View source for Giant-impact hypothesis

{{short description|Hypothesis of the formation of the Moon}}
{{redirect|Big splash||Big Splash (disambiguation)}}

[[File:Artist's concept of collision at HD 172555.jpg|thumb|270px|Artist's depiction of a collision between two planetary bodies. Such an impact between Earth and a [[Theia (planet)|Mars-sized object]] likely formed the Moon.]]

The '''giant-impact hypothesis''', sometimes called the '''Theia Impact''', is an [[astrogeology]] [[hypothesis]] for the [[origin of the Moon|formation]] of the [[Moon]] first proposed in 1946 by Canadian geologist [[Reginald Daly]]. The hypothesis suggests that the [[Early Earth]] collided with a [[Mars]]-sized [[protoplanet]] of the [[Earth's orbit|same orbit]] approximately 4.5&nbsp;billion years ago in the early [[Hadean eon]] (about 20 to 100&nbsp;million years after the [[Solar System]] coalesced), and the [[ejecta]] of the [[impact event]] later [[accretion (astrophysics)|accrete]]d to form the Moon.<ref name="NYT-20140907">{{cite news  |first=Natalie|last=Angier|title=Revisiting the Moon |url=https://www.nytimes.com/2014/09/09/science/revisiting-the-moon.html|newspaper=[[The New York Times]]|location=New York City|date=September 7, 2014}}</ref> The impactor planet is sometimes called [[Theia (planet)|Theia]], named after the [[Theia|mythical Greek Titan]] who was the mother of [[Selene]], the goddess of the Moon.<ref name=eapsl176/>

Analysis of [[lunar rock]]s published in a 2016 report suggests that the impact might have been a direct hit, causing a fragmentation and thorough mixing of both parent bodies.<ref name="YoungEtAl" />

The giant-impact hypothesis is currently the favored hypothesis for lunar formation among [[astronomy|astronomers]].<ref>{{Cite web |date=9 June 2022 |title=Moon - Origin and Evolution |url=https://www.britannica.com/place/Moon/Origin-and-evolution |access-date=14 May 2023 |website=Encyclopedia Britannica}}</ref> Evidence that supports this hypothesis includes:
* The [[Moon's orbit]] has a similar orientation to [[Earth's rotation]],<ref name=mackenzie03/> both of which are [[axial tilt|at a similar angle]] to the [[ecliptic plane]] of the Solar System.
* The [[stable isotope]] ratios of lunar and terrestrial rock are identical, implying a common origin.<ref name=wiechert/>
* The [[Earth–Moon system]] contains an anomalously high [[angular momentum]], meaning the momentum contained in Earth's rotation, the Moon's rotation and the Moon revolving around Earth is significantly higher than the other [[terrestrial planet]]s. A giant impact might have supplied this excess momentum.
* Moon samples indicate that [[lunar magma ocean|the Moon was once molten]] to a substantial, but unknown, depth. This might have required much more [[energy]] than predicted to be available from the accretion of a [[celestial body]] of the Moon's size and [[mass]]. An extremely energetic process, such as a giant impact, could provide this energy.
* The Moon has a relatively small [[iron]] [[planetary core|core]], which gives it a much lower [[density]] than Earth. Computer models of a giant impact of a Mars-sized body with Earth indicate the impactor's core would likely penetrate deep into Earth and fuse with its own core. This would leave the Moon, which was formed from the ejecta of lighter [[Earth's crust|crust]] and [[Earth's mantle|mantle]] fragments that went beyond the [[Roche limit]] and were not pulled back by [[gravity of Earth|gravity]] to re-fuse with Earth, with less remaining metallic iron than other planetary bodies.
* The Moon is depleted in [[volatile (astrogeology)|volatile]] elements compared to Earth. Vaporizing at comparably lower temperatures, they could be lost in a high-energy event, with the Moon's smaller [[gravity]] unable to recapture them while Earth did.
* There is evidence in other [[star system]]s of similar collisions, resulting in [[debris disc]]s.
* Giant collisions are consistent with the leading theory of the [[formation and evolution of the Solar System|formation of the Solar System]].

However, several questions remain concerning the best current models of the giant-impact hypothesis.<ref>{{cite journal | first = Daniel |last=Clery | title = Impact Theory Gets Whacked | journal = [[Science (journal)|Science]]|publisher=[[American Association for the Advancement of Science]]|location=Washington DC|volume = 342 | issue = 6155 | pages = 183–85 | date = October 11, 2013 | doi = 10.1126/science.342.6155.183|bibcode = 2013Sci...342..183C | pmid=24115419}}</ref> The energy of such a giant impact is predicted to have heated Earth to produce a global [[magma ocean]], and evidence of the resultant [[planetary differentiation]] of the heavier material sinking into Earth's mantle has been documented.<ref>{{Cite book|title=Formation of Earth's Core A2 – Schubert, Gerald|last1=Rubie|first1=D. C.|last2=Nimmo|first2=F.|last3=Melosh|first3=H. J.|year=2007|publisher=[[Elsevier]]|isbn=978-0444527486|location=Amsterdam|pages=51–90}}</ref> However, there is no self-consistent model that starts with the giant-impact event and follows the evolution of the debris into a single moon. 

== History==
In 1898, [[George Darwin]] made the suggestion that Earth and the Moon were once a single body. Darwin's hypothesis was that a molten Moon had been spun from Earth because of [[centrifugal force]]s, and this became the dominant academic explanation.<ref name="Binder 1974 53–76"/> Using [[Newtonian mechanics]], he calculated that the Moon had orbited much more closely in the past and was drifting away from Earth. This drifting was later confirmed by [[Apollo program|American]] and [[Roscosmos|Soviet]] experiments, using [[Lunar Laser Ranging experiment|laser ranging targets]] placed on the Moon.

Nonetheless, Darwin's calculations could not resolve the mechanics required to trace the Moon back to the surface of Earth. In 1946, [[Reginald Aldworth Daly]] of [[Harvard University]] challenged Darwin's explanation, adjusting it to postulate that the creation of the Moon was caused by an impact rather than centrifugal forces.<ref name=dalypaps/> Little attention was paid to Professor Daly's challenge until a conference on satellites in 1974, during which the idea was reintroduced and later published and discussed in ''[[Icarus (journal)|Icarus]]'' in 1975 by [[William Kenneth Hartmann|William K. Hartmann]] and [[Donald R. Davis (astronomer)|Donald R. Davis]]. Their models suggested that, at the end of the planet formation period, several satellite-sized bodies had formed that could collide with the planets or be captured. They proposed that one of these objects might have collided with Earth, ejecting refractory, volatile-poor dust that could coalesce to form the Moon. This collision could potentially explain the unique geological and geochemical properties of the Moon.<ref name=icarus24_504/>

A similar approach was taken by Canadian astronomer [[Alastair G. W. Cameron]] and American astronomer [[William Ward (astronomer)|William R. Ward]], who suggested that the Moon was formed by the [[tangent]]ial impact upon Earth of a body the size of Mars. It is hypothesized that most of the outer silicates of the colliding body would be vaporized, whereas a metallic core would not. Hence, most of the collisional material sent into orbit would consist of silicates, leaving the coalescing Moon deficient in iron. The more volatile materials that were emitted during the collision probably would escape the Solar System, whereas [[silicate]]s would tend to coalesce.<ref name=alpc7_120/>

