The giant-impact hypothesis, sometimes called the Big Splash, or the Theia Impact, suggests that the Moon formed from the ejecta of a collision between the proto-Earth and a Mars-sized planet, approximately 4.5 billion years ago, in the Hadean eon (about 20 to 100 million years after the Solar System coalesced). The colliding body is sometimes called Theia, from the name of the mythical Greek Titan who was the mother of Selene, the goddess of the Moon. Analysis of lunar rocks, published in a 2016 report, suggests that the impact might have been a direct hit, causing a thorough mixing of both parent bodies.
- Earth's spin and the Moon's orbit have similar orientations.
- 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 planets. A giant impact might have supplied this excess momentum.
- Moon samples indicate that the Moon was once molten down to a substantial, but unknown, depth. This might have required more energy than predicted to be available from the accretion of a body of the Moon's size. An extremely energetic process, such as a giant impact, could provide this energy.
- The Moon has a relatively small iron core. This gives the Moon a 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 Earth and fuse with its own core. This would leave the Moon with less metallic iron than other planetary bodies.
- The Moon is depleted in 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 systems of similar collisions, resulting in debris discs.
- Giant collisions are consistent with the leading theory of the formation of the Solar System.
- The stable-isotope ratios of lunar and terrestrial rock are identical, implying a common origin.
However, there remain several questions concerning the best current models of the giant-impact hypothesis. 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. 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. Other remaining questions include when the Moon lost its share of volatile elements and why Venus – which experienced giant impacts during its formation – does not host a similar moon.
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 forces, and this became the dominant academic explanation. 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 American and Soviet experiments, using laser ranging targets placed on the Moon.
Nonetheless, Darwin's calculations could not resolve the mechanics required to trace the Moon backward 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. 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 in 1975 by Drs. William K. Hartmann and 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.
A similar approach was taken by Canadian astronomer Alastair G. W. Cameron and American astronomer William R. Ward, who suggested that the Moon was formed by the tangential impact upon Earth of a body the size of Mars. It is hypothesised that most of the outer silicates of the colliding body would be vaporised, 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 silicates would tend to coalesce.
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, 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.
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.
The name of the hypothesised protoplanet is derived from the mythical Greek titan Theia //, who gave birth to the Moon goddess Selene. This designation was proposed initially by the English geochemist Alex N. Halliday in 2000 and has become accepted in the scientific community. 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 occurred later – approximately 3.9 billion years ago.
Astronomers think the collision between Earth and Theia happened at about 4.4 to 4.45 bya; about 0.1 billion years after the Solar System began to form. 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 at infinity below 4 kilometres per second (2.5 mi/s), increasing as it fell to over 9.3 km/s (5.8 mi/s) at impact, and an impact angle of about 45°. However, oxygen isotope abundance in lunar rock suggests "vigorous mixing" of Theia and Earth, indicating a steep impact angle. Theia's iron core would have sunk into the young Earth's core, and most of Theia's mantle accreted onto Earth's mantle. However, a significant portion of the mantle material from both Theia and Earth would have been ejected into orbit around Earth (if ejected with velocities between orbital velocity and escape velocity) or into individual orbits around the Sun (if ejected at higher velocities). Modelling 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 orbits was thus likely 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 simulations 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 coplanar.
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 1,000 km (620 mi) 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. 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.
In 2001, a team at the Carnegie Institution of Washington reported that the rocks from the Apollo program carried an isotopic signature that was identical with rocks from Earth, and were different from almost all other bodies in the Solar System.
In 2014, a team in Germany reported that the Apollo samples had a slightly different isotopic signature from Earth rocks. The difference was slight, but statistically significant. One possible explanation is that Theia formed near Earth.
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.
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). 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?] to determine whether or not this is possible.
Direct collision hypothesis
According to research (2012) to explain similar compositions of 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.
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) before it cooled down and gave birth to Earth and the Moon.
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 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.
Indirect evidence for the giant impact scenario comes from rocks collected during the 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 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 bodies. Appropriate impact conditions satisfying the angular momentum constraints of the Earth–Moon system yield a Moon formed mostly from the mantles of Earth and the impactor, while the core of the impactor accretes to Earth. Earth has the highest density of all the planets in the Solar System; 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. Zinc is strongly fractionated when volatilised in planetary rocks, but not during normal igneous processes, 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.
