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84-611: Montes Rook is a ring-shaped mountain range that lies along the western limb of the Moon , crossing over to the far side . It completely encircles the Mare Orientale , and forms part of a massive impact basin feature. This range in turn is encircled by the larger Montes Cordillera , which is separated from the Montes Rook by a rugged, ring-shaped plain. The Montes Rook is actually a double-ring formation, sometimes divided into

168-419: A chemical differentiate between the crust and the mantle, with occasional eruptions to the surface. Earth 's Moon probably formed out of material splashed into orbit by the impact of a large body into the early Earth. Differentiation on Earth had probably already separated many lighter materials toward the surface, so that the impact removed a disproportionate amount of silicate material from Earth, and left

252-425: A decisive role on local surface temperatures . Parts of many craters, particularly the bottoms of many polar craters, are permanently shadowed, these " craters of eternal darkness " have extremely low temperatures. The Lunar Reconnaissance Orbiter measured the lowest summer temperatures in craters at the southern pole at 35 K (−238 °C; −397 °F) and just 26 K (−247 °C; −413 °F) close to

336-434: A few kilometers wide), shallower, and more irregularly shaped than impact craters. They also lack the upturned rims characteristic of impact craters. Several geologic provinces containing shield volcanoes and volcanic domes are found within the near side maria. There are also some regions of pyroclastic deposits , scoria cones and non-basaltic domes made of particularly high viscosity lava. Almost all maria are on

420-503: A global dipolar magnetic field and only has crustal magnetization likely acquired early in its history when a dynamo was still operating. Early in its history, 4 billion years ago, its magnetic field strength was likely close to that of Earth today. This early dynamo field apparently expired by about one billion years ago, after the lunar core had crystallized. Theoretically, some of the remnant magnetization may originate from transient magnetic fields generated during large impacts through

504-504: A higher density. A light mineral such as plagioclase would rise. They may take on dome-shaped forms called diapirs when doing so. On Earth, salt domes are salt diapirs in the crust which rise through surrounding rock. Diapirs of molten low-density silicate rocks such as granite are abundant in the Earth's upper crust. The hydrated, low-density serpentinite formed by alteration of mantle material at subduction zones can also rise to

588-718: A hospitable environment for future astronauts, protecting them from extreme temperatures, solar radiation, and micrometeorites. However, challenges include accessibility and risks of avalanches and cave-ins. This discovery offers potential for future lunar bases or emergency shelters. The main features visible from Earth by the naked eye are dark and relatively featureless lunar plains called maria (singular mare ; Latin for "seas", as they were once believed to be filled with water) are vast solidified pools of ancient basaltic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water. The majority of these lava deposits erupted or flowed into

672-533: A landscape featuring craters of all ages. The Moon was volcanically active until 1.2 billion years ago, which laid down the prominent lunar maria . Most of the mare basalts erupted during the Imbrian period , 3.3–3.7 billion years ago, though some are as young as 1.2 billion years and some as old as 4.2 billion years. There are differing explanations for the eruption of mare basalts, particularly their uneven occurrence which mainly appear on

756-474: A metal to successfully travel through the fracture toughness of the surrounding material. The size of the metal intruding and the viscosity of the surrounding material determines the rate of the sinking process. The direct delivery of impacts occurs when an impactor of similar proportions strikes the target planetary body.  During the impact, there is an exchange of pre-existing cores containing metallic material. The planetary differentiation event

840-479: A radius of about 500 kilometres (310 mi). This structure is thought to have developed through the fractional crystallization of a global magma ocean shortly after the Moon's formation 4.5 billion years ago. Crystallization of this magma ocean would have created a mafic mantle from the precipitation and sinking of the minerals olivine , clinopyroxene , and orthopyroxene ; after about three-quarters of

