The small moon Helene leads Dione (not shown) by 60 degrees in the moons' shared orbit.
Helene (33 kilometers, or 21 miles across) is a "Trojan" moon of Dione (1,123 kilometers, or 698 miles across), named for the Trojan group of asteroids that orbit 60 degrees ahead of and behind Jupiter as it circles the Sun.
The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Nov. 24, 2008 at a distance of approximately 68,000 kilometers (42,000 miles) from Helene and at a Sun-Helene-spacecraft, or phase, angle of 30 degrees. Image scale is 408 meters (1,338 feet) per pixel.
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