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Whether there is life on Titan, the largest moon of Saturn, is at present an open question and a topic of scientific assessment and research. Titan is far colder than Earth, and its surface lacks stable liquid water; factors which have led some scientists to consider life there unlikely. On the other hand, its thick atmosphere is chemically active and rich in carbon compounds. On the surface there are bodies of liquid methane and ethane; some scientists speculate that these liquids might take the place of water in living cells different from those on Earth. In June 2010, scientists analysing data from the Cassini–Huygens mission reported anomalies in the atmosphere near the surface which could be consistent with the presence of methane-producing organisms, but may alternatively be due to non-living chemical or meteorological processes.〔 The Cassini–Huygens mission was not equipped to look directly for micro-organisms or to provide a thorough inventory of complex organic compounds. A hypothetical cell membrane capable of functioning in liquid methane has been modeled.〔(Life 'not as we know it' possible on Saturn's moon Titan )〕 ==Surface temperature== Due to its distance from the Sun, Titan is much colder than Earth. Its surface temperature is about 90 K (−179 °C, or −290 °F). At these temperatures, water ice—if present—does not melt, evaporate or sublime, but remains solid. Because of the extreme cold and also because of lack of carbon dioxide (CO2) in the atmosphere, scientists such as Jonathan Lunine have viewed Titan less as a likely habitat for extraterrestrial life, than as an experiment for examining hypotheses on the conditions that prevailed prior to the appearance of life on Earth. Even though the usual surface temperature on Titan is not compatible with liquid water, calculations by Lunine and others suggest that meteor strikes could create occasional "impact oases"—craters in which liquid water might persist for hundreds of years or longer, which would enable water-based organic chemistry.〔Committee on the Limits of Organic Life in Planetary Systems, Committee on the Origins and Evolution of Life, National Research Council; (); The National Academies Press, 2007; page 74〕 However, Lunine does not rule out life in an environment of liquid methane and ethane, and has written about what discovery of such a life form (even if very primitive) would imply about the prevalence of life in the universe.〔(Jonathan Lunine "Saturn’s Titan: A Strict Test for Life’s Cosmic Ubiquity" ) (accepted for publication in ''Proceedings of the American Philosophical Society''), July 21, 2009 (Revised November 7, 2009)〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Life on Titan」の詳細全文を読む スポンサード リンク
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