Overstable Modes in Planetary Rings

Peter Goldreich

May 16, 2011

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Abstract: The morphology of planetary rings is shaped by the transfer of angular momentum internally due to particle collisions and externally due to gravitational tides raised by satellites. Many novel features were predicted, revealed, and understood during the era of the Voyager missions. Nevertheless, outstanding puzzles remained unresolved. Recent observations of Saturn’s rings by the Cassini spacecraft provide essential new clues. These will be described. Particular attention will be given to the dynamic nature of the viscosity due to particle collisions and its role in exciting large scale modes in the outer B-ring. Implications for the migration of planets in protostellar disks will be drawn.