Editing Magnetosphere (section)

==Structure==
[[File:Magnetosphere Levels.svg|thumb|An artist's rendering of the structure of a magnetosphere: 1)&nbsp;Bow shock. 2)&nbsp;Magnetosheath. 3)&nbsp;Magnetopause. 4)&nbsp;Magnetosphere. 5)&nbsp;Northern tail lobe. 6)&nbsp;Southern tail lobe. 7)&nbsp;Plasmasphere.]]

===Bow shock===
[[File:Red Giant Plunging Through Space.jpg|thumb|[[Thermographic camera|Infrared image]] and artist's concept of the bow shock around [[R Hydrae]]]]
{{main|Bow shock}}
The bow shock forms the outermost layer of the magnetosphere; the boundary between the magnetosphere and the surrounding medium. For stars, this is usually the boundary between the [[stellar wind]] and [[interstellar medium]]; for planets, the speed of the solar wind there decreases as it approaches the magnetopause.<ref>{{cite arXiv|last1=Sparavigna|first1=A.C.|last2=Marazzato|first2=R.|title=Observing stellar bow shocks|date=10 May 2010|class=physics.space-ph |eprint=1005.1527}}</ref> Due to interactions with the bow shock, the [[stellar wind]] [[Plasma (physics)|plasma]] gains a substantial [[anisotropy]], leading to various [[plasma instabilities]] upstream and downstream of the bow shock. <ref>{{cite journal|last1=Pokhotelov|first1=D.|last2=von Alfthan|first2=S.|last3=Kempf|first3=Y.|last4=Vainio|first4=R.|display-authors=et al. |title= Ion distributions upstream and downstream of the Earth's bow shock: first results from Vlasiator| journal=Annales Geophysicae|date=2013-12-17|volume=31|issue=12 |pages=2207–2212|doi=10.5194/angeo-31-2207-2013|doi-access=free |bibcode=2013AnGeo..31.2207P }}</ref>

===Magnetosheath===
{{main|Magnetosheath}}
The magnetosheath is the region of the magnetosphere between the bow shock and the magnetopause. It is formed mainly from shocked solar wind, though it contains a small amount of plasma from the magnetosphere.<ref name=cluster>{{Cite book|editor1-last=Paschmann|editor1-first=G.|editor2-last=Schwartz|editor2-first=S.J.|editor3-last=Escoubet|editor3-first=C.P.|editor4-last=Haaland|editor4-first=S.|title=Outer Magnetospheric Boundaries: Cluster Results|journal=Space Science Reviews|date=2005|volume=118|issue=1–4|isbn=978-1-4020-3488-6|doi=10.1007/1-4020-4582-4 |url=https://cds.cern.ch/record/1250411/files/978-1-4020-4582-0_BookTOC.pdf|series=Space Sciences Series of ISSI|bibcode=2005ombc.book.....P }}</ref> It is an area exhibiting high particle [[energy flux]], where the direction and magnitude of the magnetic field varies erratically. This is caused by the collection of solar wind gas that has effectively undergone [[thermalization]]. It acts as a cushion that transmits the pressure from the flow of the solar wind and the barrier of the magnetic field from the object.<ref name="Van Allen"/>

===Magnetopause===
{{main|Magnetopause}}
The magnetopause is the area of the magnetosphere wherein the pressure from the planetary magnetic field is balanced with the pressure from the solar wind.<ref name=Britannica/> It is the convergence of the shocked solar wind from the magnetosheath with the magnetic field of the object and plasma from the magnetosphere. Because both sides of this convergence contain magnetized plasma, the interactions between them are complex. The structure of the magnetopause depends upon the [[Mach number]] and [[Beta (plasma physics)|beta ratio]] of the plasma, as well as the magnetic field.<ref>{{cite book |chapter=The Magnetopause |last1=Russell |first1=C.T. |editor-last1=Russell |editor-first1=C.T. |editor-last2=Priest |editor-first2=E.R. |editor-last3=Lee |editor-first3=L.C. |title=Physics of magnetic flux ropes |date=1990 |publisher=American Geophysical Union |isbn=9780875900261 |pages=439–453 |url=http://www-ssc.igpp.ucla.edu/ssc/tutorial/magnetopause.html |archive-url=https://web.archive.org/web/19990202125049/http://www-ssc.igpp.ucla.edu/ssc/tutorial/magnetopause.html |archive-date=2 February 1999}}</ref> The magnetopause changes size and shape as the pressure from the solar wind fluctuates.<ref>{{cite web |first1=David P. |last1=Stern |first2=Mauricio |last2=Peredo |title=The Magnetopause |url=https://www-spof.gsfc.nasa.gov/Education/wmpause.html |website=The Exploration of the Earth's Magnetosphere |publisher=NASA |date=20 November 2003 |access-date=19 August 2019 |archive-date=19 August 2019 |archive-url=https://web.archive.org/web/20190819221711/https://www-spof.gsfc.nasa.gov/Education/wmpause.html |url-status=dead }}</ref>

