Bibcode:2010Icar..208..878S. doi:10.1016/j.icarus.2010.03.003. ↑ Could Alien Life Exist in the Methane Habitable Zone? Keith Cooper, Astrobiology Magazine16 November 2011 ↑ Andew Hough (June 5, 2010). "Titan: Nasa scientists discover evidence 'that alien life exists on Saturn's moon'".