Editing Europa (moon) (section)

=== Atmosphere ===
[[File:PIA26239-EuropaMoon-OxygenProduction-20240304.jpg|thumb|right|270px|Diagram of how Europa's atmosphere is created by bombardment from ionized particles]]
The atmosphere of Europa can be categorized as thin and tenuous (often called an exosphere), primarily composed of oxygen and trace amounts of water vapor.<ref name=":2">{{Cite web |title=Life Beyond Earth - The Habitable Zone - Europa |url=https://www.pbs.org/lifebeyondearth/alone/europa.html#:~:text=Europa%20does%20have%20an%20atmosphere,surface%20and%20produce%20water%20vapor. |access-date=13 May 2022 |website=www.pbs.org |archive-date=13 May 2022 |archive-url=https://web.archive.org/web/20220513202621/https://www.pbs.org/lifebeyondearth/alone/europa.html#:~:text=Europa%20does%20have%20an%20atmosphere,surface%20and%20produce%20water%20vapor. |url-status=live }}</ref> However, this quantity of oxygen is produced in a non-biological manner. Given that Europa's surface is icy, and subsequently very cold; as solar ultraviolet radiation and charged particles (ions and electrons) from the Jovian magnetospheric environment collide with Europa's surface, water vapor is created and instantaneously separated into oxygen and hydrogen constituents. As it continues to move, the hydrogen is light enough to pass through the surface gravity of the atmosphere leaving behind only oxygen.<ref name=":02">{{Cite web |title=Hubble Finds Oxygen Atmosphere on Jupiter's Moon, Europa |url=http://hubblesite.org/contents/news-releases/1995/news-1995-12 |access-date=13 May 2022 |website=HubbleSite.org |language=en |archive-date=16 April 2023 |archive-url=https://web.archive.org/web/20230416151919/https://hubblesite.org/contents/news-releases/1995/news-1995-12.html |url-status=live }}</ref> The surface-bounded atmosphere forms through radiolysis, the [[Dissociation (chemistry)|dissociation]] of molecules through radiation.<ref name="Johnson1982">{{cite journal |last1=Johnson |first1=Robert E. |last2=Lanzerotti |first2=Louis J. |last3=Brown |first3=Walter L. |date=1982 |title=Planetary applications of ion induced erosion of condensed-gas frosts |journal=Nuclear Instruments and Methods in Physics Research |volume=198 |issue=1 |page=147 |doi=10.1016/0167-5087(82)90066-7|bibcode=1982NIMPR.198..147J }}</ref> This accumulated oxygen atmosphere can get to a height of {{convert|190|km|mi|abbr=on}} above the surface of Europa. Molecular oxygen is the densest component of the atmosphere because it has a long lifetime; after returning to the surface, it does not stick (freeze) like a water or [[hydrogen peroxide]] molecule but rather desorbs from the surface and starts another [[External ballistics|ballistic]] arc. Molecular hydrogen never reaches the surface, as it is light enough to escape Europa's surface gravity.<ref name="Liang">{{cite journal |last1=Liang |first1=Mao-Chang |date=2005 |title=Atmosphere of Callisto |journal=Journal of Geophysical Research |volume=110 |issue=E2 |pages=E02003 |bibcode=2005JGRE..110.2003L |doi=10.1029/2004JE002322 |s2cid=8162816 |url=https://resolver.caltech.edu/CaltechAUTHORS:20140825-144257305 |access-date=15 July 2022 |archive-date=16 April 2023 |archive-url=https://web.archive.org/web/20230416151918/https://authors.library.caltech.edu/48861/ |url-status=live |doi-access=free }}</ref><ref name="Smyth">{{cite conference |last1=Smyth |first1=W. H. |last2=Marconi |first2=M. L. |year=2007 |title=Processes Shaping Galilean Satellite Atmospheres from the Surface to the Magnetosphere |conference=Workshop on Ices |volume=1357 |pages=131 |bibcode=2007LPICo1357..131S}}</ref> Europa is one of the few moons in the [[Solar System]] with a quantifiable atmosphere, along with [[Titan (moon)|Titan]], [[Io (moon)#Atmosphere|Io]], [[Triton (moon)|Triton]], [[Ganymede (moon)#Atmosphere and ionosphere|Ganymede]] and [[Callisto (moon)#Atmosphere and ionosphere|Callisto]].<ref name=":3">{{Cite web |title=Hubble Finds Oxygen Atmosphere On Jupiter's Moon Europa |url=https://solarviews.com/eng/europapr.htm |access-date=13 May 2022 |website=solarviews.com |archive-date=2 October 2022 |archive-url=https://web.archive.org/web/20221002191429/https://solarviews.com/eng/europapr.htm |url-status=live }}</ref> Europa is also one of several moons in the Solar System with very large quantities of [[Volatile (astrogeology)|ice (volatiles)]], otherwise known as "icy moons".<ref name=":4">{{Cite web |last=Cartier |first=Kimberly M. S. |date=14 December 2020 |title=Do Uranus's Moons Have Subsurface Oceans? |url=http://eos.org/articles/do-uranuss-moons-have-subsurface-oceans |access-date=13 May 2022 |website=Eos |language=en-US |archive-date=16 May 2022 |archive-url=https://web.archive.org/web/20220516065456/https://eos.org/articles/do-uranuss-moons-have-subsurface-oceans |url-status=live }}</ref>[[Image:Europa field.png|thumb|left|upright|Magnetic field around Europa. The red line shows a trajectory of the ''Galileo'' spacecraft during a typical flyby (E4 or E14).]]Europa is also considered to be geologically active due to the constant release of hydrogen-oxygen mixtures into space. As a result of the moon's particle venting, the atmosphere requires continuous replenishment.<ref name=":02" /> Europa also contains a small magnetosphere (approximately 25% of Ganymede's). However, this magnetosphere varies in size as Europa orbits through Jupiter's magnetic field. This confirms that a conductive element, such as a large ocean, likely lies below its icy surface.<ref>{{Cite web |title=Europa |url=https://solarsystem.nasa.gov/moons/jupiter-moons/europa/in-depth |access-date=13 May 2022 |website=NASA Solar System Exploration |archive-date=14 May 2022 |archive-url=https://web.archive.org/web/20220514053708/https://solarsystem.nasa.gov/moons/jupiter-moons/europa/in-depth/ |url-status=live }}</ref> As multiple studies have been conducted over Europa's atmosphere, several findings conclude that not all oxygen molecules are released into the atmosphere. This unknown percentage of oxygen may be absorbed into the surface and sink into the subsurface. Because the surface may interact with the subsurface ocean (considering the geological discussion above), this molecular oxygen may make its way to the ocean, where it could aid in biological processes.<ref name="Chyba">{{Cite journal |last1=Chyba |first1=C. F. |last2=Hand |first2=K. P. |year=2001 |title=PLANETARY SCIENCE: Enhanced: Life Without Photosynthesis |journal=Science |volume=292 |issue=5524 |pages=2026–2027 |doi=10.1126/science.1060081 |pmid=11408649 |s2cid=30589825}}</ref><ref>{{Cite journal |last1=Chyba |first1=Christopher F. |last2=Hand |first2=Kevin P. |date=15 June 2001 |title=Life Without Photosynthesis |url=https://www.science.org/doi/10.1126/science.1060081 |journal=Science |language=en |volume=292 |issue=5524 |pages=2026–2027 |doi=10.1126/science.1060081 |pmid=11408649 |s2cid=30589825 |issn=0036-8075 |access-date=13 May 2022 |archive-date=13 May 2022 |archive-url=https://web.archive.org/web/20220513202621/https://www.science.org/doi/10.1126/science.1060081 |url-status=live }}</ref> One estimate suggests that, given the turnover rate inferred from the apparent ~0.5&nbsp;Gyr maximum age of Europa's surface ice, subduction of radiolytically generated oxidizing species might well lead to oceanic free oxygen concentrations that are comparable to those in terrestrial deep oceans.<ref name="ChemDisequilib">{{cite journal |author1=Hand, Kevin P. |author2=Carlson, Robert W. |author3=Chyba, Christopher F. |date=December 2007 |title=Energy, Chemical Disequilibrium, and Geological Constraints on Europa |journal=Astrobiology |volume=7 |issue=6 |pages=1006–1022 |bibcode=2007AsBio...7.1006H |citeseerx=10.1.1.606.9956 |doi=10.1089/ast.2007.0156 |pmid=18163875}}</ref>

