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Orbiter spots an alien Nile on Titan

NASA / JPL-Caltech /ASI

This radar image from NASA's Cassini spacecraft, acquired on Sept. 26, shows a vast river system on Saturn's moon Titan. Check out the full-size version from NASA or the European Space Agency.

NASA's Cassini orbiter has spotted a river system on the Saturnian moon Titan that's reminiscent of the River Nile — except that this river is presumably filled with liquid ethane and methane instead of water.

The Titanic Nile shows up on a grainy, black-and-white picture from Cassini's radar imager, which can look through Titan's thick, smoggy atmosphere to map the surface features beneath.

The picture was taken on Sept. 26 and released today by NASA's Jet Propulsion Laboratory and the European Space Agency. It shows a branching river valley, running more than 200 miles (320 kilometers) from its headwaters to Titan's Kraken Mare, a hydrocarbon sea that's somewhere between the Caspian Sea and the Mediterranean in size.

Just as Earth has a water-based hydrological cycle, Titan has a weather cycle that moves ethane and methane around its surface and through the atmosphere. That's due to Titan's surface temperature (averaging minus-290 degrees Fahrenheit, or -179 degrees Celsius) and atmospheric pressure (one and a half times that of Earth's atmosphere).

"Titan is the only place we've found besides Earth that has a liquid in continuous movement on its surface," Steve Wall, the radar deputy team lead, said in JPL's news release. "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."

During the eight and a half years that Cassini has been passing over Saturn and its moons, the bus-sized orbiter has mapped Titan's seas, lakes and rivers in amazing detail. The orbiter even dropped a mini-probe known as Huygens down to Titan's surface for an on-the-ground view of the terrain.

From March 14, 2007: Cassini finds evidence of huge seas on Titan. NBC News' Dara Brown has the details.

Scientists have proposed sending out another, more sophisticated probe that would parachute through the atmosphere and float on one of the moon's seas — either Kraken Mare or another huge lake called Ligeia Mare. Two proposed missions are in the works, nicknamed TiME and TALISE. So far, neither of the missions have gotten the go-ahead for launch — but who knows? Maybe this view of an alien Nile will whet our appetite for a taste of Titanic seas.

More about Titan's lakes and seas:

Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.