Editing Uranus (section)

== Magnetosphere ==
[[File:PIA23683-Uranus-MagneticField-20200325.gif|thumb|upright=1.4|The magnetic field of Uranus<br />(animated; 25 March 2020)]]
Before the arrival of ''Voyager&nbsp;2'', no measurements of the Uranian [[magnetosphere]] had been taken, so its nature remained a mystery. Before 1986, scientists had expected the [[magnetic field]] of Uranus to be in line with the [[solar wind]], because it would then align with Uranus's poles that lie in the [[ecliptic]].<ref name="Ness Acuña et al. 1986" />

''Voyager''{{'}}s observations revealed that Uranus's magnetic field is peculiar, both because it does not originate from its geometric centre, and because it is tilted at 59° from the axis of rotation.<ref name="Ness Acuña et al. 1986" /><ref name="Russell993" /> In fact, the magnetic dipole is shifted from Uranus's centre towards the south rotational pole by as much as one-third of the planetary radius.<ref name="Ness Acuña et al. 1986" /> This unusual geometry results in a highly asymmetric magnetosphere, where the magnetic field strength on the surface in the southern hemisphere can be as low as 0.1&nbsp;[[Gauss (unit)|gauss]] (10&nbsp;[[microtesla|μT]]), whereas in the northern hemisphere it can be as high as 1.1&nbsp;gauss (110&nbsp;μT).<ref name="Ness Acuña et al. 1986" /> The average field at the surface is 0.23&nbsp;gauss (23&nbsp;μT).<ref name="Ness Acuña et al. 1986" />
[[File:Uranian Magnetic field.gif|left|thumb|A diagram showing Uranus's asymmetric magnetosphere]]
Studies of ''Voyager&nbsp;2'' data in 2017 suggest that this asymmetry causes Uranus's magnetosphere to connect with the solar wind once a Uranian day, opening the planet to the Sun's particles.<ref>{{cite web |last=Maderer |first=Jason |date=26 June 2017 |title=Topsy-Turvy Motion Creates Light Switch Effect at Uranus |url=http://www.news.gatech.edu/2017/06/26/topsy-turvy-motion-creates-light-switch-effect-uranus |url-status=live |archive-url=https://web.archive.org/web/20170707101644/http://www.news.gatech.edu/2017/06/26/topsy-turvy-motion-creates-light-switch-effect-uranus |archive-date=7 July 2017 |access-date=8 July 2017 |publisher=Georgia Tech}}</ref> In comparison, the magnetic field of Earth is roughly as strong at either pole, and its "magnetic equator" is roughly parallel with its geographical equator.<ref name="Russell993" /> The dipole moment of Uranus is 50&nbsp;times that of Earth.<ref name="Ness Acuña et al. 1986" /><ref name="Russell993" /> Neptune has a similarly displaced and tilted magnetic field, suggesting that this may be a common feature of ice giants.<ref name="Russell993" /> One hypothesis is that, unlike the magnetic fields of the terrestrial and gas giants, which are generated within their cores, the ice giants' magnetic fields are generated by motion at relatively shallow depths, for instance, in the water–ammonia ocean.<ref name="Atreya2006" /><ref>{{Cite journal |last1=Stanley |first1=Sabine |author-link1=Sabine Stanley |last2=Bloxham |first2=Jeremy |date=March 2004 |title=Convective-region geometry as the cause of Uranus' and Neptune's unusual magnetic fields |url=http://mahi.ucsd.edu/johnson/ES130/stanley2004-nature.pdf |url-status=dead |journal=[[Nature (journal)|Nature]] |volume=428 |issue=6979 |pages=151–153 |bibcode=2004Natur.428..151S |doi=10.1038/nature02376 |issn=0028-0836 |pmid=15014493 |s2cid=33352017 |archive-url=https://web.archive.org/web/20070807213745/http://mahi.ucsd.edu/johnson/ES130/stanley2004-nature.pdf |archive-date=7 August 2007 |access-date=5 August 2007}}</ref> Another possible explanation for the magnetosphere's alignment is that there are oceans of liquid diamond in Uranus's interior that would deter the magnetic field.<ref name="Bland, Eric" />

