Helene (33 kilometers, 21 miles across) and tiny Polydeuces (not seen here), are Trojan moons of Dione (1,123 kilometers, 698 miles across), orbiting about 60 degrees ahead of and behind the much larger moon. Polydeuces (or S/2004 S5) was discovered by the Cassini Imaging Team.
(Tethys also has two of its own Trojan moons.)
The image was taken in visible light with the narrow angle camera on May 20, 2005, from a distance of approximately 760,000 kilometers (472,000 miles) from Helene. The image scale is 5 kilometers (3 miles) per pixel. This view of Helene has been magnified by a factor of three and sharpened to aid visibility.
[Caption updated on October 5, 2005.]
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.