Charnoz, S., Beurle, K., Burns, J., Evans, M., Murray, C., Porco, C. (2007). "Saturn's F ring: a story of a core, moonlets and spirals." American Astronomical Society, DPS meeting #39, #10.07.

Since 2004, Cassini has explored the complex dynamical environment surrounding the F ring (Porco et al. 2005, Murray et al. 2005a) and revealed the presence of dynamical spiral structures on both sides of the F ring, with radial width about +/-300 km (Charnoz et al. 2005). After 3 years, the spiral structure always seems to be there (Murray et al. in preparation). Beside this, small moons orbiting in the F ring region were also imaged (Spitale et al. 2004, Murray et al. 2005b).

We numerically investigate the dynamical evolution of the F ring impacted by small km-sized moonlets. Both gravitational and physical rebounds are considered. We show that physical rebound at a moonlet's surface is an efficient mechanism to scatter material over large distances and can create spiral structures with radial width matching observations, provided a low coefficient of restitution is assumed. Conversely gravitational scattering seems inefficient in creating large-scale spiral structures.

Different scenarios are investigated in which the F ring core is either made of massless dust or consists of solid bodies. Numerical simulation of spirals best match observations when massive bodies embedded in the F ring are hit by incoming moonlets that are loosely bound aggregates.

These results show that the F ring's spirals could be the "smoking gun" of on going collisional processes, suggesting the presence of massive moonlets embedded in the F ring core. This also strengthens the idea that the F ring may be massive.