Despite all the new data, the nature of planetary rings is stíII
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 partícle ring, The large number of structures observed in planetary rings seems to indicate that many different physícal 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 ímportant role, but through complex mechanisms. Appropriate observations and more sophísticated models are needed to improve our understanding of rings and to identify the main physícal mechanisms involved.
The new observations of planetary rings, including those acquired during the encounters of Voyager with Jupiter, Saturn and Uranus and the discovery of incomplete rings around Neptune, reveal the great importance of resonances in determining the dynamics and the shape of planetary rings. Several types of resonances play a part in planetary rings. Current questions of interest are related to the nonlinear theory of density waves, the confinement of the Uranian rings, and the arcs of rings around Neptune.