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IAU Rules Pluto Still a Planet 244

Posted by CmdrTaco
from the we-can-all-rest-easy-now dept.
scottyscout writes "NPR reports that Pluto has dodged a bullet. An international panel has unanimously recommended that Pluto retain its title as a planet, and it may be joined by other undersized objects that revolve around the sun. Some astronomers had lobbied for reclassifying Pluto as its so tiny. And at least one major museum has excluded Pluto from its planetary display. But sources tell NPR that under the proposal, to be presented at a big meeting of astronomers in Prague next week for a vote, Pluto would become part of a new class of small planets and several more objects could be granted membership."
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IAU Rules Pluto Still a Planet

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  • If they have the power to make or unmake planets, why can't they do something really useful with Pluto, such as decree it to be a really huge scoop of chocolate cookie-dough ice cream?
    • by mrxak (727974) on Thursday August 10, 2006 @02:49PM (#15883387)
      People will debate Pluto's class until the end of the solar system. This is not a new story, in the sense that this is not the first time Pluto's status has been discussed. I think it should just be grandfathered in, if anything. Plus we have a bunch of other objects out there that could be considered planets too. Sedna, Xena, Quaoar, Varuna, Ixion... what do we do with those?
      • Sedna, Xena, Quaoar, Varuna, Ixion... what do we do with those?

        Xena is a warrior princess, she's hot so she gets to be a planet. The other celestial objects sound ugly, I would never date a Sedna, unless she gave good head.
      • by MBGMorden (803437) on Thursday August 10, 2006 @03:03PM (#15883537)
        Why not just call them planets? People keep throwing up the excuse that "if we call Pluto a planet then there's lots of things that would be planets.". So? Why should we readjust our definition just to keep numbers low? They don't care about some elite social status. If there's 9 in this system or 853, we should call them planets. If we want to nitpick on composition, then Earth and Jupiter certainly aren't the same type of thing either.
        • by 2short (466733) on Thursday August 10, 2006 @04:57PM (#15884495)
          It's not a matter of adjusting our definition. It's a matter of having one, which we don't.

          Various people (not generally astronomers) want a strict, reasonable definition of "Planet", but find that these either exclude Pluto, or include a vast number of things no one would really consider a planet.

          Astronomers generally don't care. They know Plutos properties, and don't use "planet" as a terribly specific term. This is purely a laymans controversy. It's significant only because something you learned in grade school was an over-simplification. Experts understand the details, and exactly which over-simplification is better is not very interesting to them.

          But since I'm a layman, my 2 cents:
          Juptier and Earth aren't like each other. They also aren't like anything else in their repsective orbital neighborhoods. There's a whole lot of stuff that orbits the sun at roughly the same distance as Earth, and none of it is much like Earth. Ditto for Jupter and 6 other object whose names you know. There's a whole lot of stuff that orbits at similar distance as Pluto, and quite a bit of it is a lot like Pluto.

            Somewhere in there is my own favorite over-simplification, which kicks out Pluto.

    • I agree implicitly.. They should do something big with it- like name a cartoon dog after it or something.
  • by ExE122 (954104) * on Thursday August 10, 2006 @02:38PM (#15883257) Homepage Journal
    According to wikipedia [wikipedia.org]:

    -Earth's Diameter: 12,756.274 km
    -Pluto's Diameter: 2306±20 km
    -Jupiter's Diameter: 142,984 km
    -Proportion of Earth to Pluter: 12756.274 / 2306 = 5.531
    -Proportion of Jupiter to Earth: 142984 / 12756.274 = 11.209

    Hmm... Jupiter has over twice the proportional difference with Earth as Earth has with Pluto. So I guess Jupiter wouldn't really consider Earth a real planet.

    Personally, I think we should leave the little guy alone. Throw UB313 [wikipedia.org] in there as well. Just give it a cool name that fits in with that whole "my very educated mother..." thing.

