Editing Aurora (section)

== Extraterrestrial auroras ==
{{See also|Magnetosphere of Jupiter#Aurorae}}
[[File:Jupiter.Aurora.HST.UV.jpg|thumb|[[Jupiter]] aurora; the far left bright spot connects magnetically to [[Io (moon)|Io]]; the spots at the bottom of the image lead to [[Ganymede (moon)|Ganymede]] and [[Europa (moon)|Europa]].]]
[[File:Saturns Northern Aurora still.jpg|thumb|An aurora high above the northern part of Saturn; image taken by the [[Cassini spacecraft]].

[[:File:Saturns Northern Aurora in Motion.gif|A movie]] shows images from 81 hours of observations of Saturn's aurora.]]

Both [[Jupiter]] and [[Saturn]] have magnetic fields that are stronger than Earth's (Jupiter's equatorial field strength is 4.3 [[Gauss (unit)|gauss]], compared to 0.3 gauss for Earth), and both have extensive radiation belts. Auroras have been observed on both gas planets, most clearly using the [[Hubble Space Telescope]], and the [[Cassini–Huygens|''Cassini'']] and [[Galileo (spacecraft)|''Galileo'']] spacecraft, as well as on [[Uranus]] and [[Neptune]].<ref name="european space agency-2004">{{cite web|url=http://www.esa.int/esaCP/SEMLQ71DU8E_index_0.html|title=ESA Portal – Mars Express discovers auroras on Mars|publisher=European Space Agency|date=11 August 2004|access-date=5 August 2010|archive-date=19 October 2012|archive-url=https://web.archive.org/web/20121019183824/http://www.esa.int/esaCP/SEMLQ71DU8E_index_0.html|url-status=live}}</ref>

The auroras on Saturn seem, like Earth's, to be powered by the solar wind. However, Jupiter's auroras are more complex. Jupiter's main auroral oval is associated with the plasma produced by the volcanic moon [[Io (moon)|Io]], and the transport of this plasma within the planet's [[Magnetosphere of Jupiter|magnetosphere]]. An uncertain fraction of Jupiter's auroras are powered by the solar wind. In addition, the moons, especially Io, are also powerful sources of aurora. These arise from electric currents along field lines ("field aligned currents"), generated by a dynamo mechanism due to the relative motion between the rotating planet and the moving moon. Io, which has active [[volcanism]] and an ionosphere, is a particularly strong source, and its currents also generate radio emissions, which have been studied since 1955. Using the Hubble Space Telescope, auroras over Io, Europa, and Ganymede have all been observed.

Auroras have also been observed on [[Venus]] and [[Mars]]. Venus has no magnetic field so Venusian auroras appear as bright and diffuse patches of varying shape and intensity, sometimes distributed over the full disc of the planet.<ref>{{Cite journal|last1=Phillips|first1=J. L.|last2=Stewart|first2=A. I. F.|last3=Luhmann|first3=J. G.|date=1986|title=The Venus ultraviolet aurora: Observations at 130.4 nm|url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/GL013i010p01047|journal=Geophysical Research Letters|language=en|volume=13|issue=10|pages=1047–1050|doi=10.1029/GL013i010p01047|bibcode=1986GeoRL..13.1047P|issn=1944-8007|access-date=17 January 2021|archive-date=22 January 2021|archive-url=https://web.archive.org/web/20210122212248/https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/GL013i010p01047|url-status=live}}</ref> A Venusian aurora originates when electrons from the solar wind collide with the night-side atmosphere.

An aurora was detected on Mars, on 14 August 2004, by the SPICAM instrument aboard ''[[Mars Express]]''. The aurora was located at [[Terra Cimmeria]], in the region of 177° east, 52° south. The total size of the emission region was about 30&nbsp;km across, and possibly about 8&nbsp;km high. By analysing a map of crustal magnetic anomalies compiled with data from the [[Mars Global Surveyor]], scientists observed that the region of the emissions corresponded to an area where the strongest magnetic field is localized. This correlation indicated that the origin of the light emission was a flux of electrons moving along the crust magnetic lines and exciting the upper atmosphere of Mars.<ref name="european space agency-2004" /><ref>{{cite news|date=18 February 2006|url=http://www.universetoday.com/am/publish/mars_express_aurorae.html?1722006|title=Mars Express Finds Auroras on Mars|work=Universe Today|access-date=5 August 2010|archive-date=10 February 2007|archive-url=https://web.archive.org/web/20070210031424/http://www.universetoday.com/am/publish/mars_express_aurorae.html?1722006|url-status=live}}</ref>

