Titan has a thick nitrogen-rich atmosphere and lakes of liquid methane. It is Saturn’s largest moon and the only moon in the Solar System known to have a dense atmosphere and stable bodies of liquid on its surface.
Titan’s atmosphere is composed mainly of nitrogen, with methane as an important secondary component. At its surface temperature of about 94 kelvins, or −179 °C, methane and ethane can participate in a cycle resembling Earth’s water cycle: they evaporate, form clouds, fall as rain, and collect in rivers and lakes.
NASA’s Cassini spacecraft studied Titan from 2004 to 2017, while the Huygens probe landed there in 2005. Radar observations revealed seas and lakes concentrated near the polar regions. Titan is also scientifically important because its carbon-rich chemistry may resemble some conditions present on the early Earth, despite its extremely cold environment.