| Lunar meteorite (Lunaite) | |
|---|---|
| — Clan — | |
 Lunar meteorite Allan Hills 81005 | |
| Type | Achondrite |
| Subgroups |
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| Parent body | Moon |
| Total known specimens | 306 |
| Alternative names | Lunaite |
A lunar meteorite is a meteorite that is known to have originated on the Moon. A meteorite hitting the Moon is normally classified as a transient lunar phenomenon.
In January 1982, John Schutt, leading an expedition in Antarctica for the ANSMET program, found a meteorite that he recognized to be unusual. Shortly thereafter, the meteorite now called Allan Hills 81005 was sent to Washington, DC, where Smithsonian Institution geochemist Brian Mason recognized that the sample was unlike any other known meteorite and resembled some rocks brought back from the Moon by the Apollo program. [2] Several years later, Japanese scientists[ who? ] recognized that they had also collected a lunar meteorite, Yamato 791197, during the 1979 field season in Antarctica. As of July 2019 [update] , 371 lunar meteorites have been discovered, [3] perhaps representing more than 30 separate meteorite falls (i.e., many of the stones are "paired" fragments of the same meteoroid). [4] The total mass is more than 1,090 kilograms (2,400 lb). [4] All lunar meteorites have been found in deserts; most have been found in Antarctica, northern Africa, and the Sultanate of Oman. None have yet been found in North America, South America, or Europe. [5]
Lunar origin is established by comparing the mineralogy, the chemical composition, and the isotopic composition between meteorites and samples from the Moon collected by Apollo missions.
Most lunar meteorites are launched from the Moon by impacts making lunar craters of a few kilometers in diameter or less. [6] No source crater of lunar meteorites has been positively identified, although there is speculation that the highly anomalous lunar meteorite Sayh al Uhaymir 169 derives from the Lalande impact crater on the lunar nearside. [7] [8]
Cosmic-ray exposure history established with noble-gas measurements have shown that all lunar meteorites were ejected from the Moon in the past 20 million years. Most left the Moon in the past 100,000 years. After leaving the Moon, most lunar meteoroids go into orbit around Earth and eventually succumb to Earth's gravity. Some meteoroids ejected from the Moon get launched into orbits around the Sun. These meteoroids remain in space longer, but eventually intersect the Earth's orbit and land. [9]
All six of the Apollo missions on which samples were collected landed in the central nearside of the Moon, an area that has subsequently been shown to be geochemically anomalous by the Lunar Prospector mission. In contrast, the numerous lunar meteorites are random samples of the Moon and consequently provide a more representative sampling of the lunar surface than the Apollo samples. Half the lunar meteorites, for example, likely sample material from the farside of the Moon.
At the time the first meteorite from the Moon was discovered in 1982, there was speculation that some other unusual meteorites that had been found originated from Mars. The positive identification of lunar meteorites on Earth supported the hypothesis that meteoroid impacts on Mars could eject rocks from that planet. There are also speculations about the possibility of finding "Earth meteorites" on the surface of the Moon. [10] This would be very interesting because in this case stones from Earth older than 3.9 billion years, which are destroyed on Earth by various geological processes, may have survived on the Moon. Thus some scientists propose new missions to the Moon to search for ancient rocks from Earth.
About one in every thousand newly discovered meteorites is a lunar meteorite, [11] whereas the vast majority of meteorites are from the asteroid belt. In the early 19th century most scientists believed that all meteorites falling towards the Earth were from the Moon. Although today supported only by a minority of researchers, there are also theories that tektites are from the Moon and should therefore also be regarded as lunar meteorites. However, most scientists regard such theories as outdated. [ citation needed ]
Lunar meteorites collected in Africa and Oman are, for all practical purposes, the only source of Moon rocks available for private ownership. This is because all rocks collected during the Apollo Moon-landing program are property of the United States government or of other nations to which the U.S. conveyed them as gifts. Similarly, all lunar meteorites collected by the U.S. and Japanese Antarctic programs are, by treaty, held by those governments for research and education purposes only. Although there is no U.S. law specifically against the ownership of Apollo Moon rocks, none has ever been (or is likely to ever be) given or sold by the U.S. government to private citizens. Even in the cases of plaques containing genuine Apollo Moon rocks given in 2004 to astronauts and Walter Cronkite, NASA retained ownership of the rocks themselves. [12] Most of the moonrocks collected by the Luna 16 probe are also unavailable for private ownership, although three tiny samples were sold at auction for $442,500 in 1993. [13] [14] [15]
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than the surrounding terrain. Lunar impact craters range from microscopic craters on lunar rocks returned by the Apollo program and small, simple, bowl-shaped depressions in the lunar regolith to large, complex, multi-ringed impact basins. Meteor Crater is a well-known example of a small impact crater on Earth.
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical interactions with the atmospheric gases cause it to heat up and radiate energy. It then becomes a meteor and forms a fireball, also known as a shooting star; astronomers call the brightest examples "bolides". Once it settles on the larger body's surface, the meteor becomes a meteorite. Meteorites vary greatly in size. For geologists, a bolide is a meteorite large enough to create an impact crater.
A Martian meteorite is a rock that formed on Mars, was ejected from the planet by an impact event, and traversed interplanetary space before landing on Earth as a meteorite. As of September 2020, 277 meteorites had been classified as Martian, less than half a percent of the 72,000 meteorites that have been classified. The largest complete, uncut Martian meteorite, Taoudenni 002, was recovered in Mali in early 2021. It weighs 14.5 kilograms and is on display at the Maine Mineral & Gem Museum.
