Both Cassini observations and N-body simulations of Saturn's rings point towards extensive particle clumping in Saturn's B ring. As a result, observed optical depths are actually measuring the fractional area between these opaque clumps rather than the density of material within the clumps themselves. The inferred total mass of Saturn's ring is therefore likely to be at least three times more massive than previously estimated, or three times more massive than the satellite, Mimas. Such a massive ring system is unlikely to have formed by the tidal disruption of comets or by the collisional disruption of a former satellite during the last 4 billion years. Instead, we argue that the massive B ring must have a primordial origin, dating back from the period of late heavy bombardment when the collisional disruption of a massive satellite was more probable (Harris 1984). Placing a massive satellite inside Saturn's Roche zone by orbital migration due to resonant interactions with a proto-satellite disk may even be a natural outcome in the context of Canup and Ward's model of satellite formation in a "gas-starved” accretion disk around Saturn. So how do we reconcile this scenario with youthful features in Saturn's rings? The massive B ring could be quite ancient while the A and C rings are still relatively young. N-body simulations suggest that the spreading rate of the B ring is substantially slower than in the A ring. In this scenario, the massive B ring evolves slowly while the lower mass A ring and C ring evolve faster and show the most evidence for youthful features.
AAS/Division for Planetary Sciences Meeting Abstracts #39
- Pub Date:
- October 2007