The science team for the Huygens probe released on January 21 the first results from the January 14 landing of the probe onto Titan, the largest moon of Saturn. From the images that Huygens created as it descended to the surface one can clearly see a river network cut by liquid methane. This network winds through the Titan highlands, dumping onto a flat, dry basin.
An image of Titan's surface taken by the Huygens probe as it descends to the surface. River channels are clearly visible, as is a coast line of a dry basin. The fluid responsible for these features is liquid methane, which precipitates from methane clouds in Titan's atmosphere. (Courtesy ESA/NASA/JPL/University of Arizona)
Huygens landed in a dry basin of loose soil and pebbles. While resembling earth in appearance, the composition of Titan's surface is quite different: Titan has a surface of water-ice, frozen by Titan's below -170° C temperatures. The action of liquid methane on the water-ice soil and pebbles is similar to the action of water on earth's silicate rocks. The process of liquid methane flowing over the plane and then evaporating has broken down the surface to fine granules that is similar to sand. Dark organic compounds appear to have precipitated from the atmosphere and to have been deposited by flowing methane at the bottoms of the river channels and collection basins.
These results confirm earlier speculations that Titan has a weather cycle based on liquid and gaseous methane. Methane clouds form in Titan's atmosphere, and a methane rain falls to the surface. After flowing through the river network to river basins, the methane evaporates back into the atmosphere. At the time of the landing, the river beds and basin were dry.
Observations by Huygens suggests that Titan is geologically active. It had been thought that Titan has a core of liquid water and ammonia. The detection by Huygens of the isotope argon-40 in Titan's atmosphere suggests that volcanic activity is taking place on Titan. These volcanoes would spew water and ammonia from Titan's interior.