Beneath the orange haze cloaking Titan, Saturn’s largest moon, it’s raining methane. While not much falls — a couple of meters every few centuries — it’s enough to fill seas 200 meters deep in the moon’s northern hemisphere (SN: 12/13/14, p. 13
Despite having an average temperature of about – 180° Celsius, Titan is the only world in the solar system other than Earth with liquid on its surface (SN: 1/25/14, p. 14
). Researchers are starting to understand how the alien seas, mapped by the Cassini spacecraft, help drive a global process strikingly similar to Earth’s hydrological cycle.