Saturn’s moon Daphnis raises waves wherever it goes. In fact, such waves are one way that scientists search for undiscovered moons in the ring gaps. The waves that Daphnis (8 km across) raises on the edges of the Keeler Gap can also be used to deduce the moon’s mass and even some of its orbital behaviour. The image was taken in visible light by the international Cassini spacecraft on 10 October. See http://photojournal.jpl.nasa.gov/catalog/PIA20511
