Orbiting in the Encke Gap of Saturn's A ring, the moon Pan casts a shadow on the ring in this image taken about six months after the planet's August 2009 equinox.
Pan (28 kilometers, or 17 miles across) can be seen overexposed on the far left of the image near one of two bright ringlets in the Encke Gap. A background star appears nearby. The gravity of Pan affects the particles of the nearby ringlet, perhaps making the ringlet appear discontinuous here.
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, unilluminated side of the rings from about 25 degrees below the ringplane.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Jan. 10, 2010. The view was acquired at a distance of approximately 783,000 kilometers (487,000 miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 147 degrees. Image scale is 4 kilometers (2 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