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Do not fill this in! == Extraterrestrial == {{main|Extraterrestrial life|Astrobiology|Astroecology}} Though life is confirmed only on Earth, many think that [[extraterrestrial life]] is not only plausible, but probable or inevitable.<ref name="RaceRandolph2002">{{cite journal |last1=Race |first1=Margaret S. |last2=Randolph |first2=Richard O. |title=The need for operating guidelines and a decision making framework applicable to the discovery of non-intelligent extraterrestrial life |journal=Advances in Space Research |volume=30 |issue=6 |year=2002 |pages=1583β1591 |doi=10.1016/S0273-1177(02)00478-7 |quote=There is growing scientific confidence that the discovery of extraterrestrial life in some form is nearly inevitable |bibcode=2002AdSpR..30.1583R |citeseerx=10.1.1.528.6507 }}</ref><ref>{{cite news |url=http://www.newser.com/story/50874/alien-life-inevitable-astronomer.html |title=Alien Life 'Inevitable': Astronomer |last=Cantor |first=Matt |date=15 February 2009 |work=Newser |quote=Scientists now believe there could be as many habitable planets in the cosmos as there are stars, and that makes life's existence elsewhere "inevitable" over billions of years, says one. |access-date=3 May 2013 |archive-url=https://web.archive.org/web/20130523141853/http://www.newser.com/story/50874/alien-life-inevitable-astronomer.html |url-status=dead |archive-date=23 May 2013 }}</ref> Other planets and [[moons]] in the [[Solar System]] and other [[planetary system]]s are being examined for evidence of having once supported simple life, and projects such as [[SETI]] are trying to detect radio transmissions from possible alien civilisations. Other locations within the [[Solar System]] that may host [[Microorganism|microbial]] life include the subsurface of [[Life on Mars (planet)|Mars]], the upper atmosphere of [[Life on Venus|Venus]],<ref>{{Cite journal |last1=Schulze-Makuch |first1=Dirk |last2=Dohm |first2=James M. |last3=FairΓ©n |first3=Alberto G. |last4=Baker |first4=Victor R. |last5=Fink |first5=Wolfgang |last6=Strom |first6=Robert G. | title=Venus, Mars, and the Ices on Mercury and the Moon: Astrobiological Implications and Proposed Mission Designs |journal=Astrobiology |volume=5 |issue=6 |pages=778β795 |date=December 2005 |doi=10.1089/ast.2005.5.778 |pmid=16379531 |bibcode=2005AsBio...5..778S |s2cid=13539394 }}</ref> and subsurface oceans on some of the [[Natural satellite habitability|moons]] of the [[giant planet]]s.<ref name="WRD-20150127">{{cite journal |last=Woo |first=Marcus |title=Why We're Looking for Alien Life on Moons, Not Just Planets |url=https://www.wired.com/2015/01/looking-alien-life-moons-just-planets/ |date=27 January 2015 |journal=[[Wired (website)|Wired]] |access-date=27 January 2015 |url-status=live |archive-url=https://web.archive.org/web/20150127120332/http://www.wired.com/2015/01/looking-alien-life-moons-just-planets/ |archive-date=27 January 2015 }}</ref><ref>{{cite web |first1=Daniel |last1=Strain |date=14 December 2009 |title=Icy moons of Saturn and Jupiter may have conditions needed for life |publisher=The University of Santa Cruz |url=http://news.ucsc.edu/2009/12/3443.html |access-date=4 July 2012 |url-status=live |archive-url=https://web.archive.org/web/20121231111334/http://news.ucsc.edu/2009/12/3443.html |archive-date=31 December 2012 }}</ref> Investigation of the tenacity and versatility of life on Earth,<ref name="NYT-20160912"/> as well as an understanding of the molecular systems that some organisms utilise to survive such extremes, is important for the search for extraterrestrial life.<ref name=astrobiology/> For example, [[lichen]] could survive for a month in a [[Life on Earth under Martian conditions|simulated Martian environment]].<ref name="Skymania-20120426">{{cite web |last=Baldwin |first=Emily |title=Lichen survives harsh Mars environment |url=http://www.skymania.com/wp/2012/04/lichen-survives-harsh-martian-setting.html |date=26 April 2012 |publisher=Skymania News |access-date=27 April 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120528145425/http://www.skymania.com/wp/2012/04/lichen-survives-harsh-martian-setting.html/ |archive-date=28 May 2012 }}</ref><ref name="EGU-20120426">{{cite journal |last1=de Vera |first1=J.