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| All Sky Fireball Network |
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On Mar. 17, 2015, the network reported 15 fireballs.
(15 sporadics)
(15 sporadics)
In this diagram of the inner solar system, all of the fireball orbits intersect at a single point--Earth. The orbits are color-coded by velocity, from slow (red) to fast (blue). [Larger image] [movies]
end quote from:
A Fireball appears to be any meteorite that eventually collides with Earth and becomes a shooting star across the skies as it burns up: hence Fireball.
Meteorite
From Wikipedia, the free encyclopedia
The Hoba meteorite in Namibia is the largest known intact meteorite, 2.7 metres long and 60 tonnes weight.
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This article is about debris from space that survives impact with the ground. For other uses of "Meteor" and "Meteors", see Meteor (disambiguation). For popular applications, see Falling star. For the fictional superhero in the Marvel Comics universe, see Meteorite (comics).
A meteorite is a solid piece of debris, from such sources as asteroids or comets, that originates in outer space and survives its impact with the Earth's surface. It is called a meteoroid
before its impact. A meteorite's size can range from small to extremely
large. When a meteoroid enters the atmosphere, friction, pressure, and
chemical interactions with the atmospheric gases cause it to heat up and
radiate that energy, thus forming a fireball, also known as a meteor or shooting/falling star. A bolide
is either an extraterrestrial body that collides with the Earth, or 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 outer space. Meteorites have been found on the moon[1][2] and Mars.[3] Meteorites that are recovered after being observed as they transit the atmosphere or impact the Earth are called meteorite fall. All other meteorites are known as finds. As of February 2010, there are approximately 1,086 witnessed falls having specimens in the world's collections. There are more than 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; iron meteorites that are largely composed of metallic iron-nickel; and, stony-iron meteorites that 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. Meteorites smaller than 2mm are classified as micrometeorites.
Contents
Naming
Meteorites are always named for the places 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)). The name designated by the Meteoritical Society is used by scientists, catalogers, and most collectors.Fall phenomena
See also: atmospheric entry and Meteorite fall
Most meteoroids disintegrate when entering Earth's atmosphere.
Usually, five to ten a year are observed to fall and are subsequently
recovered and made known to scientists.[6] 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.
The 'crater' made by a 61.9 gram Novato meteorite when it hit a person's roof on October 17, 2012.
A bolide: a very bright meteor of an apparent magnitude of −14 or brighter.
NWA 859 iron meteorite showing effects of atmospheric ablation
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.[citation needed]
Meteorite types
Main article: Meteorite classification
Murnpeowie meteorite, an iron meteorite with regmaglypts resembling thumbprints.
Marília Meteorite, a chondrite H4, which fell in Marília, São Paulo state, Brazil, on 5 October 1971, at 17:00
A cut and polished slice of the Esquel meteorite, a stony-iron
pallasite. Yellow-green olivine crystals are encased in the iron-nickel
matrix.
About 86% of the meteorites that fall on Earth are chondrites,[4][16][17] 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, 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 coalesced 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 (meaning they do not contain chondrules), some of which are similar to terrestrial igneous rocks. Most achondrites are also ancient rocks, and are thought to represent crustal material of differentiated planetesimals. One large family of achondrites (the HED meteorites) may have originated on the parent body of the Vesta Family, although this claim is disputed.[18][19] Others derive from unidentified 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 humans.
About 5% of meteorites that have been seen to fall are iron meteorites composed of iron-nickel alloys, such as kamacite and/or taenite. Most iron meteorites are thought to come from the cores of planetesimals that were once molten. As on Earth, the denser metal separated from silicate material and sank toward the center of the planetesimal, forming its core. After the planetesimal solidified, it broke up in a collision with another planetesimal. Due to the low abundance of iron meteorites in collection areas such as Antarctica, where most of the meteoric material that has fallen can be recovered, it is possible that the percentage of iron-meteorite falls is lower than 5%. This would be explained by a recovery bias; laypeople are more likely to notice and recover solid masses of metal than most other meteorite types. The abundance of iron meteorites relative to total Antarctic finds is 0.4% [20][21]
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.
Meteorite chemistry
In March 2015, NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine and thymine, have been formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), the most carbon-rich chemical found in the Universe, may have been formed in red giants or in interstellar dust and gas clouds, according to the scientists.[22]Meteorite recovery
Falls
See also: Impact event and Meteorite fall
Car seat and muffler hit by the Benld meteorite in 1938, with the meteorite inset. An observed fall.
