Giant-impact hypothesis

Last updated
Artist's depiction of a collision between two planetary bodies. Such an impact between Earth and a Mars-sized object likely formed the Moon. Artist's concept of collision at HD 172555.jpg
Artist's depiction of a collision between two planetary bodies. Such an impact between Earth and a Mars-sized object likely formed the Moon.

The giant-impact hypothesis, sometimes called the Theia Impact, is an astrogeology hypothesis for the 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 same orbit approximately 4.5 billion years ago in the early Hadean eon (about 20 to 100 million years after the Solar System coalesced), and the ejecta of the impact event later accreted to form the Moon. [1] The impactor planet is sometimes called Theia, named after the mythical Greek Titan who was the mother of Selene, the goddess of the Moon. [2]

Contents

Analysis of lunar rocks 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. [3]

The giant-impact hypothesis is currently the favored hypothesis for lunar formation among astronomers. [4] Evidence that supports this hypothesis includes:

However, several questions remain concerning the best current models of the giant-impact hypothesis. [7] 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. [8] 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[ citation needed ] –does not host a similar 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 forces, and this became the dominant academic explanation. [9] 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 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. [10] 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 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. [11]

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 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 silicates would tend to coalesce. [12]

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.

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. [13]

Theia

The name of the hypothesised protoplanet is derived from the mythical Greek titan Theia /ˈθiːə/ , 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. [2] [14] 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 –approximately 3.9 billion years ago.

Basic model

Simplistic representation of the giant-impact hypothesis. Moon - Giant Impact Hypothesis - Simple model.png
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 Solar System began to form. [15] [16] 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 4 kilometres per second (2.5 mi/s) at "infinity" (far enough that gravitational attraction is not a factor), increasing as it approached to over 9.3 km/s (5.8 mi/s) at impact, and an impact angle of about 45°. [17] However, oxygen isotope abundance in lunar rock suggests "vigorous mixing" of Theia and Earth, indicating a steep impact angle. [3] [18] 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 [19] 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. [20]

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. [21] [22] 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. [23]

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. [24]

Composition

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. [6]

In 2014, a team in Germany reported that the Apollo samples had a slightly different isotopic signature from Earth rocks. [25] The difference was slight, but statistically significant. One possible explanation is that Theia formed near Earth. [26]

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). [27] 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 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. [28]

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 ] before it cooled down and gave birth to Earth and the Moon. [29] [30]

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. [31] [32]

Evidence

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. [33] Earth has the highest density of all the planets in the Solar System; [34] 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. [35] Zinc is strongly fractionated when volatilised in planetary rocks, [36] [37] but not during normal igneous processes, [38] 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. [35]

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. [39]

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. [40] 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. [41] A similar belt of warm dust was detected around the star BD+20°307 (HIP 8920, SAO 75016). [42]

On 1 November 2023, scientists reported that, according to computer simulations, remnants of Theia could be still visible inside the Earth as two giant anomalies of the Earth's mantle. [43] [44]

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. [45]

Composition

A number of compositional inconsistencies need to be addressed.

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. [54] 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. [55]

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. [56]

Possible origin of Theia

One suggested pathway for the impact as viewed from the direction of Earth's south pole (not to scale). BigSplashEnglish.svg
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), [57] [58] similar to a trojan asteroid. [5] 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). [57] 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. [57]

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. [59] 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. [60]

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. [61] 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. [62] 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. [63] 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.[ citation needed ]

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. [64]

Alternative hypotheses

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; [9] that it was formed elsewhere and was subsequently captured by Earth's gravitational field; [65] 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. [20]

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). [66] 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. [67] [68]

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 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. [69] [70] After the re-collision, Earth was surrounded by a disk of material which accreted to form the Moon. [70]

Moon – Oceanus Procellarum ("Ocean of Storms")
14-236-LunarGrailMission-OceanusProcellarum-Rifts-Overall-20141001.jpg
Ancient rift valleys – rectangular structure (visible – topography – GRAIL gravity gradients) (October 1, 2014).
PIA18822-LunarGrailMission-OceanusProcellarum-Rifts-Overall-20141001.jpg
Ancient rift valleys – context.
PIA18821-LunarGrailMission-OceanusProcellarum-Rifts-Closeup-20141001.jpg
Ancient rift valleys – closeup (artist's concept).

