Those Pesky Rings
 A false-color image from the Cassini spacecraft shows Saturn's glorious rings. The colors indicate how much material is contained in each ring, including the size of the ring particles. Cassini is passing close to the outer rim of the rings, and will use its main radio antenna as a shield to protect it from possible collisions. [NASA/JPL/Univ. Colorado]
Cassini arrived at Saturn three years ago today, when it flew past the moon Phoebe. Since then, it's made 45 wide orbits around the planet and rings, looping past several other moons in the process. It's discovered lakes and seas of liquid methane on the moon Titan, geysers of liquid water on Enceladus, and powerful storms on Saturn itself.
Cassini has also spent a lot of time looking at Saturn's rings.
There are thousands of rings around the planet. They span about 300,000 miles -- greater than the distance from Earth to the Moon -- yet they're no more than a hundred yards thick. They consist of small bits of ice and rock, plus lots of dust. Several tiny moons that orbit inside the ring system help to keep the rings in place.
Cassini has seen amazing details in the rings -- loops and braids and kinks, usually caused by the gravity of the little moons. It's found that one of the rings is replenished by the geysers from Enceladus, and that another recently got fresh material from a pulverized space rock.
Today, Cassini is passing just outside the rings, where it could encounter some ring material. A collision with a big-enough piece could damage the craft. So it'll keep its big radio antenna aimed straight ahead -- using it as a shield as it flies past Saturn's amazing rings.
Script by Damond Benningfield, Copyright 2007
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