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A meteorite classification system attempts to group similar meteorites and allows scientists to communicate with a standardized terminology when discussing them. Meteorites are classified according to a variety of characteristics, especially minerological, petrological, chemical, and isotopic properties.
A Chondrule is a round grain found in a chondrite. Chondrules form as molten or partially molten droplets in space before being accreted to their parent asteroids. Because chondrites represent one of the oldest solid materials within the Solar System and are believed to be the building blocks of the planetary system, it follows that an understanding of the formation of chondrules is important to understand the initial development of the planetary system.
Chondrites are stony (non-metallic) 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 early solar system accreted to form primitive asteroids. They are the most common type of meteorite that falls to Earth with estimates for the proportion of the total fall that they represent varying between 85.7% and 86.2%.
The H type ordinary chondrites are the most common type of meteorite, accounting for approximately 40% of all those catalogued, 46% of the ordinary chondrites, and 44% of the chondrites. The ordinary chondrites are thought to have originated from three parent asteroids, whose fragments make up the H chondrite, L chondrite and LL chondrite groups respectively.
The ordinary chondrites are a class of stony chondritic meteorites. They are by far the most numerous group and comprise about 87% of all finds. Hence, they have been dubbed "ordinary". The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively.
The L type ordinary chondrites are the second most common group of meteorites, accounting for approximately 35% of all those catalogued, and 40% of the ordinary chondrites. The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively.
The LL chondrites are a group of stony meteorites, the least abundant group of the ordinary chondrites, accounting for about 10–11% of observed ordinary-chondrite falls and 8–9% of all meteorite falls. The ordinary chondrites are thought to have originated from three parent asteroids, with the fragments making up the H chondrite, L chondrite and LL chondrite groups respectively. The composition of the Chelyabinsk meteor is that of a LL chondrite meteorite. The material makeup of Itokawa, the asteroid visited by the Hayabusa spacecraft which landed on it and brought particles back to Earth also proved to be type LL chondrite.
Gao–Guenie is a H5 ordinary chondrite meteorite that fell on Burkina Faso, West Africa, on March 5, 1960. The fall was composed of many fragments and it is one of the largest observed meteorite showers in Africa to date.
Andura is an H chondrite meteorite that fell to Earth on August 9, 1939 in Maharashtra, India.
Archie is an H chondrite meteorite that fell to earth on August 10, 1932 in Archie, Missouri, United States.
Allegan is a type 5 H chondrite meteorite that landed in Michigan on July 10, 1899. Allegan weighed around fifty pounds after its landing. As of 1964, it was one of only seven known meteorites to land in Michigan.
Ambapur Nagla is an H chondrite meteorite that fell to earth on May 27, 1895, in Uttar Pradesh, India.
Anlong is an H chondrite meteorite that fell to earth on May 2, 1971 in Guizhou, China.
Arbol Solo is an H chondrite meteorite that fell to earth on September 11, 1954 in the province of San Luis, Argentina.
Arroyo Aguiar is an H chondrite meteorite that fell to earth during the summer of 1950 in the province of Santa Fe, Argentina.
Assisi is an H chondrite meteorite that fell to earth at 7am on May 24, 1886 in Perugia, Umbria, Italy.
Akbarpur is an H chondrite meteorite that fell to earth on April 18, 1838, in Uttar Pradesh, India.
Ankober is an H chondrite meteorite that fell to Earth on July 7, 1942 in Shewa, Ethiopia.
The Ordovician meteor event was a dramatic increase in the rate at which L chondrite meteorites fell to Earth during the Middle Ordovician period, about 467.5±0.28 million years ago. This is indicated by abundant fossil L chondrite meteorites in a quarry in Sweden and enhanced concentrations of ordinary chondritic chromite grains in sedimentary rocks from this time. This temporary increase in the impact rate was most likely caused by the destruction of the L-chondrite parent body 468 ± 0.3 million years ago having scattered fragments into Earth-crossing orbits, a chronology which is also supported by shock ages in numerous L-chondrite meteorites that fall to Earth today. It has been speculated that this influx contributed to, or possibly even instigated, the Great Ordovician Biodiversification Event, although this has been questioned.
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.
References
- 1 2 Meteoritical Bulletin Database: Agen
- ↑ Taricco, C.; Sinha, N.; Bhandari, N.; Colombetti, P.; Mancuso, S.; Rubinetti, S.; Barghini, D. (2016-09-26). "Early 18th century cosmic ray flux inferred from 44Ti in Agen meteorite". Astrophysics and Space Science. 361 (10): 338. Bibcode:2016Ap&SS.361..338T. doi:10.1007/s10509-016-2909-7. hdl:2318/1610590. ISSN 1572-946X.
