Misplaced Pages

#284715

90-610: Lunarian may refer to: Supposed inhabitants of the Moon in fiction A fictional race of the Final Fantasy IV video game A fictional race of the anime/manga One Piece A fictional race from Touhou Project franchise Lunarian (album) , a 2021 Donovan album See also [ edit ] Luna (disambiguation) Lunar (disambiguation) Lunatic (disambiguation) Moon people (disambiguation) Topics referred to by

180-519: A lunar eclipse , always illuminated by 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

270-414: A synestia , a mass of vaporized rock and metal which forms a biconcave disc extending beyond the lunar orbit. The synestia will eventually shrink and cool to accrete the satellite and reform the impacted planet. This hypothesis states that the Moon was captured by the Earth. This model was popular until the 1980s, and some points in its favor are the Moon's size, orbit, and tidal locking. One problem

360-462: A collision between a proto-Earth about 90% of the diameter of present Earth, and another body the diameter of Mars (half of the terrestrial diameter and a tenth of its mass). The latter has sometimes been referred to as Theia , the name of the mother of Selene , the Moon goddess in Greek mythology . This size ratio is needed in order for the resulting system to have sufficient angular momentum to match

450-425: 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

540-434: 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

630-503: 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

720-718: 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

810-528: 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

900-480: A notable group of Russian astronomers in 2013 and later, in 2017, by planetary researchers at Weizmann Institute of Science in Rehovot, Israel. In general terms, the main idea of the model suggests that the Moon was formed as a result of a violent rain of large asteroids (1–100 km) that repeatedly hammered the fledgling Earth over millions of years. Such a series of smaller impacts, which were probably more common in

990-425: A nuclear explosion caused by the centrifugal force of an earlier, spinning proto-Earth. The centrifugal force would have concentrated heavy elements such as thorium and uranium on the equatorial plane and at the boundary between the Earth's outer core and mantle . If the concentrations of these radioactive elements were high enough, this could have led to a nuclear chain reaction that became supercritical, causing

SECTION 10

#1732855918285

1080-404: A nuclear explosion ejecting the Moon into orbit. This natural nuclear fission reactor has been observed on Earth at a much smaller scale. The fission hypothesis can adequately explain the similarities and differences in the elemental and isotopic compositions of the Earth and the Moon. In 2011, it was theorized that a second moon existed 4.5 billion years ago, and later had an impact with

1170-428: 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

1260-555: A result of tectonic events. Origin of the Moon The standard giant-impact hypothesis suggests that a Mars-sized body called Theia impacted the proto-Earth, creating a large debris ring around Earth, which then accreted to form the Moon. This collision also resulted in the 23.5° tilted axis of the Earth, thus causing the seasons . The Moon's oxygen isotopic ratios seem to be essentially identical to Earth's. Oxygen isotopic ratios, which may be measured very precisely, yield

1350-454: 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

1440-467: 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

1530-502: 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

1620-439: 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,

1710-416: A unique and distinct signature for each Solar System body. If Theia had been a separate protoplanet , it probably would have had a different oxygen isotopic signature than proto-Earth, as would the ejected mixed material. Also, the Moon's titanium isotope ratio ( Ti / Ti ) appears so close to the Earth's (within 4 parts per million) that little if any of the colliding body's mass could have been part of

1800-489: 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

1890-521: 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

SECTION 20

#1732855918285

1980-449: Is different from Wikidata All article disambiguation pages All disambiguation pages 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 the Moon have synchronized the Moon's orbital period ( lunar month ) with its rotation period ( lunar day ) at 29.5 Earth days, causing

2070-561: 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

2160-440: 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

2250-477: 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

2340-571: 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

2430-476: 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

2520-474: Is understanding the capture mechanism. A close encounter of two planetary bodies typically results in either collision or altered trajectories. For this hypothesis to work, there might have been a large atmosphere around the primitive Earth, which would slow the movement of the Moon by aerobraking before it could escape. The hypothesis may also explain the irregular satellite orbits of Jupiter and Saturn . However, this hypothesis does not adequately explain

2610-645: 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 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

2700-529: 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 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

