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Definition of Planet to be Announced in September 200

Posted by Zonk
from the bigger-than-a-breadbox dept.
MasaMuneCyrus writes "After over seven years of debating, the International Astronomical Union announced that it expects to announce the official definition of a planet in September. After many-a-deadlock, they handed the task of deciding exactly what a planet is to a new committee, which includes historians and educators. 'They wanted a different perspective from that of planetary scientists,' said Edward Bowell, an astronomer at Lowell Observatory who is also vice president of the IAU's Division III-Planetary Systems Sciences group. If all goes according to plan, the wording will be proposed in their 12-day General Assembly meeting in Prague."
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Definition of Planet to be Announced in September

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  • by Anonymous Coward on Saturday June 10, 2006 @02:22AM (#15507867)
    ....or is it? :-P
    • Man, if they say Pluto isn't a planet I'll be out in the streets. First they tell me there was no such dinosaur as the Brontosaurus, now Pluto.

      This is all too much, I hate the future.
  • by mgabrys_sf (951552) on Saturday June 10, 2006 @02:28AM (#15507881) Journal
    Pluto?

    I've been 50-50 on it myself. I'm a fan of anything Arizona (having lived there), but apart from the moon system, I'm hard pressed to call it a planet.
    If Pluto sticks - then there's probably 100s of Kuiper Belt objects that qualify.
    • All discovered Kuiper Belt objects are smaller than Pluto except for one: 2003 UB313, also known as 'Xena'. And the discovery of Xena also happens to be the reason that led scientists to question the current definition of planets. So it's practically impossible that 100's of Kuiper Belt objects would suddenly be called planets.
    • "Moon system" (Score:5, Interesting)

      by vlad_petric (94134) on Saturday June 10, 2006 @03:07AM (#15507972) Homepage
      The baricenter of Pluto and Charon is outside Pluto (in space). That's one reason, I guess, for scientist to also call it a "dual planet" system.

      OTOH the other two moons are small enough to be called moons.

    • it's the only planet (in our solar system) discovered by an American.

      Therefore whatever definition is used, Pluto will always be included as a planet.

      Same reason why American's will always keep the penny. Ego and historical pride.

    • but other minor objects have moons too - not just asteroids, but Kuiper belt objects and other trans-Neptunian objects besides Pluto.

      Pluto is a planet only because of tradition, and I for one will be somewhat disappointed if Pluto is NOT demoted, because scientific chategorization based on emotion, "what will the kids think" and public opinion is the reason we're dealing with this creationism bullshit.

      The only logical definition of planethood that would include Pluto is a broad one, such as any object massi

    • by Anonymous Coward
      Vowels:

      a, e, i, o, u, and sometimes y

      Planets:

      Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and SOMETIMES Pluto

      Why waste any more time (or money) on this? Add "sometimes Ceres" et al. if you want. Doesn't matter
      what you call it, its still a hunk of rock in space (except for the ones that aren't hunks of rock, but I digress).
    • by Phreakiture (547094) on Saturday June 10, 2006 @09:24AM (#15508749) Homepage

      Maybe they should break the deadlock over Pluto by playing one (1) game of Rock, Paper Scissors.

  • by Schraegstrichpunkt (931443) on Saturday June 10, 2006 @02:38AM (#15507901) Homepage
    ... debian-legal will notice that Earth is not a planet under the new definition.
    • Re:In October... (Score:3, Insightful)

      by paul248 (536459)
      Wow, I'd never looked at debial-legal before, so I went there and the first thing I saw was people arguing over whether the GPL itself violates the Debian Free Software Guidelines...

