Janus

satellite of Saturn

Also known as: S10

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Last updated

June 29, 2026

Quick Summary

Janus is a small, irregularly shaped moon of Saturn, discovered in 1966. It shares its orbit with another moon, Epimetheus, and they periodically swap orbits in a phenomenon known as co-orbital behavior. Janus is also considered a "shepherd moon" because its gravitational influence helps to shape Saturn's F ring.1

The name Janus originates from Roman mythology, where Janus was the god of doorways, gates, and beginnings, often depicted with two faces looking in opposite directions. This name is fitting for the moon due to its co-orbital relationship with Epimetheus.23

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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…
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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…
Read More