Titan and Saturn. Artwork showing Titan (left) and a crescent view of Saturn (right) and its rings. Titan, the largest moon of Saturn, has a diameter of 5150 kilometres. Titan's atmosphere (orange) is mainly nitrogen, with traces of methane. The atmospheric pressure is greater than that on Earth, and a layer of clouds obscures the view of the surface. The orange colour results from the action of sunlight on the methane, producing a thick smog of hydrocarbons. The surface temperature is -180 degrees Celsius. The Huygens probe landed on Titan in January 2005, but was unable to confirm whether liquid hydrocarbons are present on the surface.