    Like the well learned and professional scientist said: "We'll call them dwarf planets or something".

    --
    "A man is asked if he is wise or not. He replies that he is otherwise" ~Mao Zedong
  • by Anonymous Coward
    No less a personage than Gustav Holst refused to include Pluto among The Planets.

    Why should I listen to this "IAU" instead of to him?
  • Most of the Astronomers are having trouble making it to Prague because of the security anthill that's been kicked over by the hair-gel bomb plot. This will probably have a big effect on how the IAU vote turns out.
    • by krell (896769)
      "Most of the Astronomers are having trouble making it to Prague because of the security anthill that's been kicked over by the hair-gel bomb plot. This will probably have a big effect on how the IAU vote turns out."

      All the better to have them converge on Prague without the benefit of the latest in hair care products, and to all end up coiff'ed like Einstein.
  • by crmartin (98227) on Thursday August 10, 2006 @02:39PM (#15883264)
    ... mickey, minnie, donald.

    In other news, Pixar announces corporate sponsorship of IAU.
  • I don't get it (Score:4, Interesting)

    by susano_otter (123650) on Thursday August 10, 2006 @02:42PM (#15883290) Homepage
    Why all the controversy anyway?

    Why not fix the "official" number of planets at nine, including the largest, nearest, and most well-known of the Kuyper Belt Objects, and leave it at that?

    Pluto's nature won't change either way, and our understanding of it won't change either way. This kind of legalistic controversy just for the sake of legalistic controversy is getting pretty annoying.

    Traditionally, Pluto has been a planet. Now, I'm not saying tradition trumps everything, but I see no reason why it shouldn't trump meaningless debate.

    Let me know if I've got it all wrong, and there is actually meaningful debate on this topic.
    • Traditionally, Pluto has been a planet not because we think it falls under the definition of planet, but rather that we don't have a proper definition of what a planet is.

      Assuming the latter is a meaningful debate, yes, there is a meaningful debate on this topic.
    • Re:I don't get it (Score:5, Interesting)

      by Billosaur (927319) * <wgrotherNO@SPAMoptonline.net> on Thursday August 10, 2006 @02:52PM (#15883422) Journal
      Why not fix the "official" number of planets at nine, including the largest, nearest, and most well-known of the Kuyper Belt Objects, and leave it at that?

      Because there's nothing the scientific community loves more than controversy, and this is beginning to rival the great Newton vs. Einstein debate, where some purists were not convinced that Einstein's theories were realistic. Clyde Tombaugh [wikipedia.org] discovered Pluto back in 1930 after a systematic search for planets beyond Neptune. He had to pore through photographic plates, trying to find the tiniest relative shift of an object in the starfield that would lead him to a body that was orbiting the Sun. That he found Pluto was remarkable for the time, and I think all this debate over Pluto's status is a disservice to him. Let sleeping dogs lie, let Pluto remain one of the original nine planets, and let's move on.

      • Re:I don't get it (Score:5, Interesting)

        by StupendousMan (69768) on Thursday August 10, 2006 @03:04PM (#15883547) Homepage
        Why not fix the "official" number of planets at nine, including the largest, nearest, and most well-known of the Kuyper Belt Objects, and leave it at that?
        Because there's nothing the scientific community loves more than controversy

        No, actually, I (and most of the astronomers in my peer group) do NOT enjoy the ongoing saga. We would like the whole matter to go away.

        The real answer is

        Because there's nothing the media loves more than controversy

        Editors know that "telling people that stuff they learned in elementary school is wrong" can pull emotional strings and get a rise out of some people ... and that leads to profit.

        Sigh.

        • No, actually, I (and most of the astronomers in my peer group) do NOT enjoy the ongoing saga. We would like the whole matter to go away.

