Editing Jupiter (section)

== Moons ==
{{Main|Moons of Jupiter}}
{{See also|Timeline of discovery of Solar System planets and their moons|Satellite system (astronomy)}}

Jupiter has 97 known [[natural satellite]]s,<ref name="jplsats-disc">{{cite web|title = Planetary Satellite Discovery Circumstances|url = https://ssd.jpl.nasa.gov/sats/discovery.html|work = JPL Solar System Dynamics|publisher = NASA|date = 30 April 2025|accessdate = 30 April 2025|archive-date = 27 September 2021|archive-url = https://web.archive.org/web/20210927162554/https://ssd.jpl.nasa.gov/sats/discovery.html|url-status = live}}</ref> and it is likely that this number will go up due to increasing telescopic observations.<ref>{{Cite web |last=Greenfieldboyce |first=Nell |date=February 9, 2023 |title=Here's why Jupiter's tally of moons keeps going up and up |url=https://www.npr.org/2023/02/09/1155425572/heres-why-jupiters-tally-of-moons-keeps-going-up-and-up |website=NPR |access-date=March 29, 2023 |archive-date=March 5, 2023 |archive-url=https://web.archive.org/web/20230305203115/https://www.npr.org/2023/02/09/1155425572/heres-why-jupiters-tally-of-moons-keeps-going-up-and-up |url-status=live }}</ref> Of these, only 16 are larger than 10&nbsp;km in diameter.<ref name="SheppardMoons">{{Cite web |last=Sheppard |first=Scott S. |title=Moons of Jupiter |url=https://sites.google.com/carnegiescience.edu/sheppard/moons/jupitermoons|publisher=Carnegie Institution for Science|accessdate=30 April 2025}}</ref> The four largest moons, known as the [[Galilean moons]], are Ganymede, Callisto, Io, and Europa (in order of decreasing size), and are visible from Earth with binoculars on a clear night.<ref>{{cite book|title=A Stargazing Program for Beginners|page=104|year=2015|last1=Carter|first1=Jamie|publisher=Springer International Publishing|isbn=978-3-319-22072-7}}</ref>

=== Galilean moons ===
{{Main|Galilean moons}}
The moons discovered by Galileo—Io, Europa, Ganymede, and Callisto—are among the largest in the Solar System. The orbits of Io, Europa, and Ganymede form a pattern known as a [[Laplace resonance]]; for every four orbits that Io makes around Jupiter, Europa makes exactly two orbits and Ganymede makes exactly one. This resonance causes the gravitational effects of the three large moons to distort their orbits into elliptical shapes, because each moon receives an extra tug from its neighbours at the same point in every orbit it makes. The [[tidal force]] from Jupiter, on the other hand, works to [[Tidal circularization|circularize]] their orbits.<ref>{{cite journal | last1=Musotto | first1=S. | last2=Varadi | first2=F. | last3=Moore | first3=W. B. | last4=Schubert | first4=G. |title=Numerical simulations of the orbits of the Galilean satellites |url=http://cat.inist.fr/?aModele=afficheN&cpsidt=13969974 |journal=Icarus |year=2002 |volume=159 |issue=2 |pages=500–504 |doi=10.1006/icar.2002.6939 |bibcode=2002Icar..159..500M |access-date=February 19, 2007 |archive-date=August 10, 2011 |archive-url=https://web.archive.org/web/20110810071532/http://cat.inist.fr/?aModele=afficheN&cpsidt=13969974 |url-status=dead }}</ref>

The [[Orbital eccentricity|eccentricity]] of their orbits causes regular flexing of the three moons' shapes, with Jupiter's gravity stretching them out as they approach it and allowing them to spring back to more spherical shapes as they swing away. The [[friction]] created by this tidal flexing [[Tidal acceleration#Tidal heating|generates heat]] in the interior of the moons.<ref name=Eccen304>{{cite book|page=304|title=The Cambridge Guide to the Solar System|date=March 3, 2011|last1=Lang|first1=Kenneth R.|publisher=Cambridge University Press|isbn=978-1-139-49417-5}}</ref> This is seen most dramatically in the [[Io (moon)#Volcanism|volcanic activity]] of Io (which is subject to the strongest tidal forces),<ref name="Eccen304"/> and to a lesser degree in the geological youth of [[Europa (moon)#Surface features|Europa's surface]], which indicates recent resurfacing of the moon's exterior.<ref>{{cite book|page=446|title=Encyclopedia of the Solar System|year=2006|last1=McFadden|first1=Lucy-Ann|last2=Weissmann|first2=Paul|last3=Johnson|first3=Torrence|publisher=Elsevier Science|isbn=978-0-08-047498-4}}</ref>

