Have you ever before seen such a large river system in high resolution outside Earth? No, you have not.
Scientists deduce that the river is filled with liquid because it appears dark along its entire extent in the high-resolution radar image, indicating a smooth surface. Titan is the only other world we know of that has stable liquid on its surface. While Earth’s hydrologic cycle relies on water, Titan’s equivalent cycle involves hydrocarbons such as ethane and methane.
Images from Cassini’s visible-light cameras in late 2010 revealed regions that darkened after recent rainfall. Cassini’s visual and infrared mapping spectrometer confirmed liquid ethane at a lake in Titan’s southern hemisphere known as Ontario Lacus in 2008.
Sort of 'Nile River' on Titan. Image was acquired on 26 September 2012, on Cassini’s 87th close flyby. The river valley crosses Titan’s north polar region and runs into Kraken Mare, one of the three great seas in the high northern latitudes of the moon. Credit: NASA/JPL–Caltech/ASI
“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,” says Jani Radebaugh, a 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.”
“This radar-imaged river by Cassini provides another fantastic snapshot of a world in motion, which was first hinted at from the images of channels and gullies seen by ESA’s Huygens probe as it descended to the moon’s surface in 2005,” says Nicolas Altobelli, ESA’s Cassini Project Scientist.