Editing Callisto (moon) (section)

===Internal structure===
[[File:Callisto diagram.svg|thumb|upright=2|Model of Callisto's internal structure showing a surface ice layer, a possible liquid water layer, and an ice–rock interior]]
Callisto's battered surface lies on top of a cold, stiff and icy [[lithosphere]] that is between 80 and 150&nbsp;km thick.<ref name=Kuskov2005/><ref name="Spohn 2003"/> A salty ocean 150–200&nbsp;km deep may lie beneath the [[crust (geology)|crust]],<ref name=Kuskov2005/><ref name="Spohn 2003"/> indicated by studies of the [[magnetic field]]s around Jupiter and its moons.<ref name="Khurana 2000">{{cite journal |last1=Khurana|first1=K. K.|title=Induced magnetic fields as evidence for subsurface oceans in Europa and Callisto| journal=Nature| year=1998|volume=395|pages=777–780|doi=10.1038/27394| url=http://www.igpp.ucla.edu/people/mkivelson/Publications/N395777.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.igpp.ucla.edu/people/mkivelson/Publications/N395777.pdf |archive-date=9 October 2022 |url-status=live|pmid=9796812 | issue=6704| bibcode = 1998Natur.395..777K |last2=Kivelson|first2=M. G.| last3=Stevenson| first3=D. J.| last4=Schubert|first4=G.|last5=Russell|first5=C. T.|last6=Walker|first6=R. J.| last7=Polanskey| first7=C.|s2cid=4424606}}</ref><ref name="Zimmer 2000">{{cite journal| last1=Zimmer| first1=C.|last2=Khurana, K. K.|title=Subsurface Oceans on Europa and Callisto: Constraints from Galileo Magnetometer Observations|journal=Icarus|year=2000|volume=147|issue=2|pages=329–347|doi=10.1006/icar.2000.6456| url=http://www.igpp.ucla.edu/people/mkivelson/Publications/ICRUS147329.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.igpp.ucla.edu/people/mkivelson/Publications/ICRUS147329.pdf |archive-date=9 October 2022 |url-status=live| bibcode=2000Icar..147..329Z| last3=Kivelson| first3=Margaret G.| citeseerx=10.1.1.366.7700}}</ref> It was found that Callisto responds to Jupiter's varying background magnetic field like a perfectly [[electrical conductivity|conducting]] sphere; that is, the field cannot penetrate inside Callisto, suggesting a layer of highly conductive fluid within it with a thickness of at least 10&nbsp;km.<ref name="Zimmer 2000"/> The existence of an ocean is more likely if water contains a small amount of [[ammonia]] or other [[antifreeze]], up to 5% by weight.<ref name="Spohn 2003">{{cite journal |last1=Spohn|first1=T.|last2=Schubert, G.|title=Oceans in the icy Galilean satellites of Jupiter?|journal=Icarus|year=2003|volume=161 |issue=2|pages=456–467|doi=10.1016/S0019-1035(02)00048-9| url=http://www.igpp.ucla.edu/public/mkivelso/refs/PUBLICATIONS/SpohnSchubrt03GLLsats.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.igpp.ucla.edu/public/mkivelso/refs/PUBLICATIONS/SpohnSchubrt03GLLsats.pdf |archive-date=9 October 2022 |url-status=live|bibcode=2003Icar..161..456S}}</ref> In this case the water+ice layer can be as thick as 250–300&nbsp;km.<ref name=Kuskov2005/> Failing an ocean, the icy lithosphere may be somewhat thicker, up to about 300&nbsp;km.