{| style="width:550px; margin:0 auto;" cellpadding=0 cellspacing=0
|
{| class="wikitable" style="text-align:right; margin:0 auto;"
|+ The Galilean moons compared to the Earth's [[Moon]]
|-
! rowspan=2 | Name
! rowspan=2 | [[Help:IPA/English|IPA]]
! colspan=2 | Diameter
! colspan=2 | Mass
! colspan=2 | Orbital radius
! colspan=2 | Orbital period
|-
! km
! ''D''<sub>☾</sub>
! kg
! ''M''<sub>☾</sub>
! km
! ''a''<sub>☾</sub>
! days
! ''T''<sub>☾</sub>
|-
! [[Io (moon)|Io]]
| align=left | {{small|{{IPAc-en|ˈ|aɪ|.|oʊ}}}}
| 3,643
| 1.05
| 8.9×10<sup>22</sup>
| 1.20
| 421,700
| 1.10
| 1.77
| 0.07
|-
! [[Europa (moon)|Europa]]
| align=left | {{small|{{IPAc-en|j|ʊ|ˈ|r|oʊ|p|ə}}}}
| 3,122
| 0.90
| 4.8×10<sup>22</sup>
| 0.65
| 671,034
| 1.75
| 3.55
| 0.13
|-
! [[Ganymede (moon)|Ganymede]]
| align=left | {{small|{{IPAc-en|ˈ|ɡ|æ|n|ɪ|m|iː|d}}}}
| 5,262
| 1.50
| 14.8×10<sup>22</sup>
| 2.00
| 1,070,412
| 2.80
| 7.15
| 0.26
|-
! [[Callisto (moon)|Callisto]]
| align=left | {{small|{{IPAc-en|k|ə|ˈ|l|ɪ|s|t|oʊ}}}}
| 4,821
| 1.40
| 10.8×10<sup>22</sup>
| 1.50
| 1,882,709
| 4.90
| 16.69
| 0.61
|}
|-
| [[File:The Galilean satellites (the four largest moons of Jupiter).tif|frameless|561px|center|The Galilean satellites in false colour. From left to right, in order of increasing distance from Jupiter: [[Io (moon)|Io]], [[Europa (moon)|Europa]], [[Ganymede (moon)|Ganymede]], [[Callisto (moon)|Callisto]].]]
|-
| style="font-size:0.9em; text-align:center;" | The Galilean satellites [[Io (moon)|Io]], [[Europa (moon)|Europa]], [[Ganymede (moon)|Ganymede]], and [[Callisto (moon)|Callisto]] (in order of increasing distance from Jupiter) in false colour
|}

=== Classification ===

Jupiter's moons were classified into four groups of four, based on their similar [[orbital elements]].<ref>{{cite journal|url=https://www.sciencedirect.com/science/article/abs/pii/0019103581901512|title=Derivation of the collision probability between orbiting objects: the lifetimes of jupiter's outer moons|date=October 1981|volume=48|issue=1|last1=Kessler|first1=Donald J.|journal=Icarus|pages=39–48|doi=10.1016/0019-1035(81)90151-2|bibcode=1981Icar...48...39K|s2cid=122395249 |access-date=December 30, 2020|archive-date=September 29, 2021|archive-url=https://web.archive.org/web/20210929074926/https://www.sciencedirect.com/science/article/abs/pii/0019103581901512|url-status=live}}</ref> This picture has been complicated by the discovery of numerous small outer moons since 1999. Jupiter's moons are divided into several different groups, although there are two known moons which are not part of any group ([[Themisto (moon)|Themisto]] and [[Valetudo (moon)|Valetudo]]).<ref>{{cite book|page=14|title=Moons of the Solar System|year=2013|last1=Hamilton|first1=Thomas W. M.|publisher=SPBRA|isbn=978-1-62516-175-8}}</ref>

The eight innermost [[regular moon]]s, which have nearly circular orbits near the plane of Jupiter's equator, are thought to have formed alongside Jupiter, while the remainder are [[irregular moons]] and are thought to be [[Asteroid capture|captured asteroids]] or fragments of captured asteroids. The irregular moons within each group may have a common origin, perhaps as a larger moon or captured body that broke up.<ref>{{cite book | last1=Jewitt | first1=D. C. | last2=Sheppard | first2=S. | last3=Porco | first3=C. | editor1-last=Bagenal | editor1-first=F. | editor2-last=Dowling | editor2-first=T. | editor3-last=McKinnon | editor3-first=W. | date=2004 | title=Jupiter: The Planet, Satellites and Magnetosphere | publisher=Cambridge University Press | isbn=978-0-521-81808-7 | url=http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf | archive-url=https://web.archive.org/web/20090326065151/http://www.ifa.hawaii.edu/~jewitt/papers/JUPITER/JSP.2003.pdf | archive-date=March 26, 2009 }}</ref><ref name="Nesvorný">{{cite journal | last1=Nesvorný | first1=D. | last2=Alvarellos | first2=J. L. A. | last3=Dones | first3=L. | last4=Levison | first4=H. F. | title=Orbital and Collisional Evolution of the Irregular Satellites | journal=The Astronomical Journal | year=2003 | volume=126 | issue=1 | pages=398–429 | bibcode=2003AJ....126..398N | doi=10.1086/375461 | s2cid=8502734 | url=http://www.boulder.swri.edu/%7Edavidn/papers/irrbig.pdf | access-date=August 25, 2019 | archive-date=August 1, 2020 | archive-url=https://web.archive.org/web/20200801203200/https://www.boulder.swri.edu/~davidn/papers/irrbig.pdf | url-status=live }}</ref>

