The Walnut-Shaped Moons of Saturn
The Cassini spacecraft has made some truly remarkable discoveries within the Saturnian system, where it has been orbiting for the last 13 years. One such discovery is of the walnut-shaped moons: Atlas, Daphnis, and Pan. These moons sport a prominent equatorial ridge pattern circumnavigating the moons (Saturn's moon Iapetus also as an equatorial feature, though not as prominent as these). The ridges are due to where the moons are located. They are all located in or very near to the ring system, and as a result, have 'swept up' material over the millions of years they've orbited Saturn, producing equatorial ridge patterns of various sizes.