about , but still leaves much to be discovered . The Cassini-Huygens spacecraft was sent to study Saturn , its rings , and its moons , and it provided us with important information on Titan ’ s structure and composition . Titan is , indeed , special . It ’ s the only moon in the solar system that maintains a substantial atmosphere , an important factor in the protection of life that could exist on its surface . Also , it is the only body in the Solar System , besides the Earth , to have liquid oceans and rivers , as well as a cycle of rains and evaporation . However , those rivers are not made of water ; Titan ’ s atmosphere is composed mainly of nitrogen and methane , and the liquid on its surface is expected to be methane . In our planet , methane comes from biological sources – think of cows emitting methane gas into the atmosphere through their digestive processes , a major source of greenhouse gases which are now contributing to climate change . This has led to previous hypotheses of the large amount of methane gas in Titan ’ s atmosphere to be the result of extraterrestrial metabolisms . Although we do not expect Titanian “ cows ” ( methane-producing microbes ) to be responsible for the methane in its atmosphere , which could be the result of liquid methane on the surface , Cornell scientists have simulated a methane-based life form that could survive with a nitrogen-based cell membrane , in anoxic environments . If there is life in Titan ’ s surface , it is
IMAGES AND CAPTION TEXT COURTESY OF NASA / JPL / ESA / University of Arizona expected to be very much like this ; an extremely resistant one-celled organism , surviving on methane . This hypothetical organism would be completely different from life as we know it . Although it is one of the best candidates in the solar system to host life outside of Earth , it is still a freezing world . At such low temperatures as -179 degrees Celsius , it is impossible to host Earth-like life , which requires liquid water . Still , Titan has large amounts of water ice on its surface , playing a similar role to Earth ’ s rocks . It has been hypothesized that Titan ’ s volcanoes may expel liquid water , as Earth volcanos expel lava . Also , asteroid
This image was returned January 14 , 2005 , by the Huygens probe during its successful descent to land on Titan . This is the colored view , following processing to add reflection spectra data , and gives a better indication of the actual color of the surface .
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