Spitale, J. N. , Porco, C. C. (2010). "Detection of Free Unstable Modes and Massive Bodies in Saturn's Outer B Ring" American Astronomical Society, DDA meeting #41, #11.05 .


Abstract
Voyager images and Cassini occultation data have previously shown that the behavior of the outer edge of Saturn's massive B-ring is forced only in part by the 2:1 inner Lindblad resonance with Mimas. In Cassini images of this region, we find, in addition to the wavenumber-2 forced distortion, evidence for unforced self-excited wavenumber-3, wavenumber-2, and wavenumber-1 free oscillations, the first observations to suggest substantial wave amplification in Saturn's broad rings. Interference between the forced and free wavenumber-2 modes yields a single wavenumber-2 pattern that varies in amplitude and orientation with a characteristic period of ~ 7 years. We also find localized disturbances, including 3.5-km-tall vertical structures, that move with speeds near the expected Keplerian rate for that region of the rings, which are likely caused by embedded massive bodies. The presence of such bodies is supported by the direct discovery of a moonlet ~ 0.3 km wide near the ring's edge.