Editing Biosphere (section)

== Extraterrestrial biospheres ==
No biospheres have been detected beyond the Earth; therefore, the existence of extraterrestrial biospheres remains hypothetical. The [[rare Earth hypothesis]] suggests they should be very rare, save ones composed of [[microbe|microbial]] life only.<ref>{{cite book|last1=Ward|first1=Peter D.|last2=Brownlee|first2=Donald|title=Rare earth: why complex life is uncommon in the universe|date=2004|publisher=Copernicus|location=New York|isbn=978-0-387-95289-5|edition=2nd rev.|title-link=Rare Earth (book)}}</ref> On the other hand, [[Earth analog]]s may be quite numerous, at least in the [[Milky Way galaxy]], given the large number of planets.<ref>{{cite news|last1=Choi|first1=Charles Q.|title=New Estimate for Alien Earths: 2 Billion in Our Galaxy Alone|url=https://www.space.com/11188-alien-earths-planets-sun-stars.html|access-date=25 September 2017|work=Space.com|date=21 March 2011|archive-url=https://web.archive.org/web/20170824002233/https://www.space.com/11188-alien-earths-planets-sun-stars.html|archive-date=24 August 2017|url-status=live}}</ref> Three of the planets discovered orbiting [[TRAPPIST-1]] could possibly contain biospheres.<ref>{{cite news|last1=Rees|first1=Sir Martin|title=These new worlds are just the start. There are many more life-supporting planets out there waiting to be discovered|url=https://www.telegraph.co.uk/science/2017/02/22/many-life-supporting-planets-soon-will-see-clearly/|access-date=25 September 2017|work=The Telegraph|date=22 February 2017|archive-url=https://web.archive.org/web/20170925175603/http://www.telegraph.co.uk/science/2017/02/22/many-life-supporting-planets-soon-will-see-clearly/|archive-date=25 September 2017|url-status=live}}</ref> Given limited understanding of [[abiogenesis]], it is currently unknown what percentage of these planets actually develop biospheres.

Based on observations by the [[Kepler Space Telescope]] team, it has been calculated that provided the probability of abiogenesis is higher than 1 to 1000, the closest alien biosphere should be within 100 light-years from the Earth.<ref>Amri Wandel, [https://www.researchgate.net/publication/269116658_On_the_abundance_of_extraterrestrial_life_after_the_Kepler_mission On the abundance of extraterrestrial life after the Kepler mission] {{Webarchive|url=https://web.archive.org/web/20180817225423/https://www.researchgate.net/publication/269116658_On_the_abundance_of_extraterrestrial_life_after_the_Kepler_mission |date=2018-08-17 }}</ref>

It is also possible that artificial biospheres will be created in the future, for example with the [[terraforming of Mars]].<ref>{{cite book|author1=Zubrin, Robert|author2=Wagner, Richard|title=The Case for Mars: The Plan to Settle the Red Planet and Why We Must|date=2011|publisher=Simon & Schuster|isbn=978-1-4516-0811-3|title-link=The Case for Mars}}</ref>