Daphnis Edge Wave Shadows in Motion

In images released by the Cassini Imaging Team and its leader, Carolyn Porco, Saturn's little moon Daphnis and its entourage of waves on the edge of the Keeler gap in Saturn's rings cast long shadows in this movie created from images taken as the planet approaches its mid-August 2009 equinox. This movie is a sequence of 10 images, each taken about one minute 30 seconds apart. The small moon Daphnis (8 kilometers or 5 miles across) occupies an inclined orbit within the 42-kilometer (26-mile) wide Keeler Gap in Saturn's outer A ring. Recent analyses -- released June 11, 2009 -- by imaging scientists illustrate how the moon's gravitational pull perturbs the orbits of the particles forming the gap's edge and sculpts the edge into waves having both horizontal (radial) and out-of-plane components. Measurements of the shadows in this and other images indicate that the vertical structures range between one-half to 1.5 kilometers tall (about one-third to one mile), making them as much as 150 times as high as the ring is thick. The main A, B and C rings are only about 10 meters (about 30 feet) thick. Daphnis itself can be seen casting a shadow onto the nearby ring. These images of shadows cast onto the rings and others like it are only possible around the time of Saturn's equinox which occurs every half-Saturn-year (equivalent to about 15 Earth years). The illumination geometry that accompanies equinox lowers the sun's angle to the ringplane and causes out-of-plane structures to cast long shadows across the rings. Additional images and more information can be found at http://ciclops.org . (Images: NASA/JPL/SSI)