On Aug 26, 2009, at 8:24 AM, Alberto Monteiro wrote:
Probably (my guess) Mars's moons are recent acquisitions, and won't
last forever. Venus and Mercury may have had moonlets in the past
too, that lasted a few million years and then either crashed or
flew away.
And it's entirely likely that Mars has had other moons in the past
before Phobos and Deimos. I know of at least one equatorial oblique
crater.
IIRC, Phobos is falling and Deimos is leaving Mars.
That's pretty consistent with my understanding.
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. (As
much as any orbit in this environment could truly be called "stable",
that is.) They would tend to become co-orbiting moons of the parent
body before one would actually orbit the other.
And co-orbiting bodies aren't entirely known even in solar orbit:
http://en.wikipedia.org/wiki/3753_Cruithne
http://en.wikipedia.org/wiki/J002E3
"It is the mark of a higher culture to value the little unpretentious
truths which have been discovered by means of rigorous method more
highly than the errors handed down by metaphysical and artistic ages
and men, which blind us and make us happy." -- Nietszche
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