It is, however, unclear whether the observed asymmetry of Uranus's magnetic field represents the typical state of the magnetosphere, or a coincidence of observing it during unusual [[space weather]] conditions. A post-analysis of Voyager data from 2024 suggests that the strongly asymmetric shape of the magnetosphere observed during the fly-by represents an anomalous state, as the measured values of solar wind density at the time were unusually high, which could have compressed Uranus's magnetosphere. The interaction with the solar wind event could also explain the apparent paradox of presence of strong electron [[Van Allen radiation belt|radiation belts]] despite the otherwise low magnetospheric [[Plasma (physics)|plasma]] density measured. Such conditions are estimated to occur less than 5% of the time.<ref>{{cite web |url=https://www.nasa.gov/missions/voyager-program/voyager-2/mining-old-data-from-nasas-voyager-2-solves-several-uranus-mysteries/ |title=Mining Old Data From NASA's Voyager 2 Solves Several Uranus Mysteries |date=11 November 2024 |publisher=[[NASA]] |access-date=26 December 2024}}</ref><ref>{{cite journal |last1=Jasinski |first1=Jamie M. |last2=Cochrane |first2=Corey J. |last3=Jia |first3=Xianzhe |last4=Dunn |first4=William R. |last5=Roussos |first5=Elias |last6=Nordheim |first6=Tom A. |last7=Regoli |first7=Leonardo H. |last8=Achilleos |first8=Nick |last9=Krupp |first9=Norbert |last10=Murphy |first10=Neil |year=2024 |title=The anomalous state of Uranus's magnetosphere during the Voyager 2 flyby |journal=[[Nature Astronomy]] |volume=9 |issue=1 |pages=66–74 |doi=10.1038/s41550-024-02389-3 |bibcode=2025NatAs...9...66J |s2cid=273973089 |doi-access=free|pmid=39866552 |pmc=11757144 }}</ref>

Despite its curious alignment, in other respects the Uranian magnetosphere is like those of other planets: it has a [[bow shock]] at about 23 Uranian radii ahead of it, a [[magnetopause]] at 18 Uranian radii, a fully developed [[magnetotail]], and [[radiation belt]]s.<ref name="Ness Acuña et al. 1986" /><ref name="Russell993" /><ref name="Krimigis Armstrong et al. 1986" /> Overall, the structure of Uranus's magnetosphere is different from Jupiter's and more similar to Saturn's.<ref name="Ness Acuña et al. 1986" /><ref name="Russell993" /> Uranus's [[magnetotail]] trails behind it into space for millions of kilometres and is twisted by its sideways rotation into a long corkscrew.<ref name="Ness Acuña et al. 1986" /><ref>{{cite web |date=2003 |title=Voyager: Uranus: Magnetosphere |url=http://voyager.jpl.nasa.gov/science/uranus_magnetosphere.html |url-status=dead |archive-url=https://web.archive.org/web/20110827125820/http://voyager.jpl.nasa.gov/science/uranus_magnetosphere.html |archive-date=27 August 2011 |access-date=13 June 2007 |publisher=NASA}}</ref>[[File:Alien aurorae on Uranus (remastered).jpg|thumb|Aurorae on Uranus taken by the [[Space Telescope Imaging Spectrograph]] (STIS) installed on [[Hubble Space Telescope|Hubble]].<ref>{{cite web |title=Alien aurorae on Uranus |url=https://www.spacetelescope.org/images/potw1714a/ |url-status=live |archive-url=https://web.archive.org/web/20170403160412/http://spacetelescope.org/images/potw1714a/ |archive-date=3 April 2017 |access-date=3 April 2017 |website=www.spacetelescope.org}}</ref>]]Uranus's magnetosphere contains [[charged particle]]s: mainly [[proton]]s and [[electron]]s, with a small amount of [[Dihydrogen cation|H<sub>2</sub><sup>+</sup>]] ions.<ref name="Russell993" /><ref name="Krimigis Armstrong et al. 1986" /> Many of these particles probably derive from the thermosphere.<ref name="Krimigis Armstrong et al. 1986" /> The ion and electron energies can be as high as 4 and 1.2&nbsp;[[megaelectronvolt]]s, respectively.<ref name="Krimigis Armstrong et al. 1986" /> The density of low-energy (below 1&nbsp;[[kiloelectronvolt]]) ions in the inner magnetosphere is about 2&nbsp;cm<sup>−3</sup>.<ref name="Bridge1986" /> The particle population is strongly affected by the Uranian moons, which sweep through the magnetosphere, leaving noticeable gaps.<ref name="Krimigis Armstrong et al. 1986" /> The particle [[flux]] is high enough to cause darkening or [[space weathering]] of their surfaces on an astronomically rapid timescale of 100,000&nbsp;years.<ref name="Krimigis Armstrong et al. 1986" /> This may be the cause of the uniformly dark colouration of the Uranian satellites and rings.<ref name="summary" />