===Magnetotail===
Opposite the compressed magnetic field is the magnetotail, where the magnetosphere extends far beyond the astronomical object. It contains two lobes, referred to as the <i>northern</i> and <i>southern</i> tail lobes. Magnetic field lines in the northern tail lobe point towards the object while those in the southern tail lobe point away. The tail lobes are almost empty, with few charged particles opposing the flow of the solar wind. The two lobes are separated by a plasma sheet, an area where the magnetic field is weaker, and the density of charged particles is higher.<ref name="tail">{{cite web|title=The Tail of the Magnetosphere|url=http://www-spof.gsfc.nasa.gov/Education/wtail.html|publisher=NASA|access-date=22 December 2012|archive-date=7 February 2018|archive-url=https://web.archive.org/web/20180207114437/https://www-spof.gsfc.nasa.gov/Education/wtail.html|url-status=dead}}</ref>

===Earth's magnetosphere{{anchor|Earth}}===
<!-- [[Magnetosphere of Earth]] redirects to this section. If this section's name is changed, please update that incoming redirect. Thanks! -->

{{See also|Earth's magnetic field#Magnetosphere|Van Allen radiation belt}}
{{further|Plasmasphere}}
[[File:Magnetosphere rendition.jpg|thumb|Artist's rendition of Earth's magnetosphere]]
[[File:Structure_of_the_magnetosphere_LanguageSwitch.svg|lang=en|thumb|upright=1.5|Diagram of Earth's magnetosphere]]
Over Earth's [[equator]], the magnetic field lines become almost horizontal, then return to reconnect at high latitudes. However, at high altitudes, the magnetic field is significantly distorted by the solar wind and its solar magnetic field. On the dayside of Earth, the magnetic field is significantly compressed by the solar wind to a distance of approximately {{convert|65000|km|sp=us}}. Earth's bow shock is about {{convert|17|km|sp=us}} thick<ref>{{cite news|title=Cluster reveals Earth's bow shock is remarkably thin|url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=49637|newspaper=[[European Space Agency]]|date=16 November 2011}}</ref> and located about {{convert|90000|km|sp=us}} from Earth.<ref>{{cite news|title=Cluster reveals the reformation of Earth's bow shock|url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=40994|newspaper=European Space Agency|date=11 May 2011}}</ref> The magnetopause exists at a distance of several hundred kilometers above Earth's surface. Earth's magnetopause has been compared to a [[sieve]] because it allows solar wind particles to enter. [[Kelvin–Helmholtz instability|Kelvin–Helmholtz instabilities]] occur when large swirls of plasma travel along the edge of the magnetosphere at different velocities from the magnetosphere, causing the plasma to slip past. This results in [[magnetic reconnection]], and as the magnetic field lines break and reconnect, solar wind particles are able to enter the magnetosphere.<ref>{{cite news|title=Cluster observes a 'porous' magnetopause|url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=50977|newspaper=European Space Agency|date=24 October 2012}}</ref> On Earth's nightside, the magnetic field extends in the magnetotail, which lengthwise exceeds {{convert|6300000|km|sp=us}}.<ref name=Britannica/> Earth's magnetotail is the primary source of the [[Aurora (astronomy)|polar aurora]].<ref name=tail/> Also, NASA scientists have suggested that Earth's magnetotail might cause "dust storms" on the Moon by creating a potential difference between the day side and the night side.<ref>http://www.nasa.gov/topics/moonmars/features/magnetotail_080416.html {{Webarchive|url=https://web.archive.org/web/20211114122639/https://www.nasa.gov/topics/moonmars/features/magnetotail_080416.html |date=14 November 2021 }} NASA, ''The Moon and the Magnetotail''</ref>

