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A Meteorite is a body that survives an Earth collision.
A meteorite is an extraterrestrial body that survives its impact with the Earth's surface without being destroyed. While in space, a meteorite is called a meteoroid. When it enters the atmosphere, air resistance causes the meteorite body to heat up and emit light, thus forming a fireball, also known as a meteor or shooting 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 an object that has come from elsewhere in space. Meteorites have been found on the Moon and Mars.
Meteorites that are recovered after being observed as they transitted the atmosphere or impacted the Earth are called falls. All other meteorites are known as finds. As of mid-2006, there are approximately 1050 witnessed falls having specimens in the world's collections. In contrast, there are over 31,000 well-documented meteorite finds.
Meteorites are always named for the place where they were found, 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).)
Meteorites have traditionally been divided into three broad categories: stony meteorites are rocks, mainly composed of silicate minerals; iron meteorites 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.
Meteorite fall phenomena.
Most meteoroids disintegrate when entering the Earth's atmosphere. However an estimated 500 meteorites ranging in size from marbles to basketballs 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 impact craters. Instead, they typically arrive at the surface at their terminal velocity (free-fall) and, at most, create a small pit. Even so, falling meteorites have caused damage to property, livestock, and even people.
Very large meteoroids may strike the ground with a significant fraction of their cosmic velocity, leaving behind a hypervelocity 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. 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, 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 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 considerable concussion to occur; the famed Tunguska event likely resulted from such an incident. 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, 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 in South Africa, was reported in May, 2006.)
Several phenomena are well-documented during witnessed meteorite falls too small to produce hypervelocity craters. 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 as well as shock waves 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 passage through the atmosphere, their surfaces melt and experience ablation. 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, and others forming a frost upon their surface.
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 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.
About 86% of the meteorites that fall on Earth are chondrites, 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. Chondrites also contain small amounts of organic matter, including amino acids, and presolar grains. Chondrites are typically about 4.55 billion years old and are thought to represent material from the asteroid belt that never formed into large bodies. Like comets, 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, some of which appear to be similar to terrestrial mafic igneous rocks. Most achondrites are also ancient rocks, and are thought to represent crustal material of asteroids. One large family of achondrites may have originated on the asteroid 4 Vesta. 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 and Luna programs. The other group is almost certainly from Mars and are the only materials from other planets ever recovered by man.
About 5% of meteorites that fall are iron meteorites with intergrowths of iron-nickel alloys, such as kamacite and taenite. 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 near absence of irons from finds in collection areas such as Antarctica, where little, if any meteoric material that has fallen is not found, it is thought that, although irons constitute approximately 5% of recovered falls, they might actually be considerably less common than previously supposed.
Stony-iron meteorites constitute the remaining 1%. They are a mixture of iron-nickel metal and silicate minerals. One type, called pallasites, 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 as volcanic ejecta, but this theory has lost much of its support over the last few decades.
Most meteorite falls 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 densities such as Europe, Japan, and northern India.
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 Pribram meteorite, which fell in Czechoslovakia (now the Czech Republic) in 1959. 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. Another program in Canada, the Meteorite Observation and Recovery Project, ran from 1971 to 1985. It too recovered a single meteorite, Innisfree, in 1977. 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.
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 a man named Harvey H. Nininger that many meteorites may be found if you know how and where to look.
Meteorites on 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.
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.
Meteorites found in Antarctica.
A few meteorites had been found by field parties in Antarctica between 1912 and 1964. Then 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. Most recently, a Chinese program, the Antarctic Scientific Exploration of China, has conducted highly successful meteorite searches since the year 2000. The combined efforts of all of these expeditions have produced over 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).
Meteorites located in 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 desert 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, ~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.
Meteorites: The Sahara and rising commercialization.
In 1986-1987, 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. These were the first hint that vast numbers of meteorites could be found in certain parts of the Sahara. A few years later, an anonymous engineer who was a desert enthusiast saw photographs of meteorites being recovered in Antarctica, and thought he had seen similar occurrences on Jeep adventure tours he had organized in north Africa. In 1989, he returned to Algeria and recovered about 100 meteorites from at least 5 locations. Over the next four years, he and others who followed found at least 400 more meteorites at the same locations, plus new areas in Algeria and Libya. 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. Dark-colored meteorites can be easily spotted in these places, where they have been well-preserved due to the arid climate.
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 profitibility 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.
Meteorite discovered in Oman.
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 2000 meteorites as of mid-2006. 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.
Meteorites in history.
One of the leading theories for the cause of the Cretaceous-tertiary mass extinction that included the dinosaurs is a large meteorite 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.
A famous case is the alleged Chinguetti meteorite, a find reputed to come from a large unconfirmed 'iron mountain' in Africa.
