1.
Meteorite classification
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The ultimate goal of meteorite classification is to group all meteorite specimens that share a common origin on a single, identifiable parent body. This could be a planet, asteroid, Moon, or other current Solar System object, as such information comes to light, the classification system will most likely evolve. Beyond the assignment of meteorites into groups, which essentially universally accepted and it is also fairly common for groups that seem to be closely related to be referred to as clans. In turn, groups or clans that appear to be loosely related are often referred to as chondrite classes, but higher order terms for aggregating groups of meteorites tend to be somewhat chaotic in the scientific and popular literature. There is little agreement on how to fit nonchondritic meteorite groups into an overall scheme, several other classification terms are in widespread use, Type, a historic top level of classification that grouped all meteorites into one of four types, chondrite, achondrite, iron or stony-iron. Anomalous, meteorites that are members of well-established groups that are different enough in some important property to merit distinction from the other members, grouplet, a provisional group with less than 5 members. Duo, a group with only 2 members. Ungrouped, meteorites that do not fit any known group, though they may fit into a clan or class, meteorites are often divided into three overall categories based on whether they are dominantly composed of rocky material, metallic material, or mixtures. These categories have been in use since at least the early 19th century but do not have much significance, they are simply a traditional. In fact, the term stony iron is a misnomer as currently used, one group of chondrites has over 50% metal by volume and contains meteorites that were called stony irons until their affinities with chondrites were recognized. Some iron meteorites also contain silicate inclusions but are rarely described as stony irons. Nevertheless, these three categories sit at the top of the most widely used classification system. Stony meteorites are then divided into two other categories, chondrites, and achondrites. Stony–iron meteorites have always been divided into pallasites and mesosiderites. g, E. Rubin classification scheme, Two alternative general classification schemes were recently published, illustrating the lack of consensus on how to classify meteorites beyond the level of groups. In the Krot et al. scheme the following hierarchy is used, modern meteorite classification was worked out in the 1860s, based on Gustav Roses and Nevil Story Maskelynes classifications. Gustav Rose worked on the collection of the Museum für Naturkunde, Berlin and Maskelyne on the collection of the British Museum. Rose was the first to make different categories for meteorites with chondrules, story-Maskelyne differentiated between siderites, siderolites and aerolites. In 1872 Gustav Tschermak published his first meteorite classification based on Gustav Roses catalog from 1864, further modifications were made by Aristides Brezina
2.
Allende meteorite
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The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01,05 on February 8,1969, after breaking up in the atmosphere, an extensive search for pieces was conducted and it is often described as the best-studied meteorite in history. The Allende meteorite is notable for possessing abundant, large calcium-aluminium-rich inclusions, carbonaceous chondrites comprise about 4 percent of all meteorites observed to fall from space. Prior to 1969, the carbonaceous chondrite class was known from a number of uncommon meteorites such as Orgueil. Meteorites similar to Allende were known, but many were small, the original stone is believed to have been approximately the size of an automobile traveling towards the Earth at more than 10 miles per second. The fall occurred in the morning hours of February 8,1969. At 01,05 a huge, brilliant fireball approached from the southwest and lit the sky and it exploded and broke up to produce thousands of fusion crusted individuals. This is typical of falls of large stones through the atmosphere and is due to the braking effect of air resistance. The fall took place in northern Mexico, near the village of Pueblito de Allende in the state of Chihuahua. Allende stones became one of the most widely distributed meteorites and provided an amount of material to study. Stones were scattered over a huge area – one of the largest meteorite strewnfields known and this strewnfield measures approximately 8 by 50 kilometers. The region is desert, mostly flat, with sparse to moderate low vegetation, hundreds of meteorites were collected shortly after the fall. Approximately 2 or 3 tonnes of specimens were collected over a period of more than 25 years, some sources guess that an even larger amount was recovered, but there is no way to make an accurate estimate. Even today, over 40 years later, specimens are occasionally found. Fusion crusted individual Allende specimens ranged from 1 gram to 110 kilograms, Allende is often called the best-studied meteorite in history. There are several reasons for this, Allende fell in early 1969 and this was a time of great excitement and energy among planetary scientists. The field was attracting many new workers and laboratories were being improved, as a result, the scientific community was immediately ready to study the new meteorite. A number of museums launched expeditions to Mexico to collect samples, including the Smithsonian Institution, the CAIs are billions of years old, and help to determine the age of the Solar System
3.
