Titan, Saturn's largest moon, is considered the most Earth-like world we've ever discovered. It has seasons and a liquid precipitation cycle just like our own. Sort of. Titan's seasons each last 7.5 years, and instead of water, methane and ethane rain down into hydrocarbon lakes and precipitate up into clouds. When the Cassini spacecraft arrived at Titan in 2004, it was winter in the northern hemisphere. Now that we've hit summer, NASA has been able to see bright clouds of methane moving through the thick atmosphere.