File:Saturn's Moon - Daphnis edge wave shadows.jpg

Summary
Never-before-seen looming vertical structures created by the tiny moon Daphnis cast long shadows across the rings in this startling image taken as Saturn approaches its mid-August 2009 equinox. Daphnis, 8 kilometers (5 miles) across, occupies an inclined orbit within the 42-kilometer (26-mile) wide Keeler Gap in Saturn's outer A ring. Recent analyses by imaging scientists published in the Astronomical Journal 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 and vertical 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.

This image of shadows on the rings and others like it (see PIA11656 and PIA11655) 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.

This view looks toward the sunlit side of the rings from about 57 degrees below the ringplane. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 24, 2009. The view was acquired at a distance of approximately 826,000 kilometers (513,000 miles) from Daphnis and at a Sun-Daphnis-spacecraft, or phase, angle of 121 degrees. Image scale is 5 kilometers (3 miles) per pixel.