Through the slow release of oxygen and hydrogen, a neutral torus around Europa's orbital plane is formed. This "neutral cloud" has been detected by both the ''[[Cassini–Huygens|Cassini]]'' and ''Galileo'' spacecraft, and has a greater content (number of atoms and molecules) than the neutral cloud surrounding Jupiter's inner moon Io.<ref name="Smyth2006">{{cite journal |last=Smyth |first=William H. |author2=Marconi, Max L. |date=2006 |title=Europa's atmosphere, gas tori, and magnetospheric implications |journal=[[Icarus (journal)|Icarus]] |volume=181 |issue=2 |page=510 |bibcode=2006Icar..181..510S |doi=10.1016/j.icarus.2005.10.019}}</ref> This torus was officially confirmed using Energetic Neutral Atom (ENA) imaging. Europa's torus ionizes through the process of neutral particles exchanging electrons with its charged particles. Since Europa's magnetic field rotates faster than its orbital velocity, these ions are left in the path of its magnetic field trajectory, forming a plasma. It has been hypothesized that these ions are responsible for the plasma within Jupiter's magnetosphere.<ref>{{Cite journal |last1=Smith |first1=Howard Todd |last2=Mitchell |first2=Donald G. |last3=Johnson |first3=Robert E. |last4=Mauk |first4=Barry H. |last5=Smith |first5=Jacob E. |date=22 January 2019 |title=Europa Neutral Torus Confirmation and Characterization Based on Observations and Modeling |journal=The Astrophysical Journal |language=en |volume=871 |issue=1 |pages=69 |doi=10.3847/1538-4357/aaed38 |bibcode=2019ApJ...871...69S |s2cid=126922049 |issn=1538-4357 |doi-access=free }}</ref>