-P. |last2=Kohler |first2=Ulrich |title=The adaptation potential of extremophiles to Martian surface conditions and its implication for the habitability of Mars |journal=EGU General Assembly Conference Abstracts |volume=14 |page=2113 |url=http://media.egu2012.eu/media/filer_public/2012/04/05/10_solarsystem_devera.pdf |archive-url=https://web.archive.org/web/20120504224706/http://media.egu2012.eu/media/filer_public/2012/04/05/10_solarsystem_devera.pdf |archive-date=4 May 2012 |url-status=dead |date=26 April 2012 |access-date=27 April 2012|bibcode=2012EGUGA..14.2113D }}</ref> Beyond the Solar System, the region around another [[main sequence|main-sequence star]] that could support Earth-like life on an Earth-like planet is known as the [[habitable zone]]. The inner and outer radii of this zone vary with the luminosity of the star, as does the time interval during which the zone survives. Stars more massive than the Sun have a larger habitable zone, but remain on the Sun-like "main sequence" of [[stellar evolution]] for a shorter time interval. Small [[red dwarf]]s have the opposite problem, with a smaller habitable zone that is subject to higher levels of magnetic activity and the effects of [[tidal locking]] from close orbits. Hence, stars in the intermediate mass range such as the Sun may have a greater likelihood for Earth-like life to develop.<ref name=selis2006>{{Cite book |first1=Frank |last1=Selis |date=2006 |chapter=Habitability: the point of view of an astronomer |title=Lectures in Astrobiology |volume=2 |editor1-first=Muriel |editor1-last=Gargaud |editor2-first=HervΓ© |editor2-last=Martin |editor3-first=Philippe |editor3-last=Claeys |publisher=Springer |isbn=978-3-540-33692-1 |pages=210β214 |chapter-url=https://books.google.com/books?id=3uYmP0K5PXEC&pg=PA210 |access-date=10 August 2023 |archive-date=5 November 2023 |archive-url=https://web.archive.org/web/20231105190206/https://books.google.com/books?id=3uYmP0K5PXEC&pg=PA210#v=onepage&q&f=false |url-status=live }}</ref> The location of the star within a galaxy may also affect the likelihood of life forming. Stars in regions with a greater abundance of heavier elements that can form planets, in combination with a low rate of potentially [[habitat]]-damaging [[supernova]] events, are predicted to have a higher probability of hosting planets with complex life.<ref name=science303_5654_59>{{Cite journal |last1=Lineweaver |first1=Charles H. |last2=Fenner |first2=Yeshe |last3=Gibson |first3=Brad K. |date=January 2004 |title=The Galactic Habitable Zone and the age distribution of complex life in the Milky Way |journal=Science |volume=303 |issue=5654 |pages=59β62 |doi=10.1126/science.1092322 |bibcode=2004Sci...303...59L |pmid=14704421 |arxiv=astro-ph/0401024 |s2cid=18140737 |url=https://cds.cern.ch/record/704101 |access-date=30 August 2018 |archive-date=31 May 2020 |archive-url=https://web.archive.org/web/20200531022432/https://cds.cern.ch/record/704101 |url-status=live }}</ref> The variables of the [[Drake equation]] are used to discuss the conditions in planetary systems where civilisation is most likely to exist, within wide bounds of uncertainty.<ref name=vakoch_harrison2011>{{Cite book |first1=Douglas A. |last1=Vakoch |first2=Albert A. |last2=Harrison |title=Civilizations beyond Earth: extraterrestrial life and society |series=Berghahn Series |pages=37β41 |publisher=Berghahn Books |date=2011 |url=https://books.google.com/books?id=BVJzsvqWip0C&pg=PA37 |isbn=978-0-85745-211-5 |access-date=25 August 2020 |archive-date=13 April 2023 |archive-url=https://web.archive.org/web/20230413194802/https://books.google.com/books?id=BVJzsvqWip0C&pg=PA37 |url-status=live }}</ref> A "Confidence of Life Detection" scale (CoLD) for reporting evidence of life beyond Earth has been proposed.<ref name="NAT-20211027">{{cite journal |first1=James |last1=Green |first2=Tori |last2=Hoehler |first3=Marc |last3=Neveu |first4=Shawn |last4=Domagal-Goldman |first5=Daniella |last5=Scalice |first6=Mary |last6=Voytek |author6-link=Mary Voytek |title=Call for a framework for reporting evidence for life beyond Earth |url=https://www.nature.com/articles/s41586-021-03804-9 |date=27 October 2021 |journal=[[Nature (journal)|Nature]] |volume=598 |issue=7882 |pages=575β579 |doi=10.1038/s41586-021-03804-9 |pmid=34707302 |arxiv=2107.10975 |bibcode=2021Natur.598..575G |s2cid=236318566 |accessdate=1 November 2021 |archive-date=1 November 2021 |archive-url=https://web.archive.org/web/20211101023448/https://www.nature.com/articles/s41586-021-03804-9 |url-status=live }}</ref><ref name="COS-20211030">{{cite news |last=Fuge |first=Lauren |title=NASA proposes playbook for communicating the discovery of alien life β Sensationalising aliens is so 20th century, according to NASA scientists. |url=https://cosmosmagazine.com/space/astrobiology/what-happens-when-we-find-aliens/ |date=30 October 2021 |work=[[Cosmos (Australian magazine)|Cosmos]] |accessdate=1 November 2021 |archive-date=31 October 2021 |archive-url=https://web.archive.org/web/20211031221719/https://cosmosmagazine.com/space/astrobiology/what-happens-when-we-find-aliens/ |url-status=live }}</ref> Summary: Please note that all contributions to Christianpedia may be edited, altered, or removed by other contributors. 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