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Defining "Planet"

Posted by michael on from the round-and-round dept.

beardoc writes "The Sydney Morning Herald is running a story today about a controversial proposal to define what size a planet might be - depending on what the final definition of how big a planet is, we could end up losing Pluto (at 2300 kilometres) to the status of "asteroid" or gaining three more planets - Quaoar, Varuna and Ceres."

4 of 441 comments (clear)

  1. How about "Life sustaining?" by beernutz · · Score: 5, Interesting

    Wouldn't it make sense to take into account whether the planet could feasibly sustain life too? I mean could a 700km round body in space support an atmosphere?

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    (stolen from DaBum) I am dyslexia of borg - your ass will be laminated.
    1. Re:How about "Life sustaining?" by Anonymous Coward · · Score: 5, Interesting
      I mean could a 700km round body in space support an atmosphere?

      Well, sometimes Pluto has an atmosphere, and sometimes it doesn't. Only when it gets closer to the Sun in it's orbit does it "generate" an atmosphere from sublimation of ice. Later on it evaporates away be due to lack of gravity to hold it there. I doubt we would classify it as a part-time planet. BTW.. comets can have a "pseudo atmosphere" too.
  2. Why not set a defined width? by Jailbrekr · · Score: 5, Interesting

    they say bodies larger than 700km go from being potatoe shaped to round. why not set a defined width above this 'minimum', and anything larger be called a planet? twice the minimum sounds plausible, and that means Pluto would still be defined as planet.

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  3. Re:silliness by 1u3hr · · Score: 5, Interesting
    why can't we be content to keep the traditional designations of what make up a planet?

    a) this is science, not tradition, scientific terms need an absolute definition.

    b) traditionally, you only had the naked-eye planets: Mercury, venus, Mars, Jupiter, Saturn. What do you call the other gas giants? Not to mention, Mercury was thought to be two planets by some (the morning and evening star).

    c) my opinion, just set it so that Pluto-size is the cut-off. Anything smaller isn't one. However, in a few centuries when we can detect "planets" in other solar systems this would seem a bit heliocentric, so I can see the Basri's point (in the FA: "Basri's definition, a planet must orbit a star, not another planet, and it must be round. That means it must be 700 kilometres in diameter, when gravity moulds it into a sphere, or bigger.").