Shepherd Moons

Prometheus, one of the inner moon and ring-shaper of Saturn is seen in this picture 30 minutes after it is tore into Saturn's F ring. Cassini snapped this image just as the moon was creating a new streamer in the ring.

Prometheus is one of the “shepherd moon” or ring-shaper of Saturn’s F ring. Shepherd moons act as maintainer of the ring, keeping the sharpness of the ring’s edge by either deflecting the material back into the ring, eject it from the system, or accreted it onto the moon itself. Other known shepherd moons are Metis and Adrastea (Jupiter), Pandora (Saturn), Galatea (Neptune), and some others.

The process of deflecting, ejecting, and accreting ring materials is studied extensively by Cassini. Some of this study involves a movie sequence of what might look as if the moon is playing on a “water surface” (the ring), which is kind of mesmerizing.

Shaping the Drapes. Prometheus appears first, then Pandora follows along outside of the F ring.

Prometheus’s Soft Collision. As Prometheus was located inside the F ring’s, during Prometheus outermost distance from Saturn, it nearly touches the F ring, as seen in this image sequence.