The Cassini spacecraft has been in orbit around Saturn for a little more than three years now. During that time, it has returned data revealing details of several dynamical processes that determine the structure and evolution of the planet's rings. Those phenomena not only give clues about the physical nature of the ring material but also provide a severe test of planetary physicists' understanding of the gravitational and collisional physics involved. In that sense, Saturn's rings act as a dynamical laboratory in which researchers can observe processes and apply their knowledge to other disk systems under more extreme conditions.
All the giant planets in our solar system have nearly circular ring systems. In addition, all have small moons orbiting among or near the rings and larger moons beyond. The rings could be material that failed to accrete into moons or even the debris from fragmentation due to tidal forces of...