See also

Related Research Articles

<span class="mw-page-title-main">Moon</span> Natural satellite orbiting Earth

The Moon is Earth's only natural satellite. It orbits at an average distance of 384,400 km (238,900 mi), about 30 times the diameter of Earth. Tidal forces between Earth and the Moon have synchronized the Moon's orbital period with its rotation period at 29.5 Earth days, causing the same side of the Moon to always face Earth. The Moon's gravitational pull—and, to a lesser extent, the Sun's—are the main drivers of Earth's tides.

<span class="mw-page-title-main">Crust (geology)</span> Outermost solid shell of astronomical bodies

In geology, the crust is the outermost solid shell of a planet, dwarf planet, or natural satellite. It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase.

<span class="mw-page-title-main">Planetary differentiation</span> Astrogeological concept

In planetary science, planetary differentiation is the process by which the chemical elements of a planetary body accumulate in different areas of that body, due to their physical or chemical behavior. The process of planetary differentiation is mediated by partial melting with heat from radioactive isotope decay and planetary accretion. Planetary differentiation has occurred on planets, dwarf planets, the asteroid 4 Vesta, and natural satellites.

<span class="mw-page-title-main">Planetary core</span> Innermost layer(s) of a planet

A planetary core consists of the innermost layers of a planet. Cores may be entirely liquid, or a mixture of solid and liquid layers as is the case in the Earth. In the Solar System, core sizes range from about 20% to 85% of a planet's radius (Mercury).

Planet V is a hypothetical fifth terrestrial planet posited by NASA scientists John Chambers and Jack J. Lissauer to have once existed between Mars and the asteroid belt. In their hypothesis the Late Heavy Bombardment of the Hadean era began after perturbations from the other terrestrial planets caused Planet V's orbit to cross into the asteroid belt. Chambers and Lissauer presented the results of initial tests of this hypothesis during the 33rd Lunar and Planetary Science Conference, held from March 11 through 15, 2002.

<span class="mw-page-title-main">Origin of water on Earth</span> Hypotheses for the possible sources of the water on Earth

The origin of water on Earth is the subject of a body of research in the fields of planetary science, astronomy, and astrobiology. Earth is unique among the rocky planets in the Solar System in having oceans of liquid water on its surface. Liquid water, which is necessary for all known forms of life, continues to exist on the surface of Earth because the planet is at a far enough distance from the Sun that it does not lose its water, but not so far that low temperatures cause all water on the planet to freeze.

<span class="mw-page-title-main">North Polar Basin (Mars)</span> Large basin in the northern hemisphere of Mars

The North Polar Basin, more commonly known as the Borealis Basin, is a large basin in the northern hemisphere of Mars that covers 40% of the planet. Some scientists have postulated that the basin formed during the impact of a single, large body roughly 2% of the mass of Mars, having a diameter of about 1,900 km early in the history of Mars, around 4.5 billion years ago. However, the basin is not currently recognized as an impact basin by the IAU. The basin is one of the flattest areas in the Solar System, and has an elliptical shape.

<span class="mw-page-title-main">Formation and evolution of the Solar System</span>

There is evidence that the formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.

<span class="mw-page-title-main">Internal structure of the Moon</span>

Having a mean density of 3,346.4 kg/m3, the Moon is a differentiated body, being composed of a geochemically distinct crust, mantle, and planetary core. This structure is believed to have resulted from the fractional crystallization of a magma ocean shortly after its formation about 4.5 billion years ago. The energy required to melt the outer portion of the Moon is commonly attributed to a giant impact event that is postulated to have formed the Earth-Moon system, and the subsequent reaccretion of material in Earth orbit. Crystallization of this magma ocean would have given rise to a mafic mantle and a plagioclase-rich crust.

