Surface of Titan, computer artwork. This is Saturn's largest moon and the only moon to have a planet-like atmosphere. The atmosphere consists of nitrogen and organic compounds, mainly ethane and methane, which give it its distinctive orange colour. The surface of Titan is depicted as being covered in liquid methane, forming rivers and deltas that empty into lakes. It is thought that the hydrocarbons form as sunlight acts on the methane in Titan's upper atmosphere. There are also mountains, thought to be made of rock and ice. Titan's atmosphere could resemble that of primitive Earth and could hold clues about the origin of life.