924-694: A result of tectonic events. Planetary differentiation High- density materials tend to sink through lighter materials. This tendency is affected by the relative structural strengths, but such strength is reduced at temperatures where both materials are plastic or molten. Iron , the most common element that is likely to form a very dense molten metal phase, tends to congregate towards planetary interiors. With it, many siderophile elements (i.e. materials that readily alloy with iron) also travel downward. However, not all heavy elements make this transition as some chalcophilic heavy elements bind into low-density silicate and oxide compounds, which differentiate in

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1008-458: 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. On November 1, 2023, scientists reported that, according to computer simulations, remnants of Theia could still be present inside

1092-475: A study of Ina , a tiny depression in Lacus Felicitatis , found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old. Moonquakes and releases of gas indicate continued lunar activity. Evidence of recent lunar volcanism has been identified at 70 irregular mare patches , some less than 50 million years old. This raises

1176-502: A texture resembling snow and a scent resembling spent gunpowder . The regolith of older surfaces is generally thicker than for younger surfaces: it varies in thickness from 10–15 m (33–49 ft) in the highlands and 4–5 m (13–16 ft) in the maria. Beneath the finely comminuted regolith layer is the megaregolith , a layer of highly fractured bedrock many kilometers thick. These extreme conditions are considered to make it unlikely for spacecraft to harbor bacterial spores at

1260-498: A timeline for accretion. Heating due to radioactivity, impacts, and gravitational pressure melted parts of protoplanets as they grew toward being planets . In melted zones, it was possible for denser materials to sink towards the center, while lighter materials rose to the surface. The compositions of some meteorites ( achondrites ) show that differentiation also took place in some asteroids (e.g. Vesta ), that are parental bodies for meteoroids. The short-lived radioactive isotope Al

1344-400: A total solar eclipse . From Earth about 59% of the lunar surface is visible over time due to cyclical shifts in perspective ( libration ), making parts of the far side of the Moon visible. The Moon has been an important source of inspiration and knowledge for humans, having been crucial to cosmography , mythology, religion , art, time keeping , natural science , and spaceflight . In 1959,

1428-439: A trans-Atlantic flight, 200 times more than on Earth's surface. For further comparison radiation on a flight to Mars is about 1.84 millisieverts per day and on Mars on average 0.64 millisieverts per day, with some locations on Mars possibly having levels as low as 0.342 millisieverts per day. The Moon's axial tilt with respect to the ecliptic is only 1.5427°, much less than the 23.44° of Earth. Because of this small tilt,

1512-489: Is around 3 × 10   atm (0.3  nPa ); it varies with the lunar day. Its sources include outgassing and sputtering , a product of the bombardment of lunar soil by solar wind ions. Elements that have been detected include sodium and potassium , produced by sputtering (also found in the atmospheres of Mercury and Io ); helium-4 and neon from the solar wind; and argon-40 , radon-222 , and polonium-210 , outgassed after their creation by radioactive decay within

1596-581: Is asymmetric, being more dense near the boundary between the Moon's dayside and nightside. Ionizing radiation from cosmic rays , the Sun and the resulting neutron radiation produce radiation levels on average of 1.369 millisieverts per day during lunar daytime , which is about 2.6 times more than on the International Space Station with 0.53 millisieverts per day at about 400 km above Earth in orbit, 5–10 times more than during

1680-401: Is covered in lunar dust and marked by mountains , impact craters , their ejecta , ray-like streaks , rilles and, mostly on the near side of the Moon, by dark maria ("seas"), which are plains of cooled lava . These maria were formed when molten lava flowed into ancient impact basins. The Moon is, except when passing through Earth's shadow during a lunar eclipse , always illuminated by

1764-561: Is estimated from about 500 km (300 miles) to 1,737 km (1,079 miles). While the giant-impact theory explains many lines of evidence, some questions are still unresolved, most of which involve the Moon's composition. Models that have the Moon acquiring a significant amount of the proto-earth are more difficult to reconcile with geochemical data for the isotopes of zirconium, oxygen, silicon, and other elements. A study published in 2022, using high-resolution simulations (up to 10 particles), found that giant impacts can immediately place

