GEYSERS AND ICEFIELDS
Voyager 2 confirmed the existence of five thin rings around Neptune and added six satellites to the two already known. It also took a close look at the largest satellite, Triton.
Two-thirds the size of our Moon, Triton displayed a varied face to the cameras— plains, impact craters, a strange cantaloupe terrain of pits and depressions crossed by ridges, and a southern hemisphere with a thin, pinkish ice cap of nitrogen. Triton also has plumes—geysers of nitrogen gas shooting 5 miles (8 km) straight up into a thin atmosphere of nitrogen and some methane. Winds then blow the gas plumes about 60 miles (100 km) downrange.
Triton is the only major satellite with a retrograde orbit. Scientists think it was captured by Neptune, maybe after drifting in from the Kuiper Belt (see p. 138). However, it has a much rockier composition than the comet-like objects orbiting in the belt. Perhaps it changed during capture, which possibly involved collisions with other, now-vanished moons.
Planetary scientists believe Triton may be providing us with a preview of Pluto, which is probably another Kuiper Belt refugee and has not yet been visited by any spacecraft.