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Is {pluto|sedna} A Planet?

Posted by ryuzaki0 on from the three-votes-for-maybe dept.

Dr. Zowie writes "NASA's announcement last week of Sedna's discovery reignited the debate over whether Pluto is a planet. Dr. Alan Stern a noted planetary scientist and leader of the New Horizons mission to Pluto, pours on some gasoline with this article in which he skewers the various arguments against Pluto-as-planet. Choice quotes include 'You wouldn't deny a chihauhau a place among dogs because it is too small,' and 'if your brain was so completely full of names of people that it just couldn't take any more, would anyone new who you met after that, therefore not be a person?'"

4 of 594 comments (clear)

  1. Requirements? Look to gravity! by Pi_0's+don't+shower · · Score: 5, Interesting

    How about the simple argument that planets are gravitationally strong enough to pull themselves into nearly spherical objects, whereas asteroids are not. Pluto, BTW, Sedna, and many of the largest moons can all do this.

    I also think, for the record, that if something as large as Luna, or Titan, or Europa were out floating in space orbiting the sun and not another planet, they would be considered planets too.

  2. Well.. by LordK3nn3th · · Score: 5, Interesting

    A problem with this is that there really is no clear-cut differentiation between "planet" and "planetoid". There's no qualifying size-- it's more subjective than anything. Almost like different species: we all differ genetically, yet a species is a generally-recognized "set".

    One agreed-upon qualification is being formed round by its own gravity. I'm not sure if that applies to Sedna.

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  3. Re:Requirements? Look to gravity! by CrowScape · · Score: 5, Interesting

    The definition that makes Pluto not a planet is not based completely on arbitary size and so would probably not demote Mercury as well. The most prevalent definition of a planet (which was not stated in the article as far as I could tell, at least not completely) is any gravitationaly round object that is more massive than the rest of the mass in a similar orbit COMBINED. Mercury would be safe with this definition, while Pluto would be quickly tossed out. I actually like this better as the term "planetoid" now means something different than either "planet", "asteroid" or "satelite." (it would become a synonym of one of these otherwise) I propose the following definitions:

    Planetoid: Any object that becomes round by its own gravity but does not sustain fussion.

    Moon: Any planetoid that orbits another planetoid (let's face it, it's a generic term and nothing will ever change that). BTW: This would demote a lot of "moons" to mere satelites.

    Planet: Any planetoid that is more massive than the the rest of the matter in its orbit combined.

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  4. Is Earth a planet? by Paranoid · · Score: 5, Interesting

    I bet the folks who live on Jupiter think our solar system only has 4 planets. After all, Earth and Venus aren't so much bigger or different than Pluto or Sedna. Certainly, Earth is closer in size to Pluto than to Jupiter.

    People argue so much over where to draw the line between Planet and non-Planet, but everyone seems to take for granted that Earth is a member of the former class.

    Bigots.

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