Porco, C., Weiss, J., Thomas, P., Richardson, D., Spitale, J. (2006). "Accretionary Origins for Saturn's Small Satellites: Sizes, Shapes, and Numerical Simulations of Growth." Eos Trans. AGU 87(52), Fall Meet. Suppl., Abstract P34A-01.


Abstract
Cassini imaging observations have yielded sizes and shapes of Saturn's small (< or ~ 100 km radius) satellites from standard techniques [1]. For most of these satellites, masses (and thence densities) have been determined either from orbital integrations, when the satellite measurably perturbs another [2], or from the moon's effect on the rings [3]. Sizes, shapes and densities together can yield clues to the internal structure and origins of these bodies. We examine here the possibility that, rather than being monolithic collisional shards covered with a thin dusty regolith, these satellites have formed by accretion from a disk of smaller- sized material to their present size. The observed shapes of the satellites, especially the innermost ones, compare favorably with those expected for 'rubble piles' that have formed by accretion at the satellites' orbital distances from Saturn. Numerical simulations of the accretionary growth of embedded higher density `cores' in a ring of material indicate that bodies grow to a specific critical density at which they fill their Roche lobes. This critical density resulting from our numerical simulations is in agreement with the observed densities for these small bodies, supporting the notion that these bodies formed by accretion and are not themselves monolithic structures. The final size of the body depends on the size and density of the core, and the density of the accreted ring material. [1] Thomas, P. C. 1993. Icarus 105, 326-344. [2] Spitale et al. 2006. Astron. J. 132, 692-710 . [3] Porco, C. et al. 2005. Science 307, 1226-1236.