Neptune from Triton Artwork of a geyser black erupting on Triton the largest moon of Neptune upper right Triton among the coldest places in the solar system has temperatures of degrees Celsius The nitrogen and methane atmosphere forms ice on the surface The Voyager space probe passed near Triton in August Pictures were beamed back of dark stains in the sunlit regions These were explained as soot ejected by geysers of nitrogen gas and blown into streaks by the prevailing winds Triton orbits kilometres from Neptune the eighth planet and has a gravity that is less than one tenth that of Earth