A meteorite is a natural object originating in outer space Outer space is the void that exists beyond any celestial body including the Earth. It is not completely empty (i.e. a perfect vacuum), but contains a low density of particles, predominantly hydrogen plasma, as well as electromagnetic radiation, magnetic fields, and neutrinos. Theoretically, it also contains dark matter and dark energy that survives impact with the Earth's surface. Meteorites can be big or small. Most meteorites derive from small astronomical objects Astronomical objects are significant naturally occurring physical entities, associations or structures which current science has demonstrated to exist in outer space. The term astronomical object is sometimes used interchangeably with astronomical body. Typically an astronomical body refers to a single, cohesive structure that is bound together by called meteoroids A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteor reaches the ground and survives impact, then it is called a meteorite. Many meteors appearing seconds or minutes apart are, but they are also sometimes produced by impacts of asteroids Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are smaller than planets but larger than meteoroids. The term "asteroid" has historically been applied primarily to minor planets of the inner Solar System, as the outer Solar System. When it enters the atmosphere, impact pressure causes the body to heat up and emit light, thus forming a fireball A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteor reaches the ground and survives impact, then it is called a meteorite. Many meteors appearing seconds or minutes apart are, also known as a meteor A meteoroid is a sand- to boulder-sized particle of debris in the Solar System. The visible path of a meteoroid that enters Earth's atmosphere is called a meteor, or colloquially a shooting star or falling star. If a meteor reaches the ground and survives impact, then it is called a meteorite. Many meteors appearing seconds or minutes apart are or shooting/falling star. The term bolide refers to either an extraterrestrial body that collides with the Earth, or to an exceptionally bright, fireball-like meteor regardless of whether it ultimately impacts the surface.

More generally, a meteorite on the surface of any celestial body is a natural object that has come from elsewhere in space. Meteorites have been found on the Moon The Moon is Earth's only natural satellite[nb 4] and is the fifth largest satellite in the Solar System. It is the largest natural satellite in the Solar System relative to the size of its planet, a quarter the diameter of Earth and 1/81 its mass, and is the second densest satellite after Io. It is in synchronous rotation with Earth, always[1][2] and Mars Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact.[3]

Meteorites that are recovered after being observed as they transited the atmosphere or impacted the Earth are called falls. All other meteorites are known as finds. As of February 2010, there are approximately 1,086 witnessed falls Meteorite falls are those meteorites that were witnessed by people or automated devices as they moved through the atmosphere or hit the Earth, and were subsequently collected. As of April 2010, there are about 1,087 documented falls that are listed in widely used databases, most of which have specimens in modern collections having specimens in the world's collections. In contrast, there are over 38,660 well-documented meteorite finds.[4]

Meteorites have traditionally been divided into three broad categories: stony meteorites are rocks, mainly composed of silicate minerals The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group. Silicate minerals all contain silicon and oxygen; iron meteorites Iron meteorites consist overwhelmingly of nickel-iron alloys. The metal taken from these meteorites is known as meteoric iron and was one of the earliest sources of usable iron available to man are largely composed of metallic iron-nickel; and, stony-iron meteorites contain large amounts of both metallic and rocky material. Modern classification schemes divide meteorites into groups according to their structure, chemical and isotopic composition and mineralogy. See meteorites classification.

Contents

Naming

Meteorites are always named for the place where they were found,[5] usually a nearby town or geographic feature. In cases where many meteorites were found in one place, the name may be followed by a number or letter (e.g., Allan Hills 84001 or Dimmitt (b)). Some meteorites have informal nicknames: the Sylacauga meteorite is sometimes called the "Hodges meteorite" after Ann Hodges, the woman who was struck by it; the Canyon Diablo meteorite, which formed Meteor Crater Meteor Crater is a meteorite impact crater located approximately 43 miles east of Flagstaff, near Winslow in the northern Arizona desert of the United States. Because the US Department of the Interior Division of Names commonly recognizes names of natural features derived from the nearest post office, the feature acquired the name of "Meteor has dozens of these aliases. However, the single, official name designated by the Meteoritical Society is used by scientists, catalogers, and most collectors.

Fall phenomena

See also: atmospheric entry Meteorite which fell in Wisconsin The word Wisconsin has its origins in the name given to the Wisconsin River by one of the Algonquian speaking American Indian groups living in the region at the time of European contact. French explorer Jacques Marquette was the first European to reach the Wisconsin River and record its name, arriving in 1673 and calling the river Meskousing in in 1868 (Full image).