{| class="wikitable"
! colspan="2" | Regular moons
|-
| [[Inner satellites of Jupiter|Inner group]]
| The inner group of four small moons all have diameters of less than 200&nbsp;km, orbit at radii less than 200,000&nbsp;km, and have orbital inclinations of less than half a degree.<ref name="nasa_orbit_parameters">{{Cite web |date=August 23, 2013 |title=Planetary Satellite Mean Orbital Parameters |url=http://ssd.jpl.nasa.gov/?sat_elem |access-date=February 1, 2016 |publisher=[[JPL]], [[NASA]] |archive-date=November 3, 2013 |archive-url=https://web.archive.org/web/20131103134221/http://ssd.jpl.nasa.gov/?sat_elem |url-status=live }}, and references therein.</ref> 
|-
| [[Galilean moons|Galilean&nbsp;moons]]<ref>{{cite journal | title=The Galilean Satellites | last1=Showman | first1=A. P. | last2=Malhotra | first2=R. | journal=Science | year=1999 | volume=286 | issue=5437 | pages=77–84 | doi=10.1126/science.286.5437.77 | pmid=10506564 | s2cid=9492520 | bibcode=1999Sci...296...77S }}</ref>
| These four moons, discovered by [[Galileo Galilei]] and by [[Simon Marius]] in parallel, orbit between 400,000 and 2 million&nbsp;km, and are some of the largest moons in the Solar System.
|-
! colspan="2" | Irregular moons
|-
| [[Himalia group]]
| A tightly clustered group of [[Retrograde motion|prograde-orbiting]] moons with orbits around 11–12 million&nbsp;km from Jupiter<ref>{{cite journal|first1=Scott S.|last1=Sheppard|first2=David C.|last2=Jewitt|author-link1=Scott S. Sheppard|author-link2=David C. Jewitt|title=An abundant population of small irregular satellites around Jupiter|journal=Nature|volume=423|date=May 2003|issue=6937|pages=261–263|url=http://www.ifa.hawaii.edu/~jewitt/papers/JSATS/SJ2003.pdf|archive-url=https://web.archive.org/web/20060813235622/http://www.ifa.hawaii.edu/~jewitt/papers/JSATS/SJ2003.pdf|doi=10.1038/nature01584|pmid=12748634|bibcode=2003Natur.423..261S|s2cid=4424447|archive-date=August 13, 2006}}</ref>
|-
| [[Carpo (moon)|Carpo group]]
|  A sparsely populated group of small moons with highly inclined prograde orbits around 16–17 million&nbsp;km from Jupiter<ref name="SheppardMoons"/>
|-
| [[Ananke group|Ananke&nbsp;group]]
| This group of [[Retrograde motion|retrograde-orbiting]] moons has rather indistinct borders, averaging 21.3 million&nbsp;km from Jupiter with an average inclination of 149 degrees.<ref name="Nesvorný"/>
|-
| [[Carme group]]
| A tightly clustered group of retrograde-orbiting moons that averages 23.4 million&nbsp;km from Jupiter with an average inclination of 165 degrees<ref name="Nesvorný"/>
|-
| [[Pasiphae group]]
| A dispersed and vaguely distinct retrograde group that covers all the outermost moons<ref>{{cite journal|first1=David|last1=Nesvorný|first2=Cristian|last2=Beaugé|first3=Luke|last3=Dones|last4=Levison|first4=Harold F.|title=Collisional Origin of Families of Irregular Satellites|journal=The Astronomical Journal|volume=127|date=July 2003|issue=3|pages=1768–1783|doi=10.1086/382099 | bibcode=2004AJ....127.1768N |s2cid=27293848 | url=http://www.boulder.swri.edu/~davidn/papers/irrbig.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.boulder.swri.edu/~davidn/papers/irrbig.pdf |archive-date=October 9, 2022 |url-status=live}}</ref>
|}