On 4 March 2024, astronomers reported that the surface of Europa may have much less [[oxygen]] than previously inferred.<ref name="NYT-20240304km">{{cite news |last=Miller |first=Katrina |title=An Ocean Moon Thought to Be Habitable May Be Oxygen-Starved - A new study suggests that the amount of the element on the moon of Jupiter is on the lower end of previous estimates. |url=https://www.nytimes.com/2024/03/04/science/europa-moon-oxygen.html |date=4 March 2024 |work=[[The New York Times]] |url-status=live |archiveurl=https://archive.today/20240305000839/https://www.nytimes.com/2024/03/04/science/europa-moon-oxygen.html |archivedate=5 March 2024 |accessdate=5 March 2024 }}</ref><ref name="NYT-20240304jrs">{{cite journal |author=Szalay, J.R. |display-authors=et al |title=Oxygen production from dissociation of Europa's water-ice surface |date=4 March 2024 |journal=[[Nature Astronomy]] |volume=8 |issue=5 |pages=567–576 |doi=10.1038/s41550-024-02206-x |doi-access=free |pmid=38798715 |pmc=11111413 |bibcode=2024NatAs...8..567S }}</ref>

==== Discovery of atmosphere ====
The atmosphere of Europa was first discovered in 1995 by astronomers D. T. Hall and collaborators using the [[Goddard High Resolution Spectrograph]] instrument of the [[Hubble Space Telescope]].<ref name="Hall1995">{{cite journal |last1=Hall |first1=D. T. |last2=Strobel |first2=D. F. |last3=Feldman |first3=P. D. |last4=McGrath |first4=M. A. |last5=Weaver |first5=H. A. |title=Detection of an oxygen atmosphere on Jupiter's moon Europa |date=23 February 1995 |journal=Nature |volume=373 |issue=6516 |pages=677–679 |doi=10.1038/373677a0 |pmid=7854447 |bibcode=1995Natur.373..677H }}</ref> This observation was further supported in 1997 by the ''Galileo'' orbiter during its mission within the Jovian system. The ''Galileo'' orbiter performed three radio occultation events of Europa, where the probe's radio contact with Earth was temporarily blocked by passing behind Europa. By analyzing the effects Europa's sparse atmosphere had on the radio signal just before and after the occultation, for a total of six events, a team of astronomers led by A. J. Kliore established the presence of an [[ionosphere|ionized layer]] in Europa's atmosphere.<ref name="Kliore1997">{{cite journal |last1=Kliore |first1=A. J. |last2=Hinson |first2=D. P. |last3=Flaser |first3=F. M. |last4=Nagy |first4=A. F. |last5=Cravens |first5=T. E. |title=The Ionosphere of Europa from Galileo Radio Occultations |date=18 July 1997 |journal=Science |volume=277 |issue=5324 |pages=355–358 |doi=10.1126/science.277.5324.355 |doi-access=free |pmid=9219689 |bibcode=1997Sci...277..355K }}</ref>

==== Climate and weather ====
Despite the presence of a [[gas torus]], Europa has no weather producing clouds. As a whole, Europa has no wind, precipitation, or presence of sky color as its gravity is too low to hold an atmosphere substantial enough for those features. Europa's gravity is approximately 13% of Earth's. The temperature on Europa varies from −160&nbsp;°C at the equator, to −220&nbsp;°C at either of its poles.<ref>{{Cite web |author1=Elizabeth Howell |date=22 March 2018 |title=Europa: Facts About Jupiter's Icy Moon and Its Ocean |url=https://www.space.com/15498-europa-sdcmp.html |access-date=13 May 2022 |website=Space.com |language=en |archive-date=13 May 2022 |archive-url=https://web.archive.org/web/20220513202621/https://www.space.com/15498-europa-sdcmp.html |url-status=live }}</ref> Europa's subsurface ocean is thought to be significantly{{clarify|date=September 2023}} warmer however. It is hypothesized that because of radioactive and tidal heating (as mentioned in the sections above), there are points in the depths of Europa's ocean that may be only slightly cooler than Earth's oceans. Studies have also concluded that Europa's ocean would have been rather acidic at first, with large concentrations of sulfate, calcium, and carbon dioxide. But over the course of 4.5&nbsp;billion years, it became full{{clarify|date=September 2023}} of [[chloride]], thus resembling our 1.94% chloride oceans on Earth.