NationMaster - Encyclopedia: MOON

The Moon (Latin: Luna) is Earth's only natural satellite, and the fifth largest moon in the Solar System. The average centre-to-centre distance from the Earth to the Moon is 384,403 km, which is about thirty times the diameter of the Earth. The Moon has a diameter of 3,474 km ^[8]—slightly more than a quarter that of the Earth and slightly smaller than the east-west distance across the United States. This means that the volume of the Moon is about 2 percent that of Earth. The gravitational pull at its surface is about 17 percent of the Earth's. The Moon makes a complete orbit around the Earth every 27.3 days, and the periodic variations in the geometry of the Earth–Moon–Sun system are responsible for the lunar phases that repeat every 29.5 days. A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... The NOUN Moon refers, among other things, to: Look up moon in Wiktionary, the free dictionary A common term for large natural satellites of a planet. ... Image File history File links Moon_symbol_decrescent. ... Image File history File links Metadata Size of this preview: 594 Ã— 599 pixelsFull resolution (1411 Ã— 1424 pixel, file size: 903 KB, MIME type: image/jpeg) File historyClick on a date/time to view the file as it appeared at that time. ... This article is about Earth as a planet. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... A diagram of Keplerian orbital elements. ... The astronomical unit (AU or au or a. ... A diagram of Keplerian orbital elements. ... The semi-major axis of an ellipse In geometry, the term semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae. ... (This page refers to eccitricity in astrodynamics. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... The orbital period is the time it takes a planet (or another object) to make one full orbit. ... The orbital speed of a body, generally a planet, a natural satellite, an artificial satellite, or a multiple star, is the speed at which it orbits around the barycenter of a system, usually around a more massive body. ... For the science fiction novella by William Shunn, see Inclination (novella). ... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... The Longitude of the ascending node (â˜Š, also noted Î©) is one of the orbital elements used to specify the orbit of an object in space. ... The argument of periapsis (Ï‰) is the orbital element describing the angle between an orbiting bodys ascending node (the point where the body crosses the plane of reference from South to North) and its periapsis (the point of closest approach to the central body), measured in the orbital plane and... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... This article is about Earth as a planet. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses IlhÃ©u das Rolas, in SÃ£o TomÃ© and PrÃncipe. ... A geographical pole is either of two fixed points on the surface of a spinning body or planet, at 90 degrees from the equator, based on the axis around which a body spins. ... The flattening, ellipticity, or oblateness of an oblate spheroid is the relative difference between its equatorial radius a and its polar radius b: The flattening of the Earth is 1:298. ... World map showing the equator in red In tourist areas, the equator is often marked on the sides of roads The equator marked as it crosses IlhÃ©u das Rolas, in SÃ£o TomÃ© and PrÃncipe. ... In mathematics, a spheroid is a quadric surface in three dimensions obtained by rotating an ellipse about one of its principal axes. ... For other uses, see Volume (disambiguation). ... For other uses, see Mass (disambiguation). ... For other uses, see Density (disambiguation). ... The surface gravity of a Killing horizon is the acceleration, as exerted at infinity, needed to keep an object at the horizon. ... The term g force or gee force refers to the symbol g, the force of acceleration due to gravity at the earths surface. ... Space Shuttle Atlantis launches on mission STS-71. ... On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ... Due to synchronous rotation of their moon, the inhabitants of the central body will never be able to see its green side. ... In astronomy, axial tilt is the inclination angle of a planets rotational axis in relation to a perpendicular to its orbital plane. ... For other uses, see Albedo (disambiguation). ... For other uses, see Temperature (disambiguation). ... For other uses, see Kelvin (disambiguation). ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... For other uses, see Full Moon. ... The angular diameter of an object as seen from a given position is the diameter measured as an angle. ... Diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure at any point in the Earths atmosphere. ... For other uses, see Pascal. ... For other uses, see Pascal. ... For other uses, see Latin (disambiguation). ... This article is about Earth as a planet. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... This is a list of natural satellites in the solar system, ordered from largest to smallest by average diameter. ... This article is about the Solar System. ... Gravity redirects here. ... Two bodies with a slight difference in mass orbiting around a common barycenter. ... Sol redirects here. ... Lunar phase refers to the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. ...

