major moon · moon of Saturn
Rhea
Saturn's second-largest moon, a heavily cratered ball of ice and rock wrapped in an extremely thin oxygen-bearing exosphere.
- Distance from Earth today
- 1.28 billion km8.564 AU · light: 1 h 11 min
- Distance from the Sun today
- 1.41 billion km9.425 AU
- As of
- 3 November 2026position from NASA/JPL orbital elements
Where it is today
Top view of the plane of Earth’s orbit, compressed distance scale. Open on the big map with the time slider →
Facts
- Diameter
- 1,527 km
- Mass
- 2,306 × 10¹⁸ kg
- Density
- 1,237 kg/m³
- Mean distance from the planet
- 527,200 km
- Orbital period
- 4.52 days
- Orbital eccentricity
- 0.0010
- Orbital inclination
- 0.3°
Source of the figures: JPL SSD – Planetary Satellites (public domain).
Discovery: 1672 – Giovanni Domenico Cassini
Description
Rhea is the second-largest moon of Saturn, after Titan, and was discovered by Giovanni Domenico Cassini in 1672. It is a cold, heavily cratered mixture of water ice and rock, with bright fractured cliffs on one hemisphere similar to those on Dione. During close flybys the Cassini spacecraft detected an extremely tenuous exosphere containing oxygen and carbon dioxide, produced as Saturn's magnetosphere strikes the icy surface. The Voyagers imaged it from a distance before Cassini's detailed mapping.