NASA has identified what appears to be a huge river system on Saturn's moon Titan, after the spacecraft Cassini performed a close flyby and snapped photos of what's believed to be a 200 mile long, liquid-filled trench. The river valley, compared to Earth's Nile River by NASA by virtue of its sheer scale, is the largest ever to have been observed other than on our planet, though it's not filled with water. Instead, the Titan river is believed to be made up of the liquid hydrocarbons that give the moon its unusual precipitation.
In fact, Titan experiences rainfall of those liquid hydrocarbons, and scientists say the liquid in the river is most like a combination of ethane and methane. It crosses across the north polar region of the moon, and then runs into Ligeia Mare, one of Titan's three great seas in the high northern latitudes.
From the shape of the river - an almost continuous straight line - the belief is that it traces at least one fault running across Titan's surface. "This picture gives us a snapshot of a world in motion" Steve Wall, radar deputy team lead at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "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."
While it may be compared to the Nile, the Titan river is actually a fraction of the size. The real Nile is around 4,100 miles in length, and only sections were caused by faulting of the same sort that are believed to have created the moon river.
"Titan is the only place we've found besides Earth that has a liquid in continuous movement on its surface" Wall said of the new discovery. Signs of liquid methane were first identified on the moon back in 2008, while evidence of rainfall didn't come until late in 2010.