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1848-440: Is on average about 1.9 km (1.2 mi) higher than that of the near side. The discovery of fault scarp cliffs suggest that the Moon has shrunk by about 90 metres (300 ft) within the past billion years. Similar shrinkage features exist on Mercury . Mare Frigoris, a basin near the north pole long assumed to be geologically dead, has cracked and shifted. Since the Moon does not have tectonic plates, its tectonic activity

1932-502: Is said to have most likely happened after the accretion process of either the asteroid or a planetary body. Terrestrial bodies and iron meteorites consist of Fe-Ni alloys.  The Earth's core is primarily composed Fe-Ni alloys. Based on the studies of short lived radionuclides , the results suggest that core formation process occurred during an early stage of the solar system. Siderophile elements such as, sulfur , nickel , and cobalt can dissolve in molten iron; these elements help

2016-477: Is simply Moon , with a capital M. The noun moon is derived from Old English mōna , which (like all its Germanic cognates) stems from Proto-Germanic *mēnōn , which in turn comes from Proto-Indo-European *mēnsis 'month' (from earlier *mēnōt , genitive *mēneses ) which may be related to the verb 'measure' (of time). Occasionally, the name Luna / ˈ l uː n ə / is used in scientific writing and especially in science fiction to distinguish

2100-574: Is slow and cracks develop as it loses heat. Scientists have confirmed the presence of a cave on the Moon near the Sea of Tranquillity , not far from the 1969 Apollo 11 landing site. The cave, identified as an entry point to a collapsed lava tube, is roughly 45 meters wide and up to 80 m long. This discovery marks the first confirmed entry point to a lunar cave. The analysis was based on photos taken in 2010 by NASA's Lunar Reconnaissance Orbiter . The cave's stable temperature of around 17 °C could provide

2184-476: Is the lowest point on the surface of the Moon. The highest elevations of the Moon's surface are located directly to the northeast, which might have been thickened by the oblique formation impact of the South Pole–Aitken basin. Other large impact basins such as Imbrium , Serenitatis , Crisium , Smythii , and Orientale possess regionally low elevations and elevated rims. The far side of the lunar surface

2268-400: Is thus depleted of those elements. Study of trace elements in igneous rocks thus gives us information about what source melted by how much to produce a magma, and which minerals have been lost from the melt. When material is unevenly heated, lighter material migrates toward hotter zones and heavier material migrates towards colder areas, which is known as thermophoresis , thermomigration, or

2352-527: The Soret effect . This process can affect differentiation in magma chambers . A deeper understanding of this process can be drawn back to a study done on the Hawaiian lava lakes. The drilling of these lakes led to the discovery of crystals formed within magma fronts. The magma containing concentrations of these large crystals or phenocrysts demonstrated differentiation through the chemical melt of crystals. On

2436-452: The Earth and the material accreted and formed the Moon just beyond the Earth's Roche limit of ~ 2.56  R 🜨 . Giant impacts are thought to have been common in the early Solar System. Computer simulations of giant impacts have produced results that are consistent with the mass of the lunar core and the angular momentum of the Earth–Moon system. These simulations show that most of

2520-406: The Earth is produced by partial melting of a source rock, ultimately in the mantle . The melt extracts a large portion of the "incompatible elements" from its source that are not stable in the major minerals. When magma rises above a certain depth the dissolved minerals start to crystallize at particular pressures and temperatures. The resulting solids remove various elements from the melt, and melt

2604-520: The Earth's moon from others, while in poetry "Luna" has been used to denote personification of the Moon. Cynthia / ˈ s ɪ n θ i ə / is another poetic name, though rare, for the Moon personified as a goddess, while Selene / s ə ˈ l iː n iː / (literally 'Moon') is the Greek goddess of the Moon. The English adjective pertaining to the Moon is lunar , derived from the Latin word for

