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
(181 kilometers, or 113 miles across at right) is about 40,000 kilometers
(25,000 miles) farther away from Cassini than Epimetheus (116 kilometers,
or 72 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 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.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov/home/index.cfm. The Cassini imaging team
homepage is at http://ciclops.org.