The Moon is the only celestial body to which humans have travelled and upon which humans have landed. The first artificial object to escape Earth's gravity and pass near the Moon was the Soviet Union's Luna 1, the first artificial object to impact the lunar surface was Luna 2, and the first photographs of the normally occluded far side of the Moon were made by Luna 3, all in 1959. The first spacecraft to perform a successful lunar soft landing was Luna 9, and the first unmanned vehicle to orbit the Moon was Luna 10, both in 1966.^[8] The United States (U.S.) Apollo program achieved the only manned missions to date, resulting in six landings between 1969 and 1972. Human exploration of the Moon ceased with the conclusion of the Apollo program, although several countries have announced plans to send people or robotic spacecraft to the Moon. Astronomical objects are significant physical entities, associations or structures which current science has confirmed to exist in space. ... Luna 1 is the first spacecraft to reach the vicinity of the Moon and the first of the Luna programme of Soviet automatic interplanetary stations successfully launched in the direction of the Moon. ... Luna 2 (E-1A series) was the second of the Soviet Unions Luna program spacecraft launched in the direction of the Moon. ... Far side of the Moon. ... Luna 3 (E-3 series) was the third spacecraft sent successfully to the moon and was an early triumph in the human exploration of outer space. ... Luna 9 (E-6 series), also known as Lunik 9 (internal name E-6 N. 13), was an unmanned space mission of the Soviet Unions Luna program. ... Luna 10 was an unmanned space mission of the Luna program, also called Lunik 10. ... This article is about the series of human spaceflight missions. ...

Name and etymology

Unlike the moons of other planets, the moon of the Earth has no proper English name other than "the Moon" (capitalized). The English language is a West Germanic language that originates in England. ...

The word moon is a Germanic word, related to Latin mensis; it is ultimately a derivative of the Proto-Indo-European root me-, also represented in measure^[9] (time), with reminders of its importance in measuring time in words derived from it like Monday, month and menstrual. In English, the word moon exclusively meant "the Moon" until 1665, when it was extended to refer to the recently-discovered natural satellites of other planets.^[9] The Moon is occasionally referred to by its Latin name, Luna, in order to distinguish it from other natural satellites, with a related adjective lunar, and an adjectival prefix seleno- or suffix -selene (from the Greek deity Selene). The Germanic languages are a group of related languages constituting a branch of the Indo-European (IE) language family. ... This article is about the baked good, for other uses see Pie (disambiguation). ... Look up Month in Wiktionary, the free dictionary. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... The bust of Zeus found at Otricoli (Sala Rotonda, Museo Pio-Clementino, Vatican) Greek mythology is the body of stories belonging to the Ancient Greeks concerning their gods and heroes, the nature of the world and the origins and significance of their own cult and ritual practices. ... This article is about the Greek goddess. ...

Lunar surface

Main article: Geology of the Moon

Exploring Shorty crater during the Apollo 17 mission to the Moon. ...

Two sides of the Moon

The Moon is in synchronous rotation, meaning that it keeps nearly the same face turned towards the Earth at all times. Early in the Moon's history, its rotation slowed and became locked in this configuration as a result of frictional effects associated with tidal deformations caused by the Earth.^[10] Due to synchronous rotation of their moon, the inhabitants of the central body will never be able to see its green side. ... Tidal locking makes one side of an astronomical body always face another, like the Moon facing the Earth. ... For other uses, see Friction (disambiguation). ...

Long ago when the Moon spun much faster, the Moon's tidal bulge preceded the Earth-Moon line because the Moon couldn't "snap back" its bulges quickly enough to keep its bulges in line with Earth.^[11] The rotation swept the bulge beyond the Earth-Moon line. This out-of-line bulge caused a torque, slowing the Moon spin, like a wrench tightening a nut. When the Moon's spin slowed enough to match its orbital rate, then the bulge always faced Earth, the bulge was in line with Earth, and the torque disappeared. That's why the Moon rotates at the same rate as it orbits and we always see the same side of the Moon.

Small variations (libration) in the angle from which the Moon is seen allow about 59% of its surface to be seen from the earth (but only half at any instant).^[8] Not to be confused with Liberation. ...


Near side of the Moon		Far side of the Moon

The side of the Moon that faces Earth is called the near side, and the opposite side the far side. The far side should not be confused with the dark side, which is the hemisphere that is not being illuminated by the Sun at a given moment (this may be the side facing the Earth, as it is once a month during the New Moon phase). The far side of the Moon was first photographed by the Soviet probe Luna 3 in 1959. One distinguishing feature of the far side is its almost complete lack of maria. Download high resolution version (1719x1719, 259 KB) Original Caption Released with Image About 50,000 Clementine images were processed to produce the four orthographic views of the Moon. ... Download high resolution version (1719x1719, 311 KB) Original Caption Released with Image About 50,000 Clementine images were processed to produce the four orthographic views of the Moon. ... The near side of the Moon is the lunar hemisphere that is permanently turned towards the Earth, and as such the side which is always seen. ... Far side of the Moon. ... The near side of the Moon is the lunar hemisphere that is permanently turned towards the Earth, and as such the side which is always seen. ... Far side of the Moon. ... Sol redirects here. ... Luna 3 (E-3 series) was the third spacecraft sent successfully to the moon and was an early triumph in the human exploration of outer space. ... Lunar nearside with major maria and craters labeled A global albedo map of the Moon obtained from the Clementine missionThe dark regions are the lunar maria, whereas the lighter regions are the highlands. ...