<span class="mw-page-title-main">Earth trojan</span> Asteroid with which Earth shares its orbit around the Sun

An Earth trojan is an asteroid that orbits the Sun in the vicinity of the Earth–Sun Lagrange points L4 (leading 60°) or L5 (trailing 60°), thus having an orbit similar to Earth's. Only two Earth trojans have so far been discovered. The name "trojan" was first used in 1906 for the Jupiter trojans, the asteroids that were observed near the Lagrangian points of Jupiter's orbit.

<span class="mw-page-title-main">History of Solar System formation and evolution hypotheses</span>

The history of scientific thought about the formation and evolution of the Solar System began with the Copernican Revolution. The first recorded use of the term "Solar System" dates from 1704. Since the seventeenth century, philosophers and scientists have been forming hypotheses concerning the origins of the Solar System and the Moon and attempting to predict how the Solar System would change in the future. René Descartes was the first to hypothesize on the beginning of the Solar System; however, more scientists joined the discussion in the eighteenth century, forming the groundwork for later hypotheses on the topic. Later, particularly in the twentieth century, a variety of hypotheses began to build up, including the now–commonly accepted nebular hypothesis.

<span class="mw-page-title-main">Late Heavy Bombardment</span> Hypothesized astronomical event

The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized astronomical event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypothesis, during this interval, a disproportionately large number of asteroids and comets collided into the terrestrial planets and their natural satellites in the inner Solar System, including Mercury, Venus, Earth and Mars. These came from both post-accretion and planetary instability-driven populations of impactors. Although it gained widespread credence, definitive evidence remains elusive.

The five-planet Nice model is a numerical model of the early Solar System that is a revised variation of the Nice model. It begins with five giant planets, the four that exist today plus an additional ice giant between Saturn and Uranus in a chain of mean-motion resonances.

<span class="mw-page-title-main">Origin of the Moon</span> Theories explaining the formation of Earths Moon

The origin of the Moon is usually explained by a Mars-sized body striking the Earth, creating a debris ring that eventually collected into a single natural satellite, the Moon, but there are a number of variations on this giant-impact hypothesis, as well as alternative explanations, and research continues into how the Moon came to be formed. Other proposed scenarios include captured body, fission, formed together, planetesimal collisions, and collision theories.

<span class="mw-page-title-main">Theia (planet)</span> Planet hypothesized to have impacted Earth and created the Moon

Theia is a hypothesized ancient planet in the early Solar System which, according to the giant-impact hypothesis, collided with the early Earth around 4.5 billion years ago, with some of the resulting ejected debris coalescing to form the Moon. Collision simulations support the idea that the large low-shear-velocity provinces in the lower mantle may be remnants of Theia. Theia is hypothesized to have been about the size of Mars, and may have formed in the outer Solar System and provided much of Earth's water, though this is debated.

<span class="mw-page-title-main">Satellite system (astronomy)</span> Set of gravitationally bound objects in orbit

A satellite system is a set of gravitationally bound objects in orbit around a planetary mass object or minor planet, or its barycenter. Generally speaking, it is a set of natural satellites (moons), although such systems may also consist of bodies such as circumplanetary disks, ring systems, moonlets, minor-planet moons and artificial satellites any of which may themselves have satellite systems of their own. Some bodies also possess quasi-satellites that have orbits gravitationally influenced by their primary, but are generally not considered to be part of a satellite system. Satellite systems can have complex interactions including magnetic, tidal, atmospheric and orbital interactions such as orbital resonances and libration. Individually major satellite objects are designated in Roman numerals. Satellite systems are referred to either by the possessive adjectives of their primary, or less commonly by the name of their primary. Where only one satellite is known, or it is a binary with a common centre of gravity, it may be referred to using the hyphenated names of the primary and major satellite.