      Your comment is starting to make perfect sense.
    • by Anonymous Coward on Saturday June 10, 2006 @04:55AM (#15508162)
      Under the new definition there are no planets. Jupiter and the other gas giants are being defined as brown dwarves and Pluto is a comet. Earth and the other rocky former planets are being called "merged asteroid masses". In the end it was far easier to explain away the existing planets than to define what is a planet. Since no known bodies fit the current nondefinition of a planet it has been declared that there are infact no known planets so extrasolar life is impossible given the lack of planets to house said life. The new findings were applauded for clarifying and simplifying science. Now that it is known that there are no planets no further NASA funds shall be wasted on studying nonexistent planets including the Asteroid "Mars". The savings will be spent on more important scientific work, military satelites.
  • by Shrithe (972491) on Saturday June 10, 2006 @02:41AM (#15507912) Journal
    I hope Pluto finally gets excluded from planet definition. It's too small (only twice the size as it's "moon", Charon, and a little less than a fifth as massive as Luna), it's out of the plane of the elliptic (a trait shared with objects like comets, but not any planets), and it's not even orbiting in a stable configuration with regard to Neptune (for part of it's orbit, Pluto is in fact eighth, and Neptune ninth).

    Then there's the fact that it only really got counted as a planet in the first place because astronomers at the time of it's discovery were hung up on the idea of discovering a ninth planet. They thought they found a disturbance in Neptune's orbit, which they attributed to a ninth planet, but ended up being caused by the fact that they were working from bad data about Neptune's mass. Pluto's much too small to have any effect on Neptune's orbit.

    This might finally put the final nail in the coffin of the idea of nine major planets in our solar system. We can only hope.
    • I don't even think this is a real "Sun" we have here. I'd say it was a "yellow dwarf".
      • Sol is HARDLY a dwarf star. In fact, it's spectral type (G) is heavily outnumbered by the smaller, red dwarf stars* (K,M). If anything, Sol is relative husky. However, it is not morbidly obese, like the other, rarer classes of stars (O,B,A,F)

        * Not related to television shows about annoying holograms and highly evolved cats
    • "I hope Pluto finally gets excluded from planet definition. It's too small"

      Well, sir, I hope that you are similarly excluded from the human definition. What have I ever done to you to deserve this?

      -Pluto

      (PS that was a really low blow, commenting on my size. I could make a crack about you and satisfying your wife, but that wouldn't be "big" of me.)
    • This is very limited thinking. Basing the definition of planet only on our own solar system leaves lots of things to be desired.
      E.g., maybe other planetary systems have more planets out of the elliptical plane, if they even have one, and might have even more irregular orbits than that of Pluto.
      • AFAIK, when planets are born in a star's circumstellar disk, this automatically puts them all in the same plane and orbital direction (the same direction as the star's rotation). Any planets orbiting differently, such as in retrograde or even polar orbits, will have been captured,
        • That assumes that only bodies born within their star's circumstellar disk are planets. What if a body escapes the attraction of a star and orbits another?

          Granted, I don't really know what I'm talking about, but it seems at least possible.
          • That assumes that only bodies born within their star's circumstellar disk are planets.

            No, but that's the theory for how our solar system formed, and there's plenty of visual evidence now that circumstellar disks are quite common. However, if another star wanders too close, it is possible for such planets to be bumped out of orbit. Also, just recently astronomers discovered some systems with central bodies not too much larger than jupiter [slashdot.org], so it seems planet-sized objects can form all on their own too.

      • maybe other planetary systems have more planets out of the elliptical plane

        It's the plane of the ecliptic, not elliptic (it's okay, the OP made the same mistake). This was named such by the ancient astronomers as it was the narrow band in the sky where eclipses of the Earth's moon were observed to happen. They observed that it turned out that all of the wandering stars (i.e., planets) traveled within this band as well. It's not strictly speaking a plane, but a range of planes at relatively small angles t
    • I do not really see why Pluto would not be able to qualify as a planet. As you have pointed out, the definition of the word planet is more historical than anything other.
      After all, a telluric planet as Mercury shares very few similarities with a gaseous planet such as Jupiter, and we are still calling both of them planets.
    • There is so much cultural and historical pull that some scientific body changing their definition probably isn't going to work for the public unless they can explain the new definition in non-jargon, and explain that people in the profession made an honest mistake and this is the fix.