Uranus has relatively well developed aurorae, which are seen as bright arcs around both magnetic poles.<ref name="Herbert & Sandel 1999" /> Unlike Jupiter's, Uranus's aurorae seem to be insignificant for the energy balance of the planetary thermosphere.<ref name="Lam Miller et al. 1997" /> They, or rather their [[trihydrogen cation]]s' infrared spectral emissions, have been studied in-depth as of late 2023.<ref name="Thomas Melin Stallard Chowdhury 2023 pp. 1473–1480">{{cite journal | last1=Thomas | first1=Emma M. | last2=Melin | first2=Henrik | last3=Stallard | first3=Tom S. | last4=Chowdhury | first4=Mohammad N. | last5=Wang | first5=Ruoyan | last6=Knowles | first6=Katie | last7=Miller | first7=Steve | title=Detection of the infrared aurora at Uranus with Keck-NIRSPEC | journal=Nature Astronomy | volume=7 | issue=12 | date=23 October 2023 | issn=2397-3366 | doi=10.1038/s41550-023-02096-5 | pages=1473–1480| arxiv=2311.06172 | bibcode=2023NatAs...7.1473T }}</ref>

In March 2020, NASA astronomers reported the detection of a large atmospheric magnetic bubble, also known as a [[plasmoid]], released into [[outer space]] from the planet Uranus, after reevaluating old data recorded by the ''[[Voyager&nbsp;2]]'' [[space probe]] during a flyby of the planet in 1986.<ref name="NASA-20200325">{{cite news |last=Hatfield |first=Mike |date=25 March 2020 |title=Revisiting Decades-Old Voyager&nbsp;2 Data, Scientists Find One More Secret - Eight and a half years into its grand tour of the solar system, NASA's Voyager&nbsp;2 spacecraft was ready for another encounter. It was Jan. 24, 1986, and soon it would meet the mysterious seventh planet, icy-cold Uranus. |work=[[NASA]] |url=https://www.nasa.gov/feature/goddard/2020/revisiting-decades-old-voyager-2-data-scientists-find-one-more-secret |url-status=live |access-date=27 March 2020 |archive-url=https://web.archive.org/web/20200327030510/https://www.nasa.gov/feature/goddard/2020/revisiting-decades-old-voyager-2-data-scientists-find-one-more-secret |archive-date=27 March 2020}}</ref><ref name="NYT-20200327">{{cite news |last=Andrews |first=Robin George |date=27 March 2020 |title=Uranus Ejected a Giant Plasma Bubble During Voyager&nbsp;2's Visit - The planet is shedding its atmosphere into the void, a signal that was recorded but overlooked in 1986 when the robotic spacecraft flew past. |work=[[The New York Times]] |url=https://www.nytimes.com/2020/03/27/science/uranus-bubble-voyager.html |url-status=live |access-date=27 March 2020 |archive-url=https://web.archive.org/web/20200327215013/https://www.nytimes.com/2020/03/27/science/uranus-bubble-voyager.html |archive-date=27 March 2020}}</ref>