Evil Dr Ganymede wrote:I'd say that it looks like it's rare for a jovian NOT to have rings. However, I think it's a lot more likely that jovians that are far from their primary star can retain rings - hot jupiters won't have them (they wouldn't be stable due to tides and temperature) and jovians within the snow line probably won't have them either for similar reasons.
Would the same be said for large (or even small) moons, then?
Evil Dr Ganymede wrote:Jupiter's ring seems to be maintained by material knocked off Amalthea and Metis and Adrastea. Not sure if Uranus' and Neptune's are maintained in a similar manner, but it seems that close asteroidal satellites have some role in maintaining them. Saturn's rings may be an entirely different kettle of fish though - given that we have four jovians and only one has a spectacular system, maybe a saturn-like ring system is rare.
As far as Jupiter goes, what does Io have to do with the rings, anything? If material falls inward to coat Amalthea, wouldn't it also contribute to the ring system?
And Saturn... is the old thought that we are lucky to be seeing the rings at all still valid? I remember reading somewhere that it had been speculated that the rings might have a life time of about 5 million years, a pretty small geological window.
Of course, if there is some other mechanism aside from a shattered satellite which made the rings, then we need to account for how they are sufficiently replenished.
...John...