Rhea, the second-largest moon of Saturn, may have a tenuous ring system consisting of three narrow, relatively dense bands within a particulate disk. This would be the first discovery of rings around a moon. The potential discovery was announced in the journal Science on March 6, 2008.
In November 2005 the Cassini orbiter found that Saturn's magnetosphere is depleted of energetic electrons near Rhea. According to the discovery team, the pattern of depletion is best explained by assuming the electrons are absorbed by solid material in the form of an equatorial disk of particles perhaps several decimeters to approximately a meter in diameter and that contains several denser rings or arcs. Subsequent targeted optical searches of the putative ring plane from several angles by Cassini's narrow-angle camera failed to find any evidence of the expected ring material, and in August 2010 it was announced that Rhea was unlikely to have rings, and that the reason for the depletion pattern, which is unique to Rhea, is unknown. However, an equatorial chain of bluish marks on the Rhean surface suggests past impacts of deorbiting ring material and leaves the question unresolved.