Most meteoroids disintegrate when entering Earth's atmosphere. However, an estimated 500 meteorites ranging in size from marbles Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or dolomite. It is commonly used for sculpture and as a building material to basketballs Basketball is a team sport in which two teams of five players try to score points by throwing or "shooting" a ball through the top of a basketball hoop while following a set of rules. Basketball is one of the most popular and widely viewed sports in the world or larger do reach the surface each year; only 5 or 6 of these are typically recovered and made known to scientists. Few meteorites are large enough to create large impact craters In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body. In most common usage, the term is used for the approximately circular depression in the surface of a planet, moon or other solid body in the Solar System, formed by the. Instead, they typically arrive at the surface at their terminal velocity In fluid dynamics an object is moving at its terminal velocity if its speed is constant due to the restraining force exerted by the air, water or other fluid through which it is moving and, at most, create a small pit. Even so, falling meteorites have reportedly caused damage to property, livestock and people.

Campo del Cielo iron meteorite with natural hole

Large meteoroids may strike the ground with a significant fraction of their cosmic velocity, leaving behind a hypervelocity The term hypervelocity usually refers to a very high velocity, approximately over 3,000 meters per second . In particular, it refers to velocities so high that the strength of materials upon impact is very small compared to inertial stresses. Thus, even metals behave like fluids under hypervelocity impact. Extreme hypervelocity results in impact crater. The kind of crater will depend on the size, composition, degree of fragmentation, and incoming angle of the impactor. The force of such collisions has the potential to cause widespread destruction.[6][7] The most frequent hypervelocity cratering events on the Earth are caused by iron meteoroids, which are most easily able to transit the atmosphere intact. Examples of craters caused by iron meteoroids include Barringer Meteor Crater, Odessa Meteor Crater, Wabar craters The Wabar craters are meteorite impact craters found by accident by an explorer searching for the legendary city of Ubar in Arabia, and Wolfe Creek crater; iron meteorites are found in association with all of these craters. In contrast, even relatively large stony or icy bodies like small comets A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma , and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei are themselves loose collections of ice, dust, and small rocky particles, ranging from a few or asteroids Asteroids, sometimes called minor planets or planetoids, are small Solar System bodies in orbit around the Sun, especially in the inner Solar System; they are smaller than planets but larger than meteoroids. The term "asteroid" has historically been applied primarily to minor planets of the inner Solar System, as the outer Solar System, up to millions of tons, are disrupted in the atmosphere, and do not make impact craters.[8] Although such disruption events are uncommon, they can cause a considerable concussion to occur; the famed Tunguska event The Tunguska Event, or Tunguska explosion, was a powerful explosion that occurred near the Podkamennaya Tunguska River in what is now Krasnoyarsk Krai of Russia, at 0 hours 13 minutes 35 seconds Greenwich Mean Time (around 7:14 a.m. local time) on June 30, 1908 (June 17 in the Julian calendar, in use locally at the time) probably resulted from such an incident. Very large stony objects, hundreds of meters in diameter or more, weighing tens of millions of tons The Ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of weight, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term or more, can reach the surface and cause large craters, but are very rare. Such events are generally so energetic that the impactor is completely destroyed, leaving no meteorites. (The very first example of a stony meteorite found in association with a large impact crater, the Morokweng crater The Morokweng crater is an impact crater buried beneath the Kalahari Desert near the town of Morokweng in the Northwest Province of South Africa, close to the border with Botswana in South Africa, was reported in May 2006.[9])

Several phenomena are well-documented during witnessed meteorite falls too small to produce hypervelocity craters.[10] The fireball that occurs as the meteoroid passes through the atmosphere can appear to be very bright, rivaling the sun in intensity, although most are far dimmer and may not even be noticed during daytime. Various colors have been reported, including yellow, green and red. Flashes and bursts of light can occur as the object breaks up. Explosions, detonations, and rumblings are often heard during meteorite falls, which can be caused by sonic booms The term sonic boom is commonly used to refer to the shocks caused by the supersonic flight of an aircraft. Sonic booms generate enormous amounts of sound energy, sounding much like an explosion. Thunder is a type of natural sonic boom, created by the rapid heating and expansion of air in a lightning discharge as well as shock waves A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium (solid, liquid, gas or plasma) or in some cases in the absence of a material medium, through a field such as the electromagnetic field. Shock waves are characterized by an abrupt, nearly discontinuous change in the resulting from major fragmentation events. These sounds can be heard over wide areas, up to many thousands of square km. Whistling and hissing sounds are also sometimes heard, but are poorly understood. Following passage of the fireball, it is not unusual for a dust trail to linger in the atmosphere for some time.