2790-452: 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

Lunarian - Misplaced Pages Continue

2880-512: 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

2970-522: The Earth). A more radical alternative hypothesis, published in 1997 by russian scientist Vladimir Anisichkin: "The Moon could have formed as a result of explosion of the Protoearth" proposes that the Moon may have been formed from the nuclear explosion of actinides located on the solid inner core of the Earth. Dutch scientists Rob de Meijer and Wim van Westrenen suggested in 2010 that the Moon may have formed from

3060-429: 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

3150-463: 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

3240-530: 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

3330-438: The Earth. A 2012 study on the depletion of zinc isotopes on the Moon found evidence for volatile depletion consistent with the giant-impact origin for Earth and the Moon. In 2013, a study was released that indicated that water in lunar magma is indistinguishable from that in carbonaceous chondrites and nearly the same as that of Earth in isotopic composition . Although the giant-impact hypothesis explains many aspects of

3420-536: The Earth–Moon system, there are still a few unresolved problems, such as the Moon's volatile elements not being as depleted as expected from such an energetic impact. Another issue is lunar and Earth isotope comparisons. In 2001, the most precise measurement yet of the isotopic signatures of Moon rocks was published. Surprisingly, the Apollo lunar samples carried an isotopic signature identical to Earth rocks, but different from other Solar System bodies. Because most of

3510-499: 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

3600-455: The Moon as cause for continental drift . It was proposed that the Pacific Ocean represented the scar of this event. Today it is known that the oceanic crust that makes up this ocean basin is relatively young, about 200 million years old or less, whereas the Moon is much older. The Moon does not consist of oceanic crust but of mantle material, which originated inside the proto-Earth in

3690-458: 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

Lunarian - Misplaced Pages Continue

3780-489: 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

3870-466: 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

3960-424: The Moon forming far from Earth's orbit. To help resolve these problems, a theory published in 2012 posits that two bodies—each five times the size of Mars—collided, then recollided, forming a large disc of mixed debris that eventually formed Earth and the Moon. The Moon is traditionally thought to have coalesced from the debris ejected by a giant impact onto the early Earth. However, such models struggle to explain

4050-455: 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

4140-554: 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

4230-433: The Moon's subsurface may be richer in metals, like iron and titanium, more than scientists had believed. In July 2020 scientists report that the Moon formed 4.425 ±0.025 bya, about 85 million years later than thought, and that it hosted an ocean of magma for substantially longer than previously thought (for ~200 million years). On 1 November 2023, scientists reported that, according to computer simulations, remnants of

4320-403: 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

4410-518: The Moon, as a part of the accretion process in the formation of the Moon. One hypothesis, presented only as a possibility, was that the Earth captured the Moon from Venus. Uranium–lead dating of Apollo 14 zircon fragments shows the age of the Moon to be about 4.51 billion years. A team of researchers of the Miniature Radio Frequency (Mini-RF) instrument on NASA's Lunar Reconnaissance Orbiter (LRO) spacecraft concluded that

4500-404: The Moon. "One of the challenges to the longstanding theory of the collision, is that a Mars-sized impacting body, whose composition probably would have differed substantially from that of Earth, probably would have left Earth and the moon with different chemical compositions, which they are not." —NASA Some theories have been stated that presume the proto-Earth had no large moons early in

4590-476: The Precambrian. The hypothesis of accretion suggests that the Earth and the Moon formed together as a double system from the primordial accretion disk of the Solar System or even a black hole . The problem with this hypothesis is that it does not explain the angular momentum of the Earth-Moon system or why the Moon has a relatively small iron core compared to the Earth (25% of its radius compared to 50% for

SECTION 50

#1732855918285

4680-402: The Roche limit can reliably and predictably survive, by being partially stripped and then torqued onto wider, stable orbits. Furthermore, the outer layers of these directly formed satellites are molten over cooler interiors and are composed of around 60% proto-Earth material. This could alleviate the tension between the Moon's Earth-like isotopic composition and the different signature expected for

4770-484: 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,

4860-461: 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

4950-426: The Sun completely during 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,

5040-413: 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

5130-433: 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

5220-420: The current orbital configuration. Such an impact would have put enough material into orbit around Earth to have eventually accumulated to form the Moon. Computer simulations show a need for a glancing blow, which causes a portion of the collider to form a long arm of material that then shears off. The asymmetrical shape of the Earth following the collision then causes this material to settle into an orbit around