Eighteen months prior to an October 1984 conference on lunar origins, Bill Hartmann, Roger Phillips, and Jeff Taylor challenged fellow lunar scientists: "You have eighteen months. Go back to your Apollo data, go back to your computer, and do whatever you have to, but make up your mind. Don't come to our conference unless you have something to say about the Moon's birth." At the 1984 conference at [[Kona, Hawaii]], the giant-impact hypothesis emerged as the most favored hypothesis. 
{{blockquote|Before the conference, there were partisans of the three "traditional" theories, plus a few people who were starting to take the giant impact seriously, and there was a huge apathetic middle who didn't think the debate would ever be resolved. Afterward, there were essentially only two groups: the giant impact camp and the agnostics.<ref name=Dana-Mackenzie>{{cite book |first=Dana | last=Mackenzie |title=The Big Splat, or How Our Moon Came to Be |url=https://archive.org/details/bigsplatorhowour00mack |url-access=registration |date=21 July 2003 |publisher=[[John Wiley & Sons]] |isbn=978-0-471-48073-0 |pages=[https://archive.org/details/bigsplatorhowour00mack/page/166 166]–168 |df=dmy-all |access-date=11 June 2019 |archive-date=17 June 2020 |archive-url=https://web.archive.org/web/20200617181357/https://archive.org/details/bigsplatorhowour00mack |url-status=live }}</ref>}}

=={{anchor|Theia}}Theia==
{{main|Theia (planet)}}
The name of the hypothesised [[protoplanet]] is derived from the mythical [[Greek mythology|Greek]] [[Titan (mythology)|titan]] [[Theia]] {{IPAc-en|ˈ|θ|iː|ə}}, who gave birth to the Moon goddess [[Selene]]. This designation was proposed initially by the English geochemist [[Alexander Halliday|Alex N. Halliday]] in 2000 and has become accepted in the scientific community.<ref name="eapsl176" /><ref name="jrasc97_6_299" /> According to modern theories of planet formation, Theia was part of a population of Mars-sized bodies that existed in the Solar System 4.5 billion years ago. One of the attractive features of the giant-impact hypothesis is that the formation of the Moon and Earth align; during the course of its formation, Earth is thought to have experienced dozens of collisions with planet-sized bodies. The Moon-forming collision would have been only one such "giant impact" but certainly the last significant impactor event. The [[Late Heavy Bombardment]] by much smaller asteroids may have occurred later{{snd}}approximately 3.9 billion years ago.

==Basic model==
[[File:Moon - Giant Impact Hypothesis - Simple model.png|alt=|thumb|449x449px|Simplistic representation of the giant-impact hypothesis]]

Astronomers think the collision between Earth and Theia happened at about 4.4 to 4.45 billion years ago ([[bya]]); about 0.1 billion years after the [[Formation and evolution of the Solar System|Solar System began to form]].<ref>{{cite web |first=David |last=Freeman|url=http://www.huffingtonpost.com/2013/09/23/how-old-is-the-moon-younger-research_n_3975109.html?ir=Science |title=How Old Is The Moon? 100 Million Years Younger Than Once Thought, New Research Suggests |website=[[The Huffington Post]] |publisher=[[Huffington Post Media Group]]|location=New York City| date=September 23, 2013 |access-date=September 25, 2013}}</ref><ref name="Soderman_2016">{{cite web|last1=Soderman|title=Evidence for Moon-Forming Impact Found Inside Meteorites|url=http://sservi.nasa.gov/articles/evidence-for-moon-forming-impact-found-inside-meteorites/|publisher=NASA-SSERVI|access-date=7 July 2016}}</ref> In astronomical terms, the impact would have been of moderate velocity. Theia is thought to have struck Earth at an [[oblique angle]] when Earth was nearly fully formed. Computer simulations of this "late-impact" scenario suggest an initial impactor velocity below {{convert|4|km/s}} at "infinity" (far enough that gravitational attraction is not a factor), increasing as it approached to over {{convert|9.3|km/s|abbr=on}} at impact, and an impact angle of about 45°.<ref name=icarus168_2_433/> However, [[oxygen]] [[isotope]] abundance in [[lunar rock]] suggests "vigorous mixing" of Theia and Earth, indicating a steep impact angle.<ref name="YoungEtAl">{{Cite journal
 |last1=Young |first1=Edward D. |last2=Kohl |first2=Issaku E. |last3=Warren |first3=Paul H. |last4=Rubie |first4=David C. |last5=Jacobson |first5=Seth A. |last6=Morbidelli |first6=Alessandro
 |date=2016-01-29 |title=Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact
 |journal=[[Science (journal)|Science]]|publisher=[[American Association for the Advancement of Science]]|location=Washington DC|language=en
 |volume=351 |issue=6272 |pages=493–496 |doi=10.1126/science.aad0525 |issn=0036-8075 |pmid=26823426
|arxiv = 1603.04536 |bibcode = 2016Sci...351..493Y |s2cid=6548599 }}</ref><ref>{{Cite magazine
 |first=John|last=Wenz|url=http://www.popularmechanics.com/space/a19143/earth-moon-theia-collision/
 |title=The Earth and Moon Both Contain Equal Parts of an Ancient Planet
 |date=January 28, 2016|magazine=[[Popular Mechanics]]|publisher=[[Hearst Corporation]]|location=New York City|access-date=April 30, 2016
}}</ref> Theia's iron [[Core (geology)|core]] would have sunk into the young Earth's core, and most of Theia's [[Mantle (geology)|mantle]] accreted onto Earth's mantle. However, a significant portion of the mantle material from both Theia and Earth would have been [[ejecta|ejected]] into orbit around Earth (if ejected with velocities between [[orbital speed|orbital velocity]] and [[escape velocity]]) or into individual orbits around the Sun (if ejected at higher velocities).

Modelling<ref name=SalmonCanup2012/> has hypothesised that material in orbit around Earth may have accreted to form the Moon in three consecutive phases, accreting first from the bodies initially present outside Earth's [[Roche limit]], which acted to confine the inner disk material within the Roche limit. The inner disk slowly and viscously spread back out to Earth's Roche limit, pushing along outer bodies via resonant interactions. After several tens of years, the disk spread beyond the Roche limit, and started producing new objects that continued the growth of the Moon, until the inner disk was depleted in mass after several hundreds of years. Material in stable [[Kepler orbit]]s was thus likely [[Late Heavy Bombardment|to hit the Earth–Moon system]] sometime later (because the Earth–Moon system's Kepler orbit around the Sun also remains stable). Estimates based on [[computer simulation]]s of such an event suggest that some twenty percent of the original mass of Theia would have ended up as an orbiting ring of debris around Earth, and about half of this matter coalesced into the Moon. Earth would have gained significant amounts of [[angular momentum]] and [[mass]] from such a collision. Regardless of the speed and tilt of Earth's rotation before the impact, it would have experienced a day some five hours long after the impact, and Earth's equator and the Moon's orbit would have become [[Coplanarity|coplanar]].<ref name=areps15/>

