Editing Moon (section)

===Formation===
{{Main|Origin of the Moon |Giant-impact hypothesis|Circumplanetary disk}}
[[File:Far side of the Moon.png|thumb|The [[far side of the Moon]] lacks the near side's characteristic large dark areas of maria. The [[near side of the Moon]] might have looked like this early in the Moon's history.<ref name="The Planetary Society 2022">{{cite web |title=The two-faced Moon |website=The Planetary Society |date=March 14, 2022 |url=https://www.planetary.org/articles/the-two-faced-moon |access-date=April 28, 2023 |archive-date=April 28, 2023 |archive-url=https://web.archive.org/web/20230428213253/https://www.planetary.org/articles/the-two-faced-moon |url-status=live}}</ref><ref name="explanet.info">{{cite web |website=explanet.info |url=https://explanet.info/Chapter04.htm |title=Exploring the Planets: Chapter 4. The Moon |access-date=April 28, 2023 |archive-date=April 28, 2023 |archive-url=https://web.archive.org/web/20230428213755/https://explanet.info/Chapter04.htm |url-status=live}}</ref>]]
[[Isotope dating]] of lunar samples suggests the Moon formed around 50&nbsp;million years after the [[origin of the Solar System]].<ref>{{cite journal |title=Early Moon formation inferred from hafnium-tungsten systematics |last1=Thiemens |first1=Maxwell M. |last2=Sprung |first2=Peter |last3=Fonseca |first3=Raúl O. C. |last4=Leitzke |first4=Felipe P. |last5=Münker |first5=Carsten |journal=Nature Geoscience |volume=12 |issue=9 |pages=696–700 |date=July 2019 |doi=10.1038/s41561-019-0398-3 |pmid=39649009 |bibcode=2019NatGe..12..696T |s2cid=198997377 |pmc=7617097}}</ref><ref name="Age">{{cite news |url=https://www.universetoday.com/143025/the-moon-is-older-than-scientists-thought/ |title=The Moon is older than scientists thought |website=Universe Today |access-date=August 3, 2019 |archive-date=August 3, 2019 |archive-url=https://web.archive.org/web/20190803125139/https://www.universetoday.com/143025/the-moon-is-older-than-scientists-thought/ |url-status=live}}</ref> Historically, several formation mechanisms have been proposed,<ref>{{cite journal |doi=10.1126/sciadv.1602365 |pmid=28097222 |pmc=5226643 |journal=Science Advances |date=2017 |volume=3 |issue=1 |title=Early formation of the Moon 4.51 billion years ago |last=Barboni |first=M. |author2=Boehnke, P. |author3=Keller, C. B. |author4=Kohl, I. E. |author5=Schoene, B. |author6=Young, E. D. |author7=McKeegan, K. D. |page=e1602365 |bibcode=2017SciA....3E2365B}}</ref> but none satisfactorily explains the features of the Earth–Moon system. A fission of the Moon from Earth's crust through [[centrifugal force]]<ref name="Binder" /> would require too great an initial rotation rate of Earth.<ref name="BotM" /> Gravitational capture of a pre-formed Moon<ref name="Mitler" /> depends on an unfeasibly extended [[atmosphere of Earth]] to [[dissipate]] the energy of the passing Moon.<ref name="BotM" /> A co-formation of Earth and the Moon together in the [[Circumplanetary disk|primordial]] [[accretion disk]] does not explain the depletion of metals in the Moon.<ref name="BotM" /> None of these hypotheses can account for the high [[angular momentum]] of the Earth–Moon system.<ref>{{cite journal |last=Stevenson |first=D. J. |title=Origin of the moon–The collision hypothesis |journal=[[Annual Review of Earth and Planetary Sciences]] |date=1987 |volume=15 |issue=1 |pages=271–315 |bibcode=1987AREPS..15..271S |doi=10.1146/annurev.ea.15.050187.001415 |s2cid=53516498}}</ref>

The prevailing theory is that the Earth–Moon system formed after a [[giant impact]] of a [[Mars]]-sized body (named ''[[Theia (planet)|Theia]]'') with the [[proto-Earth]]. The oblique impact blasted material into orbit about the Earth and the material accreted and formed the Moon<ref name="taylor1998" /><ref>{{cite web |url=http://news.nationalgeographic.com/2015/04/150416-asteroids-scars-moon-formation-space/ |title=Asteroids Bear Scars of Moon's Violent Formation |date=April 16, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20161008160812/http://news.nationalgeographic.com/2015/04/150416-asteroids-scars-moon-formation-space/ |archive-date=October 8, 2016}}</ref> just beyond the Earth's [[Roche limit]] of ~{{val|2.56|ul=Earth radius}}.<ref>{{cite journal |title=Scaling in global tidal dissipation of the Earth–Moon system |last=van Putten |first=Maurice H. P. M. |journal=New Astronomy |volume=54 |pages=115–121 |date=July 2017 |doi=10.1016/j.newast.2017.01.012 |arxiv=1609.07474 |bibcode=2017NewA...54..115V |s2cid=119285032}}</ref>