The only reported fatality from meteorite impacts is an Egyptian dog who was killed in 1911, although this report is disputed. The meteorites that struck this area were identified in the 1980s as Martian in origin.
The first known modern case of a human hit by a space rock occurred on November 30, 1954 in Sylacauga, Alabama. There a 4 kg stone chondrite crashed through a roof and hit Ann Hodges in her living room after it bounced off her radio. She was badly bruised. Several persons have since claimed to have been struck by 'meteorites' but no verifiable meteorites have resulted.
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 tops.
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.
More About Meteorites.
Nov 3, 2005 - Have you seen some really bright meteors in the sky? You might have been lucky enough to see a fireball from the Taurid meteor shower. Every year in late October, early November, the Earth slams into the dust trail left behind Comet Encke. The tiny grains strike our atmosphere travelling at 105,000 kph (65,000 mph) and explode, leaving a bright trail that we see in the sky. 2005 could be a very special year for the Taurid meteor shower, which is due to peak between November 5th and November 12th.
Sep 28, 2005 - To better understand the environment that formed the Earth, Purdue researchers are studying 29 meteorites that formed in our planet's neighbourhood. Scientists believe the Earth collided with a Mars-sized planet early on, which changed its chemical makeup (and helped to form the Moon). These meteorites formed at the same time as the Earth, but they avoided this cataclysmic collision, so they can offer clues which were wiped clean from our planet.
Sep 20, 2005 - Of all the meteorites found around the world, on 45 formed before our Solar System. They provide a unique insight into the composition of the stellar nebula that went on to form our Sun and planets. These early rocks have very few volatile materials in them, like zinc, lead and sodium. So this "volatile depletion" must have been one of the first things to happen in the stellar nebula, and not during planetary formation as previously believed.
Aug 19, 2005 - A researcher from the University of Toronto has found unexpectedly young material in meteorites, challenging theories about early events in the formation of the Solar System. A paper published in Nature reports that key minerals called chondrules have been found in meteorites that formed much later than the initial nebula that collapsed to form our Solar System. Instead, these chodrules were probably created when two newly forming planets smashed together.
Aug 9, 2005 - The Earth suffered a period of heavy bombardment in its early days when the solar system was swarming with asteroids. Although it would have been catastrophic for you and I, it might have actually been a nice environment for early microbes. This is according to researchers who spent time at Haughton Impact Crater on Devon Island, in the Canadian Arctic. They found many life-friendly features in this "ground zero", including hydrothermal vents, blasted rocks that make cosy microbe homes, and a nice, protected impact basin.
Jul 26, 2005 - Don't forget to mark your calendars for one of the best sky events of the year, the Perseid meteor shower. This year the shower peaks before dawn on August 12. Viewers in both hemispheres will be able to see meteors; however, it's folks in the north who'll get to see more. And as a special bonus, Mars will be visible in the eastern sky, near where the Perseid meteors seem to originate.
May 5, 2005 - Skywatchers are in for a treat tonight as the eta Aquarid meteors will be putting on a show. Observers in the southern hemisphere should be able to see 15-60 meteors an hour depending on the darkness of the skies. Those in the northern hemisphere won't be so lucky, seeing only about 10 meteors an hour. Look to the constellation of Aquarius, towards the East in the early morning of May 6, and you should see a more than a few meteors. Be patient, dress warmly, and bring a friend or two..
Dec 7, 2004 - On Monday, December 13, brave skywatchers should be able to see hundreds of meteors an hour when the Geminids begin. It's possibly the best meteor showers in the whole year, and happens because the Earth is plowing through bits of dust left over from Asteroid 3200 Phaethon at 129,000 kph (80,000 mph). Although you'll see more meteors at midnight, one of the best times to watch is right at sunset when the constellation of Gemini is right on the horizon. You might see an Earthgrazer, where a meteor skips across the Earth's atmosphere and leaves a long, bright and colourful tail.
Oct 20, 2004 - You might want to set your alarm clock a little earlier on Thursday morning, so you can enjoy the Orionid meteor shower. If you look towards the constellation of Orion, with its easy to find belt, and be patient, you should see at least a few meteors streak past in the sky. This annual event happens because the Earth is passing through the dust trail of Halley's Comet, which returns to the Sun every 76 years. Orionids move fast, striking the atmosphere at 66 km/s (148,000 mph), which means they can be more spectacular that other, slower moving meteor showers. In dark conditions, you can expect to see 15-30 meteors an hour; less in the city.
Aug 24, 2004 - Phosphorus is central to life on Earth for many reasons; it forms the backbone of DNA and RNA, and it's an important element in many chemical processes. The questions is, how did the Earth get so much of it? Researchers from the University of Arizona believe that the meteorites that rained down early on during the formation of the Earth could have been the source. They found that many iron-nickel meteorites are rich with minerals that contain phosphorus, and propose that life could have formed around a spot where a meteorite struck the Earth.
