Titan

Titan is Saturn's largest natural satellite and the second-largest moon in the Solar System. It is larger than the planet Mercury. Unlike most moons, Titan has a substantial atmosphere whose main components are nitrogen and methane. A thick, orange haze formed by atmospheric chemistry obscures much of its surface in visible light, although radar and infrared observations can reveal surface features.

At Titan's frigid surface, water ice behaves more like rock, while methane and ethane can exist as liquids. Clouds, rainfall, streams and lakes of these hydrocarbons create a weather cycle that is in some ways analogous to Earth's water cycle, but uses different substances. Rivers and flowing liquids shape terrain, and dark hydrocarbon-rich dunes occur across broad regions. Titan is the only world besides Earth known to have stable bodies of liquid on its surface.

Measurements from the Cassini–Huygens mission indicate that Titan may have a subsurface ocean of liquid water beneath its icy crust. This, along with Titan's organic-rich atmosphere and surface, makes the moon valuable for studying prebiotic chemistry and environments that could be habitable. These are questions about potential conditions, not evidence that life exists: no life has been detected on Titan.

NASA's Cassini spacecraft studied Saturn and made more than a hundred close flybys of Titan, using radar and other instruments to investigate its surface and atmosphere. Cassini carried ESA's Huygens probe, which descended through Titan's atmosphere and landed on 14 January 2005. Huygens measured atmospheric properties and returned images and surface measurements, finding a terrain at its landing site composed largely of water-ice material. NASA's Dragonfly mission is designed as a rotorcraft that will travel between multiple sites and analyze samples. NASA currently lists its launch as no earlier than July 2028 and its arrival at Titan in late 2034; these are mission plans, not completed events.