Ice volcanoes on Triton, artwork. Triton is the largest moon of the planet Neptune (upper centre). Tritons surface is one of the coldest in the solar system, with temperatures of minus 235 degrees Celsius. Its nitrogen and methane atmosphere forms ice on its surface, and dark stains have been observed, thought to be soot, ejected by geysers of nitrogen gas and blown into streaks by the prevailing winds (as at upper left). Triton is 355,000 kilometres from Neptune, which it itself around 4.5 billion kilometres from the Sun.