===Other objects===
Many astronomical objects generate and maintain magnetospheres. In the Solar System this includes the Sun, [[Mercury (planet)|Mercury]], [[Earth]], [[Jupiter]], [[Saturn]], [[Uranus]], [[Neptune]],<ref name="Planetary Shields: Magnetospheres">{{cite web |title=Planetary Shields: Magnetospheres |url=https://mobile.arc.nasa.gov/public/iexplore/missions/pages/yss/november2011.html |publisher=NASA |access-date=5 January 2020}}</ref> and [[Ganymede (moon)|Ganymede]]. The [[magnetosphere of Jupiter]] is the largest planetary magnetosphere in the Solar System, extending up to {{convert|7000000|km|sp=us}} on the dayside and almost to the orbit of [[Saturn]] on the nightside.<ref>{{cite encyclopedia |url=http://www.igpp.ucla.edu/people/mkivelson/Publications/279-Ch24.pdf |title=The configuration of Jupiter's magnetosphere |first=K. K. |last=Khurana |author2=Kivelson, M. G. |display-authors=etal |isbn=978-0-521-81808-7 |encyclopedia=Jupiter: The Planet, Satellites and Magnetosphere |publisher=[[Cambridge University Press]] |editor=Bagenal, Fran |editor2=Dowling, Timothy E. |editor3=McKinnon, William B. |date=2004 }}</ref> Jupiter's magnetosphere is stronger than Earth's by an [[order of magnitude]], and its [[magnetic moment]] is approximately 18,000 times larger.<ref>{{cite journal|last=Russell|first=C.T.|title=Planetary Magnetospheres|journal=Reports on Progress in Physics|volume=56|issue=6|pages=687–732|date=1993|doi=10.1088/0034-4885/56/6/001|bibcode=1993RPPh...56..687R|s2cid=250897924 }}</ref> [[Venus]], [[Mars]], and [[Pluto]], on the other hand, have no ''intrinsic'' magnetic field. This may have had significant effects on their geological history. It is hypothesized that Venus and Mars may have lost their primordial water to [[photodissociation]] and the solar wind. A strong magnetosphere, were it present, would greatly slow down this process.<ref name="Planetary Shields: Magnetospheres"/><ref>{{cite web |title=X-ray Detection Sheds New Light on Pluto |url=https://www.nasa.gov/mission_pages/chandra/x-ray-detection-sheds-new-light-on-pluto.html |access-date=3 December 2016 |date=14 September 2016 |author=NASA |website=nasa.gov}}</ref> 