5310-480: The debris from a giant impact between Earth and a hypothesized Mars-sized body called Theia . The lunar surface 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

5400-447: 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

5490-514: 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

SECTION 60

#1732855918285

5580-415: The early Solar System, could blast enough rocky Earth debris into orbit to form a protosatellite disk which later forms into a small moonlet. As repeated impacts created more balls of debris, the moonlets could merge over time into one large moon. In 2018, researchers at Harvard and UC Davis developed computer models demonstrating that one possible outcome of a planetary collision is that it creates

5670-468: 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

5760-405: The essentially identical oxygen isotope ratios of the two bodies. This is the now discredited hypothesis that an ancient, rapidly spinning Earth expelled a piece of its mass. This was first proposed by George Darwin (son of the famous biologist Charles Darwin ) in 1879 and retained some popularity until Apollo. The Austrian geologist Otto Ampferer in 1925 also suggested the emerging of

5850-422: 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

5940-1182: 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

6030-504: 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

6120-427: 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

6210-413: The formation of the Solar System, 4.425 billion years ago, Earth being basically rock and lava. Theia , an early protoplanet the size of Mars, hit Earth in such a way that it ejected a considerable amount of material away from Earth. Some proportion of these ejecta escaped into space, but the rest consolidated into a single spherical body in orbit about Earth, creating the Moon. The hypothesis requires

6300-407: The impactor. Immediate formation opens up new options for the Moon's early orbit and evolution, including the possibility of a highly tilted orbit to explain the lunar inclination, and offers a simpler, single-stage scenario for the origin of the Moon. In 2004, Russian astrophysicist Nikolai Gorkavyi proposed a novel model titled the multiple large asteroid impacts model, which found support from

6390-419: 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

6480-431: The lunar samples is also explained in part by the energy of the collision. The energy liberated during the reaccretion of material in orbit around Earth would have been sufficient to melt a large portion of the Moon, leading to the generation of a magma ocean . The newly formed Moon orbited at about one-tenth the distance that it does today, and spiraled outward because of tidal friction transferring angular momentum from

6570-421: 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

6660-492: The main mass. The energy involved in this collision is impressive: possibly trillions of tonnes of material would have been vaporized and melted. In parts of the Earth, the temperature would have risen to 10,000 °C (18,000 °F). The Moon's relatively small iron core (compared to other rocky planets and moons in the Solar System) is explained by Theia's core mostly merging into that of Earth. The lack of volatiles in

6750-516: 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

6840-406: 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

6930-487: The material that went into orbit to form the Moon was thought to come from Theia, this observation was unexpected. In 2007, researchers from Caltech showed that the likelihood of Theia having an identical isotopic signature as the Earth is very small (less than 1 percent chance). Published in 2012, an analysis of titanium isotopes in Apollo lunar samples showed that the Moon has the same composition as Earth, which conflicts with

7020-524: 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,

7110-440: 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

7200-432: 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

7290-583: 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

7380-436: 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

7470-471: 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,

7560-427: The rotations of both bodies to the Moon's orbital motion. Along the way, the Moon's rotation became tidally locked to Earth, so that one side of the Moon continually faces toward Earth. Also, the Moon would have collided with and incorporated any small preexisting satellites of Earth, which would have shared the Earth's composition, including isotopic abundances. The geology of the Moon has since been more independent of

7650-413: The same term [REDACTED] This disambiguation page lists articles associated with the title Lunarian . If an internal link led you here, you may wish to change the link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Lunarian&oldid=1120035422 " Category : Disambiguation pages Hidden categories: Short description

7740-446: The similar isotopic compositions of Earth and lunar rocks at the same time as the system's angular momentum, and the details of potential impact scenarios are hotly debated. Above a high resolution threshold for simulations, a study published in 2022 finds that giant impacts can immediately place a satellite with similar mass and iron content to the Moon into orbit far outside Earth's Roche limit . Even satellites that initially pass within

7830-455: 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

7920-446: 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

8010-424: 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

8100-401: 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

#284715