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Nitrogen
As with Earth's atmosphere, Titan's consists primarily of nitrogen gas, making up 95 percent of the total. Scientists have also detected nitrogen in Saturn's atmosphere, but they do not know if Titan got its nitrogen from Saturn or from another source, such as comets. Nitrogen remains a gas at Titan's frigid -290 degree Fahrenheit temperature, though nitrogen-containing compounds, such as ammonia, are solid, remaining on the moon's surface.
Methane
While the temperature on Titan is low enough to have liquid methane, some of its vapor finds its way into the atmosphere. Methane is a compound made from carbon and hydrogen and is found on Earth and in the outer solar system. Exposed to the sunlight in Titan's upper atmosphere, methane reacts to form other, more complex hydrocarbon molecules. Because Titan's gravity is about one-seventh that of Earth's, its methane and most of the other gases should have escaped into space long ago, so its presence poses a puzzle. Some scientists speculate that gases from volcanic explosions replenish the atmosphere.
Hydrogen and Helium
Titan has traces of hydrogen and helium, the two lightest elemental gases. Hydrogen reacts chemically with almost every other element, though helium reacts with none. Saturn has both gases: hydrogen accounts for 96 percent and helium makes up another 3 percent. Saturn's enormous gravity keeps these light gases in place; Titan does not have the advantage of strong gravity, though its low temperatures slow down the gases' rate of escape.
Other Hydrocarbons
Chemical reactions in Titan's atmosphere produce trace amounts of benzene, propane and other hydrocarbons. Titan's cold conditions turn these substances, liquids and gases, at comfortable temperatures here on Earth, into an outer-solar-system form of snow and rain. In vapor form, they give Titan's atmosphere its characteristic hazy orange color, similar to that of an industrial city's on a smoggy day.