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 Přibram meteorite, which fell in Czechoslovakia (now the Czech Republic) in 1959.[23] 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.[24] Another program in Canada, the Meteorite Observation and Recovery Project, ran from 1971 to 1985. It too recovered a single meteorite, Innisfree, in 1977.[25] 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.[26] NASA has an automated system that detects meteors and calculates the orbit, magnitude, ground track, and other parameters over the southeast USA, which often detects a number of events each night.[27]
Finds
Until the twentieth century, only a few hundred meteorite finds had ever been discovered. More than 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 more than 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.[28]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 by a single person, 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.[29]
Antarctica
A scanning electron microscope revealed structures resembling bacteria fossils - in the meteorite ALH84001
discovered in Antarctica in 1984. Microscopically, the features were
initially interpreted as fossils of bacteria-like lifeforms. It has
since been shown that similar magnetite structures can form without the
presence of microbial life in hydrothermal systems.[30]
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.[citation needed]
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.[31] 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).[32]
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 more than 500 others,[33] ~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
This small meteorite is from the NWA 869 strewn field, near Tindouf, Algeria. Currently classified as an L3.8-6 ordinary chondrite it shows brecciation and abundant chondrules.[34]
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 more than 500.[37]
Northwest Africa
Meteorite markets came into existence in the late 1990s, especially in Morocco. This trade was driven by Western commercialization and an increasing number of collectors. The meteorites were supplied 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. When they get classified, they are named "Northwest Africa" (abbreviated NWA) followed by a number.[38] It is generally accepted that NWA meteorites originate in Morocco, Algeria, Western Sahara, Mali, and possibly even further afield. Nearly all of these meteorites leave Africa through Morocco. Scores of important meteorites including Lunar and Martian meteorites have been discovered and made available to science via this route. A few of the more notable meteorites recovered include Tissint and Northwest Africa 7034. Tissint was the first witnessed Martian meteorite fall in over fifty years; NWA 7034 is the oldest meteorite known to come from Mars, and is a unique water-bearing regolith breccia.Arabian Peninsula
Meteorite find in situ on desert pavement, Rub' al Khali, Saudi Arabia. Probable chondrite, weight 408.5 grams.
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 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 US 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 historians, but there is little support for this in the scientific literature.[39]
The American Southwest
A stony meteorite (H5) found just north of Barstow, California, in 2006
Meteorites in history
Children posing behind a replica of the Tucson Meteorite on exhibit in
the “Origins Hall” of the Arizona Museum of Natural History
The oldest known iron artifacts are nine small beads hammered from meteoritic iron. They were found in northern Egypt and have been securely dated to 3200 BC.[45]
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) burial cyst near Camp Verde, Arizona, respectfully wrapped in a feather cloth.[46] 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.[46][47]
A lance made from a Narwhal tusk with a meteorite iron head
The German physicist, Ernst Florens Chladni, was the first to publish the then audacious idea that meteorites were rocks from space.[48] He published his booklet, "On the Origin of the Iron Masses Found by Pallas and Others Similar to it, and on Some Associated Natural Phenomena", in 1794.[49] 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.[50] It took nearly ten 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.[51] Biot's study, initiated by the French Academy of Sciences, was compelled by a meteorite fall of thousands of meteorites on 26 April 1803 from the skies of L'Aigle, France.[52][53][54]
One of the leading theories for the cause of the Cretaceous–Paleogene 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.
There are several reported instances of falling meteorites having killed 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 meteorite fall was identified in the 1980s as Martian in origin. There is substantial evidence that the meteorite known as Valera (Venezuela 1972, see Meteorite fall) 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. One example is from 1490 AD in China, which purportedly killed thousands of people.[55] John Lewis has compiled some of these reports, and summarizes, "No one in recorded history has ever been killed by a meteorite in the presence of a meteoriticist and a medical doctor" and "reviewers who make sweeping negative conclusions usually do not cite any of the primary publications in which the eyewitnesses describe their experiences, and give no evidence of having read them".[56]
The first known modern case of a human hit by a space rock occurred on 30 November 1954 in Sylacauga, Alabama.[57] There a 4 kilograms (8.8 lb) stone chondrite[58] 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.
Another claim 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 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.[59]
Several persons have since claimed[60] to have been struck by "meteorites" but no verifiable meteorites have resulted.
Meteorite weathering
See also: Meteorite weathering
Most meteorites date from the oldest times in the solar system and
are by far the oldest material available on our planet. Despite their
age, they are fairly vulnerable to terrestrial environment: water, salt,
oxygen attack the meteorites as soon they reach the ground.The terrestrial alteration of meteorites is called weathering. In order to quantify the degree of alteration that a meteorite experienced, several qualitative weathering indices have been applied to Antarctic and desertic samples.[61]
The most known weathering scale, used for ordinary chondrites, ranges from W0 (pristine state) to W6 (heavy alteration).
Notable meteorites
- Allende, largest known carbonaceous chondrite (Chihuahua, Mexico, 1969).
- Allan Hills A81005 – First meteorite determined to be of lunar origin.
- Allan Hills 84001 – Mars meteorite that was claimed to prove the existence of life on Mars.