Giant impacts are thought to have been common in the early Solar System. Computer simulations of giant impacts have produced results that are consistent with the mass of the lunar core and the angular momentum of the Earth–Moon system. These simulations show that most of the Moon derived from the impactor, rather than the proto-Earth.<ref>{{cite journal |last=Canup |first=R. |author1-link=Robin Canup |author2=Asphaug, E. |title=Origin of the Moon in a giant impact near the end of Earth's formation |journal=[[Nature (journal)|Nature]] |volume=412 |pages=708–712 |date=2001 |doi=10.1038/35089010 |pmid=11507633 |issue=6848 |bibcode=2001Natur.412..708C |s2cid=4413525}}</ref> However, models from 2007 and later suggest a larger fraction of the Moon derived from the proto-Earth.<ref>{{cite magazine |url=http://news.nationalgeographic.com/news/2007/12/071219-moon-collision.html |title=Earth–Asteroid Collision Formed Moon Later Than Thought |magazine=[[National Geographic]] |date=October 28, 2010 |access-date=May 7, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20090418171528/http://news.nationalgeographic.com/news/2007/12/071219-moon-collision.html |archive-date=April 18, 2009}}</ref><ref>{{cite journal |title=2008 Pellas-Ryder Award for Mathieu Touboul |journal=Meteoritics and Planetary Science |volume=43 |issue=S7 |pages=A11–A12 |date=2008 |url=http://digitalcommons.arizona.edu/objectviewer?o=uadc://azu_maps/Volume43/NumberSupplement/Touboul.pdf |bibcode=2008M&PS...43...11K |last1=Kleine |first1=Thorsten |doi=10.1111/j.1945-5100.2008.tb00709.x |s2cid=128609987 |access-date=April 8, 2020 |archive-url=https://web.archive.org/web/20180727164701/http://digitalcommons.arizona.edu/objectviewer?o=uadc%3A%2F%2Fazu_maps%2FVolume43%2FNumberSupplement%2FTouboul.pdf |archive-date=July 27, 2018 |url-status=dead}}</ref><ref>{{cite journal |doi=10.1038/nature06428 |title=Late formation and prolonged differentiation of the Moon inferred from W isotopes in lunar metals |date=2007 |last1=Touboul |first1=M. |last2=Kleine |first2=T. |last3=Bourdon |first3=B. |last4=Palme |first4=H. |last5=Wieler |first5=R. |journal=[[Nature (journal)|Nature]] |volume=450 |issue=7173 |pages=1206–1209 |pmid=18097403 |bibcode=2007Natur.450.1206T |s2cid=4416259}}</ref><ref>{{cite magazine |url=http://news.nationalgeographic.com/2015/04/150408-moon-form-giant-impact-earth |title=Flying Oceans of Magma Help Demystify the Moon's Creation |magazine=[[National Geographic]] |date=April 8, 2015 |url-status=dead |archive-url=https://web.archive.org/web/20150409220422/http://news.nationalgeographic.com/2015/04/150408-moon-form-giant-impact-earth/ |archive-date=April 9, 2015}}</ref> Other bodies of the inner Solar System such as Mars and [[4 Vesta|Vesta]] have, according to meteorites from them, very different oxygen and tungsten [[isotope|isotopic]] compositions compared to Earth. However, Earth and the Moon have nearly identical isotopic compositions. The isotopic equalization of the Earth–Moon system might be explained by the post-impact mixing of the vaporized material that formed the two,<ref name="Pahlevan2007" /> although this is debated.<ref>{{cite magazine |last=Nield |first=Ted |title=Moonwalk (summary of meeting at Meteoritical Society's 72nd Annual Meeting, Nancy, France) |magazine=[[Geoscientist (magazine)|Geoscientist]] |volume=19 |page=8 |date=2009 |url=http://www.geolsoc.org.uk/gsl/geoscientist/geonews/page6072.html |url-status=dead |archive-url=https://web.archive.org/web/20120927034348/http://www.geolsoc.org.uk/gsl/geoscientist/geonews/page6072.html |archive-date=September 27, 2012}}</ref>

