The small moon Mimas passes in front of the larger moon Rhea which is partly obscured by Saturn's rings in this movie from Cassini.
Observations of mutual moon-crossing events, in which one moon passes close to or in front of another, help scientists refine their understanding of the orbits of Saturn's moons. This movie is a concatenation of 10 still images taken over a span of about 6 minutes. The images were reprojected to a uniform view and computer interpolation was used to smooth the moons' motions between the frames.
In this movie, Mimas (396 kilometers, 246 miles across) moves in front of the rings. Rhea (1528 kilometers, 949 miles across) reveals the delicate separations within the rings as the thin line of the F ring appears before the backdrop of the mid-southern latitudes of the moon. Mimas travels at an average speed of 14 kilometers per second. Rhea's average speed is about 8 kilometers per second.
In this view Rhea, at a distance of approximately 2.7 million kilometers (1.7 million miles), is farther from Cassini than Mimas . Mimas is closer to the spacecraft at a distance of approximately 2 million kilometers (1.2 million miles).
This view looks toward the northern, sunlit side of the rings from just above the ringplane.
The images were taken in visible light with Cassini's narrow-angle camera on Oct. 19, 2009. The view was obtained at a Sun-Mimas-spacecraft, or phase, angle of 95 degrees. Scale on Mimas is 12 kilometers (7 miles) per pixel.
The Cassini Equinox Mission is a joint United States and European endeavor. 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 was designed, developed and assembled at JPL. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.