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.
Warm silica-rich dust and abundant SiO gas, products of high velocity impacts – over 10 km/s (6.2 mi/s) – between rocky bodies, have been detected by the Spitzer Space Telescope around the nearby (29 pc distant) young (~12 My old) star HD 172555 in the Beta Pictoris moving group. 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. A similar belt of warm dust was detected around the star BD+20°307 (HIP 8920, SAO 75016).
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.
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.
- The presence of volatiles such as water trapped in lunar basalts and carbon emissions from the lunar surface is more difficult to explain if the Moon was caused by a high-temperature impact.
- 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.
- If the bulk of the proto-lunar material had come from an impactor, the Moon should be enriched in siderophilic elements, when, in fact, it is deficient in them.
- The Moon's oxygen isotopic ratios are essentially identical to those of Earth. Oxygen isotopic ratios, which may be measured very precisely, yield a unique and distinct signature for each Solar System body. If a separate proto-planet Theia had existed, it probably would have had a different oxygen isotopic signature than Earth, as would the ejected mixed material.
- The Moon's titanium isotope ratio (50Ti/47Ti) 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.
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. 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.
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.
Possible origin of Theia
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), similar to a trojan asteroid. Two-dimensional computer models suggest that the stability of Theia's proposed trojan orbit would have been affected when its growing mass exceeded a threshold of approximately 10% of Earth's mass (the mass of Mars). In this scenario, gravitational perturbations by planetesimals caused Theia to depart from its stable Lagrangian location, and subsequent interactions with proto-Earth led to a collision between the two bodies.
In 2008, evidence was presented that suggests that the collision might have occurred later than the accepted value of 4.53 Gya, at approximately 4.48 Gya. A 2014 comparison of computer simulations with elemental abundance measurements in Earth's mantle indicated that the collision occurred approximately 95 My after the formation of the Solar System.
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. 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. 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), adding a thick layer of highlands crust. 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 GRAIL mission has ruled out this scenario.
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.
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; that it was formed elsewhere and was subsequently captured by Earth's gravitational field; 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.
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. Previously, the age of the Moon had been thought to be 4.527 ± 0.010 billion years. The 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.
Yet another hypothesis proposes that the Moon and Earth formed together instead of separately like the giant-impact hypothesis suggests. This model, published in 2012 by 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. After the re-collision, Earth was surrounded by a disk of material, which accreted to form the Moon. This hypothesis could explain evidence that others do not.
- Angier, Natalie (September 7, 2014). "Revisiting the Moon". The New York Times. New York City.
- Halliday, Alex N. (February 28, 2000). "Terrestrial accretion rates and the origin of the Moon". Earth and Planetary Science Letters. 176 (1): 17–30. Bibcode:2000E&PSL.176...17H. doi:10.1016/S0012-821X(99)00317-9.
- Young, Edward D.; Kohl, Issaku E.; Warren, Paul H.; Rubie, David C.; Jacobson, Seth A.; Morbidelli, Alessandro (2016-01-29). "Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact". Science. Washington DC: American Association for the Advancement of Science. 351 (6272): 493–496. arXiv:1603.04536. Bibcode:2016Sci...351..493Y. doi:10.1126/science.aad0525. ISSN 0036-8075. PMID 26823426. S2CID 6548599.
- Canup, R.; Asphaug, E. (2001). "Origin of the Moon in a giant impact near the end of the Earth's formation" (PDF). Nature. 412 (6848): 708–712. Bibcode:2001Natur.412..708C. doi:10.1038/35089010. PMID 11507633. S2CID 4413525. Archived from the original (PDF) on 2010-07-30. Retrieved 2011-12-10.
- Mackenzie, Dana (2003). The Big Splat, or How The Moon Came To Be. John Wiley & Sons. ISBN 978-0-471-15057-2.
- Wiechert, U.; et al. (October 2001). "Oxygen Isotopes and the Moon-Forming Giant Impact". Science. 294 (12): 345–348. Bibcode:2001Sci...294..345W. doi:10.1126/science.1063037. PMID 11598294. S2CID 29835446.
- Clery, Daniel (October 11, 2013). "Impact Theory Gets Whacked". Science. Washington DC: American Association for the Advancement of Science. 342 (6155): 183–85. Bibcode:2013Sci...342..183C. doi:10.1126/science.342.6155.183. PMID 24115419.
