Saturn Moon Rhea May Have Rings

PASADENA, Calif. -- New observations by a spacecraft suggest Saturn's second-largest moon may be surrounded by rings. If confirmed, it would the first time a ring system has been found around a moon.

The international Cassini spacecraft detected what appeared to be a large debris disk around the 950-mile-wide moon Rhea during a flyby in 2005. Scientists proposed that the halo likely contained particles ranging from the size of grains to boulders.
The finding was described in a study published in the March 7 issue of the journal Science.

Unlike the rings around Saturn, Jupiter, Uranus and Neptune, the apparent arcs around Rhea remain invisible and have not been directly seen. Scientists inferred their existence based on measurements by Cassini, which detected a drop in electrons on both sides of the moon, suggesting the presence of rings was absorbing the electrons.

It's unclear where the rings would have originated, but one explanation is they may be the result of an ancient asteroid or comet collision that spewed material around Rhea.
"Rings may even have survived since Rhea's formation," wrote lead author Geraint Jones, a space physicist from University College London.

Until now, only planets were known to have rings, said Jones, who began the research while at the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany.

The Cassini mission, funded by NASA and the European and Italian space agencies, was launched in 1997 and reached Saturn in 2004. The mission is managed by NASA's Jet Propulsion Laboratory in Pasadena.