Chondrule
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Chondrules are round grains found in chondrites. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids, different kinds of the stony, non-metallic meteorites called chondrites contain different fractions of chondrules. Chondrules can range in diameter from just a few micrometers to over 1 centimetre, other chondrite groups are intermediate between these. Most chondrules are composed primarily of the minerals olivine and pyroxene. Small amounts of minerals are often present, including Fe sulfide, metallic Fe-Ni, oxides such as chromite. Less common types of chondrules may be composed of feldspathic material, silica, or metallic Fe-Ni. Chondrules display a variety of textures, which can be seen when the chondrule is sliced open. Some show textural evidence for rapid cooling from a molten or nearly completely molten state. Pyroxene-rich chondrules that contain extremely fine-grained, swirling masses of fibrous crystals only a few micrometers in size or smaller are called cryptocrystalline chondrules. When the pyroxene fibers are coarser, they may appear to radiate from a single site on the surface. Other observed textural features that are clearly the result of rapid cooling are dendritic and hopper-shaped olivine grains. More commonly, chondrules display what is known as a porphyritic texture, in these, grains of olivine and/or pyroxene are equidimensional and sometimes euhedral. They are named on the basis of the dominant mineral, i. e. porphyritic olivine, porphyritic pyroxene and it seems likely that these chondrules cooled more slowly than those with radial or barred textures, however they still may have solidified in a matter of hours. The composition of olivine and pyroxene in chondrules varies widely, although the range is usually narrow within any single chondrule, some chondrules contain very little iron oxide, resulting in olivine and pyroxene that are close to forsterite and enstatite in composition. These are commonly called Type I chondrules by scientists, and often contain amounts of metallic Fe. Other chondrules formed under more oxidizing conditions and contain olivine and pyroxene with large amounts of FeO, such chondrules are called Type II. Most chondrites contain both Type I and Type II chondrules mixed together, including those with both porphyritic and nonporphyritic textures, although there are exceptions to this. Chondrules are believed to have formed by a heating and melting of solid dust aggregates of approximately Solar composition under temperatures of about 1000 K
4.
Chondrite
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Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They are formed when various types of dust and small grains that were present in the solar system accreted to form primitive asteroids. They are the most common type of meteorite falls to Earth with estimates for the proportion of the total fall that they represent varying between 85. 7% and 86. 2%. Their study provides important clues for understanding the origin and age of the Solar System, the synthesis of organic compounds, the origin of life or the presence of water on Earth. One of their characteristics is the presence of chondrules, which are round grains formed by distinct minerals, chondrites can be differentiated from iron meteorites due to their low iron and nickel content. Other non-metallic meteorites, achondrites, which lack chondrules, were formed more recently, there are currently over 27,000 chondrites in the worlds collections. The largest individual stone ever recovered, weighing 1770 kg, was part of the Jilin meteorite shower of 1976, chondrites were formed by the accretion of particles of dust and grit present in the primitive Solar System which gave rise to asteroids over 4.55 billion years ago. These asteroid parent bodies of chondrites are small to medium-sized asteroids that were never part of any body large enough to undergo melting, dating using 206Pb/204Pb gives an estimated age of 4,566.6 ±1.0 Ma, matching ages for other chronometers. Another indication of their age is the fact that the abundance of elements in chondrites is similar to that found in the atmosphere of the Sun. Many chondritic asteroids also contained significant amounts of water, possibly due to the accretion of ice along with rocky material. As a result, many chondrites contain hydrous minerals, such as clays, in addition, all chondritic asteroids were affected by impact and shock processes due to collisions with other asteroids. These events caused a variety of effects, ranging from simple compaction to brecciation, veining, localized melting, and formation of high-pressure minerals. Chondrites also contain inclusions, which are among the oldest objects to form in the solar system, particles rich in metallic Fe-Ni and sulfides. The remainder of chondrites consists of fine-grained dust, which may either be present as the matrix of the rock or may form rims or mantles around individual chondrules and refractory inclusions. Embedded in this dust are presolar grains, which predate the formation of our solar system, the chondrites have distinct texture, composition and mineralogy and their origin continues to be the object of some debate. Chondrites are divided into about 15 distinct groups on the basis of their mineralogy, bulk chemical composition, the various chondrite groups likely originated on separate asteroids or groups of related asteroids. Each chondrite group has a mixture of chondrules, refractory inclusions, matrix, and other components. Other ways of classifying chondrites include weathering and shock, chondrites can also be categorized according to their petrologic type, which is the degree to which they were thermally metamorphosed or aqueously altered
5.