Lunar libration

Image File history File links Size of this preview: 598 Ã— 600 pixelsFull resolutionâ€Ž (640 Ã— 642 pixels, file size: 9. ... Image File history File links Size of this preview: 598 Ã— 600 pixelsFull resolutionâ€Ž (640 Ã— 642 pixels, file size: 9. ... Not to be confused with Liberation. ...

Maria

Main article: Lunar mare

The dark and relatively featureless lunar plains humans can clearly see when the Moon is full are called maria (singular mare), Latin for seas, since they were believed by ancient astronomers to be filled with water. These are now known to be vast solidified pools of ancient basaltic lava. The majority of these lavas erupted or flowed into the depressions associated with impact basins that formed by the collisions of meteors and comets with the lunar surface. (Oceanus Procellarum is a major exception in that it does not correspond to a known impact basin). Maria are found almost exclusively on the near side of the Moon, with the far side having only a few scattered patches covering only about 2% of its surface,^[12] compared with about 31% on the near side.^[8] The most likely explanation for this difference is related to a higher concentration of heat-producing elements on the near-side hemisphere, as has been demonstrated by geochemical maps obtained from the Lunar Prospector gamma-ray spectrometer.^[13]^[14] Several provinces containing shield volcanoes and volcanic domes are found within the near side maria.^[15] Lunar nearside with major maria and craters labeled A global albedo map of the Moon obtained from the Clementine missionThe dark regions are the lunar maria, whereas the lighter regions are the highlands. ... Lunar nearside with major maria and craters labeled A global albedo map of the Moon obtained from the Clementine missionThe dark regions are the lunar maria, whereas the lighter regions are the highlands. ... An astronomer or astrophysicist is a person whose area of interest is astronomy or astrophysics. ... For the cities, see Basalt, Colorado and Basalt, Idaho. ... Tycho crater on Earths moon. ... The Ocean of Storms of the Moon. ... NASAs Lunar Prospector The Lunar Prospector mission was the third selected by NASA for full development and construction as part of the Discovery Program. ... Shield volcano A shield volcano is a large volcano with shallow-sloping side. ... Lunar domes on Mons RÃ¼mker. ...

Terrae

The lighter-colored regions of the Moon are called terrae, or more commonly just highlands, since they are higher than most maria. Several prominent mountain ranges on the near side are found along the periphery of the giant impact basins, many of which have been filled by mare basalt. These are believed to be the surviving remnants of the impact basin's outer rims.^[16] In contrast to the Earth, no major lunar mountains are believed to have formed as a result of tectonic events.^[17] Tycho crater on Earths moon. ...

From images taken by the Clementine mission, it appears that four mountainous regions on the rim of the 73 km-wide Peary crater at the Moon's north pole remain illuminated for the entire lunar day. These peaks of eternal light are possible because of the Moon's extremely small axial tilt to the ecliptic plane. No similar regions of eternal light were found at the south pole, although the rim of Shackleton crater is illuminated for about 80% of the lunar day. Another consequence of the Moon's small axial tilt is regions that remain in permanent shadow at the bottoms of many polar craters.^[18] Clementine was a joint space project between the Ballistic Missile Defense Organization (BMDO, previously the Strategic Defense Initiative Organization, or SDIO) and NASA. The objective of the mission was to test sensors and spacecraft components under extended exposure to the space environment and to make scientific observations of the Moon... Peary is the closest large crater to the lunar north pole. ... Peak of Eternal Light (PEL) describes a point on a body within the solar system which is eternally bathed in sunlight. ... The plane of the Ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... Shackleton is a lunar crater that lies at the south pole of the Moon. ...

Impact craters

Lunar crater Daedalus on the Moon's far side

The Moon's surface shows obvious evidence of having been affected by impact cratering.^[19] Impact craters form when asteroids and comets collide with the lunar surface, and globally about half a million craters with diameters greater than 1 km can be found. Since impact craters accumulate at a nearly constant rate, the number of craters per unit area superposed on a geologic unit can be used to estimate the age of the surface (see crater counting). The lack of an atmosphere, weather and recent geological processes ensures that many of these craters have remained relatively well preserved in comparison to those found on Earth. Download high resolution version (900x880, 293 KB)The largest crater in the picture is Daedalus. ... Download high resolution version (900x880, 293 KB)The largest crater in the picture is Daedalus. ... Daedalus is a prominent crater located near the center of the far side of the Moon. ... Tycho crater on Earths moon. ... This article, which relates to the Moon, is a stub. ...