- Rubie, D. C.; Nimmo, F.; Melosh, H. J. (2007). Formation of Earth's Core A2 – Schubert, Gerald. Amsterdam: Elsevier. pp. 51–90. ISBN 978-0444527486.
- Binder, A. B. (1974). "On the origin of the Moon by rotational fission". The Moon. 11 (2): 53–76. Bibcode:1974Moon...11...53B. doi:10.1007/BF01877794. S2CID 122622374.
- Daly, Reginald A. (1946). "Origin of the Moon and Its Topography". PAPS. 90 (2): 104–119. JSTOR 3301051.
- Hartmann, W. K.; Davis, D. R. (April 1975). "Satellite-sized planetesimals and lunar origin". Icarus. 24 (4): 504–514. Bibcode:1975Icar...24..504H. doi:10.1016/0019-1035(75)90070-6.
- Cameron, A. G. W.; Ward, W. R. (March 1976). "The Origin of the Moon". Abstracts of the Lunar and Planetary Science Conference. 7: 120–122. Bibcode:1976LPI.....7..120C.
- Mackenzie, Dana (21 July 2003). The Big Splat, or How Our Moon Came to Be. John Wiley & Sons. pp. 166–168. ISBN 978-0-471-48073-0. Archived from the original on 17 June 2020. Retrieved 11 June 2019.
- Gray, Denis (December 2003), "Book Review: The big splat or how our moon came to be / John Wiley & Sons, 2003", Journal of the Royal Astronomical Society of Canada, 97 (6): 299, Bibcode:2003JRASC..97..299G
- Freeman, David (September 23, 2013). "How Old Is The Moon? 100 Million Years Younger Than Once Thought, New Research Suggests". The Huffington Post. New York City: Huffington Post Media Group. Retrieved September 25, 2013.
- Soderman. "Evidence for Moon-Forming Impact Found Inside Meteorites". NASA-SSERVI. Retrieved 7 July 2016.
- Canup, Robin M. (April 2004), "Simulations of a late lunar-forming impact", Icarus, 168 (2): 433–456, Bibcode:2004Icar..168..433C, doi:10.1016/j.icarus.2003.09.028
- Wenz, John (January 28, 2016). "The Earth and Moon Both Contain Equal Parts of an Ancient Planet". Popular Mechanics. New York City: Hearst Corporation. Retrieved April 30, 2016.
- Jacobson, Seth A. (November 2021), "Lunar accretion from a Roche-interior fluid disk.", The Astrophysical Journal, 760 (1): 83
- Stevenson, D. J. (1987). "Origin of the moon–The collision hypothesis". Annual Review of Earth and Planetary Sciences. 15 (1): 271–315. Bibcode:1987AREPS..15..271S. doi:10.1146/annurev.ea.15.050187.001415.
- Lovett, Richard (2011-08-03). "Early Earth may have had two moons". Nature.com. Retrieved 2013-09-25.
- "Was our two-faced moon in a small collision?". Theconversation.edu.au. Retrieved 2013-09-25.
- Phil Plait, Why Do We Have a Two-Faced Moon?, Slate: Bad Astronomy blog, July 1, 2014
- Herwartz, D.; Pack, A.; Friedrichs, B.; Bischoff, A. (2014). "Identification of the giant impactor Theia in lunar rocks". Science. 344 (6188): 1146–1150. Bibcode:2014Sci...344.1146H. doi:10.1126/science.1251117. PMID 24904162. S2CID 30903580.
- "Traces of another world found on the Moon". BBC News. 2014-06-06.
- Pahlevan, Kaveh; Stevenson, David (October 2007). "Equilibration in the Aftermath of the Lunar-forming Giant Impact". Earth and Planetary Science Letters. 262 (3–4): 438–449. arXiv:1012.5323. Bibcode:2007E&PSL.262..438P. doi:10.1016/j.epsl.2007.07.055. S2CID 53064179.
- Dambeck, Thorsten (11 September 2012). "Retuschen an der Entstehungsgeschichte des Erdtrabanten" [Retouches on the genesis of Earth's moon] (in German). Archived from the original on 11 September 2012. Retrieved 23 September 2012.
- Boyle, Rebecca (25 May 2017). "Huge impact could have smashed early Earth into a doughnut shape". New Scientist. Retrieved 7 June 2017.