Meteorite
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When the object enters the atmosphere, various factors like friction, pressure, and chemical interactions with the atmospheric gases cause it to heat up and radiate that energy. It then becomes a meteor and forms a fireball, also known as a shooting/falling star, meteorites that survive atmospheric entry and impact vary greatly in size. For geologists, a bolide is a large enough to create a crater. Meteorites that are recovered after being observed as they transit the atmosphere or impact the Earth are called meteorite falls, all others are known as meteorite finds. As of April 2016, there were about 1,140 witnessed falls that have specimens in the worlds collections, there are more than 38,660 well-documented meteorite finds. Modern classification schemes divide meteorites into groups according to their structure, chemical and isotopic composition, meteorites smaller than 2 mm are classified as micrometeorites. Extraterrestrial meteorites are such objects that have impacted other celestial bodies and they have been found on the Moon and Mars. Meteorites are always named for the places they were found, usually a town or geographic feature. In cases where many meteorites were found in one place, the name may be followed by a number or letter, the name designated by the Meteoritical Society is used by scientists, catalogers, and most collectors. Most meteoroids disintegrate when entering the Earths atmosphere, usually, five to ten a year are observed to fall and are subsequently recovered and made known to scientists. Few meteorites are large enough to create large impact craters, instead, they typically arrive at the surface at their terminal velocity and, at most, create a small pit. Large meteoroids may strike the ground with a significant fraction of their escape velocity, 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, the most frequent hypervelocity cratering events on the Earth are caused by iron meteoroids, which are most easily able to transit the atmosphere intact. In contrast, even relatively large stony or icy bodies like small comets or asteroids, up to millions of tons, are disrupted in the atmosphere, and do not make impact craters. Although such disruption events are uncommon, they can cause a concussion to occur. Very large stony objects, hundreds of meters in diameter or more, weighing tens of millions of tons or more, can reach the surface and cause large craters, such events are generally so energetic that the impactor is completely destroyed, leaving no meteorites. Several phenomena are well documented during witnessed meteorite falls too small to produce hypervelocity craters, 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 as well as shock waves resulting from major fragmentation events
6.
Meteorite fall
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Meteorite falls, also called observed falls, are meteorites collected after their fall from space was observed by people or automated devices. All other meteorites are called finds, there are more than 1,100 documented falls listed in widely used databases, most of which have specimens in modern collections. As of early 2017, the Meteoritical Bulletin Database has 1,149 confirmed falls, observed meteorite falls are interesting for several reasons. Material from observed falls has not been subjected to weathering, making the find a better candidate for scientific study. Historically, observed falls were the most compelling evidence supporting the extraterrestrial origin of meteorites, furthermore, observed fall discoveries are a better representative sample of the types of meteorites which fall to Earth. For example, iron meteorites take much longer to weather and are easier to identify as unusual objects and this may explain the increased proportion of iron meteorites among finds, over that among observed falls. There is also detailed statistics on falls such as based on meteorite classification, the German physicist Ernst Cladni, sometimes considered as the father of meteoritics, was the first to publish the then audacious idea that meteorites were rocks from space. There were already several documented cases, one of the earliest was the Aegospotami meteorite of 467 BC, below is a list of 8 confirmed falls pre-1600 AD. However, unlike the Loket and Ensisheim meteorites, not all are as well-documented, while most confirmed falls involve masses between less than one kg to several kg, some reach 100 kg or more. A few are more than one metric ton. The six largest falls are listed below and five occurred during the 20th century, presumably, events of such magnitude may happen a few times per century but, especially if it occurred in remote areas, may have gone unreported. These 14 have been found in 2010 and after, since in the modern period around half a dozen falls are normally found each year, the table needs some updating. These have all been found between 1610-2010 and arranged alphabetically, glossary of meteoritics Meteorite fall statistics
7.