The largest crater on the Moon, which also has the distinction of being the largest known crater in the Solar System, is the South Pole-Aitken basin. This impact basin is located on the far side, between the South Pole and equator, and is some 2240 km in diameter and 13 km in depth.^[20] Prominent impact basins on the near side include Imbrium, Serenitatis, Crisium, and Nectaris. The South Pole-Aitken basin is an impact crater on Earths Moon. ... Oblique view of Mare Imbrium looking south towards Copernicus crater. ... A map of Mare Serenitatis. ... Mare Crisium Studios is also the name of a company formed to develop the game Stars! Supernova Genesis. ... The Sea of Nectar (Mare Nectaris) is a small lunar mare or sea (a volcanic lava plain noticeably darker than the rest of the moons surface) located between the Sea of Tranquillity (Mare Tranquillatis) and the Sea of Fecundity (Mare Fecunditatis). ...

Regolith

Blanketed atop the Moon's crust is a highly comminuted (broken into ever smaller particles) and "impact gardened" surface layer called regolith. Since the regolith forms by impact processes, the regolith of older surfaces is generally thicker than for younger surfaces. In particular, it has been estimated that the regolith varies in thickness from about 3–5 m in the maria, and by about 10–20 m in the highlands.^[21] Beneath the finely comminuted regolith layer is what is generally referred to as the megaregolith. This layer is much thicker (on the order of tens of kilometres) and comprises highly fractured bedrock.^[22] Look up comminution in Wiktionary, the free dictionary. ... Regolith (Greek: blanket rock) is a layer of loose, heterogeneous material covering solid rock. ...

Presence of water

Main article: Lunar ice

The continuous bombardment of the Moon by comets and meteoroids has most likely added small amounts of water to the lunar surface. If so, sunlight would split much of this water into its constituent elements of hydrogen and oxygen, both of which would ordinarily escape into space over time, because of the Moon's weak gravity. However, because of the slightness of the axial tilt of the Moon's spin axis to the ecliptic plane—only 1.5°—some deep craters near the poles never receive direct light from the Sun and are thus in permanent shadow (see Shackleton crater). Water molecules that ended up in these craters could be stable for long periods of time. The continuous bombardment of the Moon by comets and meteoroids have added some amount of water to the lunar surface. ... Comet Hale-Bopp Comet West For other uses, see Comet (disambiguation). ... â€œMeteorâ€ redirects here. ... Shackleton is a lunar crater that lies at the south pole of the Moon. ...

Clementine has mapped craters at the lunar south pole^[23] that are shadowed in this way, and computer simulations suggest that up to 14,000 km² might be in permanent shadow.^[18] Results from the Clementine mission bistatic radar experiment are consistent with small, frozen pockets of water close to the surface, and data from the Lunar Prospector neutron spectrometer indicate that anomalously high concentrations of hydrogen are present in the upper metre of the regolith near the polar regions.^[24] Estimates for the total quantity of water ice are close to one cubic kilometre. Clementine was a joint space project between the Ballistic Missile Defense Organization (BMDO, previously the Strategic Defense Initiative Organization, or SDIO) and NASA. The objective of the mission was to test sensors and spacecraft components under extended exposure to the space environment and to make scientific observations of the Moon... NASAs Lunar Prospector The Lunar Prospector mission was the third selected by NASA for full development and construction as part of the Discovery Program. ...

Water ice can be mined and then split into its constituent hydrogen and oxygen atoms by means of nuclear generators or electric power stations equipped with solar panels. The presence of usable quantities of water on the Moon is an important factor in rendering lunar habitation cost-effective, since transporting water from Earth would be prohibitively expensive. However, recent observations made with the Arecibo planetary radar suggest that some of the near-polar Clementine radar data that were previously interpreted as being indicative of water ice might instead be a result of rocks ejected from young impact craters.^[25] The question of how much water there is on the Moon has not been resolved. An artists rendering of a lunar base. ... The Arecibo Observatory is located approximately 9 miles south-southwest from Arecibo, Puerto Rico (near the extreme southwestern corner of Arecibo pueblo). ...

Physical characteristics

Internal structure

Main article: Internal structure of the Moon

Schematic illustration of the internal structure of the Moon

The Moon is a differentiated body, being composed of a geochemically distinct crust, mantle, and 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 (see Origin and geologic evolution below). Schematic illustration of the internal structure of the Moon. ... Image File history File links Moon_Schematic_Cross_Section. ... Image File history File links Moon_Schematic_Cross_Section. ... In cosmogony, planetary differentiation is a process by which the denser portions of a planet will sink to the center; while less dense materials rise to the surface. ... Earth cutaway from core to exosphere. ... Earth cutaway from core to exosphere. ... The planetary core consists of the innermost layer(s) of a planet. ... In chemistry, Fractional Crystallization is a method of refining substances based on differences in soluability. ... This article, which relates to the Moon, is a stub. ... The Big Splash redirects here. ... In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ... Lunar Ferroan Anorthosite #60025 (Plagioclase Feldspar). ...