Comparative planetary science or comparative planetology is a branch of space science and planetary science in which different natural processes and systems are studied by their effects and phenomena on and between multiple bodies. The planetary processes in question include geology, hydrology, atmospheric physics, and interactions such as impact cratering, space weathering, and magnetospheric physics in the solar wind, and possibly biology, via astrobiology.

<span class="mw-page-title-main">Magma ocean</span> Large area of molten rock on the surface of a planet

Magma oceans are vast fields of surface magma that exist during periods of a planet's or some natural satellite's accretion when the celestial body is completely or partly molten.

The K/U Ratio is the ratio of a slightly volatile element, potassium (K), to a highly refractory element, uranium (U). It is a useful way to measure the presence of volatile elements on planetary surfaces. The K/U ratio helps explain the evolution of the planetary system and the origin of Earth's moon.

References

Notes

  1. ↑ Angier, Natalie (September 7, 2014). "Revisiting the Moon". The New York Times . New York City.
  2. 1 2 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.
  3. 1 2 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 . 351 (6272). Washington DC: American Association for the Advancement of Science: 493–496. arXiv: 1603.04536 . Bibcode:2016Sci...351..493Y. doi:10.1126/science.aad0525. ISSN   0036-8075. PMID   26823426. S2CID   6548599.
  4. ↑ "Moon - Origin and Evolution". Encyclopedia Britannica. 9 June 2022. Retrieved 14 May 2023.
  5. 1 2 Mackenzie, Dana (2003). The Big Splat, or How The Moon Came To Be . John Wiley & Sons. ISBN   978-0-471-15057-2.
  6. 1 2 3 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.
  7. ↑ Clery, Daniel (October 11, 2013). "Impact Theory Gets Whacked". Science . 342 (6155). Washington DC: American Association for the Advancement of Science: 183–85. Bibcode:2013Sci...342..183C. doi:10.1126/science.342.6155.183. PMID   24115419.
  8. ↑ 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.
  9. 1 2 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.
  10. ↑ Daly, Reginald A. (1946). "Origin of the Moon and Its Topography". PAPS. 90 (2): 104–119. JSTOR   3301051.
  11. ↑ 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.
  12. ↑ 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.
  13. ↑ 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.
  14. ↑ 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
  15. ↑ 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.
  16. ↑ Soderman. "Evidence for Moon-Forming Impact Found Inside Meteorites". NASA-SSERVI. Retrieved 7 July 2016.
  17. ↑ 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
  18. ↑ 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.
  19. ↑ Jacobson, Seth A. (November 2021), "Lunar accretion from a Roche-interior fluid disk.", The Astrophysical Journal, 760 (1): 83
  20. 1 2 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.
  21. ↑ Lovett, Richard (2011-08-03). "Early Earth may have had two moons". Nature.com. Retrieved 2013-09-25.
  22. ↑ "Was our two-faced moon in a small collision?". Theconversation.edu.au. 3 August 2011. Retrieved 2013-09-25.
  23. ↑ Phil Plait, Why Do We Have a Two-Faced Moon?, Slate: Bad Astronomy blog, July 1, 2014
  24. ↑ Kegerreis, J.A.; et al. (4 October 2022). "Immediate Origin of the Moon as a Post-impact Satellite". The Astrophysical Journal Letters. 937 (L40): L40. arXiv: 2210.01814 . Bibcode:2022ApJ...937L..40K. doi: 10.3847/2041-8213/ac8d96 . S2CID   249267497.
  25. ↑ 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.
  26. ↑ "Traces of another world found on the Moon". BBC News. 2014-06-06.
  27. ↑ 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.
  28. ↑ 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 23 September 2012. Retrieved 23 September 2012.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  29. ↑ Boyle, Rebecca (25 May 2017). "Huge impact could have smashed early Earth into a doughnut shape". New Scientist. Retrieved 7 June 2017.
  30. ↑ 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.
