Pulchritudinous Perturbations

The moon Prometheus creates an intricate pattern of perturbation in Saturn's F ring while the moon Daphnis disturbs the A ring in this image taken after the planet's August 2009 equinox.

Prometheus (86 kilometers, or 53 miles across) can be seen between the thin F ring and the A ring in the middle left of the image. The gravity of potato-shaped Prometheus periodically creates streamer-channels in the F ring. To learn more and to watch a movie of this process, see Soft Collision.

Near the bottom of the image, Daphnis (8 kilometers, or 5 miles across) can be seen creating edge waves in the Keeler Gap of the A ring. 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. These edge waves can be seen casting shadows in this image. See Wavy Shadows to learn more about this process.

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 Small Find Near Equinox).

This view looks toward the northern, sunlit side of the rings from about 6 degrees above the ringplane.

The image was taken with the Cassini spacecraft narrow-angle camera on Aug. 22, 2009 using a spectral filter sensitive to wavelengths of near-infrared light centered at 862 nanometers. The view was acquired at a distance of approximately 2 million kilometers (1.2 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 129 degrees. Image scale is 12 kilometers (7 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.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The Cassini imaging team homepage is at http://ciclops.org .

Credit: NASA/JPL/Space Science Institute