- The Bacubirito Meteorite (Meteorito de Bacubirito) – A meteorite estimated to weigh 20–30 short tons (18–27 t). It is on display at the Centro de Ciencias de Sinaloa in Culiacán, Sinaloa, Mexico.
- Campo del Cielo - a group of iron meteorites associated with a crater field (of the same name) of at least 26 craters north west of Buenos Aires, Argentina. The total weight of meteorites recovered exceeds 100 tonnes.[62]
- Canyon Diablo – Associated with Meteor Crater in Arizona.
- Cape York – One of the largest meteorites in the world. A 34 ton fragment called "Ahnighito", is exhibited at the American Museum of Natural History; the largest meteorite on exhibit in any museum.
- Gibeon – A large Iron meteorite in Namibia, created the largest known strewn field.
- Hoba – The largest known intact meteorite.
- Kaidun – An unusual carbonaceous chondrite.
- Murchison – A carbonaceous chondrite found to contain nucleobases – the building block of life.
- Nōgata – The oldest meteorite whose fall can be dated precisely (to 19 May 861, at Nōgata)
- Orgueil – A famous meteorite due to its especially primitive nature and high presolar grain content.
- Sikhote-Alin – Massive iron meteorite impact event that occurred on 12 February 1947.
- Tucson Ring – Ring shaped meteorite, used by a blacksmith as a table, in Tucson AZ. Currently at the Smithsonian.[63]
- Willamette – The largest meteorite ever found in the United States.
- The Peruvian meteorite event – On 15 September 2007, a stony meteorite that may have weighed as much as 4000 kilograms created a crater 13 meters in diameter near the village of Carancas, Peru.[64]
- 2013 Russian meteor event — a 17 metre diameter, 10 000 ton[65] asteroid hit the atmosphere above Chelyabinsk, Russia at 18 km/s around 09:20 local time (03:20 UTC) 15 February 2013, producing a very bright fireball[66] in the morning sky. A number of small meteorite fragments have since been found nearby.[67]
Notable large impact craters
- Acraman crater in South Australia (90 kilometres (56 mi) diameter)
- Ames crater in Major County, Oklahoma 16 kilometres (9.9 mi) diameter
- Brent crater in northern Ontario (3.8 kilometres (2.4 mi) diameter)
- Chesapeake Bay impact crater (90 kilometres (56 mi) diameter)
- Chicxulub Crater off the coast of Yucatán (170 kilometres (110 mi) diameter)
- Clearwater Lakes a double crater impact in Québec, Canada (26 and 36 kilometres (16 and 22 mi) in diameter)
- Lonar crater in India (1.83 kilometres (1.14 mi) diameter)
- Lumparn in the Åland Islands, in the Baltic Sea (9 kilometres (5.6 mi) diameter)
- Manicouagan Reservoir in Québec, Canada (100 kilometres (62 mi) diameter)
- Manson crater in Iowa (38 kilometres (24 mi) crater is buried)
- Meteor Crater in Arizona, also known as "Barringer Crater", the first confirmed terrestrial impact crater. (1.2 kilometres (0.75 mi) diameter)
- Mjølnir impact crater in the Barents Sea (40 kilometres (25 mi) diameter)
- Nördlinger Ries crater in Bavaria, Germany (25 kilometres (16 mi) diameter)
- Popigai crater in Russia (100 kilometres (62 mi) diameter)
- Siljan (lake) in Sweden, largest crater in Europe (52 kilometres (32 mi) diameter)
- Sudbury Basin in Ontario, Canada (250 kilometres (160 mi) diameter).
- Ungava Bay in Québec, Canada (260 by 320 kilometres (160 by 200 mi))
- Vredefort Crater in South Africa, the largest known impact crater on Earth (300 kilometres (190 mi) diameter from an estimated 10 kilometres (6.2 mi) wide meteorite).
Notable disintegrating meteoroids
- Tunguska event in Siberia 1908 (no crater)
- Vitim event in Siberia 2002 (no crater)
- Chelyabinsk event in Russia 2013 (no known crater)
See also
- Atmospheric focusing, shockwave produced in the atmosphere by a meteor or other cause
- Glossary of meteoritics
- List of meteorites
- List of Martian meteorites
- List of meteorite minerals
- List of meteorites on Mars
- Meteor shower
- Meteorite classification
- Micrometeorites
References
- Meteoritical Bulletin Database. Lpi.usra.edu. Retrieved on 17 December 2011.
External links
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- Current meteorite news articles
- The British and Irish Meteorite Society
- The Natural History Museum's meteorite catalogue database
- Meteoritical Society
- Earth Impact Database
- Every Recorded Meteorite Impact on Earth from Tableau Public
- Meteor Impact Craters Around the World
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A meteorite is a solid piece of debris, ... Following passage of the fireball, ... The oldest known iron artifacts are nine small beads hammered from meteoritic iron.
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