Credit: NASA/JPL-Caltech/Space Science Institute Public Domain — NASA Media Usage Guidelines

MOON

Rhea

Saturn's second-largest moon — a heavily cratered ice world with a tenuous oxygen exosphere.

Orbits Saturn

Second-largest moon of Saturn; very heavily cratered.
Tenuous oxygen + COu2082 atmosphere detected by Cassini in 2010.
Composition ~75% water ice, ~25% rock.

About Rhea

Rhea is the second-largest moon of Saturn and the ninth-largest moon in the Solar System. It is composed of approximately three parts water ice to one part rock, heavily cratered over 4 billion years. In 2010 the Cassini spacecraft detected a very thin but permanent oxygen and carbon-dioxide atmosphere — the first time molecular oxygen had been detected in the atmosphere of a world other than Earth or Mars.

Live · 3DSee Rhea in the Live 3D Solar SystemFly to Rhea and explore its orbit among the planets, moons & spacecraft in a full-screen interactive view.Launch 3D view

Physical Properties

Mean radius764 km

Mass2.306518e21 kg

Density1.236 g/cm³

Surface gravity0.264 m/s²

Rotation period108.42 h

Bond albedo0.949

Mean temp76 K

Atmosphere Composition

Oxygen (Ou2082) tenuous
Carbon Dioxide tenuous

Orbit

OrbitsSaturn

Semi-major axis527,108 km

Eccentricity0.001

Inclination0.345°

Orbital period4.518 d

Gallery

Hand-picked mission imagery of Rhea sourced from NASA and partner archives. Click any photo for full resolution and source attribution.

Saturn's second-largest moon Rhea, from Cassini. NASA/JPL-Caltech/Space Science Institute · Public Domain u2014 NASA Media Usage Guidelines

Crescent view of the cratered moon Rhea. NASA/JPL-Caltech/Space Science Institute

Imagery on this page is provided by the original mission teams. Full attribution terms: Image Rights & Credits.

Sources & Further Reading

Numerical values (radius, mass, orbital elements, temperatures) are drawn from NASA NSSDC Planetary Fact Sheets, JPL Horizons, and the JPL Small-Body Database. Last refreshed: 2026-06-08 01:37:02.