Saturn's tiny moon Daphnis orbits a gap in the A Ring, causing small waves with its gravity. Now, as the gas giant approaches its equinox, the Cassini probe has captured the waves on camera for the first time.
Daphnis, which is just eight kilometers in diameter, is one of Saturn's shepherd moons, tracing its orbit inside the Keeler gap in Saturn's main ring. It appears as a pin prick of light, but its gravity is sufficient to pull the ring's edges out of their plane, forming undulating vertical structures. Although astronomers have predicted the waves through simulations, they have never before been captured on film. But as Saturn approaches it equinox — an event that occurs once every 15 Earth years — the rings are illuminated in such a way that shadows from the waves are visible on the A Ring, allowing Cassini to photograph the phenomenon for the first time.