Methane (CH4), the simplest of organic compounds, is found in the form of a gas associated with many solar system objects. Methane as a gas in the atmospheres of the Jovian planets and satellites and as a liquid on some of their surfaces probably formed in a primordial chemical reaction between hydrogen and carbon, not as a result of biological processes. Of interest to planetary scientists is the predicted occurrence of solid, crystalline methane as an important mineral phase. So far, the solid phases on the icy surfaces of the cold planets and their satellites have been identified as water (H20) ice. Recently, astronomers from the University of Hawaii and from the Jet Propulsion Laboratory have discovered crystalline methane on the surfaces of the distant planet Triton, which is a large satellite of Neptune, and on Pluto. These are the only bodies within the solar system so far that may have observable methane ice, although others may have methane mixtures.