          But it won't until the member body of the IAU stands up and says "Enough!" This whole controversy required exactly one meeting, where everyone could debate the issue, and then a consensus could be formed and a standard applied. But this has dragged on and on and on. Heck, this was a problem even before the influx of larger KBO's into the public consciousness. Astronomer

          • Re:I don't get it (Score:5, Insightful)

            by StupendousMan (69768) on Thursday August 10, 2006 @03:38PM (#15883838) Homepage
            Astronomers were debating Pluto's status back in the early 90's.

            No, the overwhelming majority of astronomers were not. We don't care. Really. The issue "what is a planet?" has for most of us the same urgency and relevance that "what is a continent?" has for geologists.

            No, the scientific community is in a constant state of polarization, between the old guard, wary of new things and ideas, and the new breed, mainly young researchers thinking outside the box.

            There certainly _are_ topics on which there is vigorous debate in the astronomical community -- for example, the nature of gamma-ray bursts, or the accuracy and precision of the cosmological distance scale, or the physics of supernova explosions. But this isn't one of them. The issue exists solely because a very few people who (for some reason) are seeking publicity go to the media periodically with a "new twist" on this question.

            Adding the question "is Pluto a planet" to the list of serious astronomical questions of the day does a disservice to those other questions.

            • The issue "what is a planet?" has for most of us the same urgency and relevance that "what is a continent?" has for geologists.
              I may not be able to define it but I know it when I see it.
          • Nonsense. (Score:3, Informative)

            The truth of the matter is that Pluto is a KBO but every time the popular press runs an article pointing that out, astronomers are flooded with calls from Auntie Mabel demanding to know where they get off changing what she learned in school.

            This isn't even remotely like a dispute between two theories - it's a simply argument over nomenclature and science has no problem at all simultaneously supporting multiple naming conventions.
      • Re:I don't get it (Score:4, Informative)

        by Jugalator (259273) on Thursday August 10, 2006 @04:27PM (#15884264) Journal
        Because there's nothing the scientific community loves more than controversy

        I thought the set of planetary "rules" should be generic and work for our solar system to avoid controversies.

        Scientists generally hate controversies as far as I know. That's why they try to search for unifying theories and theories that work, instead of keeping to invent random unprofessional theories to challenge other established ones with.
    • Well, that would be like legislating the value of pi, wouldn't it?
      • Not really. "pi" is a mathematical constant, that describes a specific, precise, and unmistakable relationship between a platonic circle and its radius.

        "Planet", on the other hand, is an arbitrary term, convenient for differentiating between different types of celestial bodies, but not actually bound to a specific natural phenomenon or physical law or mathematical principle.
      • "Pi" is a mathematical discovery, "planet" is a social construct. "Planet" can't be defined any more precisely than other social concepts like "art" and "obscenity".

        It's no big deal, really. No doubt when we reach other stars, we'll classify their planets according to which solar planets they resemble - and that will be as useful as any other definition.
    • Re:I don't get it (Score:4, Interesting)

      by Bender0x7D1 (536254) on Thursday August 10, 2006 @03:59PM (#15884031)
      Well, it doesn't matter at the moment, but it may matter when we get our butts off this planet and start colonizing the rest of the solar system. Why? Well, we will need a lot of treaties and laws and rules that govern how we handle ourselves out there. For example, we may decide that no one can claim ownership of a planet - kind of like Antarctica. Or that there are certain envrionmental guidelines that apply to planets - no dumping of toxic/radioactive waste.

      However, it may be beneficial to allow political or corporate entities to lay claim to asteroids for purposes of development or mining. In fact, we may state that it is OK to change their orbits for economic gain. Let's decide that we aren't allowed to smash planets (or moons for that matter) into pieces to make mining easier. There are a lot of plans for deflecting an asteroid away from Earth, so can we deflect it to hit Mars instead? It would certainly make it easier to obtain the metals we want if it is already smashed into pieces. Is it OK to deflect it into another asteroid, but not a planet?

