Since astronomer Galileo Galilei first noticed something odd about Saturn in 1610, the planet's picturesque rings have posed many fascinating puzzles.
Earlier observations, during the Voyager flybys of 1980 and 1981, suggested the rings might be as young as 100 million years, the result of a nasty breakup between a large comet and an icy moon.
Cassini also determined that the rings are made almost entirely of water ice.
So, if they are so old, how do they stay so startlingly bright?
From Cassini's close-up perspective, the ring field appears to be composed of hundreds of thousands of concentric ringlets.
Just as in a developing planet system around any star, angular momentum and gravity tend to compress matter into a spinning disk.