Titan is the largest moon of Saturn. It is the second-largest moon in the Solar System, after Jupiter’s Ganymede, and is larger than the planet Mercury by diameter, although it has much less mass.
Dutch astronomer Christiaan Huygens discovered Titan in 1655. It was the first moon discovered around Saturn and remained the planet’s only known satellite for more than a century. Titan’s thick atmosphere made its surface difficult to observe from Earth.
Titan is famous for having a dense nitrogen-rich atmosphere and stable bodies of liquid on its surface. Those lakes and seas are made mainly of liquid methane and ethane, not water. The moon also has a weather cycle in which hydrocarbons evaporate, form clouds, and fall as rain.
NASA’s Cassini spacecraft and the Huygens probe transformed knowledge of Titan. Huygens landed there in January 2005, marking the first landing in the outer Solar System. Titan remains a major target for planetary science because of its complex chemistry and possible subsurface ocean.