      While these may seem like useless things to consider, we have learned the hard way that humans tend to exploit environments once they get their hands on them. It is only after destroying large areas that we decide we should protect what's left. Hopefully, we can create a good system to prevent that from happening with other planets and major solar system objects, while still getting the economic benefits of mining in space.
      • I have no problem with scientists wrangling out a technical scientific definition of planet, in order to productively pursue advancements in science.

        And I have no problem with politicians and their constituents wrangling out a technical political and legal definition of planets, in order to better pursue political and economic gain.

        My problem is with everybody thinking that any of this is at all relevant to the historical, social tradition of counting Pluto among the planets, or that we must now change our
    • There are 4 inner planets, with similar properties and formation histories. There are 4 outer planets with similar properties and formation histories. Pluto belongs with neither, but has the most in common with what are now known as Kuiper belt objects. More and more of these are being found, some with supposed sizes greater than Pluto. One suggestion that, in my opinion, is the most reasonable is to recognize the 4 inner planets, 4 outer planets, and recategorize Pluto into the Kuiper Belt clan. Over
  • Museum displays... (Score:5, Informative)

    by totallygeek (263191) <sellis@totallygeek.com> on Thursday August 10, 2006 @02:45PM (#15883326) Homepage
    And at least one major museum has excluded Pluto from its planetary display.


    Hell, I can show you museums that show kind, gentle dinosaurs living in harmony with man [answersingenesis.org]. So what?

  • by Quiet_Desperation (858215) on Thursday August 10, 2006 @02:46PM (#15883334)
    I declare holy^H^H^H^H science war against the IAU!
  • by sTalking_Goat (670565) on Thursday August 10, 2006 @02:46PM (#15883345) Homepage
    Has Pluto put out a press release yet. Are it and it supports going to have a celebration party? Is Jupiter going to be there? I've got a 'thing' for gas giants...
  • by iShaman (86503) <[jstanger] [at] [roadup.com]> on Thursday August 10, 2006 @02:48PM (#15883374) Homepage
    Really now...this has already been settled! Pluto is a Class C Geoinactive planet [wikipedia.org] I mean sheesh.....
  • You know... (Score:5, Funny)

    by TheOldSchooler (850678) on Thursday August 10, 2006 @02:53PM (#15883432)
    The real problem with Pluto is that it makes Uranus look huge.
  • So after this discussion is done what will be the answer to the question: How many planets are in the Solar System?
  • Pluto should stand for "and a bunch of other little ones like this". It's our Solar System's placeholder that, among other things, helps to illustrate how long it takes to go around the Sun at that distance.
  • Inaccurate (Score:5, Informative)

    by Zenaku (821866) on Thursday August 10, 2006 @03:01PM (#15883515)
    The headline and summary are extremely misleading. The agency hasn't ruled at all. The vote is yet to come. All that has happened is that a panel of 7 people has made a recommendation, which may or may not be excepted. And the recommendation has plenty of problems that might prevent it from passing a vote. From TFA:

    The panel's recommendation is being reviewed by the International Astronomical Union's executive committee. In an interview last week, executive committee member Bob Williams said the definition proposed by the panel had some potential problems, and he was not at all sure if the astronomers voting in Prague this month would approve it.

    "At this point, I don't feel confident enough to bet in favor of it," he said.

  • More than just tiny (Score:4, Informative)

    by mshurpik (198339) on Thursday August 10, 2006 @03:04PM (#15883550)
    It's more than Pluto being tiny. Pluto has a highly elliptical, out-of-plane orbit that crosses over Neptune's orbit, AND its orbit is 3/2 in phase with Neptune, suggesting that it was captured by Neptune's gravity.

    Is a "planet" something that was created with the solar system, or is a "planet" simply something that has a moon? Right now, we're using the latter definition.

    If you want to see another example of scientific retrenchment, check out Phylocode. For years biologists have been classifying species on a Linnaean 2D grid, inheritance and time, as if God somehow keeps all his evolutions in perfect lockstep. Phylocode, tree-based, uses the inheritance dimension only.
    • by Anonymous Coward on Thursday August 10, 2006 @03:23PM (#15883715)

      Pluto has a highly elliptical, out-of-plane orbit that crosses over Neptune's orbit, AND its orbit is 3/2 in phase with Neptune, suggesting that it was captured by Neptune's gravity.