Beneath the lithosphere and putative ocean, Callisto's interior appears to be neither entirely uniform nor particularly variable. ''[[Galileo (spacecraft)|Galileo]]'' orbiter data<ref name="Anderson 2001"/> (especially the dimensionless [[moment of inertia]]<ref group="lower-alpha">The dimensionless moment of inertia referred to is <math>I / (mr^2)</math>, where {{var|I}} is the moment of inertia, {{var|m}} the mass, and {{var|r}} the maximal radius. It is 0.4 for a homogenous spherical body, but less than 0.4 if density increases with depth.</ref>—0.3549&nbsp;±&nbsp;0.0042—determined during close flybys) suggest that, if Callisto is in [[hydrostatic equilibrium]], its interior is composed of compressed [[Rock (geology)|rocks]] and [[ice]]s, with the amount of rock increasing with depth due to partial settling of its constituents.<ref name=Kuskov2005/><ref name="Anderson 1998">{{cite journal|last1=Anderson|first1=J. D.|last2=Schubert, G.|last3=Jacobson, R. A.|title=Distribution of Rock, Metals and Ices in Callisto|journal=Science|year=1998|volume=280|pages=1573–1576|doi=10.1126/science.280.5369.1573|url=http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/19178/1/98-0442.pdf|pmid=9616114|issue=5369|bibcode=1998Sci...280.1573A|last4=Lau|first4=E. L.|last5=Moore|first5=W. B.|last6=Sjo Gren|first6=W. L.|url-status=dead|archive-url=https://web.archive.org/web/20070926195310/http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/19178/1/98-0442.pdf|archive-date=26 September 2007}}</ref> In other words, Callisto may be only partially [[planetary differentiation|differentiated]]. The density and moment of inertia for an equilibrium Callisto are compatible with the existence of a small [[silicate]] core in the center of Callisto. The radius of any such core cannot exceed 600&nbsp;km, and the density may lie between 3.1 and 3.6&nbsp;g/cm<sup>3</sup>.<ref name="Anderson 2001"/><ref name=Kuskov2005/> In this case, Callisto's interior would be in stark contrast to [[Ganymede (moon)#Internal structure|that of Ganymede]], which appears to be fully differentiated.<ref name=Showman1999/><ref name="Sohl2002">{{cite journal |last1=Sohl |first1=F. |last2=Spohn |first2=T. |last3=Breuer |first3=D. |last4=Nagel |first4=K. |year=2002 |title=Implications from Galileo Observations on the Interior Structure and Chemistry of the Galilean Satellites |journal=Icarus |volume=157 |issue=1 |pages=104–119 |bibcode=2002Icar..157..104S |doi=10.1006/icar.2002.6828}}</ref>

However, a 2011 reanalysis of Galileo data suggests that Callisto is not in hydrostatic equilibrium.<ref name=Monteux2014>{{cite journal |last1=Monteux |first1=J. |last2=Tobie |first2=G. |last3=Choblet |first3=G. |last4=Le Feuvre |first4=M. |title=Can large icy moons accrete undifferentiated? |journal=Icarus |year= 2014 |volume=237 |pages=377–387 |doi=10.1016/j.icarus.2014.04.041|bibcode=2014Icar..237..377M |s2cid=46172826 |url=https://hal.uca.fr/hal-01636068/file/Monteux-Icarus-V3-1-Final-2014.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://hal.uca.fr/hal-01636068/file/Monteux-Icarus-V3-1-Final-2014.pdf |archive-date=9 October 2022 |url-status=live }}</ref> In that case, the gravity data may be more consistent with a more thoroughly differentiated Callisto with a hydrated silicate core.<ref name="Castillo-Rogez2011">{{cite journal |last1=Castillo-Rogez |first1=J. C.|display-authors=etal |title=How differentiated is Callisto |journal=42nd Lunar and Planetary Science Conference |date=2011 |issue=1608 |pages=2580 |bibcode=2011LPI....42.2580C |url=https://www.lpi.usra.edu/meetings/lpsc2011/pdf/2580.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.lpi.usra.edu/meetings/lpsc2011/pdf/2580.pdf |archive-date=9 October 2022 |url-status=live |access-date=2 January 2020}}</ref>