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Meteorite
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A '''meteorite''' is a small extraterrestrial body that impacts the
Earth's surface. While in space they are called
meteoroids, and while falling through Earth's atmosphere they are called
meteors. These are small
asteroids, approximately
boulder-sized or less. When it enters the atmosphere,
air resistance causes the body to heat up and emit light, thus forming a
fireball or
shooting star.
More generally, a meteorite on a celestial body is a small body that has come from elsewhere in space. The only example of a meteorite that didn't fall on Earth is the
Heat Shield Rock, which was found on
Mars.
Meteorites are classified according to their structure and mineral composition. The three main classes of meteorite are stony, stony-iron and iron. These classes are further
divided in to
Meteorites classification sub-classes.
Overview
Image:Meteorite Lapham.jpg right|frame|Meteorite which fell in [[Wisconsin in
1868 (''
Media:Increase Lapham.meteor.jpg Full image'')]]
Most meteors disintegrate when entering the Earth's atmosphere, making
impact events (Earth impacts) on the surface uncommon. About 500 baseball-sized rocks reach the surface each year. Large meteorites may strike the ground with considerable force, leaving behind an
impact crater. The kind of crater will depend on the size, composition, degree of fragmentation, and incoming angle of the meteor. The force of collision may cause widespread destruction. Occasional damage to property, livestock, and even people has been recorded in historic times. In the case of
comet fragments, which are largely composed of
ice, a considerable concussion may occur, even though no fragment of the original meteoroid survives; the famed
Tunguska event is thought to have resulted from such an incident.
79% of meteorites are
chondrites - balls of
mafic minerals with small grain size indicative of rapid cooling. In most chondrites small spherules, called
chondrules, can be found. Chondrites are typically about 4.6 billion years old and are thought to represent material from the
asteroid belt. It is unknown how they formed. Carbonaceous chondrites, thought to be unaltered
solar nebula material, constitute about 5% of meteorites and contain small amounts of organic materials, including
amino acids. Also,
presolar grains are identified in carbonaceous chondrites. The
isotope ratios of carbonaceous chondrites are similar to those of the
Sun.
Image:Nickel-Iron-Meteorite-Slice.jpg thumb|left|Slice of meteorite on display at the [[Vanderbilt Museum,
New York.]]
Achondrites are similar to terrestrial mafic
igneous rocks and sometimes are
brecciated. Achondrites constitute about 8% of the incoming material and are thought to represent crustal material of
some of the larger asteroids (mostly
4 Vesta) and occasionally
Mars. About 6% of meteorites are
iron meteorites with intergrowths of iron-
nickel alloys, such as
kamacite. Unlike chondrites, the crystals are large and appear to represent slow crystallization. Iron meteorites are thought to be the core material of one or more planets that subsequently broke up. Stony iron meteorites constitute the remaining 2%. They are a mixture of iron-nickel and
silicate minerals. They are thought to have originated in the boundary zone above the core regions where iron meteorites originated. A small number of meteorites belong to additional groups or subgroups with unique chemical characteristics relative to other members of the larger groups, such as
lunar meteorites or
Martian meteorites.
Tektites (from Greek ''tektos'', molten), natural glass objects up to a few centimeters in size, were formed--according to most scientists--by the impact of large meteorites on Earth's surface, although a few researchers favor an origin from the
Moon as volcanic ejecta.
Meteorites in history
One
theory suggests that a large meteorite impact caused the
Cretaceous-Tertiary extinction event mass extinction of the
dinosaurs. It is also theorized that meteorites caused other
mass extinction events throughout the
history of the Earth.
Image:willamette meteorite.jpg thumb|300px|The [[Willamette Meteorite, the largest ever to be found in the
United States]]
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
Mars Martian in origin.
The first known modern case of a
human hit by a space rock [http://imca.repetti.net/metinfo/metstruck.html] occurred on
November 30 1954 in
Sylacauga, Alabama. There a 4 kg stone chondrite meteorite [http://internt.nhm.ac.uk/jdsml/research-curation/projects/metcat//detail.dsml?Key=S4530&index= ] 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 [http://home.earthlink.net/~magellon/news1.html] 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.
Notable meteorites
*
Heat Shield Rock - Found ''on''
Mars.
*
Sayh al Uhaymir - Originated from the
moon.
*
Willamette Meteorite - The largest meteorite ever found in the
United States.
*
Orgueil meteorite - Object of a 1965 hoax that involved embedding a
seed within part of the meteorite.
*
Canyon Diablo meteorite - Used by pre-historic
Native Americans.
*
Sikhote-Alin Meteorite - Massive
impact event that occurred on
February 12,
1947.
*
Cape York meteorite - One of the largest meteorites in the world.
*
ALH84001 -
Mars meteorite that was claimed to prove the existence of
life on
Mars.
*
Kaidun meteorite - Possibly from the
Mars' natural satellites martian moon Phobos (moon) Phobos.
*
Hoba meteorite - The largest known meteorite.
See also
*
Meteor
*
Baetylus
*
Carbonaceous chondrite
*
Lake Siljan
*
Leonids
*
Geminids
*
Solar System
External links
{{Commons|Meteorite}}
{{wiktionary|meteorite}}
-
www.aerolite.org: Meteorite photographs, articles on meteorite hunting
-
MeteoriteTimes.com: Free On-line Meteorite Magazine
-
Meteorites.com.au - No. 1 Meteorite Information Website
-
Meteorite.fr - All about Meteorites
-
Natural History Museum of Vienna
-
Heavenly Bodies - Meteorite information (E / NL)
-
Meteoritical Society
-
The Natural History Museum's Meteorite Catalogue Database
-
Meteorite hits
-
Largest meteorites
-
Article with image of Hoba, world's largest meteorite
Category:Meteorites *
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