Saturn's moon Telesto is visible below and to the left of center in this image from the Cassini spacecraft.
Telesto (24 kilometers, or 15 miles across) shares the orbit of Saturn's moon Tethys (1,071 kilometers, or 665 miles across), leading the larger moon in its path by 60 degrees. Similarly sized Calypso (22 kilometers, or 14 miles across) trails Tethys by the same amount. These positions, called Lagrange points, are dynamically stable. In being co-orbital moons of Tethys, Telesto and Calypso are like the Trojan moons of Jupiter, which occupy Lagrange points and orbit 60 degrees ahead and behind of Jupiter. The Saturnian moon Dione also has companion moons: Helene, which leads Dione in its orbit, and the Cassini-discovered trailing Lagrange moon, Polydeuces.
North on Saturn is to the upper left in this view. The image was taken at a Sun-Telesto-spacecraft, or phase, angle of 90 degrees. Telesto is seen here at a phase similar to that of a first-quarter moon, where only half of the visible hemisphere is illuminated by sunlight.
The planet's night side is at the upper right. The rings stretch across the top of the image and are overexposed in this view.
The image was taken in visible light with the Cassini spacecraft narrow angle camera on Jan. 18, 2005, at a distance of approximately 3.7 million kilometers (2.3 million miles) from Telesto. Resolution in the image is 7 kilometers (4 miles) per pixel. Telesto has been brightened by a factor of two to aid visibility.
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 team is based at the Space Science Institute, Boulder, Colo.
Credit: NASA/JPL/Space Science Institute