Saturn's moon Rhea also may have rings, research shows

NASA's Cassini spacecraft has found evidence of material orbiting Rhea, Saturn's second largest moon. This is the first time rings may have been found around a moon, said NASA on Thursday.

    A broad debris disk and at least one ring appear to have been detected by a suite of six instruments on Cassini specifically designed to study the atmospheres and particles around Saturn and its moons.

An artist concept of the ring of debris that may orbit Saturn's second-largest moon, Rhea. Saturn's second-largest moon Rhea may have a small ring around it -- the first time a moon has been found to have a ring, an international team of researchers reported on Thursday.

"Until now, only planets were known to have rings, but now Rhea seems to have some family ties to its ringed parent Saturn," said Geraint Jones, Cassini scientist, and lead author on a paper that appears in the March 7 issue of the journal Science.

    Rhea is roughly 1500 kilometers in diameter. The apparent debris disk measures several thousand kilometers from end to end. The particles that make up the disk and any embedded rings probably range from the size of small pebbles to boulders.

    Since the discovery, Cassini scientists have carried out numerical simulations to determine if Rhea can maintain rings. The models show that Rhea's gravity field, in combination with its orbit around Saturn, could allow rings that form to remain in place for a very long time.

    One possible explanation for these rings is that they are remnants from an asteroid or comet collision in Rhea's distant past. Such a collision may have pitched large quantities of gas and solid particles around Rhea. Once the gas dissipated, all that remained were the ring particles, said Cassini scientists.