Possible Ring System
On March 6, 2008, NASA announced that Rhea may have a tenuous ring system. This would mark the first discovery of rings about a moon. The rings' existence was inferred by observed changes in the flow of electrons trapped by Saturn's magnetic field as Cassini passed by Rhea. Dust and debris could extend out to Rhea's Hill sphere, but were thought to be denser nearer the moon, with three narrow rings of higher density. The case for a ring was strengthened by the subsequent finding of the presence of a set of small ultraviolet-bright spots distributed along Rhea's equator (interpreted as the impact points of deorbiting ring material). However, when Cassini made targeted observations of the putative ring plane from several angles, no evidence of ring material was found, suggesting that another explanation for the earlier observations is needed.
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