Not all of the ring material need have been swept up right away: the thickened crust of the Moon's far side suggests the possibility that a second moon about {{convert|1,000|km|abbr=on}} in diameter formed in a [[Lagrange point]] of the Moon. The smaller moon may have remained in orbit for tens of millions of years.  As the two moons migrated outward from Earth, solar tidal effects would have made the Lagrange orbit unstable, resulting in a slow-velocity collision that "pancaked" the smaller moon onto what is now the far side of the Moon, adding material to its crust.<ref>{{cite news |first=Richard|last=Lovett
 |url=http://www.nature.com/news/2011/110803/full/news.2011.456.html#B1
 |title=Early Earth may have had two moons
 |publisher=Nature.com |date=2011-08-03 |access-date=2013-09-25}}</ref><ref>{{cite web|url=http://theconversation.edu.au/was-our-two-faced-moon-in-a-small-collision-2659
 |title=Was our two-faced moon in a small collision?
 |date=3 August 2011
 |publisher=Theconversation.edu.au |access-date=2013-09-25}}</ref>
Lunar magma cannot pierce through the thick crust of the far side, causing fewer [[lunar maria]], while the near side has a thin crust displaying the large maria visible from Earth.<ref>[http://www.slate.com/blogs/bad_astronomy/2014/07/01/the_moon_s_two_faces_why_are_they_so_different.html Phil Plait, ''Why Do We Have a Two-Faced Moon?'', Slate: Bad Astronomy blog, July 1, 2014]</ref>

[[File:ARC-20221004-AAV3443-MoonOrigin-Social-NASAWeb-1080p medium.oggtheora.ogg|right|thumb|Simulation of the formation of the moon caused by a giant impact]]
Above a high resolution threshold for simulations, a study published in 2022 finds 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. Furthermore, the outer layers of these directly formed satellites are molten over cooler interiors and are composed of around 60% proto-Earth material. This could alleviate the tension between the Moon's Earth-like isotopic composition and the different signature expected for the impactor. Immediate formation opens up new options for the Moon's early orbit and evolution, including the possibility of a highly tilted orbit to explain the lunar inclination, and offers a simpler, single-stage scenario for the origin of the Moon.<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=4 October 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>

== Composition ==
In 2001, a team at the [[Carnegie Institution for Science|Carnegie Institution of Washington]] reported that the rocks from the [[Apollo program]] carried an [[Isotopic signature#Solar system origins|isotopic signature]] that was identical with rocks from Earth, and were different from almost all other bodies in the Solar System.<ref name=wiechert/>

In 2014, a team in Germany reported that the Apollo samples had a slightly different isotopic signature from Earth rocks.<ref name="Herwartz2014">{{Cite journal | doi = 10.1126/science.1251117| title = Identification of the giant impactor Theia in lunar rocks| journal = Science| volume = 344| issue = 6188| pages = 1146–1150| year = 2014| last1 = Herwartz | first1 = D.| last2 = Pack | first2 = A.| last3 = Friedrichs | first3 = B.| last4 = Bischoff | first4 = A.|bibcode = 2014Sci...344.1146H | pmid=24904162| s2cid = 30903580}}</ref> The difference was slight, but statistically significant. One possible explanation is that Theia formed near Earth.<ref name="Herwartz2014_BBC">{{cite news|url=https://www.bbc.com/news/science-environment-27688511|work=BBC News |date=2014-06-06|title=Traces of another world found on the Moon}}</ref>

This empirical data showing close similarity of composition can be explained only by the standard giant-impact hypothesis, as it is extremely unlikely that two bodies prior to collision had such similar composition.

=== Equilibration hypothesis ===
In 2007, researchers from the California Institute of Technology showed that the likelihood of Theia having an identical isotopic signature as Earth was very small (less than 1 percent).<ref name=ps2007/> They proposed that in the aftermath of the giant impact, while Earth and the proto-lunar disc were molten and vaporised, the two reservoirs were connected by a common silicate vapor atmosphere and that the Earth–Moon system became homogenised by convective stirring while the system existed in the form of a continuous fluid. Such an "equilibration" between the post-impact Earth and the proto-lunar disc is the only proposed scenario that explains the isotopic similarities of the Apollo rocks with rocks from Earth's interior. For this scenario to be viable, however, the proto-lunar disc would have to endure for about 100 years. Work is ongoing{{when|date=September 2020}} to determine whether or not this is possible.

===Direct collision hypothesis===
According to research (2012) to explain similar compositions of the Earth and the Moon based on simulations at the [[University of Bern]] by physicist Andreas Reufer and his colleagues, Theia collided directly with Earth instead of barely swiping it. The collision speed may have been higher than originally assumed, and this higher velocity may have totally destroyed Theia. According to this modification, the composition of Theia is not so restricted, making a composition of up to 50% water ice possible.<ref>{{cite web|url=https://www.nzz.ch/wissen/wissenschaft/retuschen-an-der-entstehungsgeschichte-des-erdtrabanten-ld.806542|title=Retuschen an der Entstehungsgeschichte des Erdtrabanten|first=Thorsten|last=Dambeck|date=11 September 2012|language=de|trans-title=Retouches on the genesis of Earth's moon|archive-url=https://web.archive.org/web/20240512001813/https://www.nzz.ch/wissen/wissenschaft/retuschen-an-der-entstehungsgeschichte-des-erdtrabanten-ld.806542|archive-date=12 May 2024|access-date=23 September 2012|url-status=live}}</ref>

=== Synestia hypothesis ===
One effort, in 2018, to homogenise the products of the collision was to energise the primary body by way of a greater pre-collision rotational speed.  This way, more material from the primary body would be spun off to form the Moon.  Further computer modelling determined that the observed result could be obtained by having the pre-Earth body spinning very rapidly, so much so that it formed a new celestial object which was given the name '[[synestia]]'.  This is an unstable state that could have been generated by yet another collision to get the rotation spinning fast enough.  Further modelling of this transient structure has shown that the primary body spinning as a doughnut-shaped object (the synestia) existed for about a century (a very short time){{Citation needed|date=July 2019}} before it cooled down and gave birth to Earth and the Moon.<ref name="Boyle_2017">{{cite web|last1=Boyle|first1=Rebecca|title=Huge impact could have smashed early Earth into a doughnut shape|url=https://www.newscientist.com/article/2132763-huge-impact-could-have-smashed-early-earth-into-a-doughnut-shape|website=New Scientist|date=25 May 2017|access-date=7 June 2017}}</ref><ref name="Lock_etal_2018">{{cite journal|last1=Lock|first1=Simon J.|last2=Stewart|first2=Sarah T.|last3=Petaev|first3=Michail I.|last4=Leinhardt|first4=Zoe M.|last5=Mace|first5=Mia T.|last6=Jacobsen|first6=Stein B.|last7=Ćuk|first7=Matija|title=The origin of the Moon within a terrestrial synestia|journal=Journal of Geophysical Research|volume=123|issue=4|pages=910|date=2018|doi=10.1002/2017JE005333|arxiv=1802.10223|bibcode=2018JGRE..123..910L|s2cid=119184520}}</ref>

=== Terrestrial magma ocean hypothesis ===

Another model, in 2019, to explain the similarity of Earth and the Moon's compositions posits that shortly after Earth formed, it was covered by a [[Magma ocean|sea of hot magma]], while the impacting object was likely made of solid material. Modelling suggests that this would lead to the impact heating the magma much more than solids from the impacting object, leading to more material being ejected from the proto-Earth, so that about 80% of the Moon-forming debris originated from the proto-Earth. Many prior models had suggested 80% of the Moon coming from the impactor.<ref>{{cite web |last1=Puiu |first1=Tibi |title=Ocean of magma blasted into space may explain how the moon formed |url=https://www.zmescience.com/space/ocean-magma-moon-formation-04232/ |website=ZME Science |access-date=12 May 2019|date=2019-04-30 }}</ref><ref>{{cite journal |last1=Hosono |first1=Natsuki |last2=Karato |first2=Shun-ichiro |last3=Makino |first3=Junichiro |last4=Saitoh |first4=Takayuki R. |title=Terrestrial magma ocean origin of the Moon |journal=Nature Geoscience |volume=12 |issue=6 |pages=418–423 |date=29 Apr 2019 |doi=10.1038/s41561-019-0354-2 |bibcode=2019NatGe..12..418H |s2cid=155215215 }}</ref>

