Cassini Spots Nile-Like River on Saturn Moon Titan

Cassini spacecraft has spotted a long river valley on Saturn's moon Titan, stretching more than 200 miles from its "headwaters" to a large sea, NASA announced Wednesday.

The river, filled with hydrocarbons, resembles a miniature version of the Earth's river Nile in Egypt. For the first time, high-resolution radar images of a river valley located anywhere beyond Earth have been taken.

The river appears dark along the entire stretch in the images taken, suggesting that it is filled with liquid and has a smooth surface.

"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," Jani Radebaugh, a Cassini radar team associate at Brigham Young University, Provo, Utah, said in a statement.

"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."

The river valley flows into a sea called Ligeia Mare, located in the north polar region of Saturn's moon. Ligeia Mare's size is between the Caspian and the Mediterranean Sea on Earth.

Apart from the Earth, Titan is the only world where stable liquid is found on the surface. Back in 2008, Cassini confirmed the presence of liquid ethane in a lake called Ontario Lacus, located in the southern hemisphere of Titan.

In 2010, Cassini detected rainfall in Titan, suggesting a methane cycle similar to the hydrologic cycle on Earth. 

While the Earth's hydrologic cycle is dependent on water, the equivalent cycle on Titan relies on liquid ethane and methane.

"This picture gives us a snapshot of a world in motion. Rain falls, and rivers move that rain to lakes and seas, where evaporation starts the cycle all over again. On Earth, the liquid is water; on Titan, it's methane; but on both it affects most everything that happens," said Steve Wall, the radar deputy team lead, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif.