Prometheus shares a 121:118 orbital resonance with Saturn’s moon Pandora.
Pandora is a small inner moon of Saturn discovered in images from the Voyager 1 spacecraft in 1980. It orbits near Saturn’s narrow F ring and is classified as an outer shepherd satellite. Prometheus, another small Saturnian moon, lies closer to Saturn and helps shape the F ring through its gravitational effects.
The 121:118 resonance means that for every 121 orbits Pandora makes, Prometheus completes approximately 118. Their repeated gravitational interactions help produce the complex structure seen in the F ring, including waves and irregular features.
Pandora is often confused with Epimetheus and Janus because those moons also occupy a notable co-orbital relationship around Saturn. That is a different orbital arrangement: Pandora’s distinctive pairing here is with Prometheus, not with either co-orbital moon.