Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System. It is the second smallest body in the Solar System for which precise measurements have confirmed a shape consistent with hydrostatic equilibrium, after dwarf planet Ceres. 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).

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