Quote:
Originally Posted by Kristophe
And this is definitely not a case of 'Logic over...' well, anything, really. As far as I can tell, by this definition, Earth has only been footnoted in as a planet. There's no way anyone could reasonably consider the Moon to be small enough to be discounted in the "orbital clearing" definition. Earth's orbit is heavily disturbed by the Earth, to the point where I can't accept it as being a dominant body, or having cleared its orbit. There's no logic in footnotes of convenience.
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I agree about the footnote. I can understand Jupiter and Saturn's satellites being considered clear since the planets are a much larger size and the accretion theories suggest the moons formed in orbit around those large planets. However, the Giant Impact Hypothesis would suggest that the moon did not form around Earth because of Earth's immense gravity but that it formes elsewhere. Perhaps it was a co-orbital twin called Theia, which the Earth attempted to clear but ended up colliding with. The Moon would, thus, represent a failed clearing attempt instead of a successful clearing event. The result is a Moon, or satellite planet, massing over 70 exatons (1.3%).
Neptune also has a large moon, Triton, which was also not formed in situ. Current theory suggests that the satellite was formerly a planet, or an uncleared object. Since Neptune will destroy and consume Triton in a short about of time (astronomically speaking), it's more precise to say that Neptune is still in the act of clearing it's orbit, but has not finished. Unlike arguments of "safe" resonances, the consumption of Triton is a relatively dynamic event and shows that the IAU definition is self-contradicting.