No. 43: Jan-Feb 1986
The more we learn about Saturn's rings, the stranger they seem. One of the latest theoretical models of the rings has them composed of balls of hard ice, which interact through mutual collision and are herded by the gravitational caresses of small moons. The successes of this model have been tempered by the fact that it also implies that Saturn's rings are very young.
"Theorists would have no problem with a broad, featureless disk surviving the 4.5 billion years since the early days of the solar system, but features such as spiral density waves are clear evidence that satellites, including the profusion of small ones found near the rings, are draining angular momentum from the rings. The satellites should be spiraling outward into ever larger orbits as they gain angular momentum, and the A-ring should collapse inward into the B-ring in just 100 million years as its particles lose angular momentum."
(Kerr, Richard A.; "Making Better Planetary Rings," Science, 229:1376, 1985.)
Reference. For other indications of youth in Saturn's rings, see ARL16 in our catalog: The Moon and the Planets. For information on this book, visit: here.