As meteoroids are heated during atmospheric entry, their surfaces melt and experience ablation Ablation means removal of material from the surface of an object by vaporization, chipping, or other erosive processes. The term occurs in spaceflight associated with atmospheric reentry, in glaciology, medicine, and passive fire protection. They can be sculpted into various shapes during this process, sometimes resulting in deep "thumb-print" like indentations on their surfaces called regmaglypts. If the meteoroid maintains a fixed orientation for some time, without tumbling, it may develop a conical "nose cone" or "heat shield" shape. As it decelerates, eventually the molten surface layer solidifies into a thin fusion crust, which on most meteorites is black (on some achondrites, the fusion crust may be very light colored). On stony meteorites, the heat-affected zone is at most a few mm deep; in iron meteorites, which are more thermally conductive, the structure of the metal may be affected by heat up to 1 cm below the surface. Meteorites are sometimes reported to be warm to the touch when they land, but they are never hot. Reports, however, vary greatly, with some meteorites being reported as "burning hot to the touch" upon landing,[11][12] and others forming a frost upon their surface.[13]

Meteoroids that experience disruption in the atmosphere may fall as meteorite showers, which can range from only a few up to thousands of separate individuals. The area over which a meteorite shower falls is known as its strewn field. Strewn fields are commonly elliptical In geometry, an ellipse is a plane curve that results from the intersection of a cone by a plane in a way that produces a closed curve. Circles are special cases of ellipses, obtained when the cutting plane is perpendicular to the axis. An ellipse is also the locus of all points of the plane whose distances to two fixed points add to the same in shape, with the major axis parallel to the direction of flight. In most cases, the largest meteorites in a shower are found farthest down-range in the strewn field.

Meteorite types

Marília Meteorite, a chondrite H4, which fell in Marília, São Paulo state, Brazil, on October 5, 1971, at 5:00p.m.

Most meteorites are stony meteorites, classed as chondrites and achondrites. Only 6% of meteorites are iron meteorites Iron meteorites consist overwhelmingly of nickel-iron alloys. The metal taken from these meteorites is known as meteoric iron and was one of the earliest sources of usable iron available to man or a blend of rock and metal, the stony-iron meteorites A pallasite is a type of stony-iron meteorite. It consists of cm-sized olivine crystals of peridot quality in an iron-nickel matrix. Coarser metal areas develop Widmanstätten patterns upon etching. Minor constituents are schreibersite, troilite, chromite, pyroxenes, and phosphates . Pallasites were once thought to originate at the core-mantle. Modern classification of meteorites is complex, the review paper of Krot et al. (2007)[14] summarizes modern meteorite taxonomy.

About 86% of the meteorites that fall on Earth are chondrites,[4][15][16] which are named for the small, round particles they contain. These particles, or chondrules, are composed mostly of silicate minerals that appear to have been melted while they were free-floating objects in space. Certain types of chondrites also contain small amounts of organic matter Organic matter is matter that has come from a once-living organism; is capable of decay, or the product of decay; or is composed of organic compounds. The definition of organic matter varies upon the subject it is being used for, including amino acids Amino acids are molecules containing an amine group, a carboxylic acid group and a side chain that varies between different amino acids. These molecules contain the key elements of carbon, hydrogen, oxygen, and nitrogen. These molecules are particularly important in biochemistry, where this term refers to alpha-amino acids with the general formula, and presolar grains. Chondrites are typically about 4.55 billion years old and are thought to represent material from the asteroid belt The asteroid belt is the region of the Solar System located roughly between the orbits of the planets Mars and Jupiter. It is occupied by numerous irregularly shaped bodies called asteroids or minor planets. The asteroid belt region is also termed the main belt to distinguish it from other concentrations of minor planets within the Solar System, that never formed into large bodies. Like comets A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma , and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet. Comet nuclei are themselves loose collections of ice, dust, and small rocky particles, ranging from a few, chondritic asteroids are some of the oldest and most primitive materials in the solar system. Chondrites are often considered to be "the building blocks of the planets".

About 8% of the meteorites that fall on Earth are achondrites (meaning they do not contain chondrules), some of which are similar to terrestrial mafic igneous rocks Igneous rock is one of the three main rock types (the others being sedimentary and metamorphic rock). Igneous rock is formed by magma or lava (molten rock) cooling and becoming solid. Igneous rock may form with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. This. Most achondrites are also ancient rocks, and are thought to represent crustal material of asteroids. One large family of achondrites (the HED meteorites) may have originated on the asteroid 4 Vesta Vesta, formal designation 4 Vesta, is an asteroid. It is the second most massive object in the asteroid belt, with a mean diameter of about 530 km and an estimated mass of 9% of the mass of the entire asteroid belt. It was discovered by the German astronomer Heinrich Wilhelm Olbers on March 29, 1807, and named after the Roman virgin goddess of. Others derive from different asteroids. Two small groups of achondrites are special, as they are younger and do not appear to come from the asteroid belt. One of these groups comes from the Moon, and includes rocks similar to those brought back to Earth by Apollo The Apollo program was the American spaceflight endeavor which landed the first humans on Earth's Moon. Conceived during the presidency of Dwight D. Eisenhower and conducted by NASA, Apollo began in earnest after President John F. Kennedy's May 25, 1961 special address to a joint session of Congress declaring a national goal of "landing a man and Luna The Luna programme , occasionally called Lunik or Lunnik, was a series of robotic spacecraft missions sent to the Moon by the Soviet Union between 1959 and 1976. Fifteen were successful, each designed as either an orbiter or lander, and accomplished many firsts in space exploration. They also performed many experiments, studying the Moon's programs. The other group is almost certainly from Mars Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact and are the only materials from other planets ever recovered by man.

