Prometheus is Pandora’s companion moon in shepherding Saturn’s F ring.
Prometheus orbits inside the F ring, while Pandora orbits outside it. Their combined gravitational effects help confine the ring and create its unusual structure. Because the two moons occupy opposite sides of the ring, they are often described as shepherd satellites.
Prometheus is an irregular, elongated moon measuring roughly 136 kilometres across at its longest dimension. It was discovered in images taken by Voyager 1 in 1980. Pandora was found in the same broad period, and both moons were later examined closely by the Cassini spacecraft.
The name can cause confusion with Epimetheus, another moon of Saturn and the mythological brother of Prometheus. Epimetheus and Janus share a distinctive orbital relationship, but they are not the pair that shepherds the F ring. The F-ring pair is Prometheus and Pandora.