Looking like an over-ripe cantaloupe, Neptune's satellite Triton is in the foreground while Neptune itself looms on the upper right. At a distance of 220 thousand miles, Triton is about the same distance from Neptune as the moon is from the Earth. A frozen world that's somewhat smaller than the moon, Triton is the seventh and largest of Neptune's satellites, completing an orbit every six days. Triton is believed to be composed primarily of rock and water ice with traces of methane and other compounds.

In his 1994 book, A Pale Blue Dot, the late astronomer Carl Sagan suggests that Triton and Saturn's haze-shrouded satellite Titan have much in common, differing primarily in the amount of warmth they receive from the Sun; Triton is three times further from the Sun than Titan, itself a frigid world, and as much as 60º F colder, difference enough to dissuade Triton from forming a substantial atmosphere.