About 5% of meteorites that fall are iron Iron is the most common element in the earth as a whole, and the fourth most common in the Earth's crust. It is produced as a result of stellar fusion in high-mass stars, and it is the heaviest stable element produced by stellar fusion because the fusion of iron is the last nuclear fusion reaction that is exothermic. Iron is the most widely used meteorites with intergrowths of iron-nickel Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements that exist around room temperature, the other three being iron, cobalt and gadolinium alloys An alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history. Alloys usually have different properties from those of the, such as kamacite Kamacite is a mineral. It is an alloy of iron and nickel, usually in the proportions of 90:10 to 95:5 although impurities such as cobalt or carbon may be present. On the surface of Earth, it occurs naturally only in meteorites. It has a metallic lustre, is grey and has no clear cleavage although the structure is isometric-hexoctahedral. Its and taenite Taenite is a mineral found naturally on Earth mostly in iron meteorites. It is an alloy of iron and nickel, with nickel proportions of 20% up to 65%. Most iron meteorites are thought to come from the core of a number of asteroids that were once molten. As on Earth, the denser metal separated from silicate material and sank toward the center of the asteroid, forming a core. After the asteroid solidified, it broke up in a collision with another asteroid. Due to the low abundance of irons in collection areas such as Antarctica, where most of the meteoric material that has fallen can be recovered, it is possible that the actual percentage of iron-meteorite falls is lower than 5%.

Stony-iron meteorites constitute the remaining 1%. They are a mixture of iron-nickel metal and silicate A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as most planets and moons. Sand, Portland cement, and thousands of minerals minerals. One type, called pallasites A pallasite is a type of stony-iron meteorite. It consists of cm-sized olivine crystals of peridot quality in an iron-nickel matrix. Coarser metal areas develop Widmanstätten patterns upon etching. Minor constituents are schreibersite, troilite, chromite, pyroxenes, and phosphates . Pallasites were once thought to originate at the core-mantle, is thought to have originated in the boundary zone above the core regions where iron meteorites originated. The other major type of stony-iron meteorites is the mesosiderites.

Tektites (from Greek tektos, molten) are not themselves meteorites, but are rather natural glass objects up to a few centimeters in size which were formed—according to most scientists—by the impacts of large meteorites on Earth's surface. A few researchers have favored Tektites originating from the Moon The Moon is Earth's only natural satellite[nb 4] and is the fifth largest satellite in the Solar System. It is the largest natural satellite in the Solar System relative to the size of its planet, a quarter the diameter of Earth and 1/81 its mass, and is the second densest satellite after Io. It is in synchronous rotation with Earth, always as volcanic ejecta, but this theory has lost much of its support over the last few decades.

Meteorite recovery

Falls

Car seat and muffler hit by the Benld meteorite in 1938, with the meteorite inset. An observed fall.

Most meteorite falls Meteorite falls are those meteorites that were witnessed by people or automated devices as they moved through the atmosphere or hit the Earth, and were subsequently collected. As of April 2010, there are about 1,087 documented falls that are listed in widely used databases, most of which have specimens in modern collections are recovered on the basis of eye-witness accounts of the fireball or the actual impact of the object on the ground, or both. Therefore, despite the fact that meteorites actually fall with virtually equal probability everywhere on Earth, verified meteorite falls tend to be concentrated in areas with high human population The world population is the population of humans on the planet Earth. In 2009, the United Nations estimated the population to reach 7,000,000,000 in 2011; current estimates by the United States Census Bureau put the population at 6,859,100,000 densities such as Europe, Japan, and northern India North India is a loosely defined region in the northern part of India. The exact meaning of the term varies by usage. The dominant geographical features of North India are the Indo-Gangetic Plain and the Himalayas, which demarcate the region from Tibet and Central Asia. North India has been the historical center of the Maurya, Gupta, Maratha,.

A small number of meteorite falls have been observed with automated cameras and recovered following calculation of the impact point. The first of these was the Příbram meteorite, which fell in Czechoslovakia (now the Czech Republic) in 1959.[17] In this case, two cameras used to photograph meteors captured images of the fireball. The images were used both to determine the location of the stones on the ground and, more significantly, to calculate for the first time an accurate orbit for a recovered meteorite.

