Links
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- Rhea on Wikipedia
Rhea
Details
Rhea is Saturn's second-largest moon, a cold icy body with an old, heavily cratered surface. Cassini also detected an extremely thin oxygen and carbon dioxide exosphere around it, making this quiet-looking moon chemically more interesting than it first appears.
Rhea matters because it is large enough to be one of Saturn's major moons, yet quiet enough to preserve an ancient surface. It is cold, airless in any ordinary sense, and heavily cratered, closer in mood to an old icy archive than to an active plume world like Enceladus.
That apparent stillness is the point. NASA describes Rhea as mostly ice with rock mixed through it, farther from Saturn than Dione and Tethys and less affected by tidal heating. Without enough internal warmth to erase old craters widely, its surface keeps a memory of impacts that more active moons can blur or rewrite.
Cassini added a subtle twist: Rhea has an extremely thin exosphere containing oxygen and carbon dioxide. That does not make it Earth-like, but it does make the surface chemistry more interesting. Rhea shows that a quiet icy moon can still participate in processes driven by radiation, ice, and planetary magnetospheres.
668km
Key facts
- Category
- Moons
- Object class
- Large icy moon
- Composition
- Water ice and rock
- Temperature
- ~99 K sunlit surface
Scale context
Where Rhea sits on the full axis
Together, these objects make the size change around Rhea easy to compare at a glance.
Sources
References for Rhea
Measurements and descriptive context are compiled by the Scale of Space team from the references below. If you find an error, please let us know.
- Rhea — Wikipedia
- Visual reference: Wikimedia Commons (NASA / JPL / Space Science Institute, Public domain)
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Scale of Space is a scroll-based journey through the universe, placing objects on a single logarithmic scale so you can compare size across an unbroken range.
Guides turn parts of that scale into curated essays, while focused views let you explore the same range through specific groups of objects.