On Aug 26, 2009, at 12:10 PM, David Hobby wrote:
And why with 100+ moons, none of them has a sub-moon?
My guess would be that there just aren't many stable solutions to a
close-in three-body problem like that. Jupiter's gravitational
effects dominate the orbital dynamics of a good part of the solar
system, and many of its satellites are fairly close to its Roche
limit to begin with, so my back-of-the-napkin guess would be that
sub=moons would be extremely rare and tend not to be in very stable
orbits.
Bruce--
I think there certainly are stable solutions
for some planet/moon systems without submoons.
The orbit of the submoon would have to be definitely
inside the Hill sphere of the moon. See:
http://en.wikipedia.org/wiki/Hill_sphere
I stand corrected. :)
To me, the problem is more that it's very unlikely
that objects will get captured by the moon.
Given how narrow the limits would be for all the parameters to line up
to a successful capture, you're almost certainly right about that.
"Correct morality can only be derived from what man is—not from what
do-gooders and well-meaning Aunt Nellies would like him to be." --
Robert A. Heinlein
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