Array ( [0] => {{short description|Region around an astronomical object in which its magnetic field affects charged particles}} [1] => [[File:Rattling Earth's Force Field.ogv|thumb|A rendering of the [[magnetic field lines]] of the magnetosphere of the Earth.]] [2] => [3] => In [[astronomy]] and [[planetary science]], a '''magnetosphere''' is a region of space surrounding an [[astronomical object]] in which [[charged particle]]s are affected by that object's [[magnetic field]].{{cite web [4] => |title=Magnetospheres [5] => |url=https://science.nasa.gov/heliophysics/focus-areas/magnetosphere-ionosphere/ [6] => |website=NASA Science [7] => |publisher=NASA}}{{cite book [8] => |last=Ratcliffe|first=John Ashworth| [9] => title=An Introduction to the Ionosphere and Magnetosphere [10] => |date=1972 [11] => |publisher=[[CUP Archive]] [12] => |isbn=9780521083416 [13] => |url=https://archive.org/details/introductiontoio0000ratc|url-access=registration}} It is created by a [[celestial body]] with an active interior [[Dynamo theory|dynamo]]. [14] => [15] => In the space environment close to a planetary body, the magnetic field resembles a [[magnetic dipole]]. Farther out, [[field line]]s can be significantly distorted by the flow of [[electrically conducting]] [[plasma (physics)|plasma]], as emitted from the Sun (i.e., the [[solar wind]]) or a nearby star.{{cite encyclopedia [16] => |date=2012 [17] => |title=Ionosphere and magnetosphere [18] => |encyclopedia=Encyclopædia Britannica [19] => |publisher=[[Encyclopædia Britannica, Inc.]] [20] => |url=https://www.britannica.com/EBchecked/topic/1369043/ionosphere-and-magnetosphere}}{{cite book [21] => |last=Van Allen|first=James Alfred| [22] => title=Origins of Magnetospheric Physics [23] => |date=2004 [24] => |publisher=[[University of Iowa Press]] [25] => |location=Iowa City, Iowa USA|isbn=9780877459217|oclc=646887856}} Planets having active magnetospheres, like the Earth, are capable of mitigating or blocking the effects of [[solar radiation]] or [[cosmic radiation]]; in Earth's case, this protects living organisms from harm. Interactions of particles and atmospheres with magnetospheres are studied under the specialized scientific subjects of [[plasma physics]], [[space physics]], and [[aeronomy]]. [26] => [27] => ==History== [28] => {{main|Magnetosphere chronology}} [29] => Study of Earth's magnetosphere began in 1600, when [[William Gilbert (astronomer)|William Gilbert]] discovered that the magnetic field on the surface of Earth resembled that of a [[terrella]], a small, magnetized sphere. In the 1940s, [[Walter M. Elsasser]] proposed the model of [[dynamo theory]], which attributes [[Earth's magnetic field]] to the motion of Earth's [[iron]] [[outer core]]. Through the use of [[magnetometer]]s, scientists were able to study the variations in Earth's magnetic field as functions of both time and latitude and longitude. [30] => [31] => Beginning in the late 1940s, rockets were used to study [[cosmic rays]]. In 1958, [[Explorer 1]], the first of the Explorer series of space missions, was launched to study the intensity of cosmic rays above the atmosphere and measure the fluctuations in this activity. This mission observed the existence of the [[Van Allen radiation belt]] (located in the inner region of Earth's magnetosphere), with the follow-up [[Explorer 3]] later that year definitively proving its existence. Also during 1958, [[Eugene Parker]] proposed the idea of the [[solar wind]], with the term 'magnetosphere' being proposed by [[Thomas Gold]] in 1959 to explain how the solar wind interacted with the Earth's magnetic field. The later mission of Explorer 12 in 1961 led by the Cahill and Amazeen observation in 1963 of a sudden decrease in magnetic field strength near the noon-time meridian, later was named the [[magnetopause]]. By 1983, the [[International Cometary Explorer]] observed the magnetotail, or the distant magnetic field. [32] => [33] => ==Structure and behavior== [34] => Magnetospheres are dependent on several variables: the type of astronomical object, the nature of sources of plasma and momentum, the [[frequency|period]] of the object's spin, the nature of the axis about which the object spins, the axis of the magnetic dipole, and the magnitude and direction of the flow of [[solar wind]]. [35] => [36] => The planetary distance where the magnetosphere can withstand the solar wind pressure is called the Chapman–Ferraro distance. This is usefully modeled by the formula wherein R_{\rm P} represents the radius of the planet, B_{\rm surf} represents the magnetic field on the surface of the planet at the equator, and V_{\rm SW} represents the velocity of the solar wind: [37] => [38] => :R_{\rm CF}=R_{\rm P} \left( \frac{B_{\rm surf}^2}{\mu_{0} \rho V_{\rm SW}^2} \right) ^{\frac{1}{6}} [39] => [40] => A magnetosphere is classified as "intrinsic" when R_{\rm CF} \gg R_{\rm P}, or when the primary opposition to the flow of solar wind is the magnetic field of the object. [[Mercury (planet)|Mercury]], Earth, [[Jupiter]], [[Ganymede (moon)|Ganymede]], [[Saturn]], [[Uranus]], and [[Neptune]], for example, exhibit intrinsic magnetospheres. A magnetosphere is classified as "induced" when R_{\rm CF} \ll R_{\rm P}, or when the solar wind is not opposed by the object's magnetic field. In this case, the solar wind interacts with the atmosphere or ionosphere of the planet (or surface of the planet, if the planet has no atmosphere). [[Venus]] has an induced magnetic field, which means that because Venus appears to have no [[Dynamo theory|internal dynamo effect]], the only magnetic field present is that formed by the solar wind's wrapping around the physical obstacle of Venus (see also [[Atmosphere of Venus#Induced magnetosphere|Venus' induced magnetosphere]]). When R_{\rm CF} \approx R_{\rm P}, the planet itself and its magnetic field both contribute. It is possible that [[Mars]] is of this type.{{cite journal|last1=Blanc|first1=M.|last2=Kallenbach|first2=R.|last3=Erkaev|first3=N.V.|title=Solar System Magnetospheres|journal=Space Science Reviews|volume=116|date=2005|issue=1–2|pages=227–298|doi=10.1007/s11214-005-1958-y|bibcode=2005SSRv..116..227B |s2cid=122318569}} [41] => [42] => ==Structure== [43] => [[File:Magnetosphere Levels.svg|thumb|An artist's rendering of the structure of a magnetosphere: 1) Bow shock. 2) Magnetosheath. 3) Magnetopause. 4) Magnetosphere. 