== Evidence ==
Indirect evidence for the giant impact scenario comes from rocks collected during the [[Apollo program|Apollo Moon landings]], which show [[oxygen]] [[isotope]] ratios nearly identical to those of Earth. The highly [[anorthositic]] composition of the lunar crust, as well as the existence of [[KREEP]]-rich samples, suggest that a large portion of the Moon once was molten; and a giant impact scenario could easily have supplied the energy needed to form such a [[lunar magma ocean|magma ocean]]. Several lines of evidence show that if the Moon has an [[iron]]-rich core, it must be a small one. In particular, the mean density, moment of inertia, rotational signature, and magnetic induction response of the Moon all suggest that the radius of its core is less than about 25% the radius of the Moon, in contrast to about 50% for most of the other [[terrestrial planet|terrestrial]] bodies. Appropriate impact conditions satisfying the angular momentum constraints of the Earth–Moon system yield a Moon formed mostly from the [[mantle (geology)|mantle]]s of Earth and the impactor, while the core of the impactor accretes to Earth.<ref name=nature412/> Earth has the highest density of all the planets in the Solar System;<ref>{{cite web |last1=Williams |first1=David R. |title=Dr |url=https://nssdc.gsfc.nasa.gov/planetary/factsheet/ |website=NASA Space Science Data Coordinated Archive |publisher=NSSDCA |access-date=15 December 2020}}</ref> the absorption of the core of the impactor body explains this observation, given the proposed properties of the early Earth and Theia.

Comparison of the [[zinc]] isotopic composition of lunar samples with that of Earth and [[Mars]] rocks provides further evidence for the impact hypothesis.<ref name="Paniello2012">{{Cite journal | last1 = Paniello | first1 = R. C. | last2 = Day | first2 = J. M. D. | last3 = Moynier | first3 = F.| doi = 10.1038/nature11507 | title = Zinc isotopic evidence for the origin of the Moon | journal = Nature | volume = 490 | issue = 7420 | pages = 376–379 | year = 2012 | pmid = 23075987|bibcode = 2012Natur.490..376P | s2cid = 4422136 }}</ref> [[Zinc]] is strongly [[Isotope fractionation|fractionated]] when [[volatilization|volatilised]] in planetary rocks,<ref name="Moynier2006">{{Cite journal | last1 = Moynier | first1 = F. | last2 = Albarède | first2 = F. | last3 = Herzog | first3 = G. F. | doi = 10.1016/j.gca.2006.02.030 | title = Isotopic composition of zinc, copper, and iron in lunar samples | journal = Geochimica et Cosmochimica Acta | volume = 70 | issue = 24 | pages = 6103 | year = 2006 |bibcode = 2006GeCoA..70.6103M }}</ref><ref name="Moynier2009">{{Cite journal | last1 = Moynier | first1 = F. | last2 = Beck | first2 = P. | last3 = Jourdan | first3 = F. | last4 = Yin | first4 = Q. Z. | last5 = Reimold | first5 = U. | last6 = Koeberl | first6 = C. | doi = 10.1016/j.epsl.2008.11.020 | title = Isotopic fractionation of zinc in tektites | journal = Earth and Planetary Science Letters | volume = 277 | issue = 3–4 | pages = 482 | year = 2009 |bibcode = 2009E&PSL.277..482M | hdl = 20.500.11937/39896 | url = https://espace.curtin.edu.au/bitstream/20.500.11937/39896/2/120258_120258Moynier-EPSL2009_Zntektite%2520ORD.pdf | hdl-access = free }}</ref> but not during normal [[igneous]] processes,<ref name="Othman2006">{{Cite journal | last1 = Ben Othman | first1 = D. | last2 = Luck | first2 = J. M. | last3 = Bodinier | first3 = J. L. | last4 = Arndt | first4 = N. T. | last5 = Albarède | first5 = F. | title = Cu–Zn isotopic variations in the Earth's mantle | doi = 10.1016/j.gca.2006.06.201 | journal = Geochimica et Cosmochimica Acta | volume = 70 | issue = 18 | pages = A46 | year = 2006 |bibcode = 2006GeCAS..70...46B }}</ref> so zinc abundance and isotopic composition can distinguish the two geological processes. Moon rocks contain more heavy isotopes of zinc, and overall less zinc, than corresponding igneous Earth or Mars rocks, which is consistent with zinc being depleted from the Moon through evaporation, as expected for the giant impact origin.<ref name="Paniello2012"/>

Collisions between ejecta escaping Earth's gravity and asteroids would have left impact heating signatures in stony meteorites; analysis based on assuming the existence of this effect has been used to date the impact event to 4.47 billion years ago, in agreement with the date obtained by other means.<ref name = Bottke>{{Cite journal | doi = 10.1126/science.aaa0602| title = Dating the Moon-forming impact event with asteroidal meteorites| journal = Science| volume = 348| issue = 6232| pages = 321–323| year = 2015| last1 = Bottke | first1 = W. F.| last2 = Vokrouhlicky | first2 = D.| last3 = Marchi | first3 = S.| last4 = Swindle | first4 = T.| last5 = Scott | first5 = E. R. D.| last6 = Weirich | first6 = J. R.| last7 = Levison | first7 = H.|bibcode = 2015Sci...348..321B | pmid=25883354| doi-access = free}}</ref>

Warm silica-rich dust and abundant SiO gas, products of high velocity impacts{{snd}}over {{convert|10|km/s|abbr=on}}{{snd}}between rocky bodies, have been detected by the [[Spitzer Space Telescope]] around the nearby (29 [[parsec|pc]] distant) young (~12 My old) star [[HD 172555]] in the [[Beta Pictoris moving group]].<ref name = apj701/> A belt of warm dust in a zone between 0.25AU and 2AU from the young star [[HD 23514]] in the [[Pleiades]] cluster appears similar to the predicted results of Theia's collision with the embryonic Earth, and has been interpreted as the result of planet-sized objects colliding with each other.<ref name=apj675/> A similar belt of warm dust was detected around the star [[BD+20°307]] (HIP 8920, SAO 75016).<ref name=nature436/>

On 1 November 2023, scientists reported that, according to computer simulations, remnants of Theia could be still visible inside the Earth as [[large low-shear-velocity provinces|two giant anomalies]] of the [[Earth's mantle]].<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=1 November 2023 |work=[[The New York Times]] |url-status=live |archiveurl=https://archive.today/20231101232849/https://www.nytimes.com/2023/11/01/science/moon-formation-theia.html |archivedate=1 November 2023 |accessdate=2 November 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=1 November 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 |url-status=live |archiveurl=https://archive.today/20231102061800/https://www.nature.com/articles/s41586-023-06589-1 |archivedate=2 November 2023 |accessdate=2 November 2023 |url-access=subscription }}</ref>

== Difficulties ==
This lunar origin hypothesis has some difficulties that have yet to be resolved. For example, the giant-impact hypothesis implies that a surface magma ocean would have formed following the impact. Yet there is no evidence that Earth ever had such a magma ocean and it is likely there exists material that has never been processed in a magma ocean.<ref name="4045.pdf"/>

=== Composition ===
A number of compositional inconsistencies need to be addressed.