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2688-581: The Earth, and its diameter is 3,474 km (2,159 mi), roughly one-quarter of Earth's (about as wide as the United States from coast to coast ). Within the Solar System , it is the largest and most massive satellite in relation to its parent planet , the fifth largest and most massive moon overall, and larger and more massive than all known dwarf planets . Its surface gravity is about one sixth of Earth's, about half of that of Mars , and

2772-429: The Earth, due to gravitational anomalies from impact basins. Its shape is more elongated than current tidal forces can account for. This 'fossil bulge' indicates that the Moon solidified when it orbited at half its current distance to the Earth, and that it is now too cold for its shape to restore hydrostatic equilibrium at its current orbital distance. The Moon is by size and mass the fifth largest natural satellite of

2856-469: The Earth-Moon system might be explained by the post-impact mixing of the vaporized material that formed the two, although this is debated. The impact would have released enough energy to liquefy both the ejecta and the Earth's crust, forming a magma ocean. The liquefied ejecta could have then re-accreted into the Earth–Moon system. The newly formed Moon would have had its own magma ocean ; its depth

2940-530: The Earth. The newly formed Moon settled into a much closer Earth orbit than it has today. Each body therefore appeared much larger in the sky of the other, eclipses were more frequent, and tidal effects were stronger. Due to tidal acceleration , the Moon's orbit around Earth has become significantly larger, with a longer period. Following formation, the Moon has cooled and most of its atmosphere has been stripped. The lunar surface has since been shaped by large impact events and many small ones, forming

3024-504: The Moon approximately 10 minutes, taking 5 minutes to rise, and 5 minutes to fall. On average, 120 kilograms of dust are present above the Moon, rising up to 100 kilometers above the surface. Dust counts made by LADEE 's Lunar Dust EXperiment (LDEX) found particle counts peaked during the Geminid , Quadrantid , Northern Taurid , and Omicron Centaurid meteor showers , when the Earth, and Moon pass through comet debris. The lunar dust cloud

3108-458: The Moon derived from the impactor, rather than the proto-Earth. However, models from 2007 and later suggest a larger fraction of the Moon derived from the proto-Earth. Other bodies of the inner Solar System such as Mars and Vesta have, according to meteorites from them, very different oxygen and tungsten isotopic compositions compared to Earth. However, Earth and the Moon have nearly identical isotopic compositions. The isotopic equalization of

3192-495: The Moon for longer than just one lunar orbit. The topography of the Moon has been measured with laser altimetry and stereo image analysis . Its most extensive topographic feature is the giant far-side South Pole–Aitken basin , some 2,240 km (1,390 mi) in diameter, the largest crater on the Moon and the second-largest confirmed impact crater in the Solar System . At 13 km (8.1 mi) deep, its floor

3276-466: The Moon formed around 50 million years after the origin of the Solar System . Historically, several formation mechanisms have been proposed, but none satisfactorily explains the features of the Earth–Moon system. A fission of the Moon from Earth's crust through centrifugal force would require too great an initial rotation rate of Earth. Gravitational capture of a pre-formed Moon depends on an unfeasibly extended atmosphere of Earth to dissipate

3360-455: The Moon have synchronized the Moon's orbital period ( lunar month ) with its rotation period ( lunar day ) 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 . In geophysical terms , the Moon is a planetary-mass object or satellite planet . Its mass is 1.2% that of

3444-455: The Moon is a crescent\decrescent, [REDACTED] \ [REDACTED] , for example in M ☾ 'lunar mass' (also M L ). The lunar geological periods are named after their characteristic features, from most impact craters outside the dark mare , to the mare and later craters, and finally the young, still bright and therefore readily visible craters with ray systems like Copernicus or Tycho . Isotope dating of lunar samples suggests

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3528-508: The Moon's solar illumination varies much less with season than on Earth and it allows for the existence of some peaks of eternal light at the Moon's north pole , at the rim of the crater Peary . The surface is exposed to drastic temperature differences ranging from 120 °C to −171 °C depending on the solar irradiance . Because of the lack of atmosphere, temperatures of different areas vary particularly upon whether they are in sunlight or shadow, making topographical details play

