Number 7 (Story #4), November 1, 1990 by Phillip F. Schewe and Ben Stein NEPTUNE'S MOON TRITON exhibited several interesting features to the passing eye of Voyager 2. The spacecraft observed at least four active plumes, emitting nitrogen, ice, and dark particles. Some of the emitted materials seemed to rise to an altitude of 8 km. It is unclear what the energy source for this activity may be. Triton's atmosphere is rather like that of Mars, with N2 instead of CO2 and CH4 instead of water. (Numerous Voyager 2 reports in Science, October 19, 1990.)