Evidence of a river in the north polar region of Saturn’s moon Titan has been reported by scientists with NASA’s Cassini mission. The river, which has several smaller tributaries, looks like a smaller version of the Nile River on Earth. As revealed in radar images taken on Sept. 26, the “mini Nile” winds through a river valley more than 200 miles (400 kilometers) from its source to a large sea called Ligeia Mare. The relative straightness of the river indicates that it follows at least one fault (crack) in Titan’s crust (outer layer), similar to the path followed by other rivers running into Ligeia Mare. The Cassini scientists concluded that the river is filled with liquid due to the dark coloration of the surface in the images.
The dark, branching channels in an image of Titan’s surface were almost certainly carved by rivers of liquid methane. The image was taken by the probe Huygens as it parachuted to Titan’s surface in January 2005. The channels appear to cross a bright plateau (top of image), then descend into a darker area (bottom) which may be a lake bed. (European Space Agency/NASA/JPL/University of Arizona)
Titan is the only other body in the solar system known to have stable liquid on its surface. On Earth, the most abundant surface liquid is water. But because Titan’s atmosphere is extremely cold, no liquid water would be found there. Instead, the liquids on Titan are such hydrocarbons as ethane and methane. These liquids have a very low freezing point. In the past several years, Cassini scientists have found evidence of rainfall, large lakes, and other rivers on Titan. Such evidence supports the theory that Titan has a cycle of hydrocarbons similar to the water cycle on Earth.
Scientists have speculated that the hydrocarbons could possibly form an environment in which life could develop. However, the thick and hazy atmosphere shrouds the moon from most forms of imaging. Detecting life or the evidence of life is not likely to be confirmed or refuted anytime in the near future.