Aug 11, 2004 - Tonight's the night when the Perseid meteor shower reaches its peak of 60 meteors/hour, and if we're lucky, a new filament of material from Comet Swift-Tuttle will give the event and extra boost. One way to make the moment last is to capture images of meteors with your camera; but, it's as hard as it sounds. First, you want to have the darkest skies you can find, and don't start until after 9:00pm. Use a standard 35 mm camera secured to a tripod, and use very fast film: ISO 400, 800 or 1,000 is recommended. Pick and area of sky, focus on infinity, and then start your camera's exposure, and then stop when a meteor streaks through the area. Don't be afraid to experiment.
Jul 26, 2004 - If you've got some dark skies, look up for a few minutes, and you're bound to see a meteor go by. That's because the annual Perseid meteor shower has begun, and it's only going to get better. The Earth began passing through the dust trail left behind Comet Swift-Tuttle on July 23rd, and we'll stay in it until August 22. The shower reaches its peak on August 12, however, when skywatchers should be able to see 80-100 meteors an hour. This is a good year for the Perseids because the Moon won't be too bright, and the Earth might be passing through an extra filament of dust for the first time on August 11.
Jul 21, 2004 - Researchers have found a new meteorite which they believe originated from Mars. The 715 gram (1.6 pound) black rock was discovered during a meteorite search in Antarctica. A total of 1358 meteorites were discovered during the search last year, but this one is unmistakably Martian in origin, according to scientists classifying the meteorites. Scientists from around the world are invited to request samples of the rock, dubbed MIL 03346, for their research. Perhaps it will be able to help clear up the controversy about whether life was found in that other rock from Mars.
Jun 28, 2004 - If you're planning your summer vacation, you might want to see if you can get your family outside of the city on Thursday, August 12 to enjoy the annual Perseid meteor shower. This year will be especially good because the Moon won't be around to brighten the sky. We might also be passing through a newer filament of dust ejected from Comet Swift-Tuttle, which is responsible for the meteor shower. Observers in North America should be might be able to see up to 200 meteors an hour when the Earth passes through this filament, in addition to the regular 40-60 meteors/hour we see every year.
Apr 15, 2004 - Researchers from the University of Chicago are analyzing hundreds of meteorite fragments that struck Park Forest, Ill. in the evening of March 26, 2003. Witnesses in several states saw the tremendous fireball when it struck last year, and volunteers eventually collected 30 kg of fragments; some that crashed through the roofs of their houses. It's believed that the original meteor weighed 900 kg when it exploded in the sky. The heavier pieces fell nearly straight down, and the lighter pieces were carried downwind a bit to create a huge swath of fragments.
Mar 5, 2004 - A group of scientists from Washington University in St. Louis found nine specks of silicate stardust inside a primitive meteorite, after examining more than 159,000 particles. This is an important discovery, because it tells researchers that the early solar system formed from gas and dust, and not in a hot solar nebula - until now, these silicate particles had only been found in interplanetary dust. The team used a special mass spectrometer to analyze the composition of individual grains in the meteorite, searching for particles which had to be formed in stars.
Nov 5, 2003 - The Leonid meteor shower will be making an appearance on November 17, 2003, and it might be an impressive show. These meteors are the minute dust trails of Comet 55P/Tempel-Tuttle which flash in the sky as they strike the Earth's atmosphere. In past years, the Leonids have been very impressive, sometimes thousands of meteors have been seen. Astronomers aren't sure how many will strike the Earth this year - it could be anywhere from a couple an hour to several hundred per hour. The best views will be in Europe, but the rest of the world will still get a show if they watch the skies after midnight.
Sep 29, 2003 - At least 20 people were injured and several homes were destroyed when a meteorite crashed into a village in eastern India. Several reports say that a fireball flew across the sky, and burning fragments rained down across a wide area. Officials are in the area now, assessing the damage, and trying to help recover pieces of the meteorite for further study.
Links For Meteorites.Arizona Skies Meteorites - We sell high quality meteorites from around the world-Satisfaction Guaranteed!
BCC Meteorites - This website deals with and provides to researchers, dealers and collectors, rare meteorite samples including, stellar grains.
Current events SAHARAMET - Meteorites Monthly News, discovery of 150kg carbonaceous chondrite, Saharan expeditions, CD-ROM and reference cards about meteorites.
Fernlea Meteorites UK - Meteorites for sale
MERGE - Spanish website of meteorites and planetary geology
Meteorite and Information
MIAC- Meteorites and Impacts Advisory Committee - Images and information on Meteorites, Impacts and Fireballs in Canada
Space Rocks Inc. - Buy, Sell, Trade Quality Meteorite Specimens!
International Meteor Association
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