3612-403: The Moon, lūna . Selenian / s ə l iː n i ə n / is an adjective used to describe the Moon as a world, rather than as a celestial object, but its use is rare. It is derived from σελήνη selēnē , the Greek word for the Moon, and its cognate selenic was originally a rare synonym but now nearly always refers to the chemical element selenium . The element name selenium and

3696-483: The Moon, a distinctive basaltic material has been found that is high in "incompatible elements" such as potassium , rare earth elements , and phosphorus and is often referred to by the abbreviation KREEP . It is also high in uranium and thorium . These elements are excluded from the major minerals of the lunar crust which crystallized out from its primeval magma ocean , and the KREEP basalt may have been trapped as

3780-494: The Solar System relative to their primary planets. The Moon's diameter is about 3,500 km, more than a quarter of Earth's, with the face of the Moon comparable to the width of either Mainland Australia , Europe or the Contiguous United States (which excludes Alaska , etc.). The whole surface area of the Moon is about 38 million square kilometers, comparable to North and South America combined,

3864-467: The Solar System, categorizable as one of its planetary-mass moons , making it a satellite planet under the geophysical definitions of the term . It is smaller than Mercury and considerably larger than the largest dwarf planet of the Solar System, Pluto . While the minor-planet moon Charon of the Pluto-Charon system is larger relative to Pluto, the Moon is the largest natural satellite of

3948-410: The Sun, but from Earth the visible illumination shifts during its orbit, producing the lunar phases . The Moon is the brightest celestial object in Earth's night sky . This is mainly due to its large angular diameter , while the reflectance of the lunar surface is comparable to that of asphalt . The apparent size is nearly the same as that of the Sun, allowing it to cover the Sun completely during

4032-425: The Sun. Rocks, and the elements comprising them, were stripped of their early atmospheres, but themselves remained, to accumulate into protoplanets . Protoplanets had higher concentrations of radioactive elements early in their history, the quantity of which has reduced over time due to radioactive decay . For example, the hafnium-tungsten system demonstrates the decay of two unstable isotopes and possibly forms

4116-413: The combined American landmass having an area (excluding all islands) of 37.7 million square kilometers. The Moon's mass is 1/81 of Earth's, being the second densest among the planetary moons, and having the second highest surface gravity , after Io , at 0.1654  g and an escape velocity of 2.38 km/s ( 8 600  km/h; 5 300  mph) . The Moon is a differentiated body that

4200-433: The crust and mantle. The absence of such neutral species (atoms or molecules) as oxygen , nitrogen , carbon , hydrogen and magnesium , which are present in the regolith , is not understood. Water vapor has been detected by Chandrayaan-1 and found to vary with latitude, with a maximum at ~60–70 degrees; it is possibly generated from the sublimation of water ice in the regolith. These gases either return into

4284-447: The dense mare basaltic lava flows that fill those basins. The anomalies greatly influence the orbit of spacecraft about the Moon. There are some puzzles: lava flows by themselves cannot explain all of the gravitational signature, and some mascons exist that are not linked to mare volcanism. The Moon has an external magnetic field of less than 0.2 nanoteslas , or less than one hundred thousandth that of Earth . The Moon does not have

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4368-514: The depressions associated with impact basins , though the Moon's largest expanse of basalt flooding, Oceanus Procellarum , does not correspond to an obvious impact basin. Different episodes of lava flows in maria can often be recognized by variations in surface albedo and distinct flow margins. As the maria formed, cooling and contraction of the basaltic lava created wrinkle ridges in some areas. These low, sinuous ridges can extend for hundreds of kilometers and often outline buried structures within

4452-401: The differentiation of iron alloys. The first stages of accretion set up the groundwork for core formation. First, terrestrial planetary bodies enter a neighboring planet's orbit. Next, a collision would take place and the terrestrial body could either grow or shrink. However, in most cases, accretion requires multiple collisions of similar sized objects to have a major difference in

