In the dark, chilly tropics of Saturn’s moon Titan, the Cassini probe has spotted what appears to be a lake of liquid methane, fueling speculation that caverns below might harbor life.
Titan has a rocky, icy surface coated by a thick atmosphere of nitrogen and methane. It’s a geologically-young moon, but below its dense atmosphere the surface is dotted by mountains and several possible cryovolcanoes, which are thought to erupt methane rather than magma.
It’s the only extraterrestrial object to have even shown clear evidence of stable bodies of surface liquid — in Titan’s case, methane — but these lakes of hydrocarbon have previously only been spotted in the planet’s polar regions. In 2009, exo-meteorologists saw evidence of weather on Titan, and since then the moon has been found to have a methane cycle rather like the water cycle on Earth — where methane evaporates and then rains down as a liquid elsewhere.