Editing Ganymede (moon) (section)

==Origin and evolution==
[[Image:Ganymede terrain.jpg|thumb|upright=1.15|A sharp boundary divides the ancient dark terrain of Nicholson Regio from the younger, finely striated bright terrain of Harpagia Sulcus.]]
Ganymede probably formed by an [[accretion (astrophysics)|accretion]] in Jupiter's [[solar nebula|subnebula]], a disk of gas and dust surrounding Jupiter after its formation.<ref name="Canup2002">{{cite journal |last1=Canup |first1=Robin M. |author1-link=Robin Canup |last2=Ward |first2=William R. |title=Formation of the Galilean Satellites: Conditions of Accretion |date=2002 |volume=124 |issue=6 |pages=3404–3423 |doi=10.1086/344684 |url=http://www.boulder.swri.edu/~robin/cw02final.pdf |journal=The Astronomical Journal |bibcode=2002AJ....124.3404C |s2cid=47631608 |access-date=January 2, 2008 |archive-date=October 9, 2022 |archive-url=https://ghostarchive.org/archive/20221009/http://www.boulder.swri.edu/~robin/cw02final.pdf |url-status=live }}</ref> The accretion of Ganymede probably took about 10,000 years,<ref name="Mosqueira2003">{{cite journal |last1=Mosqueira |first1=Ignacio |last2=Estrada |first2=Paul R |title=Formation of the regular satellites of giant planets in an extended gaseous nebula I: subnebula model and accretion of satellites |date=2003 |volume=163 |issue=1 |pages=198–231 |doi=10.1016/S0019-1035(03)00076-9 |bibcode=2003Icar..163..198M |journal=Icarus |url=https://zenodo.org/record/1259597 |access-date=August 25, 2019 |archive-date=December 1, 2020 |archive-url=https://web.archive.org/web/20201201233143/https://zenodo.org/record/1259597 |url-status=live }}</ref> much shorter than the 100,000 years estimated for Callisto. The Jovian subnebula may have been relatively "gas-starved" when the Galilean satellites formed; this would have allowed for the lengthy accretion times required for Callisto.<ref name="Canup2002" /> In contrast, Ganymede formed closer to Jupiter, where the subnebula was denser, which explains its shorter formation timescale.<ref name="Mosqueira2003" /> This relatively fast formation prevented the escape of accretional heat, which may have led to ice melt and [[Planetary differentiation|differentiation]]: the separation of the rocks and ice. The rocks settled to the center, forming the core.<ref name="Bhatia2017"/> In this respect, Ganymede is different from Callisto, which apparently failed to melt and differentiate early due to loss of the accretional heat during its slower formation.<ref name="McKinnon2006">{{cite journal |last=McKinnon |first=William B. |title=On convection in ice I shells of outer Solar System bodies, with detailed application to Callisto |date=2006 |volume=183 |issue=2 |pages=435–450 |doi=10.1016/j.icarus.2006.03.004 |bibcode=2006Icar..183..435M |journal=Icarus }}</ref> This hypothesis explains why the two Jovian moons look so dissimilar, despite their similar mass and composition.<ref name="Freeman2006" /><ref name="McKinnon2006" /> Alternative theories explain Ganymede's greater internal heating on the basis of tidal flexing<ref name="Showman2">{{cite journal |last1=Showman |first1=A. P. |last2=Malhotra |first2=R. |s2cid=55790129 |title=Tidal evolution into the Laplace resonance and the resurfacing of Ganymede |journal=[[Icarus (journal)|Icarus]] |volume=127 |issue=1 |pages=93–111 |date=March 1997 |doi=10.1006/icar.1996.5669 |bibcode=1997Icar..127...93S }}</ref> or more intense pummeling by impactors during the [[Late Heavy Bombardment]].<ref name="Baldwin">{{cite web |last=Baldwin |first=E. |title=Comet impacts explain Ganymede-Callisto dichotomy |work=[[Astronomy Now]] |date=January 25, 2010 |url=http://www.astronomynow.com/news/n1001/25galilean/ |access-date=March 1, 2010 |archive-date=January 30, 2010 |archive-url=https://web.archive.org/web/20100130231918/http://www.astronomynow.com/news/n1001/25galilean/ |url-status=dead }}</ref><ref name = "Phys.Org2010">{{cite web | url = https://phys.org/news/2010-01-explanation-differences-ganymede-callisto-moons.html | title = Researchers offer explanation for the differences between Ganymede and Callisto moons | date = January 24, 2010 | website = Phys.Org | access-date = February 3, 2017 | archive-date = February 3, 2017 | archive-url = https://web.archive.org/web/20170203163742/https://phys.org/news/2010-01-explanation-differences-ganymede-callisto-moons.html | url-status = live }}</ref><ref name="LPI1158">{{cite conference |first1=A. C. |last1=Barr |last2=Canup |first2=R. M. |title=Origin of the Ganymede/Callisto dichotomy by impacts during an outer solar system late heavy bombardment |work=41st Lunar and Planetary Science Conference (2010) |date=March 2010 |location=Houston |url=http://www.lpi.usra.edu/meetings/lpsc2010/pdf/1158.pdf |access-date=March 1, 2010 |archive-date=June 5, 2011 |archive-url=https://web.archive.org/web/20110605044843/http://www.lpi.usra.edu/meetings/lpsc2010/pdf/1158.pdf |url-status=live }}</ref><ref name="Barr3">{{cite journal |last1=Barr |first1=A. C. |last2=Canup |first2=R. M. |title=Origin of the Ganymede–Callisto dichotomy by impacts during the late heavy bombardment |journal=[[Nature Geoscience]] |volume=3 |issue=March 2010 |pages=164–167 |date=January 24, 2010 |doi=10.1038/NGEO746 |bibcode=2010NatGe...3..164B |url=http://www.planetary.brown.edu/pdfs/ab19.pdf |citeseerx=10.1.1.827.982 |access-date=April 12, 2020 |archive-date=March 1, 2021 |archive-url=https://web.archive.org/web/20210301065853/http://www.planetary.brown.edu/pdfs/ab19.pdf |url-status=dead }}</ref> In the latter case, modeling suggests that differentiation would become a [[thermal runaway|runaway process]] at Ganymede but not Callisto.<ref name="LPI1158" /><ref name="Barr3" />

