This image of Saturn's moon Rhea was captured by NASA's Cassini spacecraft. It shows the moon here in natural color, revealing bright, wispy markings similar to those on Saturn's moon Dione. The exact nature of these wispy features on Rhea is unknown. Rhea is 949 miles (1,528 km) in diameter, making it Saturn's second-largest moon. The moon's surface is heavily cratered. This indicates that the surface is extremely old and stable, with no active processes taking place to reshape it. Rhea has an extremely thin atmosphere composed of oxygen and carbon dioxide.