Editing Galilean moons (section)

=== Callisto ===
{{main|Callisto (moon)}}
[[File:Valhalla crater on Callisto.jpg|thumb|Callisto's [[Valhalla (crater)|Valhalla impact crater]] in enhanced color as seen by Voyager]]
Callisto (Jupiter IV) is the fourth and last Galilean moon, and is the second-largest of the four, and at 4820.6 kilometers in diameter, it is [[List of moons by diameter|the third largest moon]] in the Solar System, and barely smaller than Mercury, though only a third of the latter's mass. It is named after the Greek mythological nymph [[Callisto (mythology)|Callisto]], a lover of Zeus who was a daughter of the Arkadian King Lykaon and a hunting companion of the goddess Artemis. The moon does not form part of the [[orbital resonance]] that affects three inner Galilean satellites and thus does not experience appreciable [[tidal heating]].<ref>{{cite journal |doi=10.1006/icar.2002.6939 |title=Numerical Simulations of the Orbits of the Galilean Satellites |journal=Icarus |volume=159 |issue=2 |pages=500–4 |year=2002 |last1=Musotto |first1=S |last2=Varadi |first2=Ferenc |last3=Moore |first3=William |last4=Schubert |first4=Gerald |bibcode=2002Icar..159..500M }}</ref> Callisto is composed of approximately equal amounts of [[rock (geology)|rock]] and [[Volatile (astrogeology)|ices]], which makes it the least dense of the Galilean moons. It is one of the most heavily cratered satellites in the Solar System, and one major feature is a basin around 3000&nbsp;km wide called [[Valhalla (crater)|Valhalla]].<ref>{{Cite web|url=https://abyss.uoregon.edu/~js/ast121/lectures/lec13.html|title=Galilean Satellites|access-date=2022-02-20|archive-date=2021-12-20|archive-url=https://web.archive.org/web/20211220235547/http://abyss.uoregon.edu/~js/ast121/lectures/lec13.html|url-status=live}}</ref>

Callisto is surrounded by an extremely thin atmosphere composed of [[carbon dioxide]]<ref>{{cite journal |doi=10.1126/science.283.5403.820 |pmid=9933159 |title=A Tenuous Carbon Dioxide Atmosphere on Jupiter's Moon Callisto |journal=Science |volume=283 |issue=5403 |pages=820–1 |year=1999 |last1=Carlson |first1=R. W. |bibcode=1999Sci...283..820C |hdl=2014/16785 |url=https://trs-new.jpl.nasa.gov/dspace/bitstream/2014/16785/1/99-0186.pdf |url-status=dead |archive-url=https://web.archive.org/web/20081003231710/https://trs-new.jpl.nasa.gov/dspace/bitstream/2014/16785/1/99-0186.pdf |archive-date=2008-10-03 |citeseerx=10.1.1.620.9273 }}</ref> and probably [[molecular oxygen]].<ref>{{cite journal |doi=10.1029/2004JE002322 |title=Atmosphere of Callisto |journal=Journal of Geophysical Research |volume=110 |issue=E2 |pages=E02003 |year=2005 |last1=Liang |first1=Mao-Chang |last2=Lane |first2=Benjamin F. |last3=Pappalardo |first3=Robert T. |last4=Allen |first4=Mark |last5=Yung |first5=Yuk L. |bibcode=2005JGRE..110.2003L |s2cid=8162816 |doi-access=free |url=https://authors.library.caltech.edu/records/hknxa-mce17/files/jgre1905.pdf?download=1 }}</ref> Investigation revealed that Callisto may possibly have a subsurface ocean of liquid water at depths less than 300 kilometres.<ref>{{cite journal |doi=10.1006/icar.2000.6456 |title=Subsurface Oceans on Europa and Callisto: Constraints from Galileo Magnetometer Observations |journal=Icarus |volume=147 |issue=2 |pages=329–47 |year=2000 |last1=Zimmer |first1=C |last2=Khurana |first2=Krishan K. |last3=Kivelson |first3=Margaret G. |bibcode=2000Icar..147..329Z |url=https://www.igpp.ucla.edu/people/mkivelson/Publications/ICRUS147329.pdf |url-status=live |archive-url=https://web.archive.org/web/20090327052124/https://www.igpp.ucla.edu/people/mkivelson/Publications/ICRUS147329.pdf |archive-date=2009-03-27 |citeseerx=10.1.1.366.7700 }}</ref> The likely presence of an ocean within Callisto indicates that it can or could harbour [[extraterrestrial life|life]]. However, this is less likely than on nearby [[Europa (moon)|Europa]].<ref>{{Cite book |last1=Lipps |first1=Jere H. |last2=Delory |first2=Gregory |last3=Pitman |first3=Joseph T. |last4=Rieboldt |first4=Sarah |title=Instruments, Methods, and Missions for Astrobiology VIII |chapter=Astrobiology of Jupiter's icy moons |date=November 2004 |publisher=SPIE |isbn=978-0-8194-5493-5 |editor-last=Hoover |editor-first=Richard B. |series=SPIE proceedings series |volume=5555 |location=Bellingham, Wash |pages=78–92 |bibcode=2004SPIE.5555...78L |doi=10.1117/12.560356 |oclc=ocm57077468 |editor-last2=Levin |editor-first2=Gilbert V. |editor-last3=Rozanov |editor-first3=A. Y. |s2cid=140590649}}</ref> Callisto has long been considered the most suitable place for a human base for future exploration of the Jupiter system since it is furthest from the intense radiation of Jupiter's magnetic field.<ref>{{cite web|title=Revolutionary Concepts for Human Outer Planet Exploration(HOPE)|last1=Trautman|first1=Pat|author2=Bethke, Kristen|publisher=NASA|date=2003|url=https://www.nasa-academy.org/soffen/travelgrant/bethke.pdf|url-status=dead|archive-url=https://web.archive.org/web/20120119170143/https://www.nasa-academy.org/soffen/travelgrant/bethke.pdf|archive-date=2012-01-19}}</ref>