* The ratios of the Moon's volatile elements are not explained by the giant-impact hypothesis. If the giant-impact hypothesis is correct, these ratios must be due to some other cause.<ref name="4045.pdf"/>
* The presence of volatiles such as water trapped in lunar [[basalt]]s and carbon emissions from the lunar surface is more difficult to explain if the Moon was caused by a high-temperature impact.<ref name=nature454/><ref>{{cite journal | title = KAGUYA observation of global emissions of indigenous carbon ions from the Moon | journal = Science Advances | date =  6 May 2020 | first = Shoichiro | last = Yokota |author2=Kentaro Terada |author3=Yoshifumi Saito |author4=Daiba Kato |author5=Kazushi Asamura|author6=Masaki N. Nishino |author7=Hisayoshi Shimizu|author8=Futoshi Takahashi|author9=Hidetoshi Shibuya|author10=Masaki Matsushima|author11=Hideo Tsunakawa| volume = 6 | issue = 19 | pages = eaba1050 | doi=10.1126/sciadv.aba1050 | pmid = 32494721 | pmc = 7202878 | bibcode = 2020SciA....6.1050Y |issn = 2375-2548 |doi-access=free }}</ref>
* The iron oxide (FeO) content (13%) of the Moon, intermediate between that of Mars (18%) and the terrestrial mantle (8%), rules out most of the source of the proto-lunar material from Earth's mantle.<ref name=taylor07/>
* If the bulk of the proto-lunar material had come from an impactor, the Moon should be enriched in [[Siderophile element|siderophilic]] elements, when, in fact, it is deficient in them.<ref name=jess114/>
* The Moon's oxygen isotopic ratios are essentially identical to those of Earth.<ref name=wiechert/> Oxygen isotopic ratios, which may be measured very precisely, yield a unique and distinct signature for each Solar System body.<ref name=scott010312/> If a separate proto-planet [[Theia (planet)|Theia]] had existed, it probably would have had a different oxygen isotopic signature than Earth, as would the ejected mixed material.<ref name=moonwalk/>
* The Moon's [[titanium isotope]] ratio (<sup>50</sup>Ti/<sup>47</sup>Ti) appears so close to Earth's (within 4 ppm), that little if any of the colliding body's mass could likely have been part of the Moon.<ref>{{cite journal | title = The proto-Earth as a significant source of lunar material | journal = Nature Geoscience | date = 25 March 2012 | first = Junjun | last = Zhang |author2=Nicolas Dauphas |author3=Andrew M. Davis |author4=Ingo Leya |author5=Alexei Fedkin | volume = 5 | issue = 4 | pages = 251–255| doi= 10.1038/ngeo1429 |bibcode = 2012NatGe...5..251Z }}</ref><ref>{{cite web | url=https://news.uchicago.edu/article/2012/03/28/titanium-paternity-test-fingers-earth-moon-s-sole-parent | title=Titanium paternity test fingers Earth as moon's sole parent | work=UChicagoNews | date=March 28, 2012 | access-date=August 13, 2012 | last=Koppes |first=Steve}}</ref>

=== Lack of a Venusian moon ===
If the Moon was formed by such an impact, it is possible that other inner planets also may have been subjected to comparable impacts. A moon that formed around [[Venus]] by this process would have been unlikely to escape. If such a moon-forming event had occurred there, a possible explanation of why the planet does not have such a moon might be that a second collision occurred that countered the [[angular momentum]] from the first impact.<ref name=baas38_491/> Another possibility is that the strong tidal forces from the Sun would tend to destabilise the orbits of moons around close-in planets. For this reason, if Venus's slow rotation rate began early in its history, any satellites larger than a few kilometers in diameter would likely have spiraled inwards and collided with Venus.<ref name=icarus202_1_12/>

Simulations of the chaotic period of terrestrial planet formation suggest that impacts like those hypothesised to have formed the Moon were common. For typical terrestrial planets with a mass of 0.5 to 1 Earth masses, such an impact typically results in a single moon containing 4% of the host planet's mass. The inclination of the resulting moon's orbit is random, but this tilt affects the subsequent dynamic evolution of the system. For example, some orbits may cause the moon to spiral back into the planet. Likewise, the proximity of the planet to the star will also affect the orbital evolution. The net effect is that it is more likely for impact-generated moons to survive when they orbit more distant terrestrial planets and are aligned with the planetary orbit.<ref name=lewis2011/>

== Possible origin of Theia ==
[[Image: BigSplashEnglish.svg|thumb|One suggested pathway for the impact as viewed from the direction of Earth's south pole (not to scale)]]
In 2004, [[Princeton University]] mathematician [[Edward Belbruno]] and astrophysicist [[J. Richard Gott III]] proposed that Theia coalesced at the {{L4}} or {{L5}} [[Lagrangian point]] relative to Earth (in about the same orbit and about 60° ahead or behind),<ref name=belbruno-2005/><ref name=mps40_1115/> similar to a [[trojan asteroid]].<ref name=mackenzie03/> Two-dimensional computer models suggest that the stability of Theia's proposed [[Trojan (astronomy)|trojan orbit]] would have been affected when its growing mass exceeded a threshold of approximately 10% of Earth's mass (the mass of Mars).<ref name=belbruno-2005/> In this scenario, gravitational perturbations by [[planetesimal]]s caused Theia to depart from its stable Lagrangian location, and subsequent interactions with proto-Earth led to a collision between the two bodies.<ref name=belbruno-2005/>

In 2008, evidence was presented that suggests that the collision might have occurred later than the accepted value of 4.53&nbsp;[[Gya (unit)|Gya]], at approximately 4.48&nbsp;Gya.<ref name=halliday-2008/> A 2014 comparison of computer simulations with elemental abundance measurements in Earth's mantle indicated that the collision occurred approximately 95&nbsp;My after the formation of the Solar System.<ref name=jacobson-2014/>

It has been suggested that other significant objects might have been created by the impact, which could have remained in orbit between Earth and the Moon, stuck in Lagrangian points. Such objects might have stayed within the Earth–Moon system for as long as 100 million years, until the gravitational tugs of other planets destabilised the system enough to free the objects.<ref name=ns080506/> A study published in 2011 suggested that a subsequent collision between the Moon and one of these smaller bodies caused the notable differences in physical characteristics between the two hemispheres of the Moon.<ref name=nature476_69/> This collision, simulations have supported, would have been at a low enough velocity so as not to form a crater; instead, the material from the smaller body would have spread out across the Moon (in what would become its [[Far side of the Moon|far side]]), adding a thick layer of highlands crust.<ref name=yahoo20110803/> The resulting mass irregularities would subsequently produce a gravity gradient that resulted in [[tidal locking]] of the Moon so that today, only the near side remains visible from Earth. However, mapping by the [[Gravity Recovery and Interior Laboratory|GRAIL]] mission has ruled out this scenario.{{citation needed|date=December 2013}}

