The moon Iapetus, like the "force" in Star Wars, has both a light side and a dark side.
Scientists think that Iapetus' (914 miles or 1471 kilometers across) dark/light asymmetry was actually created by material migrating away from the dark side. For a simulation of how scientists think the asymmetry formed, see Thermal Runaway Model.
Lit terrain seen here is on the Saturn-facing hemisphere of Iapetus. North on Iapetus is up and rotated 43 degrees to the right. The image was taken in green light with the Cassini spacecraft narrow-angle camera on Jan. 4, 2015.
The view was acquired at a distance of approximately 2.5 million miles (4 million kilometers) from Iapetus. Image scale is 15 miles (24 kilometers) per pixel.
The Cassini Solstice 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.