5) Northern tail lobe. 6) Southern tail lobe. 7) Plasmasphere.]] [44] => [45] => ===Bow shock=== [46] => [[File:Red Giant Plunging Through Space.jpg|thumb|[[Thermographic camera|Infrared image]] and artist's concept of the bow shock around [[R Hydrae]]]] [47] => {{main|Bow shock}} [48] => The bow shock forms the outermost layer of the magnetosphere; the boundary between the magnetosphere and the ambient 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.{{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}} 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. {{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 }} [49] => [50] => ===Magnetosheath=== [51] => {{main|Magnetosheath}} [52] => 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.{{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 }} 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. [53] => [54] => ===Magnetopause=== [55] => {{main|Magnetopause}} [56] => 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. 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]] of the plasma, as well as the magnetic field.{{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}} The magnetopause changes size and shape as the pressure from the solar wind fluctuates.{{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 }} [57] => [58] => ===Magnetotail=== [59] => 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 northern and southern 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.{{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}} [60] => [61] => ===Earth's magnetosphere{{anchor|Earth}}=== [62] => [63] => [64] => {{See also|Earth's magnetic field#Magnetosphere|Van Allen radiation belt}} [65] => {{further|Plasmasphere}} [66] => [[File:Magnetosphere rendition.jpg|thumb|Artist's rendition of Earth's magnetosphere]] [67] => [[File:Structure_of_the_magnetosphere_LanguageSwitch.svg|lang=en|thumb|upright=1.5|Diagram of Earth's magnetosphere]] [68] => 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{{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}} and located about {{convert|90000|km|sp=us}} from Earth.{{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}} 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 a different velocity 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.{{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}} On Earth's nightside, the magnetic field extends in the magnetotail, which lengthwise exceeds {{convert|6300000|km|sp=us}}. Earth's magnetotail is the primary source of the [[Aurora (astronomy)|polar aurora]]. 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.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'' [69] => [70] => ===Other objects=== [71] => Many astronomical objects generate and maintain magnetospheres. In the Solar System this includes the Sun, [[Mercury (planet)|Mercury]], [[Jupiter]], [[Saturn]], [[Uranus]], [[Neptune]],{{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}} 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.{{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 }} Jupiter's magnetosphere is stronger than Earth's by an [[order of magnitude]], and its [[magnetic moment]] is approximately 18,000 times larger.{{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 }} [[Venus]], [[Mars]], and [[Pluto]], on the other hand, have no magnetic field. This may have had significant effects on their geological history. It is theorized that Venus and Mars may have lost their primordial water to [[photodissociation]] and the solar wind. A strong magnetosphere greatly slows this process.{{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}} [72] => [73] => [[File:Tau Bootis b.jpg|right|thumb|Artist impression of the magnetic field around Tau Boötis b detected in 2020.]] [74] => 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.{{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}}{{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}} 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.{{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}}{{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}} In 2020, a radio emission in the 14-30 MHz band was detected from the [[Tau Boötis]] system, likely associated with [[cyclotron radiation]] from the poles of [[Tau Boötis b]] a signature of a planetary magnetic field.{{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}}{{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}} In 2021 a magnetic field generated by [[HAT-P-11b]] became the first to be confirmed.[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 The first unconfirmed detection of a magnetic field generated by a terrestrial exoplanet was found in 2023 on [[YZ Ceti b]].{{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}}{{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}}{{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}}{{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]]}} [75] => [76] => ==See also== [77] => *[[Geospace]] [78] => *[[Plasma (physics)]] [79] => [80] => ==References== [81] => {{Reflist}} [82] => [83] => {{Magnetospherics}} [84] => {{In space}} [85] => {{Portal bar|Physics|Astronomy|Stars|Spaceflight|Solar System}} [86] => {{Authority control}} [87] => {{Use dmy dates|date=September 2019}} [88] => [89] => [[Category:Geomagnetism]] [90] => [[Category:Ionosphere]] [91] => [[Category:Planetary science]] [92] => [[Category:Terrestrial plasmas]] [93] => [[Category:Space plasmas]] [94] => [[Category:Concepts in astronomy]] [95] => [[Category:Articles containing video clips]] [] => )
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Magnetosphere

The magnetosphere is the region surrounding a planet or celestial body that is influenced by its magnetic field. This protective shield, formed by the interaction between the planet's magnetic field and the solar wind, deflects and traps charged particles from the sun.

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This protective shield, formed by the interaction between the planet's magnetic field and the solar wind, deflects and traps charged particles from the sun. Earth's magnetosphere plays a crucial role in protecting the planet from harmful solar radiation and preventing the solar wind from stripping away its atmosphere. It also interacts with other phenomena such as solar storms, auroras, and magnetic reconnection. The magnetosphere's structure and dynamics are studied through various satellite missions, ground-based observations, and computer simulations to improve our understanding of this vital component of our planet's space environment.

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