Mage, I tried out you're idea for orbiting bodies, but I used an invisible anchor creature set to the base layer instead of a sun image, so it could be use for more than just comets... I did a moon first, because the smaller distances are easier to ajust, and I can use that info for larger scale distances. I set up a few new creature classes to keep it all organised too. I made the anchor creature pretty strong too, so if a sattelitte's orbit decays enough that it reaches it's target, it's instantly destroyed.
After I got a general location for the moon, I put in quite a few and let em orbit for a while, to find the one with the cleanest orbit.
There's the winner... I cut it's speed and rotation afterwards, so it'd only do @ 1 rotation per minute.
I tried an asteroid belt too, but even with perfect placement around an object, the majority would fly off... I'm thinking of an ast belt spawner item that would release 15-20 ast items from one of the safe spots at timed intervals, but I have to get a timed script working to shut it off...