The small moon Helene (33 kilometers, 21 miles across) leads Dione by 60 degrees in the moons' shared orbit. Helene is a "Trojan" moon of Dione, 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 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.