Saturn's moon Titan has rain, rivers and seas, but they are liquid methane.
Titan is the only moon with a thick atmosphere, and the only place besides Earth known to have stable lakes and seas on its surface. At about −179°C, its rain and rivers are made of methane and ethane rather than water. In the 2030s, a flying drone is due to explore it.
Christiaan Huygens discovered Titan in 1655, the first moon of Saturn to be found. It is the second-largest moon in the Solar System, bigger than the planet Mercury though less than half as massive, because it is mostly ice rather than rock and iron. From its surface, Saturn would look more than ten times larger than the Moon does from Earth.
What makes Titan unique among moons is its air. The atmosphere is mostly nitrogen, with methane, and its surface pressure is about 1.45 times Earth's. A thick haze of organic compounds hid the surface from view until the Cassini–Huygens mission arrived in 2004. Cassini's radar and infrared instruments mapped the ground beneath, and found lakes and seas near the poles; the largest, Kraken Mare, lies near the north pole.
Titan has something like Earth's water cycle, but with methane. At around 94 kelvin, water is rock-hard ice, while methane can exist as gas, cloud, rain and liquid. The result is a landscape of dunes, river channels, deltas and seas, shaped by seasonal weather. For this reason Titan is sometimes described as the most Earth-like world in the Solar System, despite being so cold.
On 14 January 2005, the Huygens probe parachuted to its surface, still the most distant landing ever made. It photographed pale hills cut by dark channels running down to a plain. Beneath the ice, a layer of ammonia-rich liquid water is thought to exist. The Dragonfly mission, a nuclear-powered drone scheduled to launch in 2028 and arrive in the mid-2030s, will fly through the dense air to study how far its chemistry has progressed towards the ingredients of life.
Source: Wikipedia — Titan (moon) · Text summarised from Wikipedia (CC BY-SA 4.0)
