Abstract

The size distribution of Saturn’s ring particles is constrained by Voyager and Cassini data to roughly follow a (differential) power law with exponent near -2.75 to -3 ranging between 10cm to about 10m. A population of larger particles, following a much steeper distribution, was predicted by Cuzzi et al, (1984, Planetary Rings, Arizona Press). The response of the ring on the gravitational perturbation of such a 100m to km sized boulder, showing a characteristic propeller shaped signature, was calculated by Spahn and Sremcevic, AA 358 , 2000, 368, including the effect of ring viscosity. Such propellers, indicative of moolets embedded in the rings, were discovered in Cassini images of Saturn’s A ring. Interestingly they appear concentrated in a relatively narrow radial region. In this talk I review theoretical aspects of the propellers, the Cassini data, and possible interpretations.