Moon

:For other moons in the solar system see natural satellite. For the astrological meaning of the Moon, see Solar system in astrology. For other uses see Moon (disambiguation).

Origin and history

The inclination of the Moon's orbit makes it implausible that the Moon formed along with Earth or was captured later; its origin is the subject of some scientific debate.

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Early speculation proposed that the Moon broke off from the Earth's crust due to centrifugal force, leaving an ocean basin behind as a scar. This concept requires too great an initial spin of the Earth. Others speculated the Moon formed elsewhere and was captured into its orbit.

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Some propose Coformation or Condensation theory, the concept that the Earth and the Moon formed at about the same time from the accretion disk. This theory fails to explain the depletion of iron in the Moon. Yet different groups propose that the Moon formed from a debris field around Earth resulting from an asteroid or planetesimal collision.

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Currently, the only viable scientific theory is the Giant Impact theory, in which the Moon originated from the ejecta from the collision between a semi-molten Earth and a planet-like object the size of Mars (dubbed Theia).

Related Topics:
Giant Impact theory - Earth - Mars - Theia

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The geological epochs of the Moon are defined based on the dating of various significant impact events in the Moon's history. Analysis of craters and Moon rocks show that there was a late heavy bombardment by asteroids around the period 4000 to 3800 million years ago.

Related Topics:
Geological epochs - Moon rocks - Late heavy bombardment

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Tidal forces deformed the once molten Moon into an ellipsoid, with the major axis pointed towards Earth.

Related Topics:
Tidal force - Ellipsoid - Major axis

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