4536-468: The energy of the passing Moon. A co-formation of Earth and the Moon together in the primordial accretion disk does not explain the depletion of metals in the Moon. None of these hypotheses can account for the high angular momentum of the Earth–Moon system. The prevailing theory is that the Earth–Moon system formed after a giant impact of a Mars -sized body (named Theia ) with the proto-Earth . The oblique impact blasted material into orbit about

4620-422: The expansion of plasma clouds. These clouds are generated during large impacts in an ambient magnetic field. This is supported by the location of the largest crustal magnetizations situated near the antipodes of the giant impact basins. The Moon has an atmosphere so tenuous as to be nearly vacuum , with a total mass of less than 10 tonnes (9.8 long tons; 11 short tons). The surface pressure of this small mass

4704-1182: The exposed ones. Conversely, mare lava has obscured many impact melt sheets and pools. Impact melts are formed when intense shock pressures from collisions vaporize and melt zones around the impact site. Where still exposed, impact melt can be distinguished from mare lava by its distribution, albedo, and texture. Sinuous rilles , found in and around maria, are likely extinct lava channels or collapsed lava tubes . They typically originate from volcanic vents , meandering and sometimes branching as they progress. The largest examples, such as Schroter's Valley and Rima Hadley , are significantly longer, wider, and deeper than terrestrial lava channels, sometimes featuring bends and sharp turns that again, are uncommon on Earth. Mare volcanism has altered impact craters in various ways, including filling them to varying degrees, and raising and fracturing their floors from uplift of mare material beneath their interiors. Examples of such craters include Taruntius and Gassendi . Some craters, such as Hyginus , are of wholly volcanic origin, forming as calderas or collapse pits . Such craters are relatively rare, and tend to be smaller (typically

4788-510: The first human-made objects to leave Earth and reach another body arrived at the Moon, with the flyby of the Soviet Union 's Luna 1 and the intentional impact of Luna 2 . In 1966, the Moon became the first extraterrestrial body with a soft landing by Luna 9 and a orbital insertion by Luna 10 were achieved . On July 20, 1969, humans for the first time landed on the Moon and any extraterrestrial body, at Mare Tranquillitatis with

4872-427: The flood lavas that erupted onto the surface from partial melting in the mantle confirm the mafic mantle composition, which is more iron-rich than that of Earth. The crust is on average about 50 kilometres (31 mi) thick. The Moon is the second-densest satellite in the Solar System, after Io . However, the inner core of the Moon is small, with a radius of about 350 kilometres (220 mi) or less, around 20% of

4956-471: The lander Eagle of the United States ' Apollo 11 mission. Five more crews were sent between then and 1972, each with two men landing on the surface. The longest stay was 75 hours by the Apollo 17 crew. Since then, exploration of the Moon has continued robotically, and crewed missions are being planned to return beginning in the late 2020s. The usual English proper name for Earth's natural satellite

5040-421: The magma ocean had crystallized, lower-density plagioclase minerals could form and float into a crust atop. The final liquids to crystallize would have been initially sandwiched between the crust and mantle, with a high abundance of incompatible and heat-producing elements. Consistent with this perspective, geochemical mapping made from orbit suggests a crust of mostly anorthosite . The Moon rock samples of

5124-468: The majority of the dense metal behind. The Moon's density is substantially less than that of Earth, due to its lack of a large iron core. On Earth , physical and chemical differentiation processes led to a crustal density of approximately 2700 kg/m compared to the 3400 kg/m density of the compositionally different mantle just below, and the average density of the planet as a whole is 5515 kg/m . Core formation utilizes several mechanisms in order to control

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5208-521: The mantle could be responsible for prolonged activities on the far side in the Orientale basin. The lighter-colored regions of the Moon are called terrae , or more commonly highlands , because they are higher than most maria. They have been radiometrically dated to having formed 4.4 billion years ago, and may represent plagioclase cumulates of the lunar magma ocean. In contrast to Earth, no major lunar mountains are believed to have formed as

