Icy moon of SaturnAn ancient, cratered archive
Rhea
Rhea is Saturn's second-largest moon: a bright, quiet ice world with a long memory of impacts.
- Host
- Saturn
- Type
- Ancient icy moon
- Mean diameter
- 1,528 km
- Mean orbital radius
- 527,100 km
- Orbital period
- 4.52 days
- Surface gravity
- 0.264 m/s²
- Surface
- Bright water ice and regolith
- Ocean evidence
- Uncertain
Rhea up close
NASA imagery
A heavily cratered ice moon
Rhea's surface is saturated with impacts and shows little large-scale tectonic resurfacing. Bright ice and darker rocky material make the slopes and crater walls stand out.
Cassini found a tenuous oxygen-carbon dioxide exosphere around Rhea. It is far too thin to breathe or support weather, but it shows that radiation can release particles from an icy surface.
Inside Rhea
Rhea's density is close to that of water ice, indicating a deep ice-rich interior around a relatively small rocky core. Evidence for an ocean remains uncertain.
The moon may once have had a tenuous ring system, although later observations did not confirm it. Its crater record and fractures remain important tests of how Saturn's moons evolved.
Worth knowing
Rhea is named after a Titaness of Greek mythology.
It is Saturn's second-largest moon after Titan.
The moon's weak gravity means its escape velocity is only about 0.64 kilometres per second.
Watch and explore
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Rhea: Saturn's Dead Moon SpaceHorus
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Research & further reading
Mission imagery and measurements are interpreted alongside orbital data. Follow the source links for the current NASA overview and precise satellite parameters.