Ripples from Daphnis
December 22, 2009
Tiny Daphnis appears as a bright dot in the Keeler Gap next to shadows cast by the moon and the edge waves it has created in the A ring in this image taken before Saturn's August 2009 equinox.
Daphnis (8 kilometers, or 5 miles across) can be seen casting a short shadow on the left of the image. The moon has an inclined orbit and its gravitational pull perturbs the orbits of the particles of the A ring forming the Keeler Gap's edge and sculpts the edge into waves having both horizontal (radial) and out-of-plane components. Material on the inner edge of the gap orbits faster than the moon so that the waves there lead the moon in its orbit. Material on the outer edge moves slower than the moon, so waves there trail the moon. See PIA11656 to learn more about this process. Both the moon and the edge waves can be seen casting shadows in this image.
The novel illumination geometry that accompanies equinox lowers the sun's angle to the ringplane, significantly darkens the rings, and causes out-of-plane structures to look anomalously bright and cast shadows across the rings. These scenes are possible only during the few months before and after Saturn's equinox, which occurs only once in about 15 Earth years. Before and after equinox, Cassini's cameras have spotted not only the predictable shadows of some of Saturn's moons (see Across Resplendent Rings ), but also the shadows of newly revealed vertical structures in the rings themselves (see A Small Find Near Equinox).
This view looks toward the southern, sunlit side of the rings from about 20 degrees below the ringplane.
Three background stars are visible in this image.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on May 10, 2009. The view was acquired at a distance of approximately 969,000 kilometers (602,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 45 degrees. Image scale is 5 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