5292-406: The mare. Another result of maria formation is the creation of concentric depressions along the edges, known as arcuate rilles . These features occur as the mare basalts sink inward under their own weight, causing the edges to fracture and separate. In addition to the visible maria, the Moon has mare deposits covered by ejecta from impacts. Called cryptomares, these hidden mares are likely older than

5376-531: The movement of metals into the interior of a planetary body. Examples include percolation , diking , diapirism, and the direct delivery of impacts are mechanisms involved in this process. The metal to silicate density difference causes percolation or the movement of a metal downward. Diking is a process in which a new rock formation forms within a fracture of a pre-existing rock body. For example, if minerals are cold and brittle, transport can occur through fluid cracks. A sufficient amount of pressure must be met for

5460-524: The near side of the Moon, and cover 31% of the surface of the near side compared with 2% of the far side. This is likely due to a concentration of heat-producing elements under the crust on the near side, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt. Most of the Moon's mare basalts erupted during the Imbrian period , 3.3–3.7 billion years ago, though some being as young as 1.2 billion years and as old as 4.2 billion years. In 2006,

5544-440: The near-side. Causes of the distribution of the lunar highlands on the far side are also not well understood. Topological measurements show the near side crust is thinner than the far side. One possible scenario then is that large impacts on the near side may have made it easier for lava to flow onto the surface. The Moon is a very slightly scalene ellipsoid due to tidal stretching, with its long axis displaced 30° from facing

5628-479: The northeast, Shuleykin to the south, and Fryxell in the west. Out of sight from the Earth , even during favorable librations , are the craters Lowell to the northwest, and Golitsyn to the west-southwest. Moon 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

5712-472: The northeastern part of the range has been named Lacus Veris . The selenographic coordinates of this range are 20.6° S, 82.5° W, and the diameter is 791 km. The range was named after the English astronomer Lawrence Rooke . Due to its location this range is viewed from the edge from Earth , and not much detail can be seen. However a partial view of the range can be obtained by projecting an image of

5796-462: The opposite direction. The main compositionally differentiated zones in the solid Earth are the very dense iron-rich metallic core , the less dense magnesium-silicate -rich mantle and the relatively thin, light crust composed mainly of silicates of aluminium , sodium , calcium and potassium . Even lighter still are the watery liquid hydrosphere and the gaseous, nitrogen-rich atmosphere . Lighter materials tend to rise through material with

5880-417: The outer Rook and the inner Rook, having respective diameters of 620 km and 480 km. The material excavated to form Montes Rook came from a mafic layer below an anorthositic zone. Many of the peaks in this ring are composed of pure anorthosite . Sections of the gap between these sub-ranges contain long valleys filled in places with basaltic lava , forming small lunar maria . One such section along

5964-432: The possibility of a much warmer lunar mantle than previously believed, at least on the near side where the deep crust is substantially warmer because of the greater concentration of radioactive elements. Evidence has been found for 2–10 million years old basaltic volcanism within the crater Lowell, inside the Orientale basin. Some combination of an initially hotter mantle and local enrichment of heat-producing elements in

6048-587: The prefix seleno- (as in selenography , the study of the physical features of the Moon) come from this Greek word. Artemis , the Greek goddess of the wilderness and the hunt, came to also be identified as the goddess of the Moon ( Selene ) and was sometimes called Cynthia , after her birthplace on Mount Cynthus . Her Roman equivalent is Diana . The names Luna, Cynthia, and Selene are reflected in technical terms for lunar orbits such as apolune , pericynthion and selenocentric . The astronomical symbol for

6132-436: The radius of the Moon. Its composition is not well understood, but is probably metallic iron alloyed with a small amount of sulfur and nickel; analyzes of the Moon's time-variable rotation suggest that it is at least partly molten. The pressure at the lunar core is estimated to be 5 GPa (49,000 atm). On average the Moon's surface gravity is 1.62  m/s ( 0.1654  g ; 5.318  ft/s ), about half of