Geochemical mapping from orbit implies that the crust of the Moon is largely anorthositic in composition,^[6] consistent with the magma ocean hypothesis. In terms of elements, the crust is composed primarily of oxygen, silicon, magnesium, iron, calcium, and aluminium. Based on geophysical techniques, its thickness is estimated to be on average about 50 km.^[1] Anorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar (90-100%), and a minimal mafic component (0-10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most commonly present. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Not to be confused with Silicone. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... For other uses, see Iron (disambiguation). ... For other uses, see Calcium (disambiguation). ... Aluminum redirects here. ...

Partial melting within the mantle of the Moon gave rise to the eruption of mare basalts on the lunar surface. Analyses of these basalts indicate that the mantle is composed predominantly of the minerals olivine, orthopyroxene and clinopyroxene, and that the lunar mantle is more iron rich than that of the Earth. Some lunar basalts contain high abundances of titanium (present in the mineral ilmenite), suggesting that the mantle is highly heterogeneous in composition. Moonquakes have been found to occur deep within the mantle of the Moon about 1,000 km below the surface. These occur with monthly periodicities and are related to tidal stresses caused by the eccentric orbit of the Moon about the Earth.^[1] The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... General Name, symbol, number titanium, Ti, 22 Chemical series transition metals Group, period, block 4, 4, d Appearance silvery metallic Standard atomic weight 47. ... Ilmenite is a weakly magnetic iron-black or steel-gray mineral found in metamorphic and igneous rocks. ...

The Moon has a mean density of 3,346.4 kg/m³, making it the second densest moon in the Solar System after Io. Nevertheless, several lines of evidence imply that the core of the Moon is small, with a radius of about 350 km or less.^[1] This corresponds to only about 20% the size of the Moon, in contrast to about 50% as is the case for most other terrestrial bodies. The composition of the lunar core is not well constrained, but most believe that it is composed of metallic iron alloyed with a small amount of sulfur and nickel. Analyses of the Moon's time-variable rotation indicate that the core is at least partly molten.^[26] Atmosphere Surface pressure: trace Composition: 90% sulfur dioxide Io (eye-oe, IPA: , Greek á¿™ÏŽ) is the innermost of the four Galilean moons of Jupiter and, with a diameter of 3,642 kilometers, is the fourth largest moon in the Solar System. ... This article is about the chemical element. ... For other uses, see Nickel (disambiguation). ...

Topography

Main article: Topography of the Moon

Topography of the Moon, referenced to the lunar geoid

The topography of the Moon has been measured by the methods of laser altimetry and stereo image analysis, most recently from data obtained during the Clementine mission. The most visible topographic feature is the giant far side South Pole-Aitken basin, which possesses the lowest elevations of the Moon. The highest elevations are found just to the north-east of this basin, and it has been suggested that this area might represent thick ejecta deposits that were emplaced during an oblique South Pole-Aitken basin impact event. Other large impact basins, such as Imbrium, Serenitatis, Crisium, Smythii, and Orientale, also possess regionally low elevations and elevated rims. Another distinguishing feature of the Moon's shape is that the elevations are on average about 1.9 km higher on the far side than the near side.^[1] Topography of the Moon, referenced to the lunar geoid. ... Image File history File links MoonTopoGeoidUSGS.jpgâ€Ž File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links MoonTopoGeoidUSGS.jpgâ€Ž File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... For discussion of land surfaces themselves, see Terrain. ... Clementine was a joint space project between the Ballistic Missile Defense Organization (BMDO, previously the Strategic Defense Initiative Organization, or SDIO) and NASA. The objective of the mission was to test sensors and spacecraft components under extended exposure to the space environment and to make scientific observations of the Moon... The South Pole-Aitken basin is an impact crater on Earths Moon. ... In volcanology, ejecta consists of particles that came out of a volcanic vent, traveled though the air or under water, and fell back on the ground surface or on the ocean floor. ... Oblique view of Mare Imbrium looking south towards Copernicus crater. ... A map of Mare Serenitatis. ... Mare Crisium Studios is also the name of a company formed to develop the game Stars! Supernova Genesis. ... Mare Smythii (sea of William Henry Smyth) is a lunar mare located along the equator on the easternmost edge of the lunar near side. ... 1967 photograph made by NASAs Lunar Orbiter 4 Like a target ring bulls-eye, the lunar mare Mare Orientale (the eastern sea) is one of the most striking large scale lunar features. ...