The impact would have released enough energy to liquefy both the ejecta and the Earth's crust, forming a magma ocean. The liquefied ejecta could have then re-accreted into the Earth–Moon system.<ref name="Warren1985" /><ref>{{cite journal |last=Tonks |first=W. Brian |author2=Melosh, H. Jay |date=1993 |title=Magma ocean formation due to giant impacts |journal=[[Journal of Geophysical Research]] |volume=98 |issue=E3 |pages=5319–5333 |bibcode=1993JGR....98.5319T |doi=10.1029/92JE02726}}</ref> The newly formed Moon would have had [[lunar magma ocean|its own magma ocean]]; its depth is estimated from about {{Convert|500|km|4=-2|abbr=in}} to {{Convert|1737|km|4=0|abbr=in}}.<ref name="Warren1985" />

While the giant-impact theory explains many lines of evidence, some questions are still unresolved, most of which involve the Moon's composition.<ref>{{cite journal |journal=[[Science (journal)|Science]] |author=Daniel Clery |title=Impact Theory Gets Whacked |volume=342 |pages=183–185 |date=October 11, 2013 |doi=10.1126/science.342.6155.183 |bibcode=2013Sci...342..183C |issue=6155 |pmid=24115419}}</ref> Models that have the Moon acquiring a significant amount of the proto-earth are more difficult to reconcile with geochemical data for the isotopes of zirconium, oxygen, silicon, and other elements.<ref>{{cite journal |title=Zirconium isotope constraints on the composition of Theia and current Moon-forming theories |first1=W. |last1=Akram |first2=M. |last2=Schönbächler |journal=Earth and Planetary Science Letters |volume=449 |date=September 1, 2016 |pages=302–310 |doi=10.1016/j.epsl.2016.05.022 |bibcode=2016E&PSL.449..302A |doi-access=free |hdl=20.500.11850/117905 |hdl-access=free}}</ref> A study published in 2022, using high-resolution simulations (up to {{val|e=8}} particles), found that giant impacts can immediately place a satellite with similar mass and iron content to the Moon into orbit far outside Earth's [[Roche limit]]. Even satellites that initially pass within the Roche limit can reliably and predictably survive, by being partially stripped and then torqued onto wider, stable orbits.<ref>{{cite journal |last1=Kegerreis |first1=J.A. |last2=Ruiz-Bonilla |first2=S. |last3=Eke |first3=V.R. |last4=Massey |first4=R.J. |last5=Sandnes |first5=T.D. |last6=Teodoro |first6=L.F.A. |display-authors=1 |date=October 4, 2022 |title=Immediate Origin of the Moon as a Post-impact Satellite |journal=The Astrophysical Journal Letters |volume=937 |issue=L40 |pages=L40 |doi=10.3847/2041-8213/ac8d96 |arxiv=2210.01814 |bibcode=2022ApJ...937L..40K |s2cid=249267497 |doi-access=free}}</ref>

On November 1, 2023, scientists reported that, according to computer simulations, remnants of Theia could still be present inside the Earth.<ref name="NYT-20231101">{{cite news |last=Chang |first=Kenneth |title=A 'Big Whack' Formed the Moon and Left Traces Deep in Earth, a Study Suggests – Two enormous blobs deep inside Earth could be remnants of the birth of the moon. |url=https://www.nytimes.com/2023/11/01/science/moon-formation-theia.html |date=November 1, 2023 |work=[[The New York Times]] |url-status=live |archive-url=https://archive.today/20231101232849/https://www.nytimes.com/2023/11/01/science/moon-formation-theia.html |archive-date=November 1, 2023 |access-date=November 2, 2023}}</ref><ref name="NAT-20231101">{{cite journal |author=Yuan, Qian |display-authors=et al. |title=Moon-forming impactor as a source of Earth's basal mantle anomalies |url=https://www.nature.com/articles/s41586-023-06589-1 |date=November 1, 2023 |journal=[[Nature (journal)|Nature]] |volume=623 |issue=7985 |pages=95–99 |doi=10.1038/s41586-023-06589-1 |pmid=37914947 |bibcode=2023Natur.623...95Y |s2cid=264869152 |url-status=live |archive-url=https://archive.today/20231102061800/https://www.nature.com/articles/s41586-023-06589-1 |archive-date=November 2, 2023 |access-date=November 2, 2023}}</ref>