6216-440: The range acquired from the Earth onto the surface of a white globe. This is how William K. Hartmann and Gerard Kuiper discovered the ring shape of Montes Rook in the early 1960s. Several named craters are embedded within the Montes Rook. Near the southwest outer edge are the craters Nicholson and Pettit . Kopff lies along the eastern inner edge, and Maunder on the northern inner side. Smaller craters include Lallemand to

6300-417: The rare element uranium is very dense as a pure element, it is chemically more compatible as a trace element in the Earth's light, silicate -rich crust than in the dense metallic core. When the Sun ignited in the solar nebula , hydrogen , helium and other volatile materials were evaporated in the region around it. The solar wind and radiation pressure forced these low-density materials away from

6384-471: The regolith because of the Moon's gravity or are lost to space, either through solar radiation pressure or, if they are ionized, by being swept away by the solar wind's magnetic field. Studies of Moon magma samples retrieved by the Apollo missions demonstrate that the Moon had once possessed a relatively thick atmosphere for a period of 70 million years between 3 and 4 billion years ago. This atmosphere, sourced from gases ejected from lunar volcanic eruptions,

6468-410: The second highest among all Solar System moons, after Jupiter 's moon Io . The body of the Moon is differentiated and terrestrial , with no significant hydrosphere , atmosphere , or magnetic field . It formed 4.51 billion years ago, not long after Earth's formation , out of the debris from a giant impact between Earth and a hypothesized Mars-sized body called Theia . The lunar surface

6552-409: The surface as diapirs. Other materials do likewise: a low-temperature, near-surface example is provided by mud volcanoes . Although bulk materials differentiate outward or inward according to their density, the elements that are chemically bound in them fractionate according to their chemical affinities, "carried along" by more abundant materials with which they are associated. For instance, although

6636-460: The surface gravity of Mars and about a sixth of Earth's. The Moon's gravitational field is not uniform. The details of the gravitational field have been measured through tracking the Doppler shift of radio signals emitted by orbiting spacecraft. The main lunar gravity features are mascons , large positive gravitational anomalies associated with some of the giant impact basins, partly caused by

6720-427: The surface. Another external heat source is tidal heating . On Earth , a large piece of molten iron is sufficiently denser than continental crust material to force its way down through the crust to the mantle . In the outer Solar System, a similar process may take place but with lighter materials: they may be hydrocarbons such as methane , water as liquid or ice, or frozen carbon dioxide . Magma in

6804-446: The winter solstice in the north polar crater Hermite . This is the coldest temperature in the Solar System ever measured by a spacecraft, colder even than the surface of Pluto . Blanketed on top of the Moon's crust is a highly comminuted (broken into ever smaller particles) and impact gardened mostly gray surface layer called regolith , formed by impact processes. The finer regolith, the lunar soil of silicon dioxide glass, has

6888-424: Was initially in hydrostatic equilibrium but has since departed from this condition. It has a geochemically distinct crust , mantle , and core . The Moon has a solid iron-rich inner core with a radius possibly as small as 240 kilometres (150 mi) and a fluid outer core primarily made of liquid iron with a radius of roughly 300 kilometres (190 mi). Around the core is a partially molten boundary layer with

6972-435: Was probably the main source of heat. When protoplanets accrete more material, the energy of impact causes local heating. In addition to this temporary heating, the gravitational force in a sufficiently large body creates pressures and temperatures which are sufficient to melt some of the materials. This allows chemical reactions and density differences to mix and separate materials, and soft materials to spread out over

7056-401: Was twice the thickness of that of present-day Mars . The ancient lunar atmosphere was eventually stripped away by solar winds and dissipated into space. A permanent Moon dust cloud exists around the Moon, generated by small particles from comets. Estimates are 5 tons of comet particles strike the Moon's surface every 24 hours, resulting in the ejection of dust particles. The dust stays above

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