Saturn's moons do more than just orbit the planet: they interact with its rings, too. In this image, you can see the moon Prometheus' gravitational field gently sculpting the planet's F ring.
Over on the left, you can also just about make out some ripples at the edge of the Keeler gap, which are in fact a result of another moon—Daphnis—though that satellite is sadly too small to see in this image. The gravitational fields pull the dust, ice and other particles within the rings, gently changing their shape.
It's easier to make out Prometheus because it's 53 miles across, whereas Daphnis is just 5 miles in size. The image, acquired by Cassini, shows a view of Saturn acquired from 1.2 million miles away. [NASA]
Image credit: NASA/JPL-Caltech/Space Science Institute