Backlit Saturn Shows New Moons, Rings

Oct. 16, 2006 — Taking advantage of a rare photo moment, scientists using the Cassini spacecraft have found faint new rings circling Saturn and hints of hidden moons.

The images were taken as Saturn was virtually dead-set centered in front of the sun, as viewed by the orbiting Cassini probe. Cassini's cameras detected two new wispy trails of particles lit up like streams of dust in front of a brightly lit window, and confirmed two other previously discovered rings.

Scientists believe the rings are dust particles caused by asteroids or comets striking the surfaces of small inner moons circling Saturn. The moons' gravity is too weak to hold on to any kind of surface dust, so impacts blast material into Saturn's orbit, where the particles assemble into loosely packed rings in the moons' orbital paths.

"The rings we're talking about are very faint, just a few dust grains per square meter," said Matt Hedman, a Cassini scientist at Cornell University in New York.

One new ring was found sharing an orbit with the tiny moons Janus and Epimetheus. Scientists found a second ring near Pallene, a 2.5-mile diameter moon discovered by Cassini in 2004.

Oddly, a similarly sized moon named Methone, previously discovered near Pallene, does not seem to have spawned a ring, the Cassini team found.

Cassini spotted two more rings in an area known as the Cassini Division, the big gap between Saturn's main ring sets.

"One of the things we're beginning to appreciate is how really dynamic the ring system is," Hedman said. "We're finding new features, but that's partly because we're looking more closely."

The dust grains in the rings are very small — about the width of a human hair — and easily scattered by cosmic rays and other forces in Saturn's environment. Because the rings survive, however, scientists believe something is continually replenishing the material that forms them.

"They can't just be there forever," Hedman said. "You need something to be supplying the dust."

Scientists are now combing through Cassini's data hoping to find additional moons. Another backlit photo session of the rings will not be possible for several years.