Between 2014 and 2016, cometary auroras were observed on comet [[67P/Churyumov–Gerasimenko]] by multiple instruments on the [[Rosetta (spacecraft)|Rosetta]] spacecraft.<ref>{{cite web|date=21 September 2020|title=Comet Chury's ultraviolet aurora|url=https://www.unibe.ch/news/media_news/media_relations_e/media_releases/2020/media_releases_2020/comet_chury_s_ultraviolet_aurora/index_eng.html|access-date=17 January 2021|website=Portal|archive-date=16 January 2021|archive-url=https://web.archive.org/web/20210116034054/https://www.unibe.ch/news/media_news/media_relations_e/media_releases/2020/media_releases_2020/comet_chury_s_ultraviolet_aurora/index_eng.html|url-status=live}}</ref><ref name="galand-2020">{{Cite journal|last1=Galand|first1=M.|last2=Feldman|first2=P. D.|last3=Bockelée-Morvan|first3=D.|author3-link=Dominique Bockelée-Morvan|last4=Biver|first4=N.|last5=Cheng|first5=Y.-C.|last6=Rinaldi|first6=G.|last7=Rubin|first7=M.|last8=Altwegg|first8=K.|author8-link=Kathrin Altwegg|last9=Deca|first9=J.|last10=Beth|first10=A.|last11=Stephenson|first11=P.|date=21 September 2020|title=Far-ultraviolet aurora identified at comet 67P/Churyumov-Gerasimenko|url=https://www.nature.com/articles/s41550-020-1171-7.epdf?sharing_token=D757kcyUX_56njDTcvpSzdRgN0jAjWel9jnR3ZoTv0ODS5LjlN2IKlQgz2jQGPEcFej9C7svyQPjp54CQ50dBx_tkOS3bq-oMWB16Ux3zdWmIZbNCQBAGA1gFAIyXN43TupVPuTwe_oI8bjAahWq18wR7m9QXx7Yhz7zESpivB3btrTi5Qt3trSYVr1aO5yYHu6Hfcnq6u_UVzU3rpWFxvMwCy3aj-2263pTY4ThIYuLO3VW51M44nPr7Ff1Y5vP5tsgJekLXnza9PmvSWJF1Q==&tracking_referrer=www.space.com|journal=Nature Astronomy|language=en|volume=4|issue=11|pages=1084–1091|doi=10.1038/s41550-020-1171-7|bibcode=2020NatAs...4.1084G|issn=2397-3366|hdl=10044/1/82183|s2cid=221884342|hdl-access=free|access-date=17 January 2021|archive-date=9 April 2022|archive-url=https://web.archive.org/web/20220409035009/https://www.nature.com/articles/s41550-020-1171-7.epdf?sharing_token=D757kcyUX_56njDTcvpSzdRgN0jAjWel9jnR3ZoTv0ODS5LjlN2IKlQgz2jQGPEcFej9C7svyQPjp54CQ50dBx_tkOS3bq-oMWB16Ux3zdWmIZbNCQBAGA1gFAIyXN43TupVPuTwe_oI8bjAahWq18wR7m9QXx7Yhz7zESpivB3btrTi5Qt3trSYVr1aO5yYHu6Hfcnq6u_UVzU3rpWFxvMwCy3aj-2263pTY4ThIYuLO3VW51M44nPr7Ff1Y5vP5tsgJekLXnza9PmvSWJF1Q==&tracking_referrer=www.space.com|url-status=live}}</ref> The auroras were observed at [[Far ultraviolet|far-ultraviolet]] wavelengths. [[Coma (cometary)|Coma]] observations revealed atomic emissions of hydrogen and oxygen caused by the [[photodissociation]] (not [[photoionization]], like in terrestrial auroras) of water molecules in the comet's coma.<ref name="galand-2020" /> The interaction of accelerated electrons from the solar wind with gas particles in the coma is responsible for the aurora.<ref name="galand-2020" /> Since comet 67P has no magnetic field, the aurora is diffusely spread around the comet.<ref name="galand-2020" />

[[Exoplanet]]s, such as [[hot Jupiter]]s, have been suggested to experience ionization in their upper atmospheres and generate an aurora modified by [[weather]] in their turbulent [[troposphere]]s.<ref>{{Cite journal|last1=Helling|first1=Christiane|last2=Rimmer|first2=Paul B.|date=23 September 2019|title=Lightning and charge processes in brown dwarf and exoplanet atmospheres|url=|journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences|volume=377|issue=2154|page=20180398|doi=10.1098/rsta.2018.0398|arxiv=1903.04565|pmid=31378171|pmc=6710897|bibcode=2019RSPTA.37780398H}}</ref> However, there is no current detection of an exoplanet aurora.

The first ever [[Extra-solar object|extra-solar]] auroras were discovered in July 2015 over the [[brown dwarf]] star [[LSR J1835+3259]].<ref>{{cite web|url=http://news.discovery.com/space/alien-life-exoplanets/monstrous-aurora-detected-beyond-our-solar-system-150729.htm|title=Monstrous Aurora Detected Beyond our Solar System|last1=O'Neill|first1=Ian|date=29 July 2015|publisher=Discovery|access-date=29 July 2015|archive-date=31 July 2015|archive-url=https://web.archive.org/web/20150731022645/http://news.discovery.com/space/alien-life-exoplanets/monstrous-aurora-detected-beyond-our-solar-system-150729.htm|url-status=dead}}</ref> The mainly red aurora was found to be a million times brighter than the northern lights, a result of the charged particles interacting with hydrogen in the atmosphere. It has been speculated that stellar winds may be stripping off material from the surface of the brown dwarf to produce their own electrons. Another possible explanation for the auroras is that an as-yet-undetected body around the dwarf star is throwing off material, as is the case with Jupiter and its moon Io.<ref>{{cite web|url=http://www.space.com/30087-alien-auroras-found-beyond-solar-system.html|title=First Alien Auroras Found, Are 1 Million Times Brighter Than Any on Earth|last1=Q. Choi|first1=Charles|date=29 July 2015|publisher=space.com|access-date=29 July 2015|archive-date=30 July 2015|archive-url=https://web.archive.org/web/20150730212125/http://www.space.com/30087-alien-auroras-found-beyond-solar-system.html|url-status=live}}</ref>