Illustration of the atmosphere of Titan, Saturns largest moon. Titans atmosphere is primarily composed of nitrogen (about 95 percent) and methane (about 5 percent). Other carbon-rich compounds are also present in smaller amounts. When exposed to the Suns ultraviolet light and high-energy particles in Saturns magnetic field, methane and nitrogen molecules in Titans upper atmosphere are split apart. The resulting fragments recombine to form various organic chemicals that often include nitrogen, oxygen, and other elements that are vital for life on Earth.