      Basically, I'd call Pluto as "grandfathered" in forget about it. I'm not even convinced that it really matters, some scientists and pedants harrumphing doesn't change the solar system, just what they call certain bodies.
    • But if they exclude Pluto from the planets, what does that mean for Sailor Pluto [uwaterloo.ca]?

      Will she become Sailor Kuiper? Would she be the first of the Outer Outer Senshi, to be joined by Sailor Oort at a later date?
  • by cy_a253 (713262) on Saturday June 10, 2006 @02:43AM (#15507916)
    Planet: object orbiting a star, massive enough to be spherical under its own weight, but not enough to undergo nuclear fusion.

    Major planets: the eight (Mecury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune).

    Minor planets: the moon, all the spherical satellites of the major planets, Pluto, all the spherical asteroids in the asteroid belt and all similar spherical kuiper belt objects.
    • by RsG (809189)
      I think that last part that would screw you up. How large, or how spherical, would a random orbiting body have to be to fit the defninition of "minor planet"? You're gonna need an arbitrary cutoff no matter what you do.

      Plus, how do brown dwarf stars fit into that definition? A brown dwarf can't fuse hydrogen, and in many regards is similar to a planet; however it can fuse deuterium, so it does undergo fusion during it's initial collapse. Wouldn't a brown dwarf fit your definition of a major planet, sinc
      • First, "spherical" isn't exactly the right word. Ellipsoid is probably correct. The key thing is that the gross geometry is determined by gravity. We are indeed seeking an arbitrary cutoff, so that's no problem.

        A brown drawf fusing deuterium is damn well undergoing fusion. It's a star. I think we also need to exclude anything that majorly violates newtonian physics, like a neutron star or black hole.

        Last week we got a name for "rogue planet". It was something like "planemo", starting with "plan" and ending
    • Wouldn't that also make some brown dwarfs planets as well?
    • Why do you relegate Pluto to the 'minor' list, but leave Mercury on the 'major' list? IIRC, both Ganymede and Titan are larger than Mercury.
    • massive enough to be spherical under its own weight
      But even Earth is not completely spherical (the poles are closer than two points on opposite sides of the equator). So exacty how 'spherical' do they have to be and how can one possibly work out if an object outside of the solar system is sufficently so?
      • That's OK. Saturn is much worse. The right quality is "ellipsoidal", not spherical.

        Mountains are the concern.

        Earth's mountains are not significant. The highest mountain is about 1/1000 of the Earth's radius.
    • I think you'd cut through some of the arguments by semantics, in which case your candidates are fine - but a little wordsmith is in order:

      Real Planets: the eight (Mecury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune).

      Bullshit Planets: the moon, all the spherical satellites of the major planets, Pluto, all the spherical asteroids in the asteroid belt and all similar spherical kuiper belt objects.

      Now who in their right mind - or what self-respecting scientist - is going to split hairs over a "Bullshit
  • by Frans Faase (648933) on Saturday June 10, 2006 @02:44AM (#15507920) Homepage
    As there are so many parameters that a celestrical body can have, any definition of what is a planet and what is not, is highly arbitrary and thus unscientific and based on emotional considerations. And because of this, there will always be large groups of people who will reject any such definition. Especially, because it will all be wheter Pluto should be called a planet or not.

    I think the most logical thing would be to consider "planet" a part of the name of a celestrical body, just like we do with "ocean" and "sea", and not use it as a classification word.

    • any definition of what is a planet and what is not, is highly arbitrary and thus unscientific and based on emotional considerations.

      There are many ways they could classify planets which wouldn't be arbitrary at all. Base it on the minimum ammount of gravity it must have, and it's orbital path, and you have a non-arbitrary classification.

      Unless I'm mistaken and you are trying to say that ALL classification is arbitrary, and classifying something like stars by how big and bright they are is equally "arbitrar

      • I'd agree that there are non-arbitry ways to create a definition and then attach the name 'planet' to it. But you have to ask yourself why you would be doing this. Similar as with the 'ocean and sea' example, what exactly is the point of calling something a planet in the first place?

