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A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical interactions with the atmospheric gases cause it to heat up and radiate energy. It then becomes a meteor and forms a fireball, also known as a shooting star or falling star; astronomers call the brightest examples "bolides". Once it settles on the larger body's surface, the meteor becomes a meteorite. Meteorites vary greatly in size. For geologists, a bolide is a meteorite large enough to create an impact crater.
A chondrite is a stony (non-metallic) meteorite that has not been modified, by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form primitive asteroids. Some such bodies that are captured in the planet’s gravity well become the most common type of meteorite by arriving on a trajectory toward the Earth’s surface. Estimates for their contribution to the total meteorite population vary between 85.7% and 86.2%.
A micrometeorite is a micrometeoroid that has survived entry through the Earth's atmosphere. Usually found on Earth's surface, micrometeorites differ from meteorites in that they are smaller in size, more abundant, and different in composition. The IAU officially defines meteorites as 30 micrometers to 1 meter; micrometeorites are the small end of the range (~submillimeter). They are a subset of cosmic dust, which also includes the smaller interplanetary dust particles (IDPs).
ANSMET is a program funded by the Office of Polar Programs of the National Science Foundation that looks for meteorites in the Transantarctic Mountains. This geographical area serves as a collection point for meteorites that have originally fallen on the extensive high-altitude ice fields throughout Antarctica. Such meteorites are quickly covered by subsequent snowfall and begin a centuries-long journey traveling "downhill" across the Antarctic continent while embedded in a vast sheet of flowing ice. Portions of such flowing ice can be halted by natural barriers such as the Transantarctic Mountains. Subsequent wind erosion of the motionless ice brings trapped meteorites back to the surface once more where they may be collected. This process concentrates meteorites in a few specific areas to much higher concentrations than they are normally found everywhere else. The contrast of the dark meteorites against the white snow, and lack of terrestrial rocks on the ice, makes such meteorites relatively easy to find. However, the vast majority of such ice-embedded meteorites eventually slide undiscovered into the ocean.
Hedenbergite, CaFeSi2O6, is the iron rich end member of the pyroxene group having a monoclinic crystal system. The mineral is extremely rarely found as a pure substance, and usually has to be synthesized in a lab. It was named in 1819 after M.A. Ludwig Hedenberg, who was the first to define hedenbergite as a mineral. Contact metamorphic rocks high in iron are the primary geologic setting for hedenbergite. This mineral is unique because it can be found in chondrites and skarns (calc–silicate metamorphic rocks). Since it is a member of the pyroxene family, there is a great deal of interest in its importance to general geologic processes.
Queen Fabiola Mountains is a group of mountains in Antarctica, 50 kilometres long, consisting mainly of seven small massifs which trend north–south, forming a partial barrier to the flow of inland ice. The mountains stand in isolation about 140 km (90 mi) southwest of the head of Lutzow-Holm Bay. The mountains were discovered and photographed from aircraft by the Belgian Antarctic Expedition under Guido Derom on 8 October 1960. With permission from King Baudouin of Belgium, the mountains were named after his newly wedded wife Fabiola. In November–December 1960, the mountains were visited by a party of the Japanese Antarctic Research Expedition (JARE), 1957–1962, which made geomorphological and geological surveys. They applied the name Yamato Mountains. The highest massif is Mount Fukushima.
The Yamato Glacier is a glacier about 6 miles (10 km) wide, flowing west between Mount Fukushima and Mount Eyskens in the Queen Fabiola Mountains of Antarctica.
The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01:05 on February 8, 1969, falling over the Mexican state of Chihuahua. After breaking up in the atmosphere, an extensive search for pieces was conducted and over 2 tonnes (tons) of meteorite were recovered. The availability of large quantities of samples of the scientifically-important chondrite class has enabled numerous investigations by many scientists; it is often described as "the best-studied meteorite in history." The Allende meteorite has abundant, large calcium-aluminium-rich inclusions (CAI), which are among the oldest objects formed in the Solar System.
Mount Fukushima is, at 2,470 metres (8,100 ft), the highest massif in the Queen Fabiola Mountains of Antarctica, standing just north of Yamato Glacier. The rock massif rises 1,600 metres (5,200 ft) above the local ice surface and has many ragged peaks. It was discovered in 1960 by the Belgian Antarctic Expedition, under Guido Derom, and was named by Derom after Shin Fukushima, a geophysicist of the Japanese expedition, lost in a violent blizzard near the Japanese station on East Ongul Island in October 1960.