[[File:Tau Bootis b.jpg|right|thumb|Artist impression of the magnetic field around Tau Boötis b detected in 2020.]]
{| class="wikitable sortable mw-collapsible"
|+Magnetospheres of the Solar System<ref name="n675">{{cite book |last1=Kivelson |first1=Margaret Galland |title=Encyclopedia of the Solar System |last2=Bagenal |first2=Fran |publisher=Elsevier |year=2014 |isbn=978-0-12-415845-0 |pages=137–157 |chapter=Planetary Magnetospheres |doi=10.1016/b978-0-12-415845-0.00007-4}}</ref>
!Magnetosphere
!Surface equatorial field ([[Tesla (unit)|microteslas]])
!{{Sfrac|Distance to [[magnetopause]]|Planetary radius}}
!Upstream
[[Alfvén Mach number]]
!{{Sfrac|Surface [[magnetic pressure]]|Exterior [[magnetic pressure]]}}
!{{Sfrac|Solar wind speed|Rotation speed}} at magnetopause
|-
|[[Magnetosphere of Mercury|Mercury]]
|0.14-04
|1.5
|6
|1
|{{Val|3e5}}
|-
|[[Earth's magnetic field|Earth]]
|31
|10
|7
|{{Val|4e5}}
|90
|-
|[[Magnetosphere of Mars|Mars]]
|<0.01
|n/a
|8
|<0.04
|n/a
|-
|[[Magnetosphere of Jupiter|Jupiter]]
|428
|70
|10
|{{Val|7e8}}
|0.4
|-
|[[Magnetosphere of Ganymede|Ganymede]]
|0.72
|1.6
|0.4
|50
|n/a
|-
|[[Magnetosphere of Saturn|Saturn]]
|22
|20
|12
|{{Val|7e7}}
|2
|-
|[[Magnetosphere of Uranus|Uranus]]
|23
|18
|13
|{{Val|4e7}}
|7
|-
|[[Magnetosphere of Neptune|Neptune]]
|14
|24
|15
|{{Val|4e7}}
|6
|}
Magnetospheres generated by [[exoplanet]]s are thought to be common, though the first discoveries did not come until the 2010s. In 2014, a magnetic field around [[HD 209458 b]] was inferred from the way [[hydrogen]] was evaporating from the planet.<ref>{{Cite web|author1=Charles Q. Choi|date=2014-11-20|title=Unlocking the Secrets of an Alien World's Magnetic Field|url=https://www.space.com/27828-alien-planet-magnetic-field-strength.html|access-date=2022-01-17|website=Space.com|language=en}}</ref><ref>{{Cite journal|doi=10.1126/science.1257829|pmid=25414310 |title=Magnetic moment and plasma environment of HD 209458b as determined from Ly observations |journal=Science |volume=346 |issue=6212 |pages=981–984 |year=2014 |last1=Kislyakova |first1=K. G.|last2=Holmstrom |first2=M. |last3=Lammer |first3=H. |last4=Odert |first4=P. |last5=Khodachenko |first5=M. L. |bibcode=2014Sci...346..981K |arxiv = 1411.6875 |s2cid=206560188}}</ref> In 2019, the strength of the surface magnetic fields of 4 [[hot Jupiter]]s were estimated and ranged between 20 and 120 [[Gauss (unit)|gauss]] compared to Jupiter's surface magnetic field of 4.3 gauss.<ref>{{Cite web|author1=Passant Rabie|date=2019-07-29|title=Magnetic Fields of 'Hot Jupiter' Exoplanets Are Much Stronger Than We Thought|url=https://www.space.com/hot-jupiter-magnetic-fields-measured-for-first-time.html|access-date=2022-01-17|website=Space.com|language=en}}</ref><ref>{{Cite journal|last1=Cauley|first1=P. Wilson|last2=Shkolnik|first2=Evgenya L.|last3=Llama|first3=Joe|last4=Lanza|first4=Antonino F.|date=Dec 2019|title=Magnetic field strengths of hot Jupiters from signals of star-planet interactions|journal=Nature Astronomy|volume=3|issue=12|pages=1128–1134|doi=10.1038/s41550-019-0840-x|arxiv=1907.09068|bibcode=2019NatAs...3.1128C|s2cid=198147426|issn=2397-3366}}</ref> In 2020, a radio emission in the 14-30&nbsp;MHz band was detected from the [[Tau Boötis]] system, likely associated with [[cyclotron radiation]] from the poles of [[Tau Boötis b]] which might be a signature of a planetary magnetic field.<ref>{{citation |last1=Turner |first1=Jake D. |title=The search for radio emission from the exoplanetary systems 55 Cancri, υ Andromedae, and τ Boötis using LOFAR beam-formed observations |journal=Astronomy & Astrophysics |volume=645 |pages=A59 |year=2021 |arxiv=2012.07926 |bibcode=2021A&A...645A..59T |doi=10.1051/0004-6361/201937201 |s2cid=212883637 |last2=Zarka |first2=Philippe |last3=Grießmeier |first3=Jean-Mathias |last4=Lazio |first4=Joseph |last5=Cecconi |first5=Baptiste |last6=Emilio Enriquez |first6=J. |last7=Girard |first7=Julien N. |last8=Jayawardhana |first8=Ray |last9=Lamy |first9=Laurent |last10=Nichols |first10=Jonathan D. |last11=De Pater |first11=Imke}}</ref><ref>{{Cite web |last=O'Callaghan |first=Jonathan |date=2023-08-07 |title=Exoplanets Could Help Us Learn How Planets Make Magnetism |url=https://www.quantamagazine.org/exoplanets-could-help-us-learn-how-planets-make-magnetism-20230807/ |access-date=2023-08-07 |website=Quanta Magazine |language=en}}</ref> In 2021 a magnetic field generated by the [[hot Neptune]] [[HAT-P-11b]] became the first to be confirmed.<ref name= sedHatp11b>[http://data.iap.fr/doi/bjaffel/20210727/ HAT-P-11 Spectral Energy Distribution] Signatures of Strong Magnetization and Metal-poor Atmosphere for a Neptune-Size Exoplanet, Ben-Jaffel et al. 2021</ref> The first unconfirmed detection of a magnetic field generated by a terrestrial exoplanet was found in 2023 on [[YZ Ceti b]].<ref name="Pineda2023">{{cite journal |last1=Pineda |first1=J. Sebastian |last2=Villadsen |first2=Jackie |date=April 2023 |title=Coherent radio bursts from known M-dwarf planet host YZ Ceti |journal=[[Nature Astronomy]] |volume=7 |issue= 5|pages=569–578 |doi=10.1038/s41550-023-01914-0 |arxiv=2304.00031 |bibcode=2023NatAs...7..569P}}</ref><ref name="Trigilio2023">{{cite arXiv |last1=Trigilio |first1=Corrado |last2=Biswas |first2=Ayan |display-authors=etal |date=May 2023 |title=Star-Planet Interaction at radio wavelengths in YZ Ceti: Inferring planetary magnetic field |eprint=2305.00809 |class=astro-ph.EP}}</ref><ref>{{Cite web |date=2023-04-10 |title=A magnetic field on a nearby Earth-sized exoplanet? |url=https://earthsky.org/space/magnetic-field-exoplanets-yz-ceti-b/ |access-date=2023-08-07 |website=earthsky.org |language=en-US}}</ref><ref>{{Cite web |last=O'Callaghan |first=Jonathan |date=7 August 2023 |title=Exoplanets Could Help Us Learn How Planets Make Magnetism |url=https://www.quantamagazine.org/exoplanets-could-help-us-learn-how-planets-make-magnetism-20230807/ |website=[[Quanta Magazine]]}}</ref>