Nile-like river roves across Saturn's moon Titan

Coursing 400 kilometres towards a dark delta, a river found on Saturn’s moon Titan is the longest yet seen outside Earth. Bearing a striking resemblance to the Nile, the river hints at ongoing geological activity on the moon.

Titan is considered to be the most Earth-like extraterrestrial body in the solar system. In addition to its thick atmosphere, the moon boasts mountains, lakes and a liquid cycle akin to Earth’s water cycle.

But at -179 °C, Titan is too cold for flowing water. Instead, liquid hydrocarbons such as ethane and methane fill its lakes and streams.

Finding faults

Spotted by NASA’s Cassini spacecraft, the newfound river follows a relatively straight path into one of Titan’s large seas, Ligeia Mare. “We think it’s raining in the highlands and flowing down into these river valleys,” says Thomas Farr of NASA’s Jet Propulsion Laboratory in Pasadena, California.

The Nile’s relatively straight shape is partly controlled by fault lines, which on Earth mark the places where tectonic plates meet. Titan is probably too small to have plates, but the river may also be tracing a fault in the bedrock, says Farr. Pressure could build up on such faults, causing them to shift and form new chasms and lakes, he says.

“Usually when we look at another planet, we’re cautioned not to bring our Earth experience too much to bear, because we might fool ourselves,” says Farr. “But here we look at a completely alien world and it looks just like the Earth. It’s hard to believe.”