Gravity field

Main article: Gravity of the Moon

The gravitational field of the Moon has been determined through tracking of radio signals emitted by orbiting spacecraft. The principle used depends on the Doppler effect, whereby the spacecraft acceleration in the line-of-sight direction can be determined by means of small shifts in frequency of the radio signal, and the distance from the spacecraft to a station on Earth. However, because of the Moon's synchronous rotation it is not possible to track spacecraft much over the limbs of the Moon, and the farside gravity field is thus only poorly characterised.^[27] Radial gravitational anomaly at the surface of the Moon. ... A source of waves moving to the left. ... Due to synchronous rotation of their moon, the inhabitants of the central body will never be able to see its green side. ...

Radial gravitational anomaly at the surface of the Moon

The major characteristic of the Moon's gravitational field is the presence of mascons, which are large positive gravitational anomalies associated with some of the giant impact basins.^[28] These anomalies greatly influence the orbit of spacecraft about the Moon, and an accurate gravitational model is necessary in the planning of both manned and unmanned missions. The mascons are in part due to the presence of dense mare basaltic lava flows that fill some of the impact basins. However, lava flows by themselves can not explain the entirety of the gravitational signature, and uplift of the crust-mantle interface is required as well. Based on Lunar Prospector gravitational models, it has been suggested that some mascons exist that do not show evidence for mare basaltic volcanism.^[29] The huge expanse of mare basaltic volcanism associated with Oceanus Procellarum does not possess a positive gravitational anomaly. Image File history File links MoonLP150Q_grav_150_j2. ... Image File history File links MoonLP150Q_grav_150_j2. ... A mass concentration or mascon is a region of a planet or moons crust that contains a large amount of material that is denser than average for that body. ... Tycho crater on Earths moon. ... NASAs Lunar Prospector The Lunar Prospector mission was the third selected by NASA for full development and construction as part of the Discovery Program. ... The Ocean of Storms of the Moon. ...

Magnetic field

Main article: Magnetic field of the Moon

Total magnetic field strength at the surface of the Moon as derived from the Lunar Prospector electron reflectometer experiment

The Moon has an external magnetic field of the order of one to a hundred nanotesla—more than 100 times smaller than the Earth's, which is 30-60 microtesla. Other major differences are that the Moon does not currently have a dipolar magnetic field (as would be generated by a geodynamo in its core), and the magnetizations that are present are almost entirely crustal in origin.^[30] One hypothesis holds that the crustal magnetizations were acquired early in lunar history when a geodynamo was still operating. The small size of the lunar core, however, is a potential obstacle to this theory. Alternatively, it is possible that on an airless body such as the Moon, transient magnetic fields could be generated during large impact events. In support of this, it has been noted that the largest crustal magnetizations appear to be located near the antipodes of the giant impact basins. It has been proposed that such a phenomenon could result from the free expansion of an impact generated plasma cloud around the Moon in the presence of an ambient magnetic field.^[31] Total magnetic field strength at the surface of the Moon as derived from the Lunar Prospector electron reflectometer experiment. ... Image File history File links Moon_LP_ER_magnetic_field. ... Image File history File links Moon_LP_ER_magnetic_field. ... NASAs Lunar Prospector The Lunar Prospector mission was the third selected by NASA for full development and construction as part of the Discovery Program. ... Magnetic field lines shown by iron filings Magnetostatics Electrodynamics Electrical Network Tensors in Relativity This box: In physics, the magnetic field is a field that permeates space and which exerts a magnetic force on moving electric charges and magnetic dipoles. ... SI unit. ... The magnetosphere shields the surface of the Earth from the charged particles of the solar wind. ... The Earths magnetic field, which is approximately a dipole. ... The cause of Earths magnetic field (the surface magnetic field) is not known for certain, but is possibly explained by dynamo theory. ... This map shows the antipodes of each point on the Earths surface â€“ the points where the blue and pink overlap are land antipodes. ...

