Epimetheus

satellite of Saturn

Also known as: S11

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Last updated

June 26, 2026

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Epimetheus is one of Saturn's moons, discovered in 1966. It is a co-orbital moon with Janus, meaning they share the same orbit. This unique arrangement causes them to exchange angular momentum every few years, resulting in one moon moving to a higher orbit and the other to a lower one. Epimetheus is relatively small, with a mean radius of approximately 69 km, and is thought to have formed from a protoplanetary disk around Saturn. It is considered a "shepherd moon" due to its gravitational influence on Saturn's rings, particularly the F ring.12

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Saturn
Orbital and rotational dynamics
Janus and Epimetheus are co-orbital moons—they share the same average orbit. Every few years they make a close approach, interacting gravitationally in such a way that one transmits angular momentum to the other, which forces the latter into a slightly higher orbit and the former into a…
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Janus and Epimetheus are co-orbital moons—they share the same average orbit. Every few years they make a close approach, interacting gravitationally in such a way that one transmits angular momentum to the other, which forces the latter into a slightly higher orbit and the former into a…
Read More