Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System. It was discovered in 1672 by Giovanni Domenico Cassini.
Rhea is named after the Titan Rhea of Greek mythology, the “mother of the gods”. It is also designated Saturn V (being the fifth major moon going outward from the planet, after Mimas, Enceladus, Tethys, and Dione).
Rhea is an ice-cold body of weak density, indicating that the moon consists of a rocky nucleus counting only for a third of the mass of Rhea, the rest being mainly some ice-cold water. The temperature on the surface of Rhea is of-174°C in the sun, and of-200°C in-220°C in the shadow. In synchronous rotation around Saturn, Rhea always presents the same hemisphere to Saturn.
Rhea has a rather typical heavily cratered surface, with the exceptions of a few large Dione-type chasmata or fractures on the trailing hemisphere (the side facing away from the direction of motion along Rhea’s orbit) and a very faint “line” of material at Rhea’s equator that may have been deposited by material deorbiting from its rings. Rhea has two very large impact basins on its anti-Cronian hemisphere (facing away from Saturn), which are about 400 and 500 km across. The more northerly and less degraded of the two, called Tirawa, is roughly comparable to the basin Odysseus on Tethys.
On March 6, 2008, NASA announced that Rhea may have a tenuous ring system. This would mark the first discovery of rings around 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. read more
images; NASA/JPL, Kevin Gill, Lunar & Planetary Institute, 2id7 & titanio44, Gordan Ugarkovic
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