Saturn's icy moon Rhea passes in front of Titan as seen by NASA's Cassini spacecraft in 2009.
Some of the differences between the two large moons are readily apparent. While Rhea is a heavily-cratered, airless world, Titan's nitrogen-rich atmosphere is even thicker than Earth's.
This natural color image was taken in visible light with the Cassini narrow-angle camera on Nov. 19, 2009, at a distance of approximately 713,300 miles (1,148,000 kilometers) from Rhea.
The Cassini spacecraft ended its mission on Sept. 15, 2017.