Saturn's moon Prometheus casts a narrow shadow on the rings near the much larger shadow cast by the planet in this Cassini spacecraft image taken about five months after Saturn's August 2009 equinox.
Prometheus (86 kilometers, or 53 miles across) orbits in the Roche Division between the A ring and the thin F ring. The moon's shadow can be seen on the F ring above the middle of the image. The shadow of the planet covers the upper left of the image. Several background stars are visible.
The novel illumination geometry during equinox causes out-of-plane structures to look anomalously bright and cast shadows across the rings. Images with this novel illumination are only attainable 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 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 10 degrees below the ringplane.
The image was taken in visible red light with the Cassini spacecraft narrow-angle camera on Jan. 2, 2010. The view was acquired at a distance of approximately 2.3 million kilometers (1.4 million miles) from Saturn and at a Sun-Saturn-spacecraft, or phase, angle of 102 degrees. Image scale is 13 kilometers (8 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