        This is not to say that calling anything anything is pointless. But it is pointless to invent a named category of objects if that category serves no other purpose than a placeholder for the name.

        It would seem that in the case of
  • As a planet candidate, I don't see the problem with having 20 planets in the solar system! I don't see why so many people are against having a lot of planets in our solar system...is it that difficult to remember a few more of us? Sheesh!
  • to come up with "A massive body that reflects more radient engergy than it generates".
  • for what it's worth (not much):

    planet = mostly rock/metal sphere with a significant atmosphere (what "significant" means becomes a point of contention then of course)

    asteroid = solid rock/metal object that is not spherical

    moon = rock/metal sphere without an atmosphere

    a gas giant should be considered as something different than a planet (mostly gas, obviously spherical)... a star is simply a gas giant that has achieved thermonuclear fusion... and in between you have your brown dwarfs and other objects occuring at the end of a star's life time/ before it's lifetime/ malformed and never quite stars, etc.

    and comets should also come to mean any agglomeration of ice and rock and dust that is loosely packed, not just those we see streaming towards the sun on a regular basis... as we explore the oort cloud, we'll find plenty of these "dormant" comets

    and most importantly: all of these objects should be defined independently of what they orbit

    so mercury isn't a planet, it's a moon of the sun

    likewise, pluto is a moon of the sun

    and ceres and vesta are moons of the sun (small perfectly spherical "asteroids")

    titan isn't a moon, it's a planet of saturn (it has a significant atmosphere)

    the most important thing i think, no matter what nomenclature is agreed upon, is that as we discover weirder extrasolar objects out there, the "what it orbits" part of an object's identity should come to mean something totally different than "what it's made of"

    and size should never have meaning

    then of course, we have to come to grips with direction of orbit, orbits outside the elliptical, orbits with bizarre shapes, binary/ tertiary objects, binary/ tertiary/ quartanery star systems, etc.
    • The problem with that definition is that the orbit effects the composition. Titan only has a significant atmosphere because it's cold - were it in the inner solar system it would probably be like Mercury, which you're calling a moon. So something can go from moon to planet just by being futher from the Sun... not an ideal definition.
      • it is what it is what it is

        nobody said anything about the need to capture the why of something being the way it is in a naming convention

        you call something a "white dwarf", for example

        you don't need to capture the idea it is a white dwarf because the star was not massive enough to supernova, that's not something you capture in the name of an object

        you don't call it "whitedwarfleftoverfromdeathofstarthatwasnotbigeno ughtosupernova"

        you don't say "thisisamoonnotaplanetbecauseitistooclosetothesunt ohavenaatmosp
    • for what it's worth (not much):


      Indeed not much, unless the IAU did not got to any consesus after 7 years and posted it here to see real answers and then just copy and paste it.

      I see no other reason why this onouncement of the anouncement. If you have the defenition, just say it already.
    • I have a few differences.
      First I would allow multiple planet systems.
      If titan isn't a moon, but a planet of saturn I would rather call it a double planet system.
      Second, size should matter, at least in some cases.
      Otherwise a small speck of dust could be like a moon.
      Third, I disagree with your "independently of what they orbit" remark.
      I would like a moon to be changed to a planet when it stops orbiting somthing.
      Fourth, what about rings versus asteroids?
      Is the belt just rings of the sun?
      Fifth, do rouge, no wai
  • 10 bucks says the definition is broad enough to include Pluto but narrow enough to exclude any other "extraplanetary" bodies in our Solar System; they want to preserve the status quo of the Solar System, don't they?
  • Things are either black or white, up or down, good or bad. There are no shades of grey.

    Can't we just say that there are different objects in the universe that have similar properties? What's wrong with saying an object is 30% like the planet we're on, but 70% like Jupiter?

    Must everything have a category?

    It's a real flaw in western thinking. We can't just simply let things be - we have to pin them to cork boards like preserved butterflies. Why not just describe what you find as you found it? Natur

    • Yes. Everything must have a category. Nature doesn't create categories becuase it doesn't seem to need to understand itself. As humans, we need to format data about the world in ways we can understand. Categorization is part of this.

