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Posted by Dan Tilque on August 24, 2006, 4:00 am
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robert casey wrote:
> Looks
> like the lower limit's size is about 500km. Saturn's moon
> Hyperion, if it orbited the Sun, still wouldn't qualify as
> it's not round enough.
Mimas is a bit under 400 km in diameter and it's quite round
(modulo the giant crater). On the other hand, Vesta is 525 km in
diameter is it's very noticeably oblong. This is probably due to
the compositions of the two bodies: Vesta is rock and Mimas is
probably mostly ice.
Personally, I'm in favor of dropping the barycenter requirement
for double planets. Just call any object that would otherwise
qualify as a planet a double or multiple planet. According to the
proposed rule, in 40 million or so years, the Moon will
automagically become a double planet without changing in the
least. Why should it have to wait for its orbit to evolve a bit?
There's no real reason.
--
Dan Tilque
PS By this rule, the Saturn system would count as an octuple
planet...
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