  31. ↑ Puiu, Tibi (2019-04-30). "Ocean of magma blasted into space may explain how the moon formed". ZME Science. Retrieved 12 May 2019.
  32. ↑ 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.
  33. ↑ 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.
  34. ↑ Williams, David R. "Dr". NASA Space Science Data Coordinated Archive. NSSDCA. Retrieved 15 December 2020.
  35. 1 2 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.
  36. ↑ 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.
  37. ↑ 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 .
  38. ↑ 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.
  39. ↑ 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.
  40. ↑ 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.
  41. ↑ 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.
  42. ↑ 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.
  43. ↑ Chang, Kenneth (1 November 2023). "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". The New York Times . Archived from the original on 1 November 2023. Retrieved 2 November 2023.
  44. ↑ Yuan, Qian; et al. (1 November 2023). "Moon-forming impactor as a source of Earth's basal mantle anomalies". Nature . 623 (7985): 95–99. Bibcode:2023Natur.623...95Y. doi:10.1038/s41586-023-06589-1. PMID   37914947. Archived from the original on 2 November 2023. Retrieved 2 November 2023.
  45. 1 2 Jones, J. H. (1998). "Tests of the Giant Impact Hypothesis" (PDF). Lunar and Planetary Science. Origin of the Earth and Moon Conference. Monterey, California.
  46. ↑ 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.
  47. ↑ 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.
  48. ↑ 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.
  49. ↑ 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.
  50. ↑ 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.
  51. ↑ Nield, Ted (September 2009). "Moonwalk" (PDF). Geological Society of London. p. 8. Retrieved 2010-03-01.
  52. ↑ 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.
  53. ↑ Koppes, Steve (March 28, 2012). "Titanium paternity test fingers Earth as moon's sole parent". UChicagoNews. Retrieved August 13, 2012.
  54. ↑ Alemi, Alex; Stevenson, D. (September 2006), "Why Venus has No Moon", Bulletin of the American Astronomical Society, 38: 491, Bibcode:2006DPS....38.0703A
  55. ↑ 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
  56. ↑ Lewis, K. (February 2011), Bouchy, F.; Díaz, R.; Moutou, C. (eds.), "Moon formation and orbital evolution in extrasolar planetary systems - A literature review", EPJ Web of Conferences, 11, From the book "Detection and Dynamics of Transiting Exoplanets": 04003, Bibcode:2011EPJWC..1104003L, doi: 10.1051/epjconf/20101104003
  57. 1 2 3 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.
  58. ↑ 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
  59. ↑ 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.
  60. ↑ 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
  61. ↑ Than, Ker (May 6, 2008). "Did Earth once have multiple moons?". New Scientist. Reed Business Information Ltd. Retrieved 2011-12-10.
  62. ↑ 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
  63. ↑ Choi, Charles Q. (August 3, 2011), "Earth Had Two Moons That Crashed to Form One, Study Suggests", Yahoo News, retrieved 2012-02-24
  64. ↑ 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.
  65. ↑ 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.
  66. ↑ Taylor, G. Jeffrey (December 31, 1998), "Origin of the Earth and Moon", Planetary Science Research Discoveries, University of Hawaii
  67. ↑ 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
  68. ↑ Lovett, Richard A. (December 19, 2007), "Earth-Asteroid Collision Formed Moon Later Than Thought", National Geographic News, no. 12, p. 21153, Bibcode:2007PhT..2007l1153., doi:10.1063/pt.5.021778, archived from the original on December 21, 2007, retrieved 2012-02-24
  69. ↑ 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.
  70. 1 2 "NASA Lunar Scientists Develop New Theory on Earth and Moon Formation". NASA Press Release. NASA. 2012-10-30. Archived from the original on 2019-02-23. Retrieved 2012-12-05.

Further reading

Academic articles

Non-academic books

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.