NASA's Cassini spacecraft captured these raw, unprocessed images of Saturn's moon Rhea during a close flyby on March 9, 2013. This flyby marks the mission's last targeted encounter with Rhea and only the fourth Rhea targeted encounter for the whole mission.
Cassini flew by Rhea at an altitude of 620 miles (997km). This flyby was designed primarily for the radio science sub-system (RSS) to measure Rhea's gravity field.
During closest approach and while the RSS was measuring the icy satellite's gravity field, the imaging team rode along and captured 12 images of Rhea's rough and icy surface. Outbound from Rhea, Cassini's cameras captured a set of global images from a distance of 167,000 miles (269,000 kilometers) which show the ancient and heavily cratered surface on Saturn's second largest moon.
Scientists are still trying to understand some of the curious features they see in these Rhea images, including a curving, narrow fracture or graben. A graben is a block of ground, lower than its surroundings and bordered by cliffs on either side. This feature looks remarkably recent, cutting most of the craters it crosses, with only a few small craters superimposed. The feature described can be seen in preview #2.