Following the Pribram fall, other nations established automated observing programs aimed at studying infalling meteorites. One of these was the Prairie Network, operated by the Smithsonian Astrophysical Observatory from 1963 to 1975 in the midwestern US. This program also observed a meteorite fall, the Lost City chondrite, allowing its recovery and a calculation of its orbit.[18] Another program in Canada, the Meteorite Observation and Recovery Project, ran from 1971 to 1985. It too recovered a single meteorite, Innisfree, in 1977.[19] Finally, observations by the European Fireball Network, a descendant of the original Czech program that recovered Pribram, led to the discovery and orbit calculations for the Neuschwanstein meteorite in 2002.[20]

Finds

Until the 20th century, only a few hundred meteorite finds had ever been discovered. Over 80% of these were iron and stony-iron meteorites, which are easily distinguished from local rocks. To this day, few stony meteorites are reported each year that can be considered to be "accidental" finds. The reason there are now over 30,000 meteorite finds in the world's collections started with the discovery by Harvey H. Nininger that meteorites are much more common on the surface of the Earth than was previously thought.

The Great Plains of the US

Nininger's strategy was to search for meteorites in the Great Plains of the United States, where the land was largely cultivated and the soil contained few rocks. Between the late 1920s and the 1950s, he traveled across the region, educating local people about what meteorites looked like and what to do if they thought they had found one, for example, in the course of clearing a field. The result was the discovery of over 200 new meteorites, mostly stony types.[21]

In the late 1960s, Roosevelt County, New Mexico in the Great Plains was found to be a particularly good place to find meteorites. After the discovery of a few meteorites in 1967, a public awareness campaign resulted in the finding of nearly 100 new specimens in the next few years, with many being found by a single person, Mr. Ivan Wilson. In total, nearly 140 meteorites were found in the region since 1967. In the area of the finds, the ground was originally covered by a shallow, loose soil sitting atop a hardpan layer. During the dustbowl era, the loose soil was blown off, leaving any rocks and meteorites that were present stranded on the exposed surface.[22]

Antarctica

Structures resembling a lifeform on meteorite fragment ALH84001, discovered in Antarctica

A few meteorites were found in Antarctica between 1912 and 1964. In 1969, the 10th Japanese Antarctic Research Expedition found nine meteorites on a blue ice field near the Yamato Mountains. With this discovery, came the realization that movement of ice sheets might act to concentrate meteorites in certain areas. After a dozen other specimens were found in the same place in 1973, a Japanese expedition was launched in 1974 dedicated to the search for meteorites. This team recovered nearly 700 meteorites.

Shortly thereafter, the United States began its own program to search for Antarctic meteorites, operating along the Transantarctic Mountains on the other side of the continent: the ANtarctic Search for METeorites (ANSMET) program. European teams, starting with a consortium called "EUROMET" in the late 1980s, and continuing with a program by the Italian Programma Nazionale di Ricerche in Antartide have also conducted systematic searches for Antarctic meteorites.

The Antarctic Scientific Exploration of China has conducted successful meteorite searches since 2000. A Korean program (KOREAMET) was launched in 2007 and has collected a few meteorites.[23] The combined efforts of all of these expeditions have produced more than 23,000 classified meteorite specimens since 1974, with thousands more that have not yet been classified. For more information see the article by Harvey (2003).[24]

Australia

At about the same time as meteorite concentrations were being discovered in the cold desert of Antarctica, collectors discovered that many meteorites could also be found in the hot deserts of Australia. Several dozen meteorites had already been found in the Nullarbor region of Western and South Australia. Systematic searches between about 1971 and the present recovered over 500 more[25], ~300 of which are currently well characterized. The meteorites can be found in this region because the land presents a flat, featureless, plain covered by limestone. In the extremely arid climate, there has been relatively little weathering or sedimentation on the surface for tens of thousands of years, allowing meteorites to accumulate without being buried or destroyed. The dark colored meteorites can then be recognized among the very different looking limestone pebbles and rocks.

The Sahara and rising commercialization

In 1986-87, a German team installing a network of seismic stations while prospecting for oil discovered about 65 meteorites on a flat, desert plain about 100 km southeast of Dirj (Daraj), Libya. A few years later, a desert enthusiast saw photographs of meteorites being recovered by scientists in Antarctica, and thought that he had seen similar occurrences in northern Africa. In 1989, he recovered about 100 meteorites from several distinct locations in Libya and Algeria. Over the next several years, he and others who followed found at least 400 more meteorites. The find locations were generally in regions known as regs or hamadas: flat, featureless areas covered only by small pebbles and minor amounts of sand.[26] Dark-colored meteorites can be easily spotted in these places, where they have also been well-preserved due to the arid climate, and in the case of the Dal al Gani meteorite field, favorable geology consisting of basic rocks (clays, dolomites, and limestones) and lacking erosive quartz sand[27].