In 2019, a team at the [[University of Münster]] reported that the [[molybdenum]] isotopic composition in Earth's primitive mantle originates from the outer Solar System, hinting at the source of water on Earth. One possible explanation is that Theia originated in the outer Solar System.<ref>{{Cite journal|last1=Budde|first1=Gerrit|last2=Burkhardt|first2=Christoph|last3=Kleine|first3=Thorsten|date=2019-05-20|title=Molybdenum isotopic evidence for the late accretion of outer Solar System material to Earth|journal=Nature Astronomy|volume=3|issue=8|pages=736–741|language=en|doi=10.1038/s41550-019-0779-y|issn=2397-3366|bibcode=2019NatAs...3..736B|s2cid=181460133}}</ref>

==Alternative hypotheses==
{{main|Origin of the Moon}}

Other mechanisms that have been suggested at various times for the Moon's origin are that the Moon was spun off from Earth's molten surface by [[centrifugal force]];<ref name="Binder 1974 53–76"/> that it was formed elsewhere and was subsequently [[lunar capture|captured]] by Earth's gravitational field;<ref name=icarus24_256/> or that Earth and the Moon formed at the same time and place from the same [[accretion disk]]. None of these hypotheses can account for the high [[angular momentum]] of the Earth–Moon system.<ref name=areps15/>

Another hypothesis attributes the formation of the Moon to the impact of a large asteroid with Earth much later than previously thought, creating the satellite primarily from debris from Earth. In this hypothesis, the formation of the Moon occurs 60–140 million years after the formation of the Solar System (as compared to hypothesized Theia impact at 4.527 ± 0.010 billion years).<ref name=taylor1998/> The asteroid impact in this scenario would have created a magma ocean on Earth and the proto-Moon with both bodies sharing a common plasma metal vapor atmosphere. The shared metal vapor bridge would have allowed material from Earth and the proto-Moon to exchange and equilibrate into a more common composition.<ref name=nature450_1206/><ref name=ngn20071219/>

Yet another hypothesis proposes that the Moon and Earth formed together, not from the collision of once-distant bodies. This model, published in 2012 by [[Robin Canup|Robin M. Canup]], suggests that the Moon and Earth formed from a massive collision of two planetary bodies, each larger than Mars, which then re-collided to form what is now called Earth.<ref>{{cite journal |title=Forming a Moon with an Earth-like Composition via a Giant Impact |first=Robin M. |last=Canup |journal=[[Science (journal)|Science]] |volume=338 |issue=6110 |pages=1052–1055 |date=2012-11-23 |doi=10.1126/science.1226073 |pmid=23076098 |pmc=6476314 |bibcode=2012Sci...338.1052C }}</ref><ref name=SimultaneousFormation/> After the re-collision, Earth was surrounded by a disk of material which accreted to form the Moon.<ref name=SimultaneousFormation/>

{{multiple image
| total_width       = 800
| align             = center
| title             = Moon – [[Oceanus Procellarum]] ("Ocean of Storms")
| width1            = 614
| height1           = 228
| image1            = 14-236-LunarGrailMission-OceanusProcellarum-Rifts-Overall-20141001.jpg
| caption1          = Ancient [[rift valley]]s – rectangular structure (visible – topography – [[Gravity Recovery and Interior Laboratory|GRAIL gravity gradients]]) (October 1, 2014)
| width2            = 1500
| height2           = 1500
| image2            = PIA18822-LunarGrailMission-OceanusProcellarum-Rifts-Overall-20141001.jpg
| caption2          = Ancient [[rift valley]]s – context
| width3            = 1546
| height3           = 905
| image3            = PIA18821-LunarGrailMission-OceanusProcellarum-Rifts-Closeup-20141001.jpg
| caption3          = Ancient [[rift valley]]s – closeup (artist's concept)
}}

== See also ==
{{cmn|colwidth=30em|
* [[Circumplanetary disk]]
* [[Geologic time scale]]
* [[Geology of the Moon]]
* [[History of Earth]]
* [[Lunar geologic timescale]]
* [[Origin of the Moon]]
* [[Roche limit]]
* [[Phaeton (hypothetical planet)]]
}}

==References==

==Notes==
{{Reflist|refs=
<ref name=ps2007>{{Cite journal | last1=Pahlevan | first1=Kaveh | last2=Stevenson | first2=David | title=Equilibration in the Aftermath of the Lunar-forming Giant Impact | journal=[[Earth and Planetary Science Letters]] | volume=262 | issue=3–4 |date=October 2007 | pages=438–449 | doi=10.1016/j.epsl.2007.07.055 | bibcode=2007E&PSL.262..438P |arxiv = 1012.5323 | s2cid=53064179 }}</ref>

<ref name=eapsl176>{{cite journal | first=Alex N. | last=Halliday | title=Terrestrial accretion rates and the origin of the Moon | journal=Earth and Planetary Science Letters | volume=176 | issue=1 | date=February 28, 2000 | pages=17&ndash;30 | doi=10.1016/S0012-821X(99)00317-9 | bibcode=2000E&PSL.176...17H}}</ref>

<ref name=wiechert>{{Cite journal | title=Oxygen Isotopes and the Moon-Forming Giant Impact | display-authors=1 | last1=Wiechert | first1=U. | last2=Halliday | first2=A. N. | last3=Lee | first3=D.-C. | last4=Snyder | first4=G. A. | last5=Taylor | first5=L. A. | last6=Rumble | first6=D. | volume=294 | issue=12 | pages=345–348 |date=October 2001 | doi=10.1126/science.1063037 | pmid=11598294 | journal= [[Science (journal)|Science]] |bibcode = 2001Sci...294..345W | s2cid=29835446 }}</ref>

<ref name="Binder 1974 53–76">{{cite journal | last=Binder | first=A. B. | title=On the origin of the Moon by rotational fission | journal=The Moon | date=1974 | volume=11 | issue=2 | pages=53–76 | bibcode=1974Moon...11...53B | doi=10.1007/BF01877794 | s2cid=122622374 }}</ref>

<ref name=halliday-2008>{{cite journal | title=A young Moon-forming giant impact at 70–110 million years accompanied by late-stage mixing, core formation and degassing of the Earth | last=Halliday | first=Alex N | date=November 28, 2008 | doi=10.1098/rsta.2008.0209 | volume=366| issue=1883 | pages=4163–4181 | pmid=18826916 | journal=[[Philosophical Transactions of the Royal Society A]] | bibcode=2008RSPTA.366.4163H | s2cid=25704564 }}</ref>

<ref name=dalypaps>{{cite journal | title=Origin of the Moon and Its Topography | first=Reginald A. | last=Daly | journal=PAPS | volume=90 | issue=2 | pages=104–119 | date=1946 | jstor=3301051 }}</ref>

<ref name=mackenzie03>{{cite book | last1=Mackenzie | first1=Dana | date=2003 | title=The Big Splat, or How The Moon Came To Be | publisher=[[John Wiley & Sons]] | isbn=978-0-471-15057-2 | url-access=registration | url=https://archive.org/details/bigsplatorhowour00mack }}</ref>

<ref name=ns080506>{{cite news | url=https://www.newscientist.com/article/dn13836-did-earth-once-have-multiple-moons.html | access-date=2011-12-10 | title=Did Earth once have multiple moons? | work=New Scientist | publisher=Reed Business Information Ltd | date=May 6, 2008 | first=Ker | last=Than }}</ref>

