Go with the flow

Touchdown on Titan

This mosaic from NASA's Cassini mission shows the most complete view of Titan's largest liquid hydrocarbon sea in dark browns and black.
Kraken Mare, a liquid hydrocarbon sea on the surface of Titan, Saturn’s largest moon.
Credit: NASA/JPL-Caltech/ASI/Cornell/ Jason Hoftgartner/Sam Birch

Titan is Saturn’s largest moon. Its landscape was explored remotely by the NASA/ESA Cassini-Huygens mission. It revealed mountains reaching towards the sky and an astonishing sight in the valleys between: liquid rivers flowing into vast seas. These rivers are not streams of water…

… instead, they are flowing with liquid methane! Kraken Mare is Titan’s largest sea. This radar image covers an area of 1.4 million square kilometres, showing liquid methane in dark brown and black and icy mountain regions in yellow.

Liquid History

Earth and Titan are the only known places in the solar system with pools of liquid at the surface. A delicate balance of Earth’s atmospheric pressure and temperature allows water to flow, evaporate and fall as rain. Titan is so cold that all water freezes solid and methane is chilled to a liquid. The solid ice behaves like a rock, forming mountains that erode into sediment, creating dunes and deltas. Titan’s dense atmosphere holds liquid methane on its surface, just as Earth’s holds liquid water in the form of rivers, seas and oceans.

Water is vital to all life on Earth, making it an obvious starting point in the search for extra-terrestrial life. Geological landforms on Earth trace the history of ancient river systems, and these features are easily recognised on Mars’s surface. Jezero Crater, the landing site for Perseverance Rover, contains the remains of an ancient delta, suggesting traces of life could exist within its base.

An ancient river delta spreads red, orange and brown sand from the old river bed (right) to the basin (left) in Jezero Crater on Mars.
The fan-shaped remains of an ancient delta in Mars’s Jezero Crater – the landing site for NASA’s Perseverance Rover
Credit: ESA/DLR/FU-Berlin
The sinuous Horton River flows in a curved line from top to bottom of this image, breaking free around the centre and fanning out into the sea on the right-hand side.
The Horton River Delta forms a fan-shaped interruption to the otherwise straight coastline.
Credit: NASA Earth Observatory image by Jesse Allen and Robert Simmon

Explore more

Touchdown on Titan – Join ESA’s Huygens probe as it makes its descent to the surface of Saturn’s hazy moon, Titan

NASA’s Dragonfly and its search for signs of life: Explore NASA’s Dragonfly mission which they hope will commence in 2026

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