After formation, Ganymede's core largely retained the heat accumulated during accretion and differentiation, only slowly releasing it to the ice mantle.<ref name="McKinnon2006" /> The mantle, in turn, transported it to the surface by convection.<ref name="Freeman2006" /> The decay of [[radioactivity|radioactive elements]] within rocks further heated the core, causing increased differentiation: an inner, iron–iron-sulfide core and a silicate mantle formed.<ref name="Hauk2006" /><ref name="McKinnon2006" /> With this, Ganymede became a fully differentiated body.<ref name="Bhatia2017" /> By comparison, the radioactive heating of undifferentiated Callisto caused convection in its icy interior, which effectively cooled it and prevented large-scale melting of ice and rapid differentiation.<ref name="Nagel2004">{{cite journal |last1=Nagel |first1=K.A |last2=Breuer |first2=D. |last3=Spohn |first3=T. |title=A model for the interior structure, evolution, and differentiation of Callisto |date=2004 |volume=169 |issue=2 |pages=402–412 |doi=10.1016/j.icarus.2003.12.019 |bibcode=2004Icar..169..402N |journal=Icarus }}</ref> The convective motions in Callisto have caused only a partial separation of rock and ice.<ref name="Nagel2004" /> Today, Ganymede continues to cool slowly.<ref name="Hauk2006" /> The heat being released from its core and silicate mantle enables the subsurface ocean to exist,<ref name="Spohn2003">{{cite journal|last1=Spohn |first1=T. |last2=Schubert |first2=G. |title=Oceans in the icy Galilean satellites of Jupiter? |journal=Icarus |date=2003 |volume=161 |issue=2 |pages=456–467 |doi=10.1016/S0019-1035(02)00048-9 |url=http://lasp.colorado.edu/icymoons/europaclass/Spohn_Schubert_oceans.pdf |bibcode=2003Icar..161..456S |url-status=dead |archive-url=https://web.archive.org/web/20080227015925/http://lasp.colorado.edu/icymoons/europaclass/Spohn_Schubert_oceans.pdf |archive-date=February 27, 2008 }}</ref>  whereas the slow cooling of the liquid Fe–FeS core causes convection and supports magnetic field generation.<ref name="Hauk2006" /> The current [[heat flux]] out of Ganymede is probably higher than that out of Callisto.<ref name="McKinnon2006" />

A study from 2020 by Hirata, Suetsugu and Ohtsuki suggests that Ganymede probably was hit by a massive asteroid 4 billion years ago; an impact so violent that may have shifted the moon's axis. The study came to this conclusion analyzing images of the furrows system in the satellite's surface.<ref>{{cite journal | url=https://www.sciencedirect.com/science/article/abs/pii/S0019103520303158 | title='Naoyuki Hirata, Ryo Suetsugu, Keiji Ohtsuki, A global system of furrows on Ganymede indicative of their creation in a single impact event, Icarus, Volume 352, 2020, 113941,ISSN 0019-1035' | journal=Icarus | date=December 2020 | volume=352 | doi=10.1016/j.icarus.2020.113941 | last1=Hirata | first1=Naoyuki | last2=Suetsugu | first2=Ryo | last3=Ohtsuki | first3=Keiji | hdl=20.500.14094/90007458 | arxiv=2205.05221 }}</ref>