Giant impact theory
An explanation for the origin of the Moon from Earth debris which collected in space after a projectile the size of planet Mars smashed into a growing Earth.
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An explanation for the origin of the Moon from Earth debris which collected in space after a projectile the size of planet Mars smashed into a growing Earth.
The giant impact hypothesis (sometimes referred to as the big whack, or, less frequently, the big splash) is the now-dominant scientific theory for the formation of the Moon, which is thought to have formed as a result of a collision between the young Earth and a Mars-sized body that is sometimes called Theia[1] or, on rare occasion, Orpheus. The name of Theia (IPA: ['θei.a]) is derived from Greek mythology, as Theia was the Titan who gave birth to the Moon goddess Selene. The hypothesis was first proposed at a conference on satellites in 1974 and then published in Icarus in 1975 by Drs. Bill K. Hartmann and Donald R. Davis.
One hypothesis is that Theia formed at a Lagrangian point relative to Earth, that is, in about the same orbit and about 60° ahead or behind.[2] When the protoplanet Theia had grown to about the size of Mars, it became too massive to reside stably in a Trojan orbit. As a result, its angular distance from Earth fluctuated, with the fluctuations growing larger until it hit the Earth. This is calculated to have occurred 4.533 billion years ago (4.533 Ga); Theia is thought to have struck the Earth at an oblique angle, destroying Theia and ejecting most of Theia's mantle and a significant portion of the Earth's mantle into space, while Theia's core sank into Earth's core. Current estimates based on computer simulations of such an event suggest that some two percent of the original mass of Theia ended up as an orbiting ring of debris, about half of which coalesced into the Moon between one and 100 years after the impact. Regardless of the rotation and inclination the Earth had before the impact, after the impact it would have had a day some five hours long, and the Earth's equator would have shifted closer to the plane of the Moon's orbit.
Indirect evidence for this impact scenario comes from rocks collected during the Apollo Moon
landings, which show oxygen
Even the dominant lunar origin theory has some difficulties which have yet to be explained. These difficulties include:
Cited references
Scientific references
General references
| The Moon | |
|---|---|
| General | Calendar · Month · Moon in art and literature · Moon in mythology · Moon illusion · Lunar effect |
| Orbit | Orbit of the Moon · Phases of the Moon · Solar eclipse · Lunar eclipse · Tides |
| Physical characteristics | Internal structure · Gravity field · Topography · Magnetic field · Atmosphere |
| The lunar surface | Selenography · Near side · Far side · Lunar mare · Impact crater · South Pole-Aitken basin · Shackleton (crater) · Ice · Peak of eternal light · Space weathering · Transient lunar phenomenon |
| Lunar science | Geology · Lunar geologic timescale · Giant impact hypothesis · Moon rocks · Lunar meteorites · KREEP · ALSEP · Lunar laser ranging · Late heavy bombardment |
| Exploration | Exploration of the Moon · Project Apollo · Robotic exploration · Future missions · Lunar colonization· Moon Landing hoax accusations |
| See also Solar system, natural satellite | |
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