Editing Europa (moon) (section)

==Habitability==
[[File:PIA22479-Europa-JupiterMoon-ArtistConcept-20180723.jpg|thumb|400px|Europa – possible effect of radiation on biosignature chemicals]]

So far, there is no evidence that life exists on Europa, but the moon has emerged as one of the most likely locations in the Solar System for potential habitability.<ref name=ChemDisequilib/><ref name=Schulze-Makuch2001>{{cite journal |last1=Schulze-Makuch |first1=Dirk |last2=Irwin |first2=Louis N. |title=Alternative energy sources could support life on Europa |journal=Eos, Transactions American Geophysical Union |date=2001 |volume=82 |issue=13 |pages=150 |doi=10.1029/EO082i013p00150 |bibcode=2001EOSTr..82..150S |s2cid=140714995 |doi-access=free }}</ref> Life could exist in its under-ice ocean, perhaps in an environment similar to Earth's deep-ocean [[hydrothermal vent]]s.<ref name=EuropaLife/><ref name=Jones2001>{{cite web|first=Nicola|last=Jones|date=11 December 2001|url=https://www.newscientist.com/article/dn1647-bacterial-explanation-for-europas-rosy-glow/|title=Bacterial explanation for Europa's rosy glow|work=New Scientist|access-date=26 September 2016|archive-date=27 February 2015|archive-url=https://web.archive.org/web/20150227111850/http://www.newscientist.com/article/dn1647|url-status=live}}</ref> Even if Europa lacks volcanic hydrothermal activity, a 2016 NASA study found that Earth-like levels of hydrogen and oxygen could be produced through processes related to [[serpentinization]] and ice-derived oxidants, which do not directly involve [[volcanism]].<ref name=jpl_2016-05-18>{{Citation| url=http://www.jpl.nasa.gov/news/news.php?feature=6514| title=Europa's Ocean May Have An Earthlike Chemical Balance| newspaper=Jpl.nasa.gov| access-date=18 May 2016| archive-date=18 May 2016| archive-url=https://web.archive.org/web/20160518103003/http://www.jpl.nasa.gov/news/news.php?feature=6514| url-status=live}}</ref> In 2015, scientists announced that salt from a [[Extraterrestrial liquid water|subsurface ocean]] may likely be coating some geological features on Europa, suggesting that the ocean is interacting with the seafloor. This may be important in determining if Europa could be habitable.<ref name=NASA-20150512/><ref>{{cite news| last=Wall| first=Mike| url=http://www.space.com/29604-nasa-jupiter-moon-europa-surface-mission.html| title=NASA Aiming for Multiple Missions to Jupiter Moon Europa| work=Space.com| date=9 June 2015| access-date=10 June 2015| archive-date=11 June 2015| archive-url=https://web.archive.org/web/20150611133540/http://www.space.com/29604-nasa-jupiter-moon-europa-surface-mission.html| url-status=live}}</ref> The likely presence of liquid water in contact with Europa's rocky [[Mantle (geology)|mantle]] has spurred calls to send a probe there.<ref name=Phillips2006>[[Cynthia B. Phillips|Phillips, Cynthia]] (28 September 2006) [http://www.space.com/searchforlife/seti_europa_060928.html ''Time for Europa''] {{Webarchive|url=https://web.archive.org/web/20061125004853/http://www.space.com/searchforlife/seti_europa_060928.html |date=25 November 2006 }}, Space.com.</ref>

The energy provided by tidal forces drives active geological processes within Europa's interior, just as they do to a far more obvious degree on its sister moon [[Io (moon)|Io]]. Although Europa, [[Earth's internal heat budget|like the Earth]], may possess an internal energy source from radioactive decay, the energy generated by tidal flexing would be several orders of magnitude greater than any radiological source.<ref name=Wilson2007>{{cite conference |title=Tidal Heating on Io and Europa and its Implications for Planetary Geophysics |last1=Wilson |first1=Colin P. |conference=Northeastern Section – 42nd Annual Meeting |url=http://gsa.confex.com/gsa/2007NE/finalprogram/abstract_117688.htm |date=March 2007 |access-date=21 December 2007 |archive-url=https://web.archive.org/web/20080905090524/http://gsa.confex.com/gsa/2007NE/finalprogram/abstract_117688.htm |archive-date=5 September 2008 }}</ref> Life on Europa could exist clustered around hydrothermal vents on the ocean floor, or below the ocean floor, where [[endolith]]s are known to inhabit on Earth. Alternatively, it could exist clinging to the lower surface of Europa's ice layer, much like algae and bacteria in Earth's polar regions, or float freely in Europa's ocean.<ref name=limit>{{cite journal |title=The Search for Life on Europa: Limiting Environmental Factors, Potential Habitats, and Earth Analogues |author1=Marion, Giles M. |author2=Fritsen, Christian H. |author3=Eicken, Hajo |author4=Payne, Meredith C. |s2cid=23880085 |journal=Astrobiology |date=2003 |doi=10.1089/153110703322736105 |pmid=14987483 |volume=3 |issue=4 |pages=785–811 |bibcode=2003AsBio...3..785M}}</ref> Should Europa's oceans be too cold, biological processes similar to those known on Earth could not occur; too salty, only extreme [[halophile]]s could survive in that environment.<ref name=limit/> In 2010, a model proposed by Richard Greenberg of the University of Arizona proposed that irradiation of ice on Europa's surface could saturate its crust with oxygen and peroxide, which could then be transported by tectonic processes into the interior ocean. Such a process could render Europa's ocean as oxygenated as our own within just 12&nbsp;million years, allowing the existence of complex, multicellular lifeforms.<ref>{{cite journal |title=Transport Rates of Radiolytic Substances into Europa's Ocean: Implications for the Potential Origin and Maintenance of Life |author=Richard Greenberg |journal=Astrobiology |date=May 2010 |volume=10 |issue=3 |pages=275–283 |doi=10.1089/ast.2009.0386 |pmid=20446868 |bibcode = 2010AsBio..10..275G }}</ref>