      Not quite, Pluto actually formed in the original Kuiper Belt [wikipedia.org], making it part of the original Solar System, not an object captured by Neptune. Its current orbit is the result of Neptune's gravity, yes, but Pluto was formed in orbit of the sun.

      Is a "planet" something that was created with the solar system, or is a "planet" simply something that has a moon? Right now, we're using the latter definition.

      Actually, neither Mercury nor Venus have moons, yet they're accepted as planets. The problem is not that an "incorrect" definition of planet is being used, it's that there is no clear definition of what constitutes a planet. This recommendation (the title is misleading, as no actual ruling was handed down) is merely part of a much larger debate on the definition of a planet [wikipedia.org].

  • That guy gets all the attention. ;-(
  • Absolute rubbish! (Score:2, Insightful)

    by jrothwell97 (968062)
    Pluto isn't even anything special in the Kuiper Belt. There are plenty of objects, many of them probably larger than Pluto, that are classed as KBOs, so why isn't Pluto classed as such? If they found an Earth-sized rock orbiting a thousand AUs from the Sun, THAT should be classed as a planet.
  • [b]Submitter[/b], I seriously doubt that "Pluto" gives a damn what we think of it.
    Humans who have some ego/emotion/investment in the idea that Pluto be a planet, well that's another thing.
    • Besides, consider how long Pluto had to dodge the bullet . . . with a bullet having an average speed of 1500 feet per second travelling a distance of 2.66 billion miles taking 1.40448 × 10000000000000 seconds to get there, it's not like it needed lightning reflexes or anything.

  • by transami (202700) on Thursday August 10, 2006 @03:17PM (#15883659) Homepage
    Yep, I called it. Many moons ago I said if they rule it's a planet it means science is dead. Real science doesn't label something based on feel good social acceptance, but strives for as much exactness as possible.

    As of now, the modern age is officially over and dystopic post-modern has begun.
    • There not just saying Pluto is a planet, there saying objects within this size are a new classification.

      " but strives for as much exactness as possible."
      when you create a group, by definition not everyting in that group will be 100% defined by the group name.

      It puts a silly arguement to bed. Thats all.

      I don't really think there is a scientific term for 'planet' any how.
      Do you bitch that a gas giant is called a planet?

      Find your dystopia elsewhere.
    • Errr. Okay. (Score:3, Interesting)

      Please give us a scientific definition of a planet that includes Mercury but excludes Pluto and Titan.

      "Planet" - like "hacker" has always been a very vaguely defined term and meant different things to different people. The line between "planet" and "Kuiper belt object" is as blurry as the line between two species of galapagos finch.
      • OK, here's the answer. Make the definition arbitrary and exact, using values we can measure and be certain of, that won't change with whatever the planet-formation-theory de jour is.

        1. A planet is an object that orbits a star and has a mass greater than X and has a radius large enough to not be a black hole
        2. A moon is an object that orbits a planet, planetoid, or astreroid
        3. A planetoid is an object that orbits a star and has a mass greater than Y but less than X, and has a radius large enough to not be a
    • It would be a good chance to introduce a better model of the solar system for the teaching purposes.
      The solar system consist of the Sun, the inner rocks, the asteroid belt, the gas giants, the Kuiper belt, and the Oort cloud.
      This would probably give a better picture of the solar system, than the old model with a sun and nine planets.
      (For historical resons, the inner rocks, the gas giants, and the first discovered object in the Kuiper belt, are called planets).
    • Or you can spin it such that the scientific community doesn't have the balls to admit that they made a mistake. Such is human.

