Taken in 1989 by Voyager 2 during its flyby of the Neptune system, this is a global color mosaic of Triton. With a radius about 22% smaller than Earth’s moon, Triton is the largest satellite of Neptune and is one of the few bodies in the solar system known to have a nitrogen-dominated atmosphere. The others are Earth and Saturn’s giant moon, Titan.
Triton is so cold that most of its nitrogen is condensed as frost, making it the only satellite in the solar system known to have a surface made mainly of nitrogen ice. The pinkish deposits constitute a vast south polar cap believed to contain methane ice. The dark streaks overlying these pink ices are believed to be an icy and perhaps carbonaceous dust deposited from huge geyser-like plumes, some of which were found to be active during the Voyager 2 flyby.
The bluish-green band visible in this image extends all the way around Triton near the equator; it may consist of relatively fresh nitrogen frost deposits. The greenish areas includes what is called the cantaloupe terrain, whose origin is unknown, and a set of “cryovolcanic” landscapes apparently produced by icy-cold liquids (now frozen) erupted from Triton’s interior.
This image was returned by the Voyager 2 spacecraft on July 3, 1989, when it was 76 million kilometers (47 million miles) from Neptune. The planet and its largest satellite, Triton, are captured in the field of view of Voyager’s narrow-angle camera. (via)