<ref name=nature412>{{cite journal|last1=Canup |first1=R. |last2=Asphaug |first2=E. |title=Origin of the Moon in a giant impact near the end of the Earth's formation |journal=Nature |volume=412 |pages=708–712 |date=2001 |doi=10.1038/35089010 |pmid=11507633 |issue=6848 |bibcode=2001Natur.412..708C |s2cid=4413525 |url=http://www.es.ucsc.edu/~rcoe/eart206/canup_Moon_Nature_01.pdf |access-date=2011-12-10 |url-status=dead |archive-url=https://web.archive.org/web/20100730135923/http://es.ucsc.edu/~rcoe/eart206/canup_Moon_Nature_01.pdf |archive-date=2010-07-30 }}</ref>

<ref name=apj701>{{cite journal | title=Abundant Circumstellar Silica Dust and SiO Gas Created by a Giant Hypervelocity Collision in the ~12 Myr HD172555 System | display-authors=1 | first1=Carey M. | last1=Lisse | last2=Chen | first2=C. H. | last3=Wyatt | first3=M. C. | last4=Morlok | first4=A. | last5=Song | first5=I. | last6=Bryden | first6=G. | last7=Sheehan | first7=P. | date=2009 | journal=Astrophysical Journal | volume=701 | issue=2 | pages=2019–2032 | doi=10.1088/0004-637X/701/2/2019 | bibcode=2009ApJ...701.2019L |arxiv = 0906.2536 | s2cid=56108044 }}</ref>

<ref name=apj675>{{cite journal | title=Warm dust in the terrestrial planet zone of a sun-like Pleiad: collisions between planetary embryos? | first1=Joseph H. | last1= Rhee | last2=Song | first2=Inseok | last3=Zuckerman | first3=B. | date=2007 | journal=Astrophysical Journal | volume=675 | issue=1 | pages=777–783 | doi=10.1086/524935 | arxiv=0711.2111v1 | bibcode=2008ApJ...675..777R | s2cid=15836467 }}</ref>

<ref name=nature436>{{Cite journal | journal=Nature | volume=436 | pages=363–365 |date=21 July 2005| doi=10.1038/nature03853 | title=Extreme collisions between planetesimals as the origin of warm dust around a Sun-like star | display-authors=1 | first1=Inseok | last1=Song | last2=Zuckerman | first2=B. | last3=Weinberger | first3=Alycia J. | last4=Becklin | first4=E. E. | pmid=16034411 | issue=7049 | bibcode=2005Natur.436..363S | s2cid=4390247 }}</ref>

<ref name="4045.pdf">{{cite conference
| title=Tests of the Giant Impact Hypothesis | first=J. H. | last=Jones | book-title=Lunar and Planetary Science | conference=Origin of the Earth and Moon Conference | location=Monterey, California | date=1998 | url=http://www.lpi.usra.edu/meetings/origin98/pdf/4045.pdf }}</ref>

<ref name=jess114>{{Cite journal | title=Origin of the Earth-Moon System | last1=Galimov | first1=E. M. | last2=Krivtsov | first2=A. M. | journal=Journal of Earth System Science | volume=114 | pages=593–600 |date=December 2005| issue=6 |doi=10.1007/BF02715942 | bibcode=2005JESS..114..593G | url=http://www.ias.ac.in/jessci/dec2005/ilc-3.pdf | access-date=2011-12-10 | citeseerx=10.1.1.502.314 | s2cid=56094186 }}</ref>

<ref name=nature454>{{cite journal | display-authors=1 | first1=Alberto E. | last1=Saal | last2=Hauri | first2=Erik H. | last3=Cascio | first3=Mauro L. | last4=Van Orman | first4=James A. | last5=Rutherford | first5=Malcolm C. | last6=Cooper | first6=Reid F. | title=Volatile content of lunar volcanic glasses and the presence of water in the Moon's interior | journal=Nature | volume=454 | pages=192–195 | date=July 10, 2008 | doi=10.1038/nature07047 | pmid=18615079 | issue=7201 | bibcode=2008Natur.454..192S | s2cid=4394004 }}</ref>

<ref name=scott010312>{{cite journal | url=http://www.psrd.hawaii.edu/Dec01/Oisotopes.html | title=Oxygen Isotopes Give Clues to the Formation of Planets, Moons, and Asteroids | journal=Planetary Science Research Discoveries Report | pages=55 | last=Scott | first=Edward R. D. | bibcode=2001psrd.reptE..55S | date=December 3, 2001 | access-date=2010-03-19 }}</ref>

<ref name=moonwalk>{{cite web | url=http://www.geolsoc.org.uk/webdav/site/GSL/shared/pdfs/Geoscientist/Download%20PDF%20copy%20of%20Geoscientist%2019.9%20September%202009.pdf | first=Ted | last=Nield | title=Moonwalk | publisher=Geological Society of London | page=8 |date=September 2009 | access-date=2010-03-01 }}</ref>

<ref name=icarus24_256>{{cite journal | last=Mitler | first=H. E. | title=Formation of an iron-poor moon by partial capture, or: Yet another exotic theory of lunar origin | journal=[[Icarus (journal)|Icarus]] | date=1975 | volume=24 | issue=2 | pages=256–268 | bibcode=1975Icar...24..256M | doi=10.1016/0019-1035(75)90102-5 }}</ref>

<ref name=taylor07>{{cite journal | last1=Taylor | first1=Stuart R. | title=The Bulk Composition of the Moon | journal=Meteoritics and Planetary Science Supplement | volume=37 | pages=A139 | date=1997 | bibcode=2002M&PSA..37Q.139T | url=http://www.lpi.usra.edu/meetings/lpsc97/pdf/1070.PDF | access-date=2010-03-21 }}</ref>

<ref name=areps15>{{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 }}</ref>

<ref name=icarus24_504>{{Cite journal | last1=Hartmann | first1=W. K. | last2=Davis | first2=D. R. | title=Satellite-sized planetesimals and lunar origin | journal=Icarus | volume=24 | issue=4 |date=April 1975 | pages=504–514 | doi=10.1016/0019-1035(75)90070-6 | bibcode=1975Icar...24..504H }}</ref>

<ref name=alpc7_120>{{Cite journal | last1=Cameron | first1=A. G. W. | last2=Ward | first2=W. R. | title=The Origin of the Moon | journal=Abstracts of the Lunar and Planetary Science Conference | volume=7 | pages=120–122 |date=March 1976 | bibcode=1976LPI.....7..120C }}</ref>

<ref name=belbruno-2005>{{cite journal | first1=E. | last1=Belbruno | first2=J. Richard | last2=Gott III | title=Where Did The Moon Come From? | journal=The Astronomical Journal | volume=129 | issue=3 | pages=1724–1745 | date=2005 | doi=10.1086/427539 | arxiv=astro-ph/0405372 | bibcode=2005AJ....129.1724B| s2cid=12983980 }}</ref>

<ref name=mps40_1115>{{citation | last1=Howard | first1=E. | title=The effect of Lagrangian L4/L5 on satellite formation | journal=Meteoritics & Planetary Science | volume=40 | issue=7 | page=1115 |date=July 2005 | doi=10.1111/j.1945-5100.2005.tb00176.x | bibcode=2005M&PS...40.1115H | doi-access=free }}</ref>

<ref name=jrasc97_6_299>{{citation | last1=Gray | first1=Denis | title=Book Review: The big splat or how our moon came to be / John Wiley & Sons, 2003 | journal=Journal of the Royal Astronomical Society of Canada | volume=97 | issue=6 | page=299 |date=December 2003 | bibcode=2003JRASC..97..299G }}</ref>

