Saturn's moon Dione passes by the moon Tethys in this Cassini spacecraft depiction of a "mutual event." Mutual events occur when, from the vantage point of Cassini, one moon appears to pass close to or in front of another moon.
Mutual event observations help scientists refine their understanding of the orbits of Saturn's moons. See Catching Big Sister to watch a movie of a mutual event. Lit terrain seen here is on Saturn-facing, trailing hemisphere side of both Tethys (1,062 kilometers, or 660 miles across) and Dione (1,123 kilometers, or 698 miles across).
The image was taken in visible green light with the Cassini spacecraft narrow-angle camera on March 26, 2010. The view was obtained at a distance of approximately 2 million kilometers (1.2 million miles) from Dione and 2.4 million kilometers (1.5 million miles) from Tethys. Image scale in the original image was 12 kilometers (7 miles) per pixel on Dione and 14 kilometers (9 miles) per pixel on Tethys. The image was contrast enhanced and magnified by a factor of two to enhance the visibility of surface features.
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