Cassini seems to have proven that one in a whole series of ways simultaneously:

(1) The confirmation of the existence of the propeller moonlets inside the main rings (plus the accumulation of material at the equatorial zones of Pan and Atlas);

(2) The fact that we see solid signs of similar clumping and re-dispersal cycles in the F and G Rings;

(3) The fact that all of Saturn’s little inner moons out to Prometheus are exactly the size and density that one would expect if they had accumulated loose material until their density dropped to the point that they completely filled up their Hill spheres;

(4) The VIMS compositional maps of the rings that show individual narrow zones with much fresher and lighter-colored ice (just as one would expect if a snoball had recently been splattered by a large impact, and its internal ice chunks hadn’t yet had their surface re-darkened by ice-vaporizing micrometeoroid impacts that left a crust of darker material).

Add to this (as Esposito already did) the fact that all the inner moons out to Pandora should actually have been orbiting INSIDE the rings just a few hundred million years ago, given the fact that the rings’ outer edge should be slowly pushed inward by their tidal forces — unless the inner moons are actually snowballs that used to actually BE dispersed ring material, and will probably become such material again when something big enough to splatter them hits them again.

As I say, it seems to me that the longevity of the rings is one of the two long-time, major mysteries about the Saturn system that Cassini has definitely solved. (The other is Iapetus’ light-dark dichotomy. John Spencer’s “thermal segregation” theory — with the segregation being initially triggered by mild darkening of Iapetus’ leading side by infalling debris from the little outermost irregular moons — already meshed very well with Voyager’s and Cassini’s long-distance observations, and its closeups of that Dalmatian-spotted surface during the September flyby seem to nail it down absolutely conclusively.)

Of course, Cassini — like any good space probe — has obligingly set up a swarm of fascinating new mysteries. Most of them, of course, involve Titan and Enceladus; but Saturn’s own weather patterns and internal structure have produced new puzzles as well.