Atmosphere

Main article: Atmosphere of the Moon

The Moon has an atmosphere so thin as to be almost negligible, with a total atmospheric mass of less than 10⁴ kg.^[32] One source of its atmosphere is outgassing—the release of gases such as radon that originate by radioactive decay processes within the crust and mantle. Another important source is generated through the process of sputtering, which involves the bombardment of micrometeorites, solar wind ions, electrons, and sunlight.^[6] Gases that are released by sputtering can either reimplant into the regolith as a result of the Moon's gravity, or can be lost to space either by solar radiation pressure or by being swept away by the solar wind magnetic field if they are ionised. The elements sodium (Na) and potassium (K) have been detected using earth-based spectroscopic methods, whereas the element radon–222 (²²²Ra) and polonium-210 (²¹⁰Po) have been inferred from data obtained from the Lunar Prospector alpha particle spectrometer.^[33] Argon–40 (⁴⁰Ar), helium-4 (⁴He), oxygen (O₂) and/or methane (CH₄), nitrogen (N₂) and/or carbon monoxide (CO), and carbon dioxide (CO₂) were detected by in-situ detectors placed by the Apollo astronauts.^[34] The atmosphere of the Moon is very tenuous and insignificant in comparison to that of the Earth. ... Outgassing (sometimes called Offgassing, particularly when in reference to indoor air quality) is the slow release of a gas that was trapped, frozen, absorbed or adsorbed in some material. ... For other uses, see Radon (disambiguation). ... Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ... Sputtering is a physical vapor deposition, PVD process whereby atoms in a solid target material are ejected into the gas phase due to bombardment of the material by energetic ions. ... Regolith (Greek: blanket rock) is a layer of loose, heterogeneous material covering solid rock. ... For sodium in the diet, see Edible salt. ... General Name, symbol, number potassium, K, 19 Chemical series alkali metals Group, period, block 1, 4, s Appearance silvery white Standard atomic weight 39. ... For other uses, see Radon (disambiguation). ... Polonium-210 is the most readily available isotope of Polonium. ... NASAs Lunar Prospector The Lunar Prospector mission was the third selected by NASA for full development and construction as part of the Discovery Program. ... An alpha particle is deflected by a magnetic field Alpha radiation consists of helium-4 nuclei and is readily stopped by a sheet of paper. ... General Name, symbol, number argon, Ar, 18 Chemical series noble gases Group, period, block 18, 3, p Appearance colorless Standard atomic weight 39. ... Helium-4 is a non-radioactive and light isotope of helium. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Methane is a chemical compound with the molecular formula . ... General Name, symbol, number nitrogen, N, 7 Chemical series nonmetals Group, period, block 15, 2, p Appearance colorless gas Standard atomic weight 14. ... Carbon monoxide, with the chemical formula CO, is a colorless, odorless, and tasteless gas. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ...

Origin and geologic evolution

Formation

Several mechanisms have been suggested for the Moon's formation. Early speculation proposed that the Moon broke off from the Earth's crust because of centrifugal forces, leaving a basin (presumed to be the Pacific Ocean) behind as a scar.^[35] This fission concept, however, requires too great an initial spin of the Earth. Furthermore, it would have resulted in an orbit following Earth's equatorial plane, which is not the case. Others speculated that the Moon formed elsewhere and was captured into Earth's orbit.^[36] However, the conditions required for this capture mechanism to work (such as an extended atmosphere of the Earth for dissipating energy) are improbable. The coformation hypothesis posits that the Earth and the Moon formed together at the same time and place from the primordial accretion disk. In this hypothesis, the Moon formed from material surrounding the proto-Earth, similar to the formation of the planets around the Sun. Some suggest that this hypothesis fails to adequately explain the depletion of metallic iron in the Moon. A major deficiency with all of these hypotheses is that they cannot easily account for the high angular momentum of the Earth–Moon system.^[37] Centrifugal force (from Latin centrum centre and fugere to flee) is a term which may refer to two different forces which are related to rotation. ... An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... This gyroscope remains upright while spinning due to its angular momentum. ...

Today, the giant impact hypothesis for forming the Earth–Moon system is widely accepted by the scientific community. In this hypothesis, the impact of a Mars-sized body (Theia) on the proto-Earth is postulated to have put enough material into circumterrestrial orbit to form the Moon.^[8] Given that planetary bodies are believed to have formed by the hierarchical accretion of smaller bodies to larger ones, giant impact events such as this are thought to have affected most planets. Computer simulations modelling this impact are consistent with measurements of the angular momentum of the Earth–Moon system, as well as the small size of the lunar core.^[38] Unresolved questions regarding this theory have to do with determining the relative sizes of the proto-Earth and impactor, and with determining how much material from the proto-Earth and impactor ended up in the Moon. The formation of the Moon is believed to have occurred 4.527 ± 0.010 billion years ago, about 30–50 million years after the origin of the solar system.^[39] The Big Splash redirects here. ... The Big Splash redirects here. ...

Lunar magma ocean

As a result of the large amount of energy liberated during both the giant impact event and the subsequent reaccretion of material in Earth orbit, it is commonly believed that a large portion of the Moon was once initially molten. The molten outer portion of the Moon at this time is referred to as a magma ocean, and estimates for its depth range from about 500 km to the entire radius of the Moon.^[13] This article, which relates to the Moon, is a stub. ...

As the magma ocean cooled, it fractionally crystallised and differentiated, giving rise to a geochemically distinct crust and mantle. The mantle is inferred to have formed largely by the precipitation and sinking of the minerals olivine, clinopyroxene, and orthopyroxene. After about three-quarters of magma ocean crystallisation was complete, the mineral anorthite is inferred to have precipitated and floated to the surface because of its low density, forming the crust.^[13] In chemistry, Fractional Crystallization is a method of refining substances based on differences in soluability. ... In cosmogony, planetary differentiation is a process by which the denser portions of a planet will sink to the center; while less dense materials rise to the surface. ... The mineral olivine (also called chrysolite and, when gem-quality, peridot) is a magnesium iron silicate with the formula (Mg,Fe)2SiO4. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Figure 1:Mantle-peridotite xenolith with green peridot olivine and black pyroxene crystals from San Carlos Indian Reservation, Gila Co. ... Anorthite is one of the plagioclase feldspars, an important group of minerals abundant in the Earths crust. ...

