Propelling Evidence: Cassini finds clues to source of Saturn’s rings

Four propeller-shaped gaps in one of Saturn’s main rings are the latest evidence that a shattered moon produced the planet’s dazzling hoops. The discovery supports the theory that a comet or asteroid struck a large, icy Saturn moon about 100 million years ago and that the distributed debris formed rings. They cover a region broader than the distance between the Earth and its moon.