Although meteorites had been sold commercially and collected by hobbyists for many decades, up to the time of the Saharan finds of the late 1980s and early 1990s, most meteorites were deposited in or purchased by museums and similar institutions where they were exhibited and made available for scientific research. The sudden availability of large numbers of meteorites that could be found with relative ease in places that were readily accessible (especially compared to Antarctica), led to a rapid rise in commercial collection of meteorites. This process was accelerated when, in 1997, meteorites coming from both the Moon and Mars were found in Libya. By the late 1990s, private meteorite-collecting expeditions had been launched throughout the Sahara. Specimens of the meteorites recovered in this way are still deposited in research collections, but most of the material is sold to private collectors. These expeditions have now brought the total number of well-described meteorites found in Algeria and Libya to over 2000.

As word spread in Saharan countries about the growing profitability of the meteorite trade, meteorite markets came into existence, especially in Morocco, fed by nomads and local people who combed the deserts looking for specimens to sell. Many thousands of meteorites have been distributed in this way, most of which lack any information about how, when, or where they were discovered. These are the so-called "Northwest Africa" meteorites.

Arabian Peninsula

In 1999, meteorite hunters discovered that the desert in southern and central Oman were also favorable for the collection of many specimens. The gravel plains in the Dhofar and Al Wusta regions of Oman, south of the sandy deserts of the Rub' al Khali, had yielded about 5,000 meteorites as of mid-2009. Included among these are a large number of lunar and Martian meteorites, making Oman a particularly important area both for scientists and collectors. Early expeditions to Oman were mainly done by commercial meteorite dealers, however international teams of Omani and European scientists have also now collected specimens.

The recovery of meteorites from Oman is currently prohibited by national law, but a number of international hunters continue to remove specimens now deemed "national treasures." This new law provoked a small international incident, as its implementation actually preceded any public notification of such a law, resulting in the prolonged imprisonment of a large group of meteorite hunters primarily from Russia, but whose party also consisted of members from the U.S. as well as several other European countries.

The Black Stone in the wall of the Kaaba in Mecca is thought to be a meteorite by some secular historians, but there is little support for this in the scientific literature [28]

The American Southwest

A stony meteorite (H5) found just north of Barstow, California, in 2006

Beginning in the mid-1990s, amateur meteorite hunters began scouring the arid areas of the southwestern United States. To date, meteorites numbering possibly into the thousands have been recovered from the Mojave, Sonoran, Great Basin, and Chihuahuan Deserts, with many being recovered on dry lake beds. Significant finds include the Superior Valley 014 Acapulcoite, one of two of its type found within the United States[29][30] as well as the Blue Eagle meteorite, the first Rumuruti-type chondrite yet found in the Americas.[31] Perhaps the most notable find in recent years has been the Los Angeles meteorite, a martian meteorite that was reportedly found by Robert Verish.[32] A number of finds from the American Southwest have yet to be formally submitted to the , as many finders think it is unwise to publicly state the coordinates of their discoveries for fear of confiscation by the federal government, and of 'poaching' by other hunters at known find sites.[33] Several of the meteorites found recently are currently on display in the Griffith Observatory in Los Angeles.

Meteorites in history

In the 1970s a stone meteorite was uncovered during an archaeological dig at Danebury Iron Age hillfort, Danebury England. It was found deposited part way down in an Iron Age pit. Since it must have been deliberately placed there, this could indicate one of the first (known) human finds of a meteorite in Europe.

Some Native Americans treated meteorites as ceremonial objects. In 1915, a 135-pound iron meteorite was found in a Sinagua (c.1100-1200 AD) burial cyst near Camp Verde, Arizona, respectfully wrapped in a feather cloth.[34] A small pallasite was found in a pottery jar in an old burial found at Pojoaque Pueblo, New Mexico. Nininger reports several other such instances, in the Southwest US and elsewhere, such as the discovery of Native American beads of meteoric iron found in Hopewell burial mounds, and the discovery of the Winona meteorite in a Native American stone-walled crypt.[34]

A lance made from a Narwhal tusk with a Meteorite iron head

Indigenous peoples often prized iron-nickel meteorites as an easy, if limited, source of iron metal. For example, the Inuit used chips of the Cape York meteorite to form cutting edges for tools and spear tips.

The German physicist, Ernst Florens Chladni, was the first to publish the then audacious idea that that meteorites were actually rocks from space.[35] He published his booklet, "On the Origin of the Pallas Iron and Others Similar to it, and on Some Associated Natural Phenomena", in 1794. In this he compiled all available data on several meteorite finds and falls concluded that they must have their origins in outer space. The scientific community of the time responded with resistance and mockery.[36] It took nearly 10 years before a general acceptance of the origin of meteorites was achieved through the work of the French scientist Jean-Baptiste Biot and the British chemist, Edward Howard.

One of the leading theories for the cause of the Cretaceous–Tertiary extinction event that included the dinosaurs is a large meteorite impact. The Chicxulub Crater has been identified as the site of this impact. There has been a lively scientific debate as to whether other major extinctions, including the ones at the end of the Permian and Triassic periods might also have been the result of large impact events, but the evidence is much less compelling than for the end Cretaceous extinction.

