June 11, 2009
The 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 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 (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 (see Wavy Shadows and Tiny Moon, Looming Shadows) 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..
Bright specks in some movie frames are stars in the background.
This view looks toward the sunlit side of the rings from about 25 degrees below the ringplane. The images were taken in visible light with the Cassini spacecraft narrow-angle camera on May 25, 2009. The view was obtained at a distance of approximately 768,000 kilometers (477,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 52 degrees. Image scale is 4 kilometers (3 miles) per pixel.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
Credit: NASA/JPL/Space Science Institute