Editing Callisto (moon) (section)

==Orbit and rotation==
[[File:Galilean moons around Jupiter.gif|thumb|right|Galilean moons around Jupiter {{legend2|Lime|Jupiter}}{{·}}{{legend2|OrangeRed|[[Io (moon)|Io]]}}{{·}}{{legend2|RoyalBlue|[[Europa (moon)|Europa]]}}{{·}}{{legend2|Gold|[[Ganymede (moon)|Ganymede]]}}{{·}}{{legend2|Cyan|Callisto}}]]
[[File:001221 Cassini Jupiter & Europa & Callisto.jpg|thumb|upright|Callisto (bottom left), Jupiter (top right) and Europa (below and left of Jupiter's [[Great Red Spot]]) as viewed by ''[[Cassini–Huygens]]'']]
Callisto is the outermost of the four Galilean moons of Jupiter. It orbits at a distance of approximately 1,880,000&nbsp;km (26.3 times the 71,492&nbsp;km radius of Jupiter itself).<ref name=orbit>{{cite web| title=Planetary Satellite Mean Orbital Parameters| publisher=Jet Propulsion Laboratory, California Institute of Technology| url=http://ssd.jpl.nasa.gov/?sat_elem| access-date=6 July 2007| archive-date=3 November 2013| archive-url=https://web.archive.org/web/20131103134221/http://ssd.jpl.nasa.gov/?sat_elem| url-status=live}}</ref> This is significantly larger than the orbital radius—1,070,000&nbsp;km—of the next-closest Galilean satellite, Ganymede. As a result of this relatively distant orbit, Callisto does not participate in [[orbital resonance|mean-motion resonance]]—in which the three inner Galilean satellites are locked—and probably never has.<ref name=Musotto2002>{{cite journal| last1=Musotto| first1=Susanna|last2=Varadi, Ferenc |last3=Moore, William |last4= Schubert, Gerald |title=Numerical Simulations of the Orbits of the Galilean Satellites| year=2002| volume=159| issue=2|pages=500–504|doi=10.1006/icar.2002.6939| bibcode=2002Icar..159..500M | journal = Icarus}}</ref> Callisto is expected to be captured into the resonance in about 1.5 billion years, completing the 1:2:4:8 chain.<ref>{{cite journal |last1=Lari |first1=Giacomo |last2=Saillenfest |first2=Melaine |first3=Marco |last3=Fenucci |date=2020 |title=Long-term evolution of the Galilean satellites: the capture of Callisto into resonance |url=https://www.aanda.org/articles/aa/full_html/2020/07/aa37445-20/aa37445-20.html |journal=Astronomy & Astrophysics |volume=639 |pages=A40 |doi=10.1051/0004-6361/202037445 |arxiv=2001.01106 |bibcode=2020A&A...639A..40L |s2cid=209862163 |access-date=1 August 2022 |archive-date=11 June 2022 |archive-url=https://web.archive.org/web/20220611193930/https://www.aanda.org/articles/aa/full_html/2020/07/aa37445-20/aa37445-20.html |url-status=live }}</ref>

Like most other regular planetary moons, Callisto's rotation is locked to be [[synchronous rotation|synchronous]] with its orbit.<ref name="Anderson 2001">{{cite journal|last1=Anderson|first1=J. D. |last2=Jacobson, R. A. |last3=McElrath, T. P. |title=Shape, mean radius, gravity field and interior structure of Callisto |journal=Icarus| year=2001| volume=153|issue=1|pages=157–161|doi=10.1006/icar.2001.6664| bibcode=2001Icar..153..157A| last4=Moore|first4=W. B.|last5=Schubert |first5=G. |last6=Thomas |first6=P. C.|s2cid=120591546 }}</ref> The length of Callisto's day, simultaneously its [[orbital period]], is about 16.7 Earth days. Its orbit is very slightly eccentric and inclined to the Jovian [[equator]], with the [[orbital eccentricity|eccentricity]] and [[inclination]] changing [[almost periodic function|quasi-periodic]]ally due to solar and planetary gravitational perturbations on a timescale of centuries. The ranges of change are 0.0072–0.0076 and 0.20–0.60°, respectively.<ref name=Musotto2002/> These orbital variations cause the [[axial tilt]] (the angle between the rotational and orbital axes) to vary between 0.4 and 1.6°.<ref name=Bills2005>{{cite journal|last=Bills|first=Bruce G.|title=Free and forced obliquities of the Galilean satellites of Jupiter|year=2005|volume=175|issue=1|pages=233–247|doi=10.1016/j.icarus.2004.10.028|bibcode=2005Icar..175..233B|journal=Icarus|url=https://zenodo.org/record/1259023|access-date=26 August 2018|archive-date=27 July 2020|archive-url=https://web.archive.org/web/20200727063125/https://zenodo.org/record/1259023|url-status=live}}</ref>

The dynamical isolation of Callisto means that it has never been appreciably [[Tidal heating|tidally heated]], which has important consequences for its internal structure and [[evolution]].<ref name=Freeman2006/> Its distance from Jupiter also means that the [[charged particle|charged-particle]] [[flux]] from Jupiter's [[magnetosphere]] at its surface is relatively low—about 300 times lower than, for example, that at [[Europa (moon)|Europa]]. Hence, unlike the other Galilean moons, charged-particle [[irradiation]] has had a relatively minor effect on Callisto's surface.<ref name=Cooper2001>{{cite journal|last1=Cooper|first1=John F.|last2=Johnson, Robert E.|last3=Mauk, Barry H.|title=Energetic Ion and Electron Irradiation of the Icy Galilean Satellites|year=2001|volume=139|issue=1|pages=133–159|doi=10.1006/icar.2000.6498|url=http://people.virginia.edu/~rej/Icarus_Jan2001_Cooper_et_al.pdf|journal=Icarus|bibcode=2001Icar..149..133C|last4=Garrett|first4=Garry H.|last5=Gehrels|first5=Neil|access-date=25 October 2011|archive-url=https://web.archive.org/web/20120116225011/http://people.virginia.edu/~rej/Icarus_Jan2001_Cooper_et_al.pdf|archive-date=16 January 2012|url-status=dead}}</ref> The radiation level at Callisto's surface is equivalent to a dose of about 0.01 [[Röntgen equivalent man|rem]] (0.1 [[millisievert|mSv]]) per day, which is just over ten times higher than Earth's average background radiation,<ref>{{Cite book|url=http://www.unscear.org/unscear/en/publications/2008_1.html|title=United Nations Scientific Committee on the Effects of Atomic Radiation|publisher=United Nations|year=2008|isbn=978-92-1-142274-0|location=New York|pages=4|access-date=5 January 2017|archive-date=16 July 2019|archive-url=https://web.archive.org/web/20190716210835/http://www.unscear.org/unscear/en/publications/2008_1.html|url-status=live}}</ref><ref name="ringwald">{{cite web |last=Ringwald |first=Frederick A. |date=29 February 2000 |title=SPS 1020 (Introduction to Space Sciences) |url=http://zimmer.csufresno.edu/~fringwal/w08a.jup.txt |url-status=dead |archive-url=https://web.archive.org/web/20080725050708/http://zimmer.csufresno.edu/~fringwal/w08a.jup.txt |archive-date=25 July 2008 |access-date=4 July 2009 |publisher=California State University, Fresno}}</ref> but less than in [[Low Earth Orbit]] or on [[Mars]].