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How Would You Define a Planet?

It doesn't come easy asks: "The argument over the definition of a planet continues. So far, two definitions are favored but without much consensus so far: base the definition of a planet simply on an object's size. Pluto would be near the lower limit and the newly discovered Kuiper Belt objects could also qualify, giving us 10 or 11 planets so far; or define the single dominant body in its immediate neighborhood as the only qualifying object for planetary status. If no one body dominated (such as the millions of individual asteroids in the asteroid belt) then none would qualify for planetary status. In this case Pluto would be disqualified (Neptune would be the dominant body in Pluto's region of space), and the newly discovered Kuiper Belt objects would also fail to qualify. The International Astronomical Union (IAU) working group charged with pinning down the definition of a planet may vote on the proposals within the next two weeks (or they may decide to start all over again with something new). Maybe Slashdot readers can give them some help. How would you define a planet?"

15 of 410 comments (clear)

  1. Shape and orbit by Belseth · · Score: 5, Insightful

    The obvious conditions are round shape and orbits the sun. Size is somewhat subjective although to have a round shape it would have to be above a certain mass.

    1. Re:Shape and orbit by rm999 · · Score: 4, Insightful

      Thats an observational definition (all the planets are round, so that makes a good definition) but like all definitions of planets that have been so far this produces problems. A couple I can think of:

      1. We will have to define round. This is a gray scale, and picking what "round" is will create controversy too. For example, how rough can the surface be? How oval can it be (even the earth isn't a sphere).
      2. What about a baseball orbiting the sun? You need some sort of size requirement. The more liquidy a substance, the more easily it will become round at smaller sizes.

      I don't mean to put down your definition - I actually like it - just pointing out that nothing is obvious in this debate.

  2. Quick definition by brassman · · Score: 4, Funny
    Something more than 1000 miles in diameter that's named after a Greek deity.

    Oataox or whatever the hell? The guy who came up with that needs to be kicked out of the Astronomy club.

    --
    "Ain't no right way to do a wrong thing."
  3. Thank God fior the Uncyclopedia by iceborer · · Score: 4, Funny

    A nonluminous celestial body larger than an asstroid or cumbucket, illuminated by light from a star, such as Michael Jackson, around which it revolts.

    Uncyclopedia: Planet

  4. I suggested... by grub · · Score: 4, Funny

    I suggested this on www.randi.org a few weeks ago. In Pluto's case have astrologers draw up two parallel charts. One with Pluto as a planet, the other without. After a few weeks we can compare what happened in the world to the astrology charts and that'll settle it.

    "The planets don't lie" as I said there. ;)

    --
    Trolling is a art,
  5. Like this by christurkel · · Score: 4, Informative

    I would define it thus: An object is a planet if it has enough gravity to form into a sphere but not large enough to ever had fusion start in its interior and has cleared its orbit of debris left over from its formation. This would allow Pluto to remain a planet, as well as "promote" Sedna to planet stus but rule out Ceres.

    --

    CDE open sourced! https://sourceforge.net/projects/cdesktopenv/
  6. Whatever Wikipedia says. by codergeek42 · · Score: 5, Funny
  7. The Kirk Test by MattC413 · · Score: 4, Funny

    If you can land on it and score with an alien chick, it's a planet.

  8. Re:By mass & composition by iggy_mon · · Score: 5, Funny

    by your definition my ex-wife is a planet!

    --
    --iggy_mon - www.ananonymouskiller.com - Die Trying -
  9. Re:Dude... by Tatarize · · Score: 4, Funny

    I think we should just drop the name. It can still exist, but not in a scientific context. We just go with MVEMJSUNP as "planets" and make up words with given definitions before we start trying to apply them them to things.

    BOOS: Big Objects Orbiting Star.
    BOOBOOS: Big Objects Orbiting Big Objects Orbiting Star.
    LOOS: Little Objects Orbiting Star.
    FOSC: Floating Outer Space Crap.
    Planet: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.

    Oh, and since I know you'll ask the difference between a BOOS and a LOOS is that a BOOS is large enough that it's own gravity keeps it roughly spherical.