The Willamette Meteorite, the largest ever to be found in the United States

There are several reported instances of falling meteorites having killed both people and livestock, but a few of these appear more credible than others. The most infamous reported fatality from a meteorite impact is that of an Egyptian dog that was killed in 1911, although this report is highly disputed. This particular meteorite fall was identified in the 1980s as Martian in origin. However, there is substantial evidence that the meteorite known as Valera hit and killed a cow upon impact, nearly dividing the animal in two, and similar unsubstantiated reports of a horse being struck and killed by a stone of the New Concord fall also abound. Throughout history, many first and second-hand reports of meteorites falling on and killing both humans and other animals abound, but none have been well documented.

The first known modern case of a human hit by a space rock occurred on 30 November 1954 in Sylacauga, Alabama.[37] There a 4 kg stone chondrite[38] crashed through a roof and hit Ann Hodges in her living room after it bounced off her radio. She was badly bruised. The Hodges meteorite, or Sylacauga meteorite, is currently on exhibit at the Alabama Museum of Natural History.

Other than the Sylacauga event, the most plausible of these claims was put forth by a young boy who stated that he had been hit by a small (~3 gram) stone of the Mbale meteorite fall from Uganda, and who stood to gain nothing from this assertion. The stone reportedly fell through a number of banana leaves before striking the boy on the head, causing little to no pain, as it was small enough to have been slowed by both friction with the atmosphere as well as that with banana leaves, before striking the boy. Although it is impossible to prove this claim either way, it seems as though he had little reason to lie about such an event occurring.

Several persons have since claimed[39] to have been struck by "meteorites" but no verifiable meteorites have resulted.

Meteorite falls may also be the source of cultish worship. The cult in the Temple of Artemis (Diana) at Ephesus, one of the Seven Wonders of the Ancient World possibly originated with the observation of a meteorite fall which was understood by contemporaries to have fallen to the earth from Zeus, the principal Greek deity.

Notable meteorites

Apart from meteorites fallen onto the Earth, "Heat Shield Rock" is a meteorite which was found on Mars, and two tiny fragments of asteroids were found among the samples collected on the Moon by Apollo 12 (1969) and Apollo 15 (1971) astronauts.[42]

