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.

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:

• Tropical lake found on Titan
• Could Titan's seas harbor life?
• Orbiter sends images of Titan's seas
• One moon's forecast: Chance of methane rain
• Titan has a soft and crusty surface

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.

NASA / JPL-Caltech / SSI

Saturn and its rings provide a backdrop for the planet's largest moon, Titan, in a true-color picture captured by NASA's Cassini orbiter on May 6.

Saturn's shades of blue and butterscotch are changing along with the planet's seasons, as illustrated by a fresh batch of true-color photos from the bus-sized Cassini orbiter.

When Cassini arrived at Saturn, seven years ago, the planet's northern hemisphere had a tint of azure blue. Since then, Saturn has gone through an equinox and a significant shift in seasons. Summer is approaching in the north, and winter is coming to the south.

The seasonal change means ultraviolet radiation is intensifying in the north, resulting in an increasing amount of yellowish haze. Meanwhile, there's a reduction in radiation hitting the southern hemisphere, and the haze is clearing as a result. The presence of the ring shadow enhances the effect in Saturn's south.

"The reduction of haze and the consequent clearing of the atmosphere make for a bluish hue: the increased opportunity for direct scattering of sunlight by the molecules in the air makes the sky blue, as on Earth," Cassini's imaging team reports in today's advisory. "The presence of methane, which generally absorbs in the red part of the spectrum, in a now-clearer atmosphere also enhances the blue."

Although Saturn has seasons like Earth's, the fact that a Saturnian year lasts 29.5 times longer than an Earth year means that the southern hemisphere's winter solstice won't occur until May 2017. And if Cassini's mission managers have their way, the orbiter will be around to see it.

"The Cassini mission was recently given rave reviews by a panel of planetary scientists and NASA program managers for its contributions to our understanding of the solar system, a circumstance that bodes well for a well-funded continuing mission over the next five years," the imaging team's leader, Carolyn Porco of the Colorado-based Space Science Institute, reported in an email today. "Despite the fact that we can't know exactly what the next five years will bring us, we can be certain that whatever it is will be wondrous."  

Saturn's largest moon, Titan, takes center stage in one of Cassini's newly released views. The moon measures 3,200 miles (5,150 kilometers) across and is covered with its own brand of hydrocarbon-rich haze. Titan is the only moon in the solar system to have an opaque atmosphere. Cassini snapped the picture you see above from a distance of about 483,000 miles (778,000 kilometers).

Here are more pictures that show Titan's true colors:

NASA / JPL-Caltech / SSI

Saturn's rings obscure part of Titan's disk in an image from NASA's Cassini orbiter. Parts of the rings appear dark near the center of this view because of the shadow cast by the planet. This image was obtained on May 16 at a distance of about 1.9 million miles (3 million kilometers) from Titan.

NASA / JPL-Caltech / SSI

Titan's recently formed south polar vortex stands out in this natural-color view of Titan from the Cassini spacecraft. The vortex may be related to the approach of southern winter and the development of a polar "hood" of denser, high-altitude haze. This picture was acquired on July 25 at a distance of about 64,000 miles (103,000 kilometers).

NASA / JPL-Caltech / SSI

NASA's Cassini spacecraft looks toward the night side of Titan and sees sunlight scattering through the periphery of the moon's atmosphere, creating a ring of color. The picture was taken on June 6 from a distance of about 134,000 miles (216,000 kilometers).

More colors from Cassini:

• Slideshow: Cassini's greatest hits
• Saturnian storm goes wild
• Take the ultimate flight around Saturn
• Saturn floats on gossamer rings

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.