Titan's atmosphere. Cassini space probe image of Titan, the largest moon of the planet Saturn. The colours represent infrared (red and green) and ultraviolet (blue) radiation emitted by Titan's atmosphere. Infrared radiation is where methane in Titan's atmosphere has absorbed light. This varies across Titan, and the red colour in the northern hemisphere indicates that this area is brighter. Ultraviolet radiation from the upper atmosphere extends hundreds of kilometres above the surface (blue ring). Titan consists of ice and rock with a thick atmosphere of mostly nitrogen. Its diameter is over 120,000 kilometres.