CICLOPS: Cassini Imaging Central Laboratory for OPerationS

The Dancing Moons
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In their orbital ballet, Janus and Epimetheus swap positions every four years - one moon moving closer to Saturn, the other moving farther away. The two recently changed positions (the swap occurring on January 21, 2006), and Janus will remain the innermost of the pair until 2010, when they will switch positions again.

Although the moons appear to be close in the image, they are not. Janus (179 kilometers, 111 miles across, at right) is about 40,000 kilometers (25,000 miles) farther away from Cassini than Epimetheus (113 kilometers, 70 miles across, at left) in this view. In fact, even when they are at their closest, tugging at each other and swapping orbital positions, they are never closer than about 15,000 kilometers (9,000 miles).

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on March 20, 2006 at a distance of approximately 452,000 kilometers (281,000 miles) from Epimetheus and 492,000 kilometers (306,000 miles) from Janus. The image scale is 3 kilometers (2 miles) per pixel on both moons.

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 Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. 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-Huygens mission, visit and the Cassini imaging team home page,

Credit: NASA/JPL/Space Science Institute
Released: May 3, 2006 (PIA 08170)
Image/Caption Information
  The Dancing Moons
PIA 08170

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