Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System, with a surface area that is comparable to the area of Australia. It is the smallest body in the Solar System for which precise measurements have confirmed a shape consistent with hydrostatic equilibrium. It was discovered in 1672 by Giovanni Domenico Cassini.
Rhea, as imaged by the Cassini orbiter, November 2009
Giovanni Domenico Cassini, discoverer of Rhea in 1672
Size comparison of Earth (right), the Moon (left top), and Rhea (left down)
Surface features on Rhea well defined due to the lighting.
A natural satellite is, in the most common usage, an astronomical body that orbits a planet, dwarf planet, or small Solar System body. Natural satellites are colloquially referred to as moons, a derivation from the Moon of Earth.
Size comparison of Earth and the Moon
Artist impression of Rhea's proposed rings