. There are already stars where we know that there’s a Kuiper Belt analogue; in some we inferred the presence of planetary bodies through certain characteristics of dust densities. It won’t be that long until we’re able to check out dust densities in those belts to infer the presence of “dwarfplanetary” (did I just invent a word?) bodies. We won’t see them, but we’ll know they’re there.

    (these studies, BTW, are easier from outside the system than from within, much the same way we know more about the global structure of faraway galaxies than our own)

  11. greg c,

    We get your stupid radio, TV and a little WiFi leakage too. So we know all about you ‘liquid water’ sissies.

    And now, greg c, you have angered us. Beware loose Kuiper belt objects. ( Yes we use the phrase ‘Kuiper Belt’ too)

  12. As I recall, only something like 4% of the IAU voted to demote Pluto to dwarf-planet status. Since when is 4% a quorum? Now they throw the bone “Plutoid” to the rest of the astronomical community. Hubris seems to be itching for Nemesis to visit it . . .

  13. Yeah, the IAU is basically trying to recover from its embarrassing f$@! up, and doing a poor job of it. I actually like the name ‘Plutoid’ itself, and I agree that Pluto is not a planet in the typical and dynamical sense of the word – that is basically beyond debate. But they are making an absolute debacle out of the process of assigning categories to these objects.

    I mean, it’s just not that hard is it? Just call any object in the Solar System that is not already in a major category a Dwarf Solar System Body or something similar. Then you could refer to them with additional specifiers, such as trans-Neptunian DSSBs, asteroidal DSSBs, DSSBs beyond 40 AU, DSSBs in high-inclination orbits etc. You could even have Extra-Solar System Dwarf Bodies or something similar for similar objects in other solar systems.

    The problem with getting specific, and it really is bleeding obvious, is that the more specific you get with a definition, the less objects it actually covers. The IAU are in the amazing situation of trying to come up with a general definition by being more and more specific.

    Plutoid? Congratulations – you’ve just created an additional (!) definition that covers almost nothing.

  14. I was just getting myself reconciled to “dwarf planet”. (Pluto is not a ‘planet’). Now this! “Plutoid”? Surely you jest!

    Pluto is a Kuiper Belt Object. Ceres is a big asteroid.


  15. Plutoids is ugly (even my spell checker doesn’t like it) but not any more so than most of the stuff that’s floating around lately. You know, when I look at all the images on these pages, I am truly awestruck by the beauty and wonder of the Universe. And then I start reading about all the theories we have come up with to describe how it all works and they are, in a word, ugly. 11 dimensions, dark matter, dark energy, strings…ugly, ugly, ugly, ugly. Imagine for a second that we have made contact with beings from another dimension and we want to dazzle them with the splendor of our existence. What sort of an image do you think they would have of us if we were to describe it first by just the formulas associated with the above theories? And then, we sent them pictures of our reality. Do you think they’d be able to make any kind of connection between the two? Where is the elegance and the beauty in the formulas? At least, that’s the question I’d ask.
    I have to remind myself from time to time that the mathematics, in themselves, aren’ t reality. If it takes 11 dimensions for a formula to make sense, that’s okay. Because, nature (reality) could still have only 3 spatial dimensions and 1 temporal dimension (as I believe it does) and work just fine.

  16. Jorge,

    No. Believe it or not I never saw that interview. Funny that two different people come up with the ‘Angry Pluto’ meme.

  17. They want the layman to become interested in astronomy so people can continue to convince politicians to fund space and astronomy programs. Yet, instead of making things easy, they create stupidity.

    You hear ‘dwarf planet’ and you have an understanding of what it is. You hear ‘plutoid’ for the first time, and you have no idea what it means.
    If I had to guess, I would say it was a small body from Pluto itself or had to do with it.
    Way to go, genius.

  18. Pluto,

    Please! You’re not even a planet. I don’t waste my time on Plutoids. Don’t make me get Jupiter involved.

  19. Now it seems only logical that all the dwarf planets closer than Neptune are called Ceresoids ;-. So the current situation of dwarf planets is clear and easy to overwiev:

    Plutoids: Pluto, Eris
    Ceresoids: Ceres

  20. Pluto and Eris are simply just different classes of planets like the Large and Small Magellic Clouds. Ceres is the same, just made out of different material. If dwarf or satellite galaxies are galaxies, and dwarf stars–including the yellow dwarf we call the Sun are stars, Pluto, Eris and Ceres are planets. Remember, they were thrown into the Kuiper Belt. If Jupiter had migrated towards the Sun and knocked Earth or Mars out into the Kuiper Belt, would these be planets? The criteria does not work for extrasolar planets. We are just learning about these world in detail. Let’s not rush to judgment because it does not fit our preconcieved notions. We will probably find one or two Plutoids as big as the Earth.

  21. The term ‘dwarf planet’ was always linguistically absurd; to say that a dwarf planet (e.g. Pluto) is not a planet is exactly equivalent to saying that a brown cow is not a cow!
    I think Astrofiend has got it right. ‘Plutoid’ solves nothing and is far too specific. Yes, I think the term ‘DSSB’ is not a bad idea.
    Are you listening, IAU?

  22. So much attention is given to Pluto. What about the other planets?

    When are we going to get Mercuroids (Celestial bodies in orbit around the Sun at a distance lesser than that of Venus 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 neighborhood around their orbit.)?

    What about Uranoids (Celestial bodies whose names are often made the butt of a crude joke.)?

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