Round the Outside
October 6, 2009
The moon Pan casts a shadow on Saturn's outer A ring in this image taken as the planet approached its August 2009 equinox.
Pan (28 kilometers, or 17 miles across) orbits in the Encke Gap of the A ring, and its shadow has been imaged several times by Cassini cast in the direction of the interior of the A ring (see Pan's Very Own Shadow and Lengthening Shadows). In this image, the shadow is cast in the opposite direction.
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 Shadows and More Shadows).
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 29, 2009. The view was acquired at a distance of approximately 1.6 million kilometers (994,000 miles) from Pan. Image scale is 9 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