Enstatite chondrites are a rare form of meteorite, rich in the mineral enstatite. Only about 200 E-Type chondrites are currently known, comprising about 2% of the chondrites that fall on Earth. There are two main subtypes: EH and EL, classified based on their iron content.
CI chondrites, sometimes C1 chondrites, are a group of rare stony meteorites belonging to the carbonaceous chondrites. Samples have been discovered in France, Canada, India, and Tanzania. Compared to all the meteorites found so far, their overall chemical composition most closely resembles the elemental distribution in the sun's photosphere. Currently, borderline CI specimens found in Antarctica may or may not receive their own group, CY chondrites.
Richard Brice Hoover is a scientist who has authored 33 volumes and 250 papers on astrobiology, extremophiles, diatoms, solar physics, X-ray/EUV optics and meteorites. He holds 11 U.S. patents and was 1992 NASA Inventor of the Year. He was employed at the United States' NASA Marshall Space Flight Center from 1966 to 2012, where he worked on astrophysics and astrobiology. He established the Astrobiology Group there in 1997 and until his retirement in late 2011 he headed their astrobiology research. He conducted research on microbial extremophiles in the Antarctic, microfossils, and chemical biomarkers in precambrian rocks and in carbonaceous chondrite meteorites.
Wassonite is an extremely rare titanium sulfide mineral with chemical formula TiS. Its discovery was announced in a 2011 NASA press release as a single small grain within an enstatite chondrite meteorite called "Yamato 691", which was found during a 1969 Japanese expedition to Antarctica. This grain represents the first observation in nature of the synthetic compound titanium(II) sulfide.
The Zakłodzie meteorite is a stony-iron meteorite found in Poland in 1998. Its mass is 8.68 kilograms (19.1 lb). It is composed predominantly from enstatite and meteoric iron. Currently classified as an ungrouped enstatite achondrite its classification is still an ongoing scientific debate.
The Itqiy meteorite is an enstatite-rich stony-iron meteorite. It is classified as an enstatite chondrite of the EH group that was nearly melted and is therefore very unusual for that group. Other classifications have been proposed and are an ongoing scientific debate.
This is a glossary of terms used in meteoritics, the science of meteorites.
Allan Hills A81005 or ALH A81005 was the first lunar meteorite found on Earth. It was found in 1982 in the Allan Hills at the end of the Transantarctic Mountains, during a meteorite gathering expedition (ANSMET).
Yamato 000593 is the second largest meteorite from Mars found on Earth. Studies suggest the Martian meteorite was formed about 1.3 billion years ago from a lava flow on Mars. An impact occurred on Mars about 11 million years ago and ejected the meteorite from the Martian surface into space. The meteorite landed on Earth in Antarctica about 50,000 years ago. The mass of the meteorite is 13.7 kg (30 lb) and has been found to contain evidence of past water alteration.
CM chondrites are a group of chondritic meteorites which resemble their type specimen, the Mighei meteorite. The CM is the most commonly recovered group of the 'carbonaceous chondrite' class of meteorites, though all are rarer in collections than ordinary chondrites.
Gas-rich meteorites are meteorites with high levels of primordial gases, such as helium, neon, argon, krypton, xenon and sometimes other elements. Though these gases are present "in virtually all meteorites," the Fayetteville meteorite has ~2,000,000 x10−8 ccSTP/g helium, or ~2% helium by volume equivalent. In comparison, background level is a few ppm.
References
- ↑ "Catalog of Antarctic Meteorites" (PDF). Tokyo: National Institute of Polar Research. 2000. Retrieved 2011-04-07.
- 1 2 "Yamato 691". The Meteoritical Society . Retrieved 2011-04-07.
- ↑ Dwayne C. Brown; William Jeffs (2011-04-05). "Scientists Find New Type Of Mineral In Historic Meteorite". NASA . Retrieved 2011-04-07.
- ↑ Clarke, R. S. Jr. (1974). "Meteoritical Bulletin, No. 52". Meteoritics. 9: 118. Bibcode:1974Metic...9..101C . Retrieved 2011-04-07.
- ↑ Bryner, Jeanna (2011-04-06). "4.5-Billion-Year-Old Antarctic Meteorite Yields New Mineral". LiveScience. Retrieved 2011-04-07.
- ↑ "Yamato 691 Meteorite, Queen Fabiola Mountains (Yamato Mountains), Antarctica" . Retrieved 2011-04-07.