Astronomy Picture of the Day

Explanation: Yesterday, Cassini became the first spacecraft to enter orbit around gas giant Saturn, rocketing through a 25,000 kilometre wide gap in the distant planet's magnificent system of icy rings at about 15 kilometres 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 kilometres 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 kilometres wide that tiny moon, Pan, was also detected by Cassini's camera as the spacecraft approached the Saturnian system.