Saturn's rings are at present 90 to 95 percent water ice. Because dust and debris from rocky meteoroids have polluted the rings, the rings are believed to have consisted of pure ice when they formed. This composition is unusual compared to the approximately half-ice and half-rock mixture expected for materials in the outer Solar System. Similarly, the low densities of Saturn's inner moons show that they too are, as a group, unusually rich in ice.
The previous leading ring origin theory suggests the rings formed when a small satellite was disrupted by an impacting comet. "This scenario would have likely resulted in rings that were a mixture of rock and ice, rather than the ice-rich rings we see today," says the paper's author, Dr. Robin M. Canup, associate vice president of the SwRI Planetary Science Directorate in Boulder.Full Article