Quote:
Originally Posted by Varangian
Man other than the ability to clear its orbit this thing is turning out to be more planet-like than Mercury!
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I suspect (intuitively) that distance from the sun is a big driver of the ability of a small 'planet' to retain moons. Here's my (Newtonian) reasoning.
Remember that while a 2-body system (ie one planet, one moon) is stable, any more is not. In the long term, non-linearities eventually build up to large effects.
Now consider putting a 2-body system (planet and moon) in orbit around a larger body (the sun). The 2-body system 'sees' the sun as a changing gravitational field, getting weaker away from the sun. That change is the 3'rd body distortion which ulitmately destabilises the system.
Now, the closer the 2-body system is to the sun, the more dramatic the change in that back-ground field, and consequently the more pronounced the distorting effect and consequently the faster instabilities develop and potentially the 2-body system is disrupted. In a sense the further from the sun, the more the planet and moon look like an isolated 2-body system.
Intuitively I'd say this has to hold for more than one moon.
On this basis, I'd say it is unsurprising that despite their similarity Mercury has no moons and Pluto has a bunch. Pluto is so much further away from the sun.
Obviously that's a pretty rough and ready analysis. Anyone able to either poke a hole in my reasoning, or alternatively point to someone having produced a more rigorous version?