Murchison meteorite
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The Murchison meteorite is a large meteorite that fell to earth near Murchison, Victoria, in Australia, in 1969. It is one of the most studied meteorites due to its mass, the fact that it was a fall. About 30 seconds later, a tremor was heard, many fragments were found over an area larger than 13 km², with individual mass up to 7 kg, one, weighing 680 g, broke through a roof and fell in hay. The total collected mass exceeds 100 kg, the meteorite belongs to the CM group of carbonaceous chondrites. Like most CM chondrites, Murchison is petrologic type 2, which means that it experienced extensive alteration by water-rich fluids on its parent body before falling to Earth, CM chondrites, together with the CI group, are rich in carbon and are among the most chemically primitive meteorites. Like other CM chondrites, Murchison contains abundant CAIs, over 15 amino acids, some of the basic components of life, have been identified in the meteorite by multiple studies. Murchison contains common amino acids such as glycine, alanine and glutamic acid as well as unusual ones like isovaline and pseudoleucine, a complex mixture of alkanes was isolated as well, similar to that found in the Miller–Urey experiment. Serine and threonine, usually considered to be earthly contaminants, were absent in the samples. A specific family of amino acids called diamino acids was identified in the Murchison meteorite as well, the initial report stated that the amino acids were racemic and therefore formed in an abiotic manner because amino acids of terrestrial proteins are all of the L-configuration. In 1997, L-excesses were also found in an amino acid, isovaline. At the same time, L-excesses of alanine were again found in Murchison but now with enrichment in the isotope 15N, however, the list of organic materials identified in the meteorite was extended to polyols by 2001. Although the meteorite contained a mixture of left-handed and right-handed amino acids, most amino acids used by living organisms are left-handed in chirality, and most sugars used are right-handed. A team of chemists in Sweden demonstrated in 2005 that this homochirality could have triggered or catalyzed. Several lines of evidence indicate that the portions of well-preserved fragments from Murchison are pristine. A2010 study using high resolution analytical tools including spectroscopy, identified 14,000 molecular compounds including 70 amino acids in a sample of the meteorite, measured purine and pyrimidine compounds were found in the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of δ13C = +44. 5‰ and +37. 7‰, respectively and this specimen demonstrates that many organic compounds were delivered by early Solar System bodies and may have played a key role in lifes origin. Cosmochemistry Glossary of meteoritics Rosenthal, Anne M. Murchisons Amino Acids, meteorite That Fell in 1969 Still Revealing Secrets of the Early Solar System. This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration
8.
Orgueil (meteorite)
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Orgueil is a scientifically important carbonaceous chondrite meteorite that fell in southwestern France in 1864. It fell on May 14,1864, a few minutes after 20,00 local time, about 20 stones fell over an area of several square miles. He wrote that it contained carbon, hydrogen, and oxygen, an intense scientific discussion ensued, continuing into the 1870s, as to whether the organic matter might have a biological origin. Orgueil is one of five known meteorites belonging to the CI chondrite group and this group is remarkable for having a composition that is essentially identical to that of the sun, excluding gaseous elements like hydrogen and helium. Because of its extraordinarily primitive composition and relatively large mass, Orgueil is one of the most-studied meteorites, one notable discovery in Orgueil was a high concentration of isotopically anomalous xenon called xenon-HL. The carrier of this gas is extremely fine-grained diamond dust that is older than the system itself. In 1962, Nagy et al. announced the discovery of organised elements embedded in the Orgueil meteorite that were purportedly biological structures of extraterrestrial origin and these elements were subsequently shown to be either pollen and fungal spores that had contaminated the sample, or crystals of the mineral olivine. Despite great initial excitement, the capsule was shown to be that of a European rush, glued into the fragment. The outer fusion layer was in fact glue, richard B. Hoover of NASA has claimed that the Orgueil meteorite contains fossils, some of which are similar to known terrestrial species. Hoover has previously claimed the existence of fossils in the Murchison meteorite, however, NASA has formally distanced itself from Hoovers claims and his lack of expert peer-reviews. Glossary of meteoritics Nagy B, Claus G, Hennessy DJ Organic Particles Embedded in Minerals in Orgueil, nature 193 p.1129 Fitch FW, Anders E Organized Element - Possible Identification in Orgueil Meteorite
9.