      Frankly, I think this whole argument is a bit of a distraction. It strikes me to be a lot of wasted time and energy. What type of object it is called doesn't change what the object is, unless somehow quantum mechanics applis to an object several thousands of km in diameter.
    • Real science doesn't label something based on feel good social acceptance, but strives for as much exactness as possible.

      Social acceptance is a good metric for whether a classification actually makes sense. Pluto looks, and acts very much unlike asteroids, and much more like recognized planets.

      Science, however, really doesn't care about any of this. They will continue calling everything a 'body', as the boundry between planet and asteroid is really of no relevance to any of their work.

      Of course, I'd like

      • Pluto looks, and acts very much unlike asteroids, and much more like recognized planets.

        I agree that Pluto does not look or act much like an asteroid, but I disagree that it looks or acts much like the recognized planets. The recognized plaents are the rocky planets plus the gas giants, and they all formed and lie in the planetary plane. Pluto looks and acts like thousands of other Kuiper objects. Kuiper objects are not formed in the same manner. Kupier objects do not lie in the planetary plane, except perh
  • If Pluto needs to worry about damage from bullets, then it must be a lot smaller than I thought. Maybe they should reconsider.
  • by Minstrel Boy (787690) <kevin_stevens@hotmail.com> on Thursday August 10, 2006 @03:52PM (#15883964)
    Any object maneuverable enough to dodge a bullet can't possibly be considered a planet.

    KeS
  • I mean heck, it would probably be the first planet to be demoted. How frigging humiliating. Kind of like being the first schmuck voted off Survivor and having to appear on the finale.
  • by posterlogo (943853) on Thursday August 10, 2006 @04:16PM (#15884159)
    Pluto really has more of a historical importance than anything else. We do have good definitions of what a planet is (condensed remnants from star formation's accretion disk), and it should be pretty easy to prove that Pluto does not fit the bill. Size is not the important thing -- Mercury isn't huge, but it certainly is a planet. I guess NASA's New Horizons mission should help clear this up in a decade or so, but I don't think that will have to result in changing the status of Pluto -- leave it alone as a planet (even though it isn't), purely for historical reasons. The search for an object to help explain discrepencies in Neptune's orbit formed a major part of Pervical Lowell's [wikipedia.org] life, and he made significant contributions to astronomy. I think the IAU astronomers may want to leave Pluto a planet as an honor to those who discovered it at a time when such discoveries were very difficult. More and more KBO's will be discovered, but will inevitably be farther and farther away. So -- 9 planets it is, even though it's really 8.
  • Wow, it must be even smaller than I thought!
  • by ChrisA90278 (905188) on Thursday August 10, 2006 @04:40PM (#15884350)
    People seem to be mising the point. The problem here is not to vote on if Puto is a planet or not. The problem is to define what is a planet. Many people have proposed ways to define "Planet" but then what you apply the proposed definition to our solar system yu get undesired results. Almost every resonable proposed definition results in a solar system with either 8 planets or more than 9. Next problemis that you want your new definition to "work" outside the our solar system on the 100+ planets that have been discovered around other stars.
    • A planet should fit the following

      1a) Orbits a star or
      1b) Has a common center of orbit shared with another body that is outside both their masses, and orbits a star (this covers double planets, but not our Moon)
      2) Has enough mass to maintain a roughly spherical shape (ignore the little stuff)
      3) Has insufficient mass to produce heat (ignores the near-stars & stars)
      4) Does not share its orbit with other bodies (excludes 'belts', regardless of object mass)

      I imagine I've missed a few things. You'd need a na
  • by chongo (113839) * on Thursday August 10, 2006 @04:52PM (#15884446) Homepage Journal
    BTW: This is not intended to be a complete history of the topic, I'm only pointing out a few highlights that others might find interesting.


    A number of years ago, the question of a definition of a planet was raised as a result of discoveries of "planets" outside of our solar system as well as a growing number of Kuiper Belt Object (KBO) discoveries in our solar system. The IAU Division of Planetary Systems Sciences technical committee wisely chose to delay a decision on a definition until a more significant body of data was obtained.

