The effects of the small moon Prometheus loom large on two of Saturn's rings in this image taken a short time before Saturn's August 2009 equinox.
A long, thin shadow cast by the moon stretches across the A ring on the right. The gravity of potato-shaped Prometheus (86 kilometers, or 53 miles across) periodically creates streamer-channels in the F ring, and the moon's handiwork can seen be on the left of the image. To learn more and to watch a movie of this process, see Soft Collision.
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).
Prometheus is overexposed in this image. Bright specks in the image are background stars.
This view looks toward the northern, unilluminated side of the rings from about 28 degrees above the ringplane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 30, 2009. The view was acquired at a distance of approximately 1.8 million kilometers (1.1 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 97 degrees. Image scale is 10 kilometers (6 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