- Lock, Simon J.; Stewart, Sarah T.; Petaev, Michail I.; Leinhardt, Zoe M.; Mace, Mia T.; Jacobsen, Stein B.; Ćuk, Matija (2018). "The origin of the Moon within a terrestrial synestia". Journal of Geophysical Research. 123 (4): 910. arXiv:1802.10223. Bibcode:2018JGRE..123..910L. doi:10.1002/2017JE005333. S2CID 119184520.
- Puiu, Tibi (2019-04-30). "Ocean of magma blasted into space may explain how the moon formed". ZME Science. Retrieved 12 May 2019.
- Hosono, Natsuki; Karato, Shun-ichiro; Makino, Junichiro; Saitoh, Takayuki R. (29 Apr 2019). "Terrestrial magma ocean origin of the Moon". Nature Geoscience. 12 (6): 418–423. Bibcode:2019NatGe..12..418H. doi:10.1038/s41561-019-0354-2. S2CID 155215215.
- Williams, David R. "Dr". NASA Space Science Data Coordinated Archive. NSSDCA. Retrieved 15 December 2020.
- Paniello, R. C.; Day, J. M. D.; Moynier, F. (2012). "Zinc isotopic evidence for the origin of the Moon". Nature. 490 (7420): 376–379. Bibcode:2012Natur.490..376P. doi:10.1038/nature11507. PMID 23075987. S2CID 4422136.
- Moynier, F.; Albarède, F.; Herzog, G. F. (2006). "Isotopic composition of zinc, copper, and iron in lunar samples". Geochimica et Cosmochimica Acta. 70 (24): 6103. Bibcode:2006GeCoA..70.6103M. doi:10.1016/j.gca.2006.02.030.
- Moynier, F.; Beck, P.; Jourdan, F.; Yin, Q. Z.; Reimold, U.; Koeberl, C. (2009). "Isotopic fractionation of zinc in tektites" (PDF). Earth and Planetary Science Letters. 277 (3–4): 482. Bibcode:2009E&PSL.277..482M. doi:10.1016/j.epsl.2008.11.020. hdl:20.500.11937/39896.
- Ben Othman, D.; Luck, J. M.; Bodinier, J. L.; Arndt, N. T.; Albarède, F. (2006). "Cu–Zn isotopic variations in the Earth's mantle". Geochimica et Cosmochimica Acta. 70 (18): A46. Bibcode:2006GeCAS..70...46B. doi:10.1016/j.gca.2006.06.201.
- Bottke, W. F.; Vokrouhlicky, D.; Marchi, S.; Swindle, T.; Scott, E. R. D.; Weirich, J. R.; Levison, H. (2015). "Dating the Moon-forming impact event with asteroidal meteorites". Science. 348 (6232): 321–323. Bibcode:2015Sci...348..321B. doi:10.1126/science.aaa0602. PMID 25883354.
- Lisse, Carey M.; et al. (2009). "Abundant Circumstellar Silica Dust and SiO Gas Created by a Giant Hypervelocity Collision in the ~12 Myr HD172555 System". Astrophysical Journal. 701 (2): 2019–2032. arXiv:0906.2536. Bibcode:2009ApJ...701.2019L. doi:10.1088/0004-637X/701/2/2019. S2CID 56108044.
- Rhee, Joseph H.; Song, Inseok; Zuckerman, B. (2007). "Warm dust in the terrestrial planet zone of a sun-like Pleiad: collisions between planetary embryos?". Astrophysical Journal. 675 (1): 777–783. arXiv:0711.2111v1. Bibcode:2008ApJ...675..777R. doi:10.1086/524935. S2CID 15836467.
- Song, Inseok; et al. (21 July 2005). "Extreme collisions between planetesimals as the origin of warm dust around a Sun-like star". Nature. 436 (7049): 363–365. Bibcode:2005Natur.436..363S. doi:10.1038/nature03853. PMID 16034411. S2CID 4390247.
- Jones, J. H. (1998). "Tests of the Giant Impact Hypothesis" (PDF). Lunar and Planetary Science. Origin of the Earth and Moon Conference. Monterey, California.
- Saal, Alberto E.; et al. (July 10, 2008). "Volatile content of lunar volcanic glasses and the presence of water in the Moon's interior". Nature. 454 (7201): 192–195. Bibcode:2008Natur.454..192S. doi:10.1038/nature07047. PMID 18615079. S2CID 4394004.
