Links
- Wikipedia
- Epimetheus on Wikipedia
Epimetheus
Details
Epimetheus is a porous, cratered inner moon of Saturn that shares two neighboring orbits with Janus. About every four years, the pair exchange momentum and swap which moon follows the inner path.
Epimetheus is difficult to describe without Janus because the two moons were once mistaken for a single object. Observations in 1966 did not fit one stable orbit, and astronomers eventually realized that two distinct moons were following almost the same path around Saturn. Voyager 1 confirmed the pair in 1980.
About every four Earth years, the faster moon on the inner path catches the slower moon on the outer path. Their gravity transfers momentum between them, pushing the inner moon outward and pulling the outer moon inward. They effectively exchange orbits while remaining thousands of kilometers apart, a co-orbital arrangement unlike any other known pair of moons in the Solar System.
Epimetheus is also a visibly battered world. It is an irregular, porous body rich in water ice, with large craters, grooves, and a flattened south polar region that may preserve the remains of a major impact basin. Meteoroid strikes eject dust from Epimetheus and Janus into a faint ring along their shared orbit, connecting the moons' ancient surfaces directly to Saturn's ring system.
56.6km
Key facts
- Category
- Moons
- Object class
- Co-orbital inner moon
- Composition
- Water ice (porous rubble pile)
- Temperature
- 78 K surface
Scale context
Where Epimetheus sits on the full axis
By size on the journey, Epimetheus sits between 21 Lutetia and Prometheus. The band below compares Epimetheus with nearby Co-orbital inner moon objects so the size jump stays easy to read.
Shared physical scale
155km
Together, these objects make the size change around Epimetheus easy to compare at a glance.
Sources
References for Epimetheus
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.
- Epimetheus — 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.