The Cassini probe orbiting Saturn and its moons has photographed what the European Space Agency (ESA) is calling a “miniature extraterrestrial version of the Nile river” on Saturn’s moon Titan. The formation is a river valley on the the moon’s surface that runs for over 400 km (248 miles) from its source to a large sea. The radar image is the first time such a long river system has been photographed in high resolution anywhere except Earth.

“Though there are some short, local meanders, the relative straightness of the river valley suggests it follows the trace of at least one fault, similar to other large rivers running into the southern margin of this same Titan sea,” said Jani Radebaugh, a Cassini radar team associate at Brigham Young University. “Such faults – fractures in Titan’s bedrock – may not imply plate tectonics, like on Earth, but still lead to the opening of basins and perhaps to the formation of the giant seas themselves.”

Researchers explained that they believe the river is filled with liquid because it is dark along its entire extent in the image. This indicates a smooth surface, and Titan is the only other object in the solar system known to have stable liquid on its surface. The liquid likely isn’t water, though. Titan’s environment contains liquid hydrocarbons, such as ethane and methane.

“This radar-imaged river by Cassini provides another fantastic snapshot of a world in motion, which was first hinted at from the images of channels and gullies seen by ESA’s Huygens probe as it descended to the moon’s surface in 2005,” said Nicolas Altobelli, ESA’s Cassini Project Scientist.

The Cassini probe recently celebrated its 15th birthday since launch. In its time around Saturn, the probe has found lakes on Titan, signs of water ice on Enceladus, and followed huge storms in Saturn’s atmosphere.

(Image courtesy NASA/JPL–Caltech/ASI)