Evidence suggests the existence of lakes of liquid water entirely encased in Europa's icy outer shell and distinct from a liquid ocean thought to exist farther down beneath the ice shell,<ref name="europagreatlake">{{cite journal |author1=Schmidt, Britney |author2=Blankenship, Don |author3=Patterson, Wes |author4=Schenk, Paul |date=24 November 2011 |title=Active formation of 'chaos terrain' over shallow subsurface water on Europa |journal=Nature |volume=479 |issue=7374 |pages=502–505 |bibcode=2011Natur.479..502S |doi=10.1038/nature10608 |pmid=22089135 |s2cid=4405195}}</ref><ref name=europagreatlakeairhart/> as well as pockets of water that form M-shaped ice ridges when the water freezes on the surface – as in Greenland.<ref>[https://www.space.com/europa-moon-double-ridges-subsurface-water Icy Europa's mysterious double ridges may hint at hidden pockets of water] {{Webarchive|url=https://web.archive.org/web/20220422020629/https://www.space.com/europa-moon-double-ridges-subsurface-water |date=22 April 2022 }} Rahul Rao, Space.com. 21 April 2022</ref> If confirmed, the lakes and pockets of water could be yet another potential habitat for life. Evidence suggests that hydrogen peroxide is abundant across much of the surface of Europa.<ref>[http://www.nasa.gov/topics/solarsystem/features/europa20130404.html NASA – Mapping the Chemistry Needed for Life at Europa]. {{webarchive|url=https://web.archive.org/web/20130408082530/http://www.nasa.gov/topics/solarsystem/features/europa20130404.html |date=8 April 2013 }}. Nasa.gov (4 April 2013). Retrieved on 23 July 2013.</ref> Because hydrogen peroxide decays into oxygen and water when combined with liquid water, the authors argue that it could be an important energy supply for simple life forms. Nonetheless, on 4 March 2024, astronomers reported that the surface of Europa may have much less [[oxygen]] than previously inferred.<ref name="NYT-20240304km" /><ref name="NYT-20240304jrs" />

[[Clay minerals|Clay-like minerals]] (specifically, [[phyllosilicates]]), often associated with [[organic matter]] on Earth, have been detected on the icy crust of Europa.<ref name=NASA-20131211>{{cite web |last=Cook |first=Jia-Rui C. |title=Clay-Like Minerals Found on Icy Crust of Europa |url=http://www.jpl.nasa.gov/news/news.php?release=2013-362 |date=11 December 2013 |work=[[NASA]] |access-date=11 December 2013 |archive-date=30 January 2020 |archive-url=https://web.archive.org/web/20200130044515/https://www.jpl.nasa.gov/news/news.php?release=2013-362 |url-status=live }}</ref> The presence of the minerals may have been the result of a collision with an [[asteroid]] or comet.<ref name=NASA-20131211/> Some scientists have speculated that life on Earth could have been blasted into space by asteroid collisions and arrived on the moons of Jupiter in a process called [[Panspermia#Lithopanspermia|lithopanspermia]].<ref>{{cite news |first=Charles Q. |last=Choi |url=http://astrobiology.com/2013/12/life-could-have-hitched-a-ride-to-outer-planet-moons.html |title=Life Could Have Hitched a Ride to Outer Planet Moons |work=Astrobiology Magazine |publisher=Astrobiology Web |date=8 December 2013 |access-date=12 December 2013 |archive-date=12 December 2013 |archive-url=https://archive.today/20131212223353/http://astrobiology.com/2013/12/life-could-have-hitched-a-ride-to-outer-planet-moons.html |url-status=live }}</ref>