- Yokota, Shoichiro; Kentaro Terada; Yoshifumi Saito; Daiba Kato; Kazushi Asamura; Masaki N. Nishino; Hisayoshi Shimizu; Futoshi Takahashi; Hidetoshi Shibuya; Masaki Matsushima; Hideo Tsunakawa (6 May 2020). "KAGUYA observation of global emissions of indigenous carbon ions from the Moon". Science Advances. 6 (19): eaba1050. Bibcode:2020SciA....6.1050Y. doi:10.1126/sciadv.aba1050. ISSN 2375-2548. PMC 7202878. PMID 32494721.
- Taylor, Stuart R. (1997). "The Bulk Composition of the Moon" (PDF). Meteoritics and Planetary Science Supplement. 37: A139. Bibcode:2002M&PSA..37Q.139T. Retrieved 2010-03-21.
- Galimov, E. M.; Krivtsov, A. M. (December 2005). "Origin of the Earth-Moon System" (PDF). Journal of Earth System Science. 114 (6): 593–600. Bibcode:2005JESS..114..593G. CiteSeerX 10.1.1.502.314. doi:10.1007/BF02715942. S2CID 56094186. Retrieved 2011-12-10.
- Scott, Edward R. D. (December 3, 2001). "Oxygen Isotopes Give Clues to the Formation of Planets, Moons, and Asteroids". Planetary Science Research Discoveries Report: 55. Bibcode:2001psrd.reptE..55S. Retrieved 2010-03-19.
- Nield, Ted (September 2009). "Moonwalk" (PDF). Geological Society of London. p. 8. Retrieved 2010-03-01.
- Zhang, Junjun; Nicolas Dauphas; Andrew M. Davis; Ingo Leya; Alexei Fedkin (25 March 2012). "The proto-Earth as a significant source of lunar material". Nature Geoscience. 5 (4): 251–255. Bibcode:2012NatGe...5..251Z. doi:10.1038/ngeo1429.
- Koppes, Steve (March 28, 2012). "Titanium paternity test fingers Earth as moon's sole parent". UChicagoNews. Retrieved August 13, 2012.
- Alemi, Alex; Stevenson, D. (September 2006), "Why Venus has No Moon", Bulletin of the American Astronomical Society, 38: 491, Bibcode:2006DPS....38.0703A
- Sheppard, Scott S.; Trujillo, Chadwick A. (July 2009), "A survey for satellites of Venus", Icarus, 202 (1): 12–16, arXiv:0906.2781, Bibcode:2009Icar..202...12S, doi:10.1016/j.icarus.2009.02.008, S2CID 15252548
- Lewis, K. (February 2011), "Moon formation and orbital evolution in extrasolar planetary systems - A literature review", in Bouchy, F.; Díaz, R.; Moutou, C. (eds.), Detection and Dynamics of Transiting Exoplanets, EPJ Web of Conferences, vol. 11, p. 04003, Bibcode:2011EPJWC..1104003L, doi:10.1051/epjconf/20101104003
- Belbruno, E.; Gott III, J. Richard (2005). "Where Did The Moon Come From?". The Astronomical Journal. 129 (3): 1724–1745. arXiv:astro-ph/0405372. Bibcode:2005AJ....129.1724B. doi:10.1086/427539. S2CID 12983980.
- Howard, E. (July 2005), "The effect of Lagrangian L4/L5 on satellite formation", Meteoritics & Planetary Science, 40 (7): 1115, Bibcode:2005M&PS...40.1115H, doi:10.1111/j.1945-5100.2005.tb00176.x
- Halliday, Alex N (November 28, 2008). "A young Moon-forming giant impact at 70–110 million years accompanied by late-stage mixing, core formation and degassing of the Earth". Philosophical Transactions of the Royal Society A. 366 (1883): 4163–4181. Bibcode:2008RSPTA.366.4163H. doi:10.1098/rsta.2008.0209. PMID 18826916. S2CID 25704564.
- Jacobson, Seth A. (April 2014), "Highly siderophile elements in Earth's mantle as a clock or the Moon-forming impact", Nature, 508 (7494): 84–87, arXiv:1504.01421, Bibcode:2014Natur.508...84J, doi:10.1038/nature13172, PMID 24695310, S2CID 4403266
- Than, Ker (May 6, 2008). "Did Earth once have multiple moons?". New Scientist. Reed Business Information Ltd. Retrieved 2011-12-10.