Tagish Lake (meteorite)
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The Tagish Lake meteorite fell at 16,43 UTC on 18 January 2000 in the Tagish Lake area in northwestern British Columbia, Canada.7 kilotons. Following the reported sighting of a fireball in southern Yukon and northern British Columbia, Canada, post-event atmospheric photographs of the trail left by the associated fireball and U. S. Department of Defense satellite information yielded the meteor trajectory. Most of the stony, carbonaceous fragments landed on the Taku Arm of the lake, the passage of the fireball and the high-altitude explosion set off a wide array of satellite sensors as well as seismographs. The local inhabitants described the smell in the air following the airburst as sulfurous, the Tagish Lake meteoroid is estimated to have been 4 meters in diameter and 56 tonnes in weight before it entered the Earths atmosphere. However, it is estimated that only 1, of the 1.3 tonnes of fragmented rock, somewhat over 10 kilograms was found and collected. Tagish Lake is classified as a chondrite, type C2 ungrouped. The pieces of the Tagish Lake meteorite are dark grey to almost black in color with small light-colored inclusions, except for a greyish fusion crust, the meteorites have the visual appearance of a charcoal briquette. The fragments were transported in their state to research facilities after they were collected by a local resident in late January,2000. Initial studies of these fragments were done in collaboration with researchers from NASA. Snowfall covered the remaining fragments until April 2000, when an effort was mounted by researchers from the University of Calgary. Fragments of the fresh, pristine Tagish Lake meteorite totaling more than 850 g are currently held in the collections at the Royal Ontario Museum, degraded fragments from the April–May 2000 search are curated mainly at the University of Calgary and the University of Western Ontario. This meteorite shows some similarities to the two most primitive carbonaceous chondrite types, the CI and CM chondrites, it is quite distinct from either of them. Tagish Lake has a lower density than any other type of chondrite and is actually composed of two somewhat different rock types. The major difference between the two lithologies is in the abundance of minerals, one is poor in carbonates and the other is rich in them. The meteorite contains an abundance of materials, including amino acids. The organics in the meteorite may have formed in the interstellar medium and/or the solar protoplanetary disk. A portion of the carbon in the Tagish Lake meteorite is contained in what are called nanodiamonds—very tiny diamond grains at most only a few micrometers in size, in fact, Tagish Lake contains more of the nanodiamonds than any other meteorite. The age of the meteorite is estimate to be about 4.55 billion years thus being a remainder of the period when the system was formed
10.
Sutter's Mill meteorite
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The Sutters Mill meteorite is a carbonaceous chondrite which entered the Earths atmosphere and broke up at about 07,51 Pacific time on April 22,2012. The name comes from the Sutters Mill, the California Gold Rush site and this was the largest meteoroid impact over land since asteroid 2008 TC3. As of May 2014,79 fragments have been documented with a find location. The largest weighs 205 grams, and the second largest weighs 42 grams, the meteorite was found to contain some of the oldest material in the solar system. Two 10-micron diamond grains were found in the meteorite recovered before the rain fell, in primitive meteorites like Sutters Mill, some grains survived from what existed in the cloud of gas, dust and ice that formed the solar system. During the 2012 Lyrids meteor shower, a bolide and sonic boom rattled buildings in California, the bolide air burst was caused by a random meteoroid, not a member of the Lyrids shower. The bolide was so bright that witnesses were seeing spots afterward, the falling meteorites were detected by weather radar over an area centered on the Sutters Mill site in Coloma, between Auburn, California, and Placerville, California. Robert Ward found a small CM chondrite fragment in the Henningsen Lotus Park just west of Coloma, later that day, Peter Jenniskens found a crushed 4 g meteorite in the parking lot of that same park and Brien Cook found a 5 g meteorite off Petersen Road in Lotus. These were the only meteorites found before rain hit the area on 25 April, on 1 May 2012, the James W. Marshall Gold Discovery State Historic Parks Ranger Suzie Matin discovered two pieces of the meteorite in her front yard. The park contains what is now known as Sutters Mill, ground-based searches resulted in the additional recovery of two pristinely collected meteorites for scientific study. A consortium of over 50 scientists investigated the circumstances of the impact, the event was recorded by two infrasound monitoring stations of the Comprehensive Nuclear-Test-Ban Treaty Organization’s International Monitoring System. The preliminary analysis are indicative of energy yield of approximately 4 kilotons of TNT equivalent, hiroshimas Little Boy had a yield of about 16 kt. The air burst had approximate coordinates of 37. 6°N120. 5°W /37.6, before entry in Earths atmosphere, the meteoroid probably had an absolute magnitude of roughly 31. The meteoroid entered at a speed of 28.6 ±0.7 km/s. It broke apart at an altitude of 48 km, the highest breakup event on record resulting in meteorites on the ground, before entry, the meteoroid moved on an eccentric orbit, stretching from just inside the orbit of Jupiter to the orbit of Mercury. The orbit had an inclination and an orbital period suggesting that this meteoroid originated in the 3,1 mean motion resonance with Jupiter. The CM chondrite Maribo moved on an orbit, but rotated by 120 degrees in the direction of the line of apsides. The meteorite type is similar to that of the 1969 Murchison meteorite in Australia, the Sutters Mill meteorite originated from near the surface of its parent body
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