It is the smallest body in the Solar System for which precise measurements have confirmed a shape consistent with hydrostatic equilibrium.

The moon itself has a fairly low density, composed of roughly three-quarters ice and only one-quarter rock.

Rhea was discovered by Giovanni Domenico Cassini on 23 December 1672, with a 10.4-metre (34 ft) telescope made by Giuseppe Campani.

It is also designated Saturn V (being the fifth major moon going outward from the planet, after Mimas, Enceladus, Tethys, and Dione).

[14] Rhea was not named until 1847, when John Herschel (son of William Herschel, discoverer of the planet Uranus and two other moons of Saturn, Mimas and Enceladus) suggested in Results of Astronomical Observations made at the Cape of Good Hope that the names of the Titans, sisters and brothers of Kronos (Saturn, in Roman mythology), be used.

[d] The surface area of the moon can be estimated at 7,330,000 square kilometres (2,830,000 sq mi), similar to Australia (7,688,287 km2).

[e][24] Such a value indicated that Rhea had an almost homogeneous interior (with some compression of ice in the center) while the existence of a rocky core would imply a moment of inertia of about 0.34.

[25] A year later, yet another paper claimed that the moon may not be in hydrostatic equilibrium, meaning that the moment of inertia cannot be determined from the gravity data alone.

He concluded that there is a systematic error in the Cassini radio Doppler data used in the analysis, but, after restricting the analysis to a subset of data obtained closest to the moon, he arrived at his old result that Rhea was in hydrostatic equilibrium and had a moment of inertia of about 0.4, again implying a homogeneous interior.

[9] Rhea's features resemble those of Dione, with distinct and dissmillar leading and trailing hemispheres, suggesting similar composition and histories.

[35] It is believed, based on data from the Cassini probe, that these are tectonic features: depressions (graben) and troughs, with ice-covered cliff sides causing the lines' whiteness (more technically their albedo).

As the young giant planets formed, they were surrounded by discs of material that gradually coalesced into moons.

However, a model proposed by Erik Asphaug and Andreas Reufer for the formation of Titan may also shine a new light on the origin of Rhea and Iapetus.

The source of the carbon dioxide is less clear, but it may be related to oxidation of the organics present in ice or to outgassing of the moon's interior.

The rings' existence was inferred by observed changes in the flow of electrons trapped by Saturn's magnetic field as Cassini passed by Rhea.

[44][45][46] 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.