Planetary rings

Despite all new data, the nature of planetary rings is still controversial. We don't know why each planetary ring is so different from the others and we have no idea of the nature of a single particle ring. The large number of structures observed in planetary rings seems to indicate that many different physical mechanisms are simultaneously at work. We are not yet able to include all of them in a single model. Resonances with nearby satellites play an important role, but through complex mechanisms. Appropriate observations and more sophisticated models are needed to improve our understanding of rings and to identify the main physical mechanisms involved. (author). 2 figs., 45 refs