    --

    It is no longer uncommon to be uncommon.
  10. Re:anything with a roman god name by kfg · · Score: 4, Informative

    Terra Mater (Mother Earth)is not commonly held to be the same as the Goddess Bona Dea (Fauna). They would typically have seperate shrines, often in the same area, built by the same people. One is a personification of Earth itself, the other of living things. Of course here and there the lines might well blur.

    I am fauna, but not terra. The child, but not the mother. I come from, but do not share identity.

    In any case, the current official name of the earth is Earth, which is Germanic.

    http://seds.lpl.arizona.edu/nineplanets/nineplanet s/earth.html

    KFG

  11. howabout... by circletimessquare · · Score: 4, Interesting
    anything with an appreciable atmosphere that is NOT a gas giant = planet ...REGARDLESS of what it orbits

    therefore, mercury would NOT be a planet (more like a moon of the sun)

    and titan, even though it orbits saturn, WOULD be a planet

    i think that makes most the most sense: what an object orbits shouldn't matter, it's composition should be the largest consideration

    some other nomenclature can address what it orbits ("a moon of the sun" or "a planet of saturn")

    it should be considered either
    • a moon (like mercury or pluto)

    • a planet (like mars or titan)

    • an asteroid (like deimos and phobos... called moons of mars, they are clearly NOT moons, but captured asteroids of the sun) if it is not spherical

    • and then we have your comets


    REGARDLESS of what it orbits

    --
    intellectual property law is philosophically incoherent. it is your moral duty to ignore it or sabotage it
  12. Re:Gravity by radtea · · Score: 4, Insightful

    When borderline cases arise, concepts proliferate.

    Apart from the Platonists in the audience, intelligent people realize that concepts are made things, artefacts created by humans to facilitate certain types of interaction with the world. Now, the world is a particular way, and that puts constraints on the sorts of concepts that are useful to us, but it doesn't determine a single set of concepts that will do the job. Therefore, concepts vary from person to person, and one person's pornography is another person's erotica, and so on.

    Concepts, like all tools, are judged to be better or worse according to use. Some of the uses of "planet" are political--every astronomer monkey wants to be the discoverer of a "plant", because that will attract and impress other monkeys of the complementary sexual orientation. This is just part of our hertiage as monkey's, and we may as well admit it. Other uses are scientific--planetologists already divide planets into sub-categories like "gas giant" and "terrestrial planet", because quite different physical processes dominate these bodies, and distinguishing them allows us to focus our attention more fully on one set of processes or the other. For beings of definitely limited brain power, this is extremely useful.

    Historically the term "planet" mixed several completely unrelated things: size, distance from Earth, and being in orbit around the Sun. Planets were "wandering stars", and it just happens that the only things that fell into that category were large bodies far from Earth that orbited the Sun. Things like the Moon, which is close, wasn't a planet because it had a visible disk, which stars do not. But this is entirely accidental--if one of the inner planets had had a moon visible from Earth with the naked eye it is likely that the concept of planet would already be more various than it already is.

    I think it better to create a bunch of new terms that acknowledge the rich division of bodies we can now see, rather than get hung up on the historical term "planet". The things we care about include at least three axes: size, composition and orbit. Trying to assign a single word to a particular region of a three-dimensional space (which probably isn't even simply connected!) is a silly waste of time, driven purely by monkey psychology, and has no scientific value. In fact, it may even have negative consequences for science, because getting hung up on historical terms may also help keep people hung up on historical concepts.

    So my vote would be to expunge the term "planet" from the astronomical lexicon entirely. It's the only way to be sure.

    --
    Blasphemy is a human right. Blasphemophobia kills.
  13. Re:Dude... by zentigger · · Score: 5, Funny

    I think you missed a really important one:

    Big Objects Orbiting Binary Stars... /ducks

    --

    the above is my personal opinion and does not necessarily reflect that of the little voices in my head

  14. Gotta be more specific.... by cbiltcliffe · · Score: 4, Funny

    The only way to define it is obvious:

    Anything you can blow up with the Death Star!

    --
    "City hall" in German is "Rathaus" Kinda explains a few things......