Titan is known to have vast lakes - the only other body in the solar system, apart from Earth, to possess a cycle of liquids on its surface. However, the thick Titan atmosphere is a frigid one, meaning liquid water couldn't possibly flow. The liquids on Titan are therefore composed of hydrocarbons such as methane and ethane.
Interestingly, using this observation of a vast river system on Titan reveals not only that rivers flow, it could also trace the path of fault lines on the Saturnian moon, suggestive of fractures in Titan's bedrock.
"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, 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."
The discovery of vast river systems on Titan was perhaps inevitable. Cassini has previously confirmed the presence of large masses of liquids including Ontario Lacus, a lake in the southern hemisphere composed of liquid ethane. Rainfall has also been detected in the atmosphere, hinting not of a hydrological cycle (which gives us water rain, rivers and oceans on Earth), but of a methane cycle.
It is hard not to imagine what such a river system would look like when standing next to it. But looking at this radar observation, many familiar river features such as meanders and channels can be seen.
Titan is a complex and fascinating little world laced with complex prebiotic chemistry. Apart from the Huygens probe that landed on the surface in 2005, there have been no other surface missions and plans for future missions look iffy at best.
Titan might be shrouded in a cold, high pressure atmosphere that makes it difficult for our robots to explore, but it's hard to ignore the fact that the ingredients for the basic chemistry for life is there in abundance - could there be a form of life there, perhaps taking advantage of liquid methane and ethane rather than water? We may be waiting some time to find out.
*In comparison, the Nile is 6,650 kilometers (4,132 miles) long.
Image credit: NASA/JPL-Caltech/ASI