PLANETARY RING DYNAMICS

The dynamics of planetary rings are reviewed in the light of data deri ved from the recent spacecraft missions to the outer planets. It is sh own that although the ring systems of Jupiter, Saturn, Uranus and Nept une display a great diversity of phenomena and dynamical structures, t hey have many features and problems in common. The role of small satel lites in determining ring structure is reviewed, with particular empha sis on the ring system of Saturn. There is mounting evidence that some of the smaller satellites may have densities as low as 0.6 g cm(-3) B ecause Saturn has examples of most of the types of rings seen elsewher e in the Solar System, the forthcoming Cassini mission has particular importance for ring dynamicists. A summary is presented of the critica l ring observations that can only be made by a spacecraft orbiting Sat urn for an extended period.