In this image, taken on December 7, 2011, the line of Saturn's rings disrupts Cassini's view of the moons Tethys, on the right, and Titan, on the left.

Tethys was another of the four moons discovered by Giovanni Domenico Cassini, this one in 1684. Tethys is the second brightest of Saturn's moons, after Enceladus.

Titan is Saturn's largest moon by far. Its diameter is 50 percent larger than Earth's moon. In fact, only one moon in the entire solar system—Jupiter's Ganymede—is larger than Titan.