    In the mean time, a well meaning but widely misunderstood suggestion from an esteemed Astronomer suggested that the planet Pluto also be given a nice round minor planet number (i.e., reserve the next multiple of 10000). His intent was to recognize the special nature of Pluto as a large member of the KBO (Kuiper Belt Object) family. He never intended to demote Pluto from planet status. However, the press took the phrase "making Pluto a minor planet" and blew the controversy way out of proportion.

    An executive committee recommendation on Planet definition was formed to draft a proposal for a definition of a planet. Minutes from the IAU executive committee indicated that they favored definitions that were based on measurable physical properties over arbitrary values. For example, they signaled that they were NOT inclined to look favorably on proposals such as "limit the number of 9 planets", or proposals that set an arbitrary minimum size of a Planet.

    Last January at the AAS conference, an IAU liaison announced that the IAU executive committee was scheduled to produce a report on its recommendations just prior to the IAU 26th IAU General Assembly in Prague (Aug 14 to 25, 2006). The liaison recommended that any final comments and recommendations be submitted to the exectuive committee at least a month prior to the IAU general assembly.

    I was part of a group that submitted a recommendation that the definition of a Planet encompass a requirement that "it must orbit a primary fuser with sufficient mass to deform it into an spheroidal / oblate spheroidal shape". We realized that our proposal could result in redefining several bodies as planets including the large asteroid Ceres. We proposed that a new sub-class of Planets could be defined (again based on measurable physical properties) to acuminate these new dwarf planets.

    We were told that a number of other groups had submitted similar of very similar proposals. I have not examined the executive committee report in detail, however it appears that IAU executive committee agrees, in principle, with such proposals.

    On Tuesday 2006 August 22, 12:45-13:45 (local Prague time), in Forum Hall, executive committee recommendation on Planet definition will be presented. Based on the unanimous recommendation of the executive committee, I am hopeful of a favorable outcome form the IAU General assembly.

  • Sounds like canonization to me.
    People arguing for and against the title, an official body deciding.

    Geeze, just come up with a definition for a planet and stick with it.
    Or just decide that whatever enough people call a planet is one.
    You can call it a giant-dirtball-of-doom for all it matters.
  • by mc6809e (214243) on Thursday August 10, 2006 @04:55PM (#15884482)

    It's been suggested that the best way to decide what is or is not a planet is to determine if the mass is held together the force of gravity or electrostatic forces (like metal bonds).

    If by gravity then it should be considered a planet. If by chemisty then it's just a hunk of rock.

    This makes the most sense to me.

  • by Phat_Tony (661117) on Thursday August 10, 2006 @06:00PM (#15884913)
    Not that anyone cares, but I propose the following definition for a planet:

    - Its primary orbit must be around a star
    - It must be approximately spherical due to its own gravitational field being sufficient to make it so (the allowable eccentricity from a perfect spheroid would have to be defined)
    - It is not itself a star

    I see the following potential problems with this:

    - It may be hard to judge shape accurately enough to tell if an object is close enough to spherical to qualify
    - There may be very soft things that stay gravitationally round even when very small (what happens to a drop of mercury in space?)
    - Given something such as a spheroidal asteroid smaller than Pluto, it may be difficult to distinguish if it's randomly spheroidal or spheroidal due to its own gravity.

    Still, I like it better than other definitions I've seen.

    Now proceed to tear it apart, add to it, etc.
  • Criteria (Score:3, Funny)

    by jafac (1449) on Thursday August 10, 2006 @09:56PM (#15886079) Homepage
    Should not be based on size alone, but should also be based on spin, complexity of orbital perturbations (and I understand that Pluto's orbit is fairly unique in many ways).

    Because my wife always told me that it's not size, it's the technique.

Time is nature's way of making sure that everything doesn't happen at once. Space is nature's way of making sure that everything doesn't happen to you.

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