- Jutzi, M.; Asphaug, E. (August 4, 2011), "Forming the lunar farside highlands by accretion of a companion moon", Nature, 476 (7358): 69–72, Bibcode:2011Natur.476...69J, doi:10.1038/nature10289, PMID 21814278, S2CID 84558
- Choi, Charles Q. (August 3, 2011), "Earth Had Two Moons That Crashed to Form One, Study Suggests", Yahoo News, retrieved 2012-02-24
- Budde, Gerrit; Burkhardt, Christoph; Kleine, Thorsten (2019-05-20). "Molybdenum isotopic evidence for the late accretion of outer Solar System material to Earth". Nature Astronomy. 3 (8): 736–741. Bibcode:2019NatAs...3..736B. doi:10.1038/s41550-019-0779-y. ISSN 2397-3366. S2CID 181460133.
- Mitler, H. E. (1975). "Formation of an iron-poor moon by partial capture, or: Yet another exotic theory of lunar origin". Icarus. 24 (2): 256–268. Bibcode:1975Icar...24..256M. doi:10.1016/0019-1035(75)90102-5.
- Taylor, G. Jeffrey (December 31, 1998), "Origin of the Earth and Moon", Planetary Science Research Discoveries, University of Hawaii
- Touboul, Mathieu (December 20, 2007), "Late formation and prolonged differentiation of the Moon inferred from W isotopes in lunar metals", Nature, 450 (7173): 1206–1209, Bibcode:2007Natur.450.1206T, doi:10.1038/nature06428, PMID 18097403, S2CID 4416259
- Lovett, Richard A. (December 19, 2007), "Earth-Asteroid Collision Formed Moon Later Than Thought", National Geographic News, retrieved 2012-02-24
- Canup, Robin M. (2012-11-23). "Forming a Moon with an Earth-like Composition via a Giant Impact". Science. 338 (6110): 1052–1055. Bibcode:2012Sci...338.1052C. doi:10.1126/science.1226073. PMC 6476314. PMID 23076098.
- "NASA Lunar Scientists Develop New Theory on Earth and Moon Formation". NASA Press Release. NASA. 2012-10-30. Retrieved 2012-12-05.
- William K. Hartmann and Donald R. Davis, Satellite-sized planetesimals and lunar origin, (International Astronomical Union, Colloquium on Planetary Satellites, Cornell University, Ithaca, NY, Aug. 18–21, 1974) Icarus, vol. 24, April 1975, pp. 504–515
- Alastair G. W. Cameron and William R. Ward, The Origin of the Moon, Abstracts of the Lunar and Planetary Science Conference, volume 7, p. 120, 1976
- Canup, R. M.; Asphaug, E. (Fall 2001). "An impact origin of the Earth-Moon system". Abstract #U51A-02. American Geophysical Union. Bibcode:2001AGUFM.U51A..02C.
- R. Canup; K. Righter, eds. (2000). Origin of the Earth and Moon. University of Arizona Press, Tucson. p. 555.
- Shearer, C. K.; 15 coauthors (2006). "Thermal and magmatic evolution of the Moon". Reviews in Mineralogy and Geochemistry. 60 (1): 365–518. Bibcode:2006RvMG...60..365S. doi:10.2138/rmg.2006.60.4.
- Galimov, Erik M.; Krivtsov, Anton M. "Origin of the Moon. New Concept. Geochemistry and Dynamics". De Gruyter. Berlin 2012, ISBN 978-3-11-028640-3.
- Planetary Science Institute: Giant Impact Hypothesis
- Origin of the Moon by Prof. AGW Cameron
- SwRI giant impact hypothesis simulation (.wmv and .mov)
- Origin of the Moon – computer model of accretion
- Moon Archive – Including articles about the giant impact hypothesis
- Planet Smash-Up Sends Vaporized Rock, Hot Lava Flying (2009-08-10 JPL News)
- How common are Earth–Moon planetary systems? arXiv:1105.4616: 23 May 2011
- The Surprising State of the Earth after the Moon-Forming Giant Impact – Sarah Stewart (SETI Talks), Jan 28, 2015