Notable large impact craters

Notable disintegrating meteoroids

See also

References

  1. ^ McSween Jr., Harry Y. (Jul 1976). "A new type of chondritic meteorite found in lunar soil". Earth and Planetary Science Letters 31 (2): 193–199. doi:10.1016/0012-821X(76)90211-9. Bibcode: 1976E&PSL..31..193M.
  2. ^ Rubin, Alan E. (Jan 1997). "The Hadley Rille enstatite chondrite and its agglutinate-like rim: Impact melting during accretion to the Moon". Meteoritics & Planetary Science 32 (1): 135–141. doi:10.1111/j.1945-5100.1997.tb01248.x. http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1997M%26PS...32..135R.
  3. ^ "Opportunity Rover Finds an Iron Meteorite on Mars". JPL. January 19, 2005. http://marsrovers.jpl.nasa.gov/newsroom/pressreleases/20050119a.html. Retrieved 2006-12-12.
  4. ^ a b Meteoritical Bulletin Database
  5. ^
  6. ^ Chapman, Clark R.; Durda, Daniel D.; Gold, Robert E. (Feb 2001) (PDF). The Comet/Asteroid Impact Hazard: A Systems Approach. http://www.internationalspace.com/pdf/NEOwp_Chapman-Durda-Gold.pdf.
  7. ^ Make your own impact at the University of Arizona
  8. ^ Bland, P.A.; Artemieva, Natalya A. (Apr 2006). "The rate of small impacts on Earth". Meteoritics and Planetary Science 41 (4): 607–631. doi:10.1111/j.1945-5100.2006.tb00485.x. http://adsabs.harvard.edu/abs/2006M&PS...41..607B.
  9. ^ Maier, W.D.; Andreoli, M. A. G.; McDonald, I.; Higgins, M. D.; Boyce, A. J.; Shukolyukov, A.; Lugmair, G. W.; Ashwal, L. D. et al. (May 2006). "Discovery of a 25-cm asteroid clast in the giant Morokweng impact crater, South Africa". Nature 441 (7090): 203–206. doi:10.1038/nature04751. PMID 16688173.
  10. ^ Sears, D. W. (Nov 1978). The Nature and Origin of Meteorites. New York: Oxford Univ. Press. ISBN 978-0852743744.
  11. ^ Fall of the Muzaffarpur iron meteorite
  12. ^ Fall of the Menziswyl stone
  13. ^ Ward, Henry L. (Sep 1917). "A new meteorite". Science 46 (1185): 262–263. doi:10.1126/science.46.1185.262-a. PMID 17844300. Bibcode: 1917PA.....25..634W. http://articles.adsabs.harvard.edu/full/1917PA.....25..634W. } - a report of the Colby (Wisconsin) fall
  14. ^ Krot, A.N.; Keil, K.; Scott, E.R.D.; Goodrich, C.A.; Weisberg, M.K. (2007). "1.05 Classification of Meteorites". in Holland; Turekian, Karl K.. Treatise on Geochemistry. 1. Elsevier Ltd. pp. 83–128. doi:10.1016/B0-08-043751-6/01062-8. ISBN 978-0-08-043751-4.
  15. ^ The NHM Catalogue of Meteorites
  16. ^ MetBase
  17. ^ Ceplecha, Z. (1961). "Multiple fall of Příbram meteorites photographed". Bull. Astron. Inst. Czechoslovakia 12: 21–46. Bibcode: 1961BAICz..12...21C.
  18. ^ McCrosky, R.E.; Posen, A.; Schwartz, G.; Shao, C.-Y. (1971). "Lost City Meteorite–Its Recovery and a Comparison with Other Fireballs". J. Geophys. Res. 76 (17): 4090–4108. doi:10.1029/JB076i017p04090. Bibcode: 1971JGR....76.4090M.
  19. ^ Campbell-Brown, M. D.; Hildebrand, A. (Dec 2005). "A new analysis of fireball data from the Meteorite Observation and Recovery Project (MORP)". Earth, Moon, and Planets 95 (1-4): 489–499. doi:10.1007/s11038-005-0664-9.
  20. ^ Oberst, J.; Heinlein, D.; Köhler, U.; Spurný, P. (Oct 2004). "The multiple meteorite fall of Neuschwanstein: Circumstances of the event and meteorite search campaigns". Meteoritics & Planetary Science 39 (10): 1627–1641. doi:10.1111/j.1945-5100.2004.tb00062.x. http://adsabs.harvard.edu/abs/2004M%26PS...39.1627O.
  21. ^ Website by A. Mitterling
  22. ^ Huss, G.I.; Wilson, I.E. (1973). "A census of the meteorites of Roosevelt County, New Mexico". Meteoritics 8 (3): 287–290. http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1973Metic...8..287H.
  23. ^ KORea Expedition for Antarctic METeorites (KOREAMET)
  24. ^ Harvey, Ralph (2003). "The origin and significance of Antarctic meteorites". Chemie der Erde 63 (2): 93–147. doi:10.1078/0009-2819-00031.
  25. ^ Bevan, A.W.R.; Binns, R.A. (1989). "Meteorites from the Nullarbor region, Western Australia: I. A review of past recoveries and a procedure for naming new finds". Meteorites 24: 127–133. http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1989Metic..24..127B.
  26. ^ Bischoff, A.; Geiger, T. (Jan 1995). "Meteorites from the Sahara: find locations, shock classification, degree of weathering and pairing". Meteoritics 30 (1): 113–122. http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1995Metic..30..113B.
  27. ^ Schlüter, J.; Schultz, L.; Thiedig, F.; Al-Mahdi, B. O.; Abu Aghreb, A. E. (2002). "The Dar al Gani meteorite field (Libyan Sahara): Geological setting, pairing of meteorites, and recovery density". Meteoritics & Planetary Science 37 (8): 1079–1093. doi:10.1111/j.1945-5100.2002.tb00879.x. http://adsabs.harvard.edu/abs/2002M&PS...37.1079S.
  28. ^ Meteoritical Bulletin Entry for Kaaba
  29. ^ Meteoritical Bulletin entry for Superior Valley 014
  30. ^ Paper on Superior Valley 014 and associated meteorites
  31. ^ Meteoritical Bulleting entry for Blue Eagle meteorite
  32. ^ Meteoritical Bulletin entry for Los Angeles meteorite
  33. ^ [1]
  34. ^ a b H. H. Nininger, 1972, Find a Falling Star (autobiography), New York, Paul S. Erikson.
  35. ^ Williams, Henry Smith (1904). "5". A history of science. 3. Harper. p. 168ff. http://books.google.com/?id=hNEFAAAAIAAJ&pg=PA168.
  36. ^ "History of Meteoritics - The Pallas Iron and E. F. Chladni". The Earth's Memory. 7 January 2009. http://www.meteorite.fr/en/basics/meteoritics.htm. Retrieved 2009-10-10.
  37. ^ Meteorite Hits on Man-made Objects
  38. ^ Natural History Museum Database
  39. ^ Meteorite Mis-identification in the News
  40. ^ Fukang Meteorite Auction, Description, History
  41. ^ J. Borovicka and P. Spurný (2008). "The Carancas meteorite impact - Encounter with a monolithic meteoroid". Astronomy & Astrophysics 485: L1–L4. doi:10.1051/0004-6361:200809905. http://www.aanda.org/index.php?option=article&access=bibcode&bibcode=2008A%2526A...485L...1BFUL.
  42. ^ Meteoritical Bulletin Database

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