Methane is the dominant greenhouse gas in Titan’s atmosphere after nitrogen. Titan’s lower atmosphere is composed primarily of about 94.2% nitrogen and 5.65% methane, with much smaller amounts of hydrogen and other gases.
Methane is central to Titan’s weather and surface processes. It can evaporate, form clouds, condense, and fall as rain, creating a methane cycle that resembles Earth’s water cycle. Titan has methane clouds, rainfall, rivers, and polar lakes, although the temperatures are cold enough for methane rather than water to act as the main surface liquid.
Ultraviolet sunlight breaks methane apart in Titan’s upper atmosphere. The resulting chemical reactions produce more complex hydrocarbons and contribute to the moon’s thick orange haze. Because methane is gradually destroyed and lost through atmospheric chemistry and escape, scientists infer that Titan must have an internal or subsurface reservoir capable of replenishing it.
Ammonia, ozone, and carbon dioxide occur only in trace or minor amounts and are not the second-most abundant atmospheric constituent. Methane is also a greenhouse gas on Titan, contributing to its atmospheric heat balance.