The IAU...resolves that planets and other bodies in our Solar System be defined into three distinct categories in the following way:
(1) A "planet" [1] is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. It fails here.
(2) A "dwarf planet" or a planetoid is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape [2], (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite [of a planet].
(3) All other objects [3] orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".
Footnotes:
[1] The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
[2] An IAU process will be established to assign borderline objects into either "dwarf planet" and other categories.
[3] These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
They're gonna have to change that Magic School Bus episode.
Oh yeah, I also heard that by this definition, Earth may not be a planet either. Just something floating around.
Edited by the Author.
"Isn't it always amazing how we characterize a person's intelligence by how closely their thinking matches ours?"
~Belgarath
It's a pointless definition anyway. You have satellites and you have satellites of satellites. The 'classical planet' idea was alright but they didn't end up going in that direction.
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Edited by the Author.
. But it should be useful to anyone else who didn't know.
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