<ref name=baas38_491>{{citation | title=Why Venus has No Moon | last1=Alemi | first1=Alex | last2=Stevenson | first2=D. | journal=Bulletin of the American Astronomical Society | volume=38 | page=491 |date=September 2006 | bibcode=2006DPS....38.0703A }}</ref>

<ref name=icarus202_1_12>{{citation | last1=Sheppard | first1=Scott S. | last2=Trujillo | first2=Chadwick A. | title=A survey for satellites of Venus | journal=Icarus | volume=202 | issue=1 | pages=12–16 |date=July 2009 | doi=10.1016/j.icarus.2009.02.008 | bibcode=2009Icar..202...12S |arxiv = 0906.2781 | s2cid=15252548 }}</ref>

<ref name=lewis2011>{{cite journal |mode=cs2 | title=Moon formation and orbital evolution in extrasolar planetary systems - A literature review | last1=Lewis | first1=K. |others=From the book "Detection and Dynamics of Transiting Exoplanets" |editor1-first=F. |editor1-last=Bouchy |editor2-first=R. |editor2-last=Díaz |editor3-first=C. |editor3-last=Moutou |volume=11 |date=February 2011 |doi=10.1051/epjconf/20101104003 |doi-access=free |bibcode=2011EPJWC..1104003L |journal=EPJ Web of Conferences |page=04003}}</ref>

<ref name=taylor1998>{{citation | first1=G. Jeffrey | last1=Taylor | date=December 31, 1998 | title=Origin of the Earth and Moon | work=Planetary Science Research Discoveries | publisher=University of Hawaii | url=http://www.psrd.hawaii.edu/Dec98/OriginEarthMoon.html }}</ref>

<ref name=ngn20071219>{{citation | first1=Richard A. | last1=Lovett | date=December 19, 2007 | title=Earth-Asteroid Collision Formed Moon Later Than Thought | work=National Geographic News | issue=12 | page=21153 | doi=10.1063/pt.5.021778 | bibcode=2007PhT..2007l1153. | url=http://news.nationalgeographic.com/news/2007/12/071219-moon-collision.html | archive-url=https://web.archive.org/web/20071221113957/http://news.nationalgeographic.com/news/2007/12/071219-moon-collision.html | url-status=dead | archive-date=December 21, 2007 | access-date=2012-02-24 | url-access=subscription }}</ref>

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===Further reading===
'''Academic articles'''
{{refbegin}}
* {{Cite journal |last1=Hartmann |first1=William K. |author-link=William Kenneth Hartmann |last2=Davis |first2=Donald R. |author-link2=Donald R. Davis (astronomer) |date=April 1975 |title=Satellite-sized planetesimals and lunar origin |journal=[[Icarus (journal)|Icarus]] |volume=24 |issue=4 |pages=504–515 |bibcode=1975Icar...24..504H |doi=10.1016/0019-1035(75)90070-6}}
* {{Cite conference |last1=Cameron |first1=A. G. W. |author-link=Alastair G. W. Cameron |last2=Ward |first2=W. R. |author-link2=William Ward (astronomer) |date=1976 |title=The Origin of the Moon |conference=Abstracts of the Lunar and Planetary Science Conference |volume=7 |pages=120 |bibcode=1976LPI.....7..120C}}
* {{Cite conference |last1=Canup |first1=R. M. |last2=Asphaug |first2=E. |date=December 2001 |title=An impact origin of the Earth-Moon system |conference=Fall Meeting 2001 |publisher=[[American Geophysical Union]] |volume=2001 |pages=U51A–02 |bibcode=2001AGUFM.U51A..02C}}
* {{Cite book |url=https://books.google.com/books?id=8i44zjcKm4EC |title=Origin of the earth and moon |date=2000 |publisher=[[University of Arizona Press]] |isbn=978-0-8165-2073-2 |editor-last=Canup |editor-first=Robin M. |series=The University of Arizona space science series |location=Tucson, Ariz |editor-last2=Righter |editor-first2=Kevin}}
* {{Cite journal |last=Shearer |first=C. K. |display-authors=etal |date=2006 |title=Thermal and Magmatic Evolution of the Moon |journal=[[Reviews in Mineralogy and Geochemistry]] |volume=60 |issue=1 |pages=365–518 |bibcode=2006RvMG...60..365S |doi=10.2138/rmg.2006.60.4 |issn=1529-6466}}
* {{Cite book |last1=Galimov |first1=Èrik Mihajlovič |author-link=Erik Galimov |url=https://books.google.com/books?id=hICAOkfMFXoC |title=Origin of the moon, new concept: geochemistry and dynamics |last2=Krivcov |first2=Anton Miroslavovič |date=2012 |publisher=[[De Gruyter]] |isbn=978-3-11-028628-1 |location=Berlin}}
{{refend}}

'''Non-academic books'''
{{refbegin}}
* {{Cite book |last=Mackenzie |first=Dana |url=https://archive.org/details/bigsplatorhowour00mack |title=The big splat, or how our moon came to be |date=2003 |publisher=[[Wiley (publisher)|Wiley]] |isbn=978-0-471-15057-2 |location=Hoboken, New Jersey |url-access=registration}}
* {{Cite book |last=Powell |first=James Lawrence |author-link=James L. Powell |url=https://books.google.com/books?id=A83MEAAAQBAJ |title=Unlocking the moon's secrets: from Galileo to giant impact |date=2023 |publisher=[[Oxford University Press]] |isbn=978-0-19-769486-2 |location=New York}}
* {{Cite web |last=Taylor |first=G. Jeffrey |date=December 31, 1998 |title=Origin of the Earth and Moon |url=http://www.psrd.hawaii.edu/Dec98/OriginEarthMoon.html |website=Planetary Science Research Discoveries |publisher=[[University of Hawaiʻi]]}}
{{refend}}

==External links==
* [http://www.psi.edu/epo/moon/moon.html Planetary Science Institute: Giant Impact Hypothesis]
* [http://www.xtec.es/recursos/astronom/moon/camerone.htm Origin of the Moon] by Prof. AGW Cameron
* [http://burtleburtle.net/bob/physics/kempler.html Klemperer rosette and Lagrangian point simulations using JavaScript]
* [http://www.swri.org/press/impact.htm SwRI giant impact hypothesis simulation] (.wmv and .mov)
* [https://web.archive.org/web/20070103054722/http://yso.mtk.nao.ac.jp/~kokubo/moon/kit/movie.html Origin of the Moon – computer model of accretion]
* [http://www.psrd.hawaii.edu/Archive/Archive-Moon.html Moon Archive] – Including articles about the giant impact hypothesis
* [http://www.jpl.nasa.gov/news/news.cfm?release=2009-119 Planet Smash-Up Sends Vaporized Rock, Hot Lava Flying] {{Webarchive|url=https://web.archive.org/web/20120207153335/http://www.jpl.nasa.gov/news/news.cfm?release=2009-119 |date=2012-02-07 }} (2009-08-10 JPL News)
* [https://arxiv.org/abs/1105.4616 How common are Earth–Moon planetary systems?] {{arXiv|1105.4616}}: 23 May 2011
* [https://www.youtube.com/watch?v=PmhmWs71EMk The Surprising State of the Earth after the Moon-Forming Giant Impact] – Sarah Stewart (SETI Talks), Jan 28, 2015

{{The Moon}}
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