      You can let things be all you want, I'd prefer striving to make things better.
      • But we're not striving to make things better.

        We're arguing over whether Pluto is a planet or not.

        That's the problem with that kind of fixed thinking - why can't we just say agree that nobody really knows and get on with actually learning stuff that's actually useful.
        • Because, when we know of thousands of extrasolar objects, we will want to do some nice analysis of that data, and then we want some reasonable definitions.
          • Shouldn't the analysis on extrasolar data be based on the properties of celestial bodies, not if they're called planets or not? It's just a gut feeling, but defining "planet" and then looking specifically for those for life could maybe even hurt the discovery of such celestial bodies with life (which I believe is the extrasolar body analysis that's most interesting to humanity), in case the definition was such to not cover all possible bodies.

            Not going specifically for what's defined as "planets" feels like
            • Shouldn't the analysis on extrasolar data be based on the properties of celestial bodies, not if they're called planets or not? It's just a gut feeling, but defining "planet" and then looking specifically for those for life could maybe even hurt the discovery of such celestial bodies with life (which I believe is the extrasolar body analysis that's most interesting to humanity), in case the definition was such to not cover all possible bodies.

              Not going specifically for what's defined as "planets" feels lik
    • "It's a real flaw in western thinking."

      I noticed you categorized this as western thinking. That's rather boolean of you. Why not find the appropriate shade of gray and call it "thinking influenced by the scientific desire to categorize things?" The problem with complaining about black and white and suggesting shade of gray is that you're merely substituting one level of granularity for another. There is still a black and white.

      The problem is _nouns_ themselves imply a need to categorize. We have star, plane
  • by VincenzoRomano (881055) on Saturday June 10, 2006 @04:12AM (#15508090) Homepage Journal
    Is it that important to have a precise definition of what is a planet and what is not?
    Unless you are going to precisely define every single astronomical object [wikipedia.org]. from dust to galaxy filaments.
    I suspect that someone is going to claim the possession over those planets (apply the definition here).

  • 1 Earth = 1 Planet (Score:3, Interesting)

    by layer3switch (783864) on Saturday June 10, 2006 @04:39AM (#15508140)
    Why not categorize and measure like G(ravity), N(ewton), K(elvin)?

    If an object is one half earth's mass, just call it 1/2 Planet. If the object orbits around a planet, just call it satellite or moon or subplanet. After all, planet means "to wander". What doesn't wander around the universe?

    *Middle English, from Old French planete, from Late Latin planta, from Greek plants, variant of plans, plant, from plansthai, to wander.
    ref. dictionary.com
  • Planet: /'plaen.It/ Noun [c]

    "Not a star."

  • Disclaimer:
    I know nothing about astronomy.

    Wouldn't it be easiest to just state that anything that exists in the solar plane is a planet and anything that isn't is just a captured satelite?

    I know that this would exclude Pluto and all other Ort Cloud objects.

    This is a complicated question, but what is wrong with an easy answer?
    • That definition would include most of the asteriod belt, and even micrometeoriods (sp?).
    • Wouldn't it be easiest to just state that anything that exists in the solar plane is a planet and anything that isn't is just a captured satelite?

      So, how do we define "Solar plane" then?

      1 degree either side of the plane of Earth's orbit? That includes Earth and Uranus.

      2 degrees? Mars, Jupiter, Neptune get added.

      3 degrees? Add Saturn.

      4 degrees? Venus finally gets to be a planet.

      7 degrees? Mercury joins the list.

      We have to go out to 18 degrees to get Pluto on the list, but choosing 7 degrees is ju

  • ...but I know what I like! :)

    But what I really want to know is this: planets orbit stars, and moons orbit planets, right? So what would you call something orbiting a moon?

