Saturn's moon Prometheus

Saturn's moon Prometheus, orbiting near the streamer-channels it has created in the thin F ring, casts a shadow on the A ring in this image taken a little more than a week after the planet's August 2009 equinox.

The ability of the potato-shaped Prometheus to pull material out of the F ring was first theorized in the late 1990s and finally imaged by Cassini in 2004. But because these so-called "streamer-channels" have constantly shifted as Prometheus and the F ring have moved, the F ring has never looked the same twice. The gravitational pull of other moons on other rings has created waves in the edges, but nothing quite as extreme as the streamer-channels of Prometheus.