Brahic, A., Charnoz, S., Deau, E., Thomas, P., Porco, C. (2006). "Small satellites embedded the rings : impact and motion of material at the surface of Pan and Atlas." American Astronomical Society, DPS meeting #38, #72.07.


Abstract
Recent Cassini images have revealed the strange shapes of Pan and Atlas, with surprising bulges near the equator. We try here to understand the origin of the moons' equatorial bulges by examination of the detailed motion of material falling from the ring to the surface and then rolling on the surface. Two questions are treated: (1) where does the material fall on the surface? (2) where does the material roll once it is on the surface? Using numerical simulations, we show that the equatorial bulge maybe material accreted from the rings. But the resulting shape depends critically on both the orbital parameters of the satellites, and on the shape of the Hill sphere Roche Lobe compared to the 3D surface body surface which are similar (indeed Porco et al. -- LPSC 2006-- has shown that the overall shape and size of each is close to that of the body's Roche lobe). We show that the complex interplay between the Saturn tidal forces, the shape and the body's gravity creates on the surface, valleys of stability where the material is expected to migrate in a short time. All these elements may put some new constrains on the origin of Pan and Atlas, as well as on their dynamical history.