    Actually, I think we should have three categories: star, planet, asteroid. It shouldn't matter what it's orbiting. If it's big, round, and burning, it's a star. If it's big, round and not burning, it's a planet. If it's not so big and not so round, it's an asteroid. Luna, Ganymede, and Titan are both moons and planets. Phobos and De
  • by Punch-Drunk Slob (973904) on Saturday June 10, 2006 @07:41AM (#15508431)
    Dear IAU, You suck. Love, Merriam-Webster
  • Missing the Point? (Score:4, Insightful)

    by TMA1 (179096) on Saturday June 10, 2006 @07:41AM (#15508433)
    I understand why there's an effort to define what a planet is. For one thing, it's important for common usage. It helps fill in the blanks on headlines such as, Scientists Observed the Star ______ has a _________ . However, our solar system is easiest to understand if you realize it's composed of the following.
    • Four terrestrial planets
    • Four jovian planets
    • The Kuiper Belt objects
    • and the remaining comets, asteroids, dust, etc.
    (Yes, I know I'm using the word planet, but the actual dispute is being driven by the discovery of a Kuiper belt object larger than Pluto and farther from the Sun).
  • Surface Gravity (Score:3, Interesting)

    The definition should be based on surface gravity, or average surface gravity, that way the definition of a planet would be usefult. The watershed could be say, an average surface gravity that would make it feasable to build a facility of some kind where a long term human prensence can be sustained without major risk to health.

    This would also be useful as objects could be classed with a relevance that would be important to any future explorer. Even non elliptical objects could still be given a metric to judge their habitability.
    "Sir, object is a Class G planetoid! Our noses will be crushed by our feet if we set foot on it."
    "I see"
    "However sir, the Halo Ring, despite not being isomorphic to a sphere, does qualify as a planet due to a reasonable average surface gravity."
    "Cue music. We're going in.


    But even dyson spheres could qualify as planets.
  • by MrNougat (927651) <ckratschNO@SPAMgmail.com> on Saturday June 10, 2006 @08:53AM (#15508659)
    A planet must:

    Revolve around a star
          within a certain maximum aphelion
          having a maximum elliptic
    Be large enough in volume
    Not be artificial in nature (this provides that any intelligence in this universe creating an object that would fit the prior criteria would not be allowed to call it a planet)

    Define maximum aphelion and maximum elliptic and minimum volume. What else is there?
    • The idea of telling another intelligent species that the giant object in space that they created is not a planet because we say so makes me laugh. We can't get a human farther into space than the moon and we get to set the universe's policy on labelling planets? Sagan was right. Humans do want to feel special.
    • Define maximum aphelion and maximum elliptic and minimum volume. What else is there?
      The criteria categories may not be arbitrary, but the values are. Why should the maximum aphelion be X km and not (X + 1) km? The same goes for elliptic and volume values.
    • Define maximum aphelion and maximum elliptic and minimum volume. What else is there?

      Define artificial nature. The religious right would claim that all planets were created by an intelligent entity.

      What about planets that formed on their own due to the creation of an artificial star?

      What about planets that formed because the intelligent entity was so fricking huge that it accreted layers of debris via gravity, which compressed into rock from their own weight, reaching the required volume, but never intending
  • The IAU issued a press release stating that the definition would be delayed until next year while they change to the metric system. They also noted that when it is finally released, it will be the most awesome multiplayer online definition of a planet that the world has ever seen.

    The IAU has offered its Division III-Planetary Systems Sciences group $500,000 in the form of a promissory note if the definition sees commercial release by December 31, 2006.
  • Just call everything a fucking moon and be done with it!

    Seriously, this entire "is Pluto really a planet" debate is getting very old. The word is just a word and no matter what you call Pluto it's still going to play the same role in our solar system. I can't believe that intellegent people with serious educations have a hair up their ass about simple terminology.
    • I can't believe that intellegent people with serious educations have a hair up their ass about simple terminology.

      Really, I mean who cares if its open source or free software. GNU/Linux or just Linux.

      Pluto is a Planette. [TM], there problem solved. Pronounced the same so the teachers won't be wrong.

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