Saturnian Two-Fer

The Cassini spacecraft captured these images of Saturn's moons Rhea (left) and Dione as it sped past them on December 22 and 23, respectively. Cassini was about 18,000 miles (29,000 km) from Rhea, and 154,000 miles (257,000 km) from Dione. The surfaces of both moons probably consist mainly of frozen water. The wispy white markings on Dione are the faces of steep canyons where fresh ice is exposed. [NASA/JPL/SSI]