Titan is the largest natural satellite of Saturn. It is the second-largest moon in the Solar System, after Ganymede, and is larger than the planet Mercury by diameter, although Titan has much less mass.
Titan is especially notable for its dense atmosphere, which is composed mostly of nitrogen with methane and other compounds. It is the only moon known to have a thick atmosphere and the only world besides Earth known to have stable bodies of liquid on its surface. Titan’s lakes and seas, however, contain liquid methane and ethane rather than water.
The Cassini spacecraft studied Saturn and Titan from 2004 to 2017, while the Huygens probe landed on Titan in January 2005. NASA’s Dragonfly mission is planned to explore Titan with a rotorcraft lander, investigating its organic chemistry and potentially habitable environments.