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Lunar meteorite
From Wikipedia, the free encyclopedia
A Lunar meteorite is a meteorite that is known to have originated on the Moon.
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The first lunar meteorite, Yamato 791197, was discovered in 1979 in Antarctica, but its lunar origin was not discovered for several years. The first meteorite to be recognized as originating from the Moon was Allan Hills 81005 which was found in 1982[1]. About 48 (as of August, 2007) other lunar meteorites have subsequently been discovered. The total mass is more than 30kg. All lunar meteorites have been found in deserts; most have been found in Antarctica, northern Africa, and the Sultanate of Oman. None have yet been found in North America, South America, or Europe.
Lunar origin is established by comparing the mineralogy, the chemical composition, and the isotopic composition between meteorites and samples from the Moon collected by Apollo missions.
Most lunar meteorites are launched from the Moon by impacts making lunar craters of a few kilometers in diameter or less.[2] No source crater of lunar meteorites has been positively identified, although there is speculation that the highly anomalous lunar meteorite Sayh al Uhaymir 169 derives from the Lalande impact crater on the Lunar nearside[3][4].
Cosmic ray exposure history established with noble gas measurements have shown that all lunar meteorites were ejected from the Moon in the past 20 million years. Most left the Moon in the past 100,000 years. After leaving the Moon, most lunar meteoroids go into orbit around Earth and eventually succumb to Earth's gravity. Some meteoroids ejected from the Moon get launched into orbits around the sun. These meteoroids remain in space longer but eventually intersect the Earth's orbit and land.
All six of the Apollo missions on which samples were collected landed in the central nearside of the Moon, an area that has subsequently been shown to be geochemically anomalous by the Lunar Prospector mission. In contrast, the numerous lunar meteorites are random samples of the Moon and consequently provide a more representative sampling of the lunar surface than the Apollo samples. Half the lunar meteorites, for example, likely sample material from the farside of the Moon.
At the time the first meteorite from the Moon was discovered in 1982, there was speculation that some other unusual meteorites that had been found previously originated from Mars. The positive identification of lunar meteorites on Earth supported the hypothesis that meteoroid impacts on Mars could eject rocks from that planet. There are also speculations about the possibility of finding "Earth meteorites" on the surface of the Moon [5]. This would be very interesting because in this case stones from earth older than 3.9 billion years, which are destroyed on earth by various geological processes, may have survived on the Moon. Thus some scientists propose new missions to the Moon to search for ancient rocks from Earth.
Today, about one in every thousand newly discovered meteorites is a lunar meteorite, whereas the vast majority of meteorites are from the asteroid belt. In the early 19th century most scientists believed that all meteorites were from the Moon. Although today supported only by a minority of researchers, there are also theories that Tektites are from the Moon, and should therefore also be regarded as lunar meteorites. However, most scientists regard such theories as outdated.
Lunar meteorites are the only current source of moon rocks which can be owned by the public. All rocks collected during the Apollo moon-landing program are considered to be the property of humanity as a whole, held for the benefit of scientific study, and it is illegal to own, buy or sell them. (A recent attempt to sell stolen moonrocks, originally given as gifts to heads-of-state by the American Government, was foiled by an undercover "sting" after a tip-off from a meteorite expert). The small amount of moonrock returned by the Russian Luna 16 probe is also unavailable to the public.
Of those lunar meteorites which are found on Earth, those found in Antarctica are similarly considered (by Treaty) among scientists to be used only for science. Only those found elsewhere - chiefly in deserts in areas such as Oman - are freely traded on the open market, like other meteorites.
Cited references
- ^ Marvin U. B. (1983) The discovery and initial characterization of Allan Hills 81005: The first lunar meteorite, Geophys. Res. Lett. 10, 775–778
- ^ James N. Head, H. Jay Melosh, and Boris A. Ivanov. "High-speed ejecta from small craters". Science 298: 1752-1756.
- ^ Gnos E., Hofmann B. A., Al-Kathiri A., Lorenzetti S., Eugster O., Whitehouse M. J., Villa I., Jull A. J. T., Eikenberg J., Spettel B., Krähenbühl U., Franchi I. A., and Greenwood G. C. (2004) Pinpointing the source of a lunar meteorite: Implications for the evolution of the Moon, Science 305, 657–659
- ^ G. Jeffrey Taylor (October 31, 2004). New Lunar Meteorite Provides its Lunar Address and Some Clues about Early Bombardment of the Moon.
- ^ John Armstrong, Llyd Wells, and Guillermo Gonzalez (2002). "Rummaging through Earth’s Attic for Remains of Ancient Life". Icarus 160: 183-196.
Scientific reference
- Randy Korotev (2005). "Lunar geochemistry as told by lunar meteorites". Chemie der Erde 65: 297-346.
General references
- G. Jeffrey Taylor (November 22, 2005). Gamma Rays, Meteorites, Lunar Samples, and the Composition of the Moon.
- Bill Cooke (August 2006). "The Great Interplanetary Rock Swap". Astronomy 34 (8): 64-67.
- Lunar Meteorites, Washington Univ. St.Louis
- List of Lunar Meteorites
- Lunar Meteorites, Univ. of Arizona
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| Lunar science | Geology · Lunar geologic timescale · Giant impact hypothesis · Moon rocks · Lunar meteorites · KREEP · ALSEP · Lunar laser ranging · Late heavy bombardment | |
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| See also Solar system, natural satellite | ||