KREEP, an acronym built from the letters K, REE and P, is a geochemical component of some lunar impact breccia and basaltic rocks. Its most significant feature is somewhat enhanced concentration of a majority of so-called "incompatible" elements and the heat-producing elements, namely radioactive uranium, thorium, and potassium.
The far side of the Moon is the lunar hemisphere that always faces away from Earth, opposite to the near side, because of synchronous rotation in the Moon's orbit. Compared to the near side, the far side's terrain is rugged, with a multitude of impact craters and relatively few flat and dark lunar maria ("seas"), giving it an appearance closer to other barren places in the Solar System such as Mercury and Callisto. It has one of the largest craters in the Solar System, the South Pole–Aitken basin. The hemisphere has sometimes been called the "dark side of the Moon", where "dark" means "unknown" instead of "lacking sunlight" – each side of the Moon experiences two weeks of sunlight while the opposite side experiences two weeks of night.
The geology of the Moon is quite different from that of Earth. The Moon lacks a true atmosphere, and the absence of free oxygen and water eliminates erosion due to weather. Instead, the surface is eroded much more slowly through the bombardment of the lunar surface by micrometeorites. It does not have any known form of plate tectonics, it has a lower gravity, and because of its small size, it cooled faster. In addition to impacts, the geomorphology of the lunar surface has been shaped by volcanism, which is now thought to have ended less than 50 million years ago. The Moon is a differentiated body, with a crust, mantle, and core.
Moon rock or lunar rock is rock originating from Earth's Moon. This includes lunar material collected during the course of human exploration of the Moon, and rock that has been ejected naturally from the Moon's surface and landed on Earth as meteorites.
Yamato 791197, official abbreviation Y-791197, is a meteorite that was found in Antarctica on November 20, 1979.
Lunar soil is the fine fraction of lunar regolith found on the surface of the Moon and contributes to the Moon's tenuous atmosphere. Lunar soil differs in its origin and properties significantly from terrestrial soil.
Crater counting is a method for estimating the age of a planet's surface based upon the assumptions that when a piece of planetary surface is new, then it has no impact craters; impact craters accumulate after that at a rate that is assumed known. Consequently, counting how many craters of various sizes there are in a given area allows determining how long they have accumulated and, consequently, how long ago the surface has formed. The method has been calibrated using the ages obtained by radiometric dating of samples returned from the Moon by the Luna and Apollo missions. It has been used to estimate the age of areas on Mars and other planets that were covered by lava flows, on the Moon of areas covered by giant mares, and how long ago areas on the icy moons of Jupiter and Saturn flooded with new ice.
David Stewart McKay was chief scientist for astrobiology at the Johnson Space Center. During the Apollo program, McKay provided geology training to the first men to walk on the Moon in the late 1960s. McKay was the first author of a scientific paper postulating past life on Mars on the basis of evidence in Martian meteorite ALH 84001, which had been found in Antarctica. This paper has become one of the most heavily cited papers in planetary science. The NASA Astrobiology Institute was founded partially as a result of community interest in this paper and related topics. He was a native of Titusville, Pennsylvania.
Extraterrestrial material refers to natural objects now on Earth that originated in outer space. Such materials include cosmic dust and meteorites, as well as samples brought to Earth by sample return missions from the Moon, asteroids and comets, as well as solar wind particles.
The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized astronomical event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypothesis, during this interval, a disproportionately large number of asteroids and comets collided into the terrestrial planets and their natural satellites of the inner Solar System, including Mercury, Venus, Earth and Mars. These came from both post-accretion and planetary instability-driven populations of impactors. Although it used to be widely accepted, it remained difficult to provide an overwhelming amount of evidence for the hypothesis. However, recent re-appraisal of the cosmo-chemical constraints indicates that there was likely no late spike in the bombardment rate.
Nakhlites are a group of Martian meteorites, named after the first one, Nakhla meteorite.
Planetary science is the scientific study of planets, celestial bodies and planetary systems and the processes of their formation. It studies objects ranging in size from micrometeoroids to gas giants, aiming to determine their composition, dynamics, formation, interrelations and history. It is a strongly interdisciplinary field, which originally grew from astronomy and Earth science, and now incorporates many disciplines, including planetary geology, cosmochemistry, atmospheric science, physics, oceanography, hydrology, theoretical planetary science, glaciology, and exoplanetology. Allied disciplines include space physics, when concerned with the effects of the Sun on the bodies of the Solar System, and astrobiology.
Allan Hills A81005 or ALH A81005 was the first lunar meteorite found on Earth. It was found in 1982 in the Allan Hills at the end of the Transantarctic Mountains, during a meteorite gathering expedition (ANSMET).
Ursula Bailey Marvin was an American planetary geologist and author who worked for the Smithsonian Astrophysical Observatory.
Elephant Moraine 79001, also known as EETA 79001, is a Martian meteorite. It was found in Elephant Moraine, in the Antarctic during the 1979–1980 collecting season.
Lunar Sample 14321, better known as "Big Bertha", is a lunar sample containing an embedded Earth-origin meteorite collected on the 1971 Apollo 14 mission. It was found in the Fra Mauro region of the Moon. Big Bertha is the first discovered meteorite from Earth, and the embedded meteorite portion is the oldest known Earth rock. At 8.998 kg (19.84 lb), this breccia rock is the third largest Moon sample returned during the Apollo program, behind Big Muley and Great Scott.
Katherine Helen Joy is a Professor in Earth Sciences at the University of Manchester. Joy has studied lunar samples from the Apollo program as part of her research on meteorites and lunar science.
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