The final liquids to crystallise from the magma ocean would have been initially sandwiched between the crust and mantle, and would have contained a high abundance of incompatible and heat-producing elements. This geochemical component is referred to by the acronym KREEP, for potassium (K), rare earth elements (REE), and phosphorus (P), and appears to be concentrated within the Procellarum KREEP Terrane, which is a small geologic province that encompasses most of Oceanus Procellarum and Mare Imbrium on the near side of the Moon.^[1] KREEP stands for potassium (atomic symbol K), rare earth elements (REE), and phosphorus (P). ... General Name, symbol, number potassium, K, 19 Chemical series alkali metals Group, period, block 1, 4, s Appearance silvery white Standard atomic weight 39. ... de;Metalle der Seltenen Erden Categories: Stub | Chemical element groups ... General Name, symbol, number phosphorus, P, 15 Chemical series nonmetals Group, period, block 15, 3, p Appearance waxy white/ red/ black/ colorless Standard atomic weight 30. ... This article, which relates to the Moon, is a stub. ... The Ocean of Storms of the Moon. ... Oblique view of Mare Imbrium looking south towards Copernicus crater. ...

Geologic evolution

See also: Geology of the Moon

A large portion of the Moon's post–magma-ocean geologic evolution was dominated by impact cratering. The lunar geologic timescale is largely divided in time on the basis of prominent basin-forming impact events, such as Nectaris, Imbrium, and Orientale. These impact structures are characterised by multiple rings of uplifted material, and are typically hundreds to thousands of kilometres in diameter. Each multi-ring basin is associated with a broad apron of ejecta deposits that forms a regional stratigraphic horizon. While only a few multi-ring basins have been definitively dated, they are useful for assigning relative ages on the basis of stratigraphic grounds. The continuous effects of impact cratering are responsible for forming the regolith. Exploring Shorty crater during the Apollo 17 mission to the Moon. ... The lunar geologic timescale (or perhaps more properly the selenologic timescale) divides the history of Earths Moon into six generally recognized geologic periods: Copernician Period : 1100 MY to present Eratosthenian Period : 3200 MY to 1100 MY Upper Imbrian Epoch : 3800 MY to 3200 MY Lower Imbrian Epoch : 3850 MY... The Nectarian Period of the lunar geologic timescale runs from 3920 million years ago to 3850 million years ago. ... In the Lunar geologic timescale, the Lower Imbrian epoch occurred between 3850 million years ago to about 3800 million years ago. ... 1967 photograph made by NASAs Lunar Orbiter 4 Like a target ring bulls-eye, the lunar mare Mare Orientale (the eastern sea) is one of the most striking large scale lunar features. ... Stratigraphy, a branch of geology, studies rock layers and layering (stratification). ... Regolith (Greek: blanket rock) is a layer of loose, heterogeneous material covering solid rock. ...

The other major geologic process that affected the Moon's surface was mare volcanism. The enhancement of heat-producing elements within the Procellarum KREEP Terrane is thought to have caused the underlying mantle to heat up, and eventually, to partially melt. A portion of these magmas rose to the surface and erupted, accounting for the high concentration of mare basalts on the near side of the Moon.^[13] Most of the Moon's mare basalts erupted during the Imbrian period in this geologic province 3.0–3.5 billion years ago. Nevertheless, some dated samples are as old as 4.2 billion years,^[40] and the youngest eruptions, based on the method of crater counting, are believed to have occurred only 1.2 billion years ago.^[41] Lunar nearside with major maria and craters labeled A global albedo map of the Moon obtained from the Clementine missionThe dark regions are the lunar maria, whereas the lighter regions are the highlands. ... This article, which relates to the Moon, is a stub. ... Lunar nearside with major maria and craters labeled A global albedo map of the Moon obtained from the Clementine missionThe dark regions are the lunar maria, whereas the lighter regions are the highlands. ... This article, which relates to the Moon, is a stub. ...

There has been controversy over whether features on the Moon's surface undergo changes over time. Some observers have claimed that craters either appeared or disappeared, or that other forms of transient phenomena had occurred. Today, many of these claims are thought to be illusory, resulting from observation under different lighting conditions, poor astronomical seeing, or the inadequacy of earlier drawings. Nevertheless, it is known that the phenomenon of outgassing does occasionally occur, and these events could be responsible for a minor percentage of the reported lunar transient phenomena.

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