CICLOPS: Cassini Imaging Central Laboratory for OPerationS
Hidden Janus

Hidden Janus
PIA 12558

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  The small moon Janus is almost hidden between the planet's rings and the larger moon Rhea.

The northern part of Janus can be seen peeking above the rings in this image of a "mutual event" in which Janus (179 kilometers, 111 miles across) moved past Rhea (1528 kilometers, 949 miles across). Mutual event observations such as this one, in which one moon passes close to or in front of another, help scientists refine their understanding of the orbits of Saturn's moons. See PIA11692 to watch a movie of a mutual event.

The view was acquired at a distance of approximately 2.7 million kilometers (1.7 million miles) from Janus and about 3.1 million kilometers (1.9 million miles) from Rhea. Rhea is a slightly overexposed in this image.

This view looks toward the northern, sunlit side of the rings from just above the ringplane.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 11, 2009. Scale on Janus is about 16 kilometers (10 miles) per pixel. Scale on Rhea is about 19 kilometers (12 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.

For more information about the Cassini Equinox Mission visit, and

Credit: NASA/JPL/Space Science Institute
Released: February 26, 2010 (PIA 12558)
Image/Caption Information

Alliance Member Comments
Dragon_of_Luck_Mah_Jonng1971 (Feb 28, 2010 at 7:18 PM):