The Encke Gap: A Moon Goes Here

Explanation: Yesterday, Cassini became the first spacecraft to enter orbit around gas giant Saturn , rocketing through a 25,000 kilometer wide gap in the distant planet's magnificent system of icy rings at about 15 kilometers per second . Turning to snap pictures , Cassini's narrow angle camera recorded this stunning close-up of a much smaller gap in the rings, the Encke Gap. A mere 300 kilometers wide, the Encke Gap is flanked by amazing structures within the rings -- scalloped edges and patterns of density waves are clear in the sharp image. While the rings of Saturn are likely debris from the breakup of a fair-sized icy moon, the Encke Gap itself is created by the repeated passage of a tiny moon . Only 20 kilometers wide that tiny moon, Pan , was also detected by Cassini's camera as the spacecraft approached the Saturnian system .