View source for Astronomy:Allan Hills A81005

{{Infobox meteorite
|Name                      = Allan Hills A81005 (ALH A81005)
|Alternative names         = 
|Image                     = Allan Hills 81005, lunar meteorite.jpg
|Image_caption             = 
|Type                      = [[Astronomy:Achondrite|Achondrite]]
|Class                     = 
|Clan                      = [[Astronomy:Lunar meteorite|Lunar meteorite]]
|Group                     = Lunar anorthosite<ref name="MetDB ALH A81005" />
|Grouplet                  = <!-- For groups n<5 -->
|Subgroup                  = 
|Structural_classification = 
|Parent body               = [[Astronomy:Moon|Moon]]
|Composition               = Breccia with [[Chemistry:Plagioclase|plagioclase]] clasts.
|Shock                     = 
|Weathering                = A/B
|Country                   = [[Earth:Antarctica|Antarctica]]
|Region                    = Allan Hills
|Lat_Long                  = {{coord|76|49|49|S|158|15|32|E|display=inline,title}}<ref name="MetDB ALH A81005" />
|Observed_fall             = No
|Fall_date                 = 
|Found_date                = 17 January 1982<ref name="LMC ALH 81005" />
|TKW                       = {{convert|31.4|g}}
|Strewn_field              = 
|Image2                    = 
|Image2_caption            = 
}}
'''Allan Hills A81005''' or ALH A81005 (sometimes also named without the "A" in front of the number) was the first [[Astronomy:Lunar meteorite|lunar meteorite]] found on Earth.<ref name="Marvin 1983">{{cite journal|last=Marvin|first=Ursula B.|title=The discovery and initial characterization of Allan Hills 81005: The first lunar meteorite|journal=Geophysical Research Letters|date=1 January 1983|volume=10|issue=9|pages=775–778|doi=10.1029/GL010i009p00775|bibcode=1983GeoRL..10..775M}}</ref> It was found in 1982 in the Allan Hills at the end of the [[Earth:Transantarctic Mountains|Transantarctic Mountains]], during a meteorite gathering expedition ([[Organization:ANSMET|ANSMET]]).<ref name="MetDB ALH A81005">{{cite web|title=Allan Hills A81005|url=http://www.lpi.usra.edu/meteor/metbull.php?code=1965|publisher=Meteoritical Society|access-date=11 January 2013}}</ref>
 
==Discovery and naming==
ALH A81005 was found on 17 January 1982 by John Schutt and Ian Whillans.<ref name="LMC ALH 81005">{{cite web|title=Lunar Meteorite Compendium ALH A81005|url=http://curator.jsc.nasa.gov/antmet/lmc/F2%20ALHA81005.pdf|publisher=[[Organization:NASA|NASA]]|access-date=11 January 2013|author=Kevin Righter|author2=John Gruener}}</ref><ref name="LMC">{{cite web|title=The Lunar Meteorite Compendium|url=http://curator.jsc.nasa.gov/antmet/lmc/|publisher=NASA|access-date=11 January 2013|author=Kevin Righter|author2=John Gruener}}</ref>  It is named after the Allan Hills, a mountain chain in [[Earth:Antarctica|Antarctica]] where many meteorites are gathered by expeditions.<ref name="MetDB ALH A81005" /> The large number of meteorites collected in Antarctica and the lack of geographic terms that could be used for names have led to the adaption of the "Antarctic rules" for meteorite naming. Every meteorite found in Antarctica receives the names of the collection area (Allan Hills) and a number. The number consists of the year the expedition started "81" and a three digit number that is given out consecutively (005). The "A" in front of the number stands for meteorites collected by [[Organization:ANSMET|ANSMET]] expeditions and can be considered optional.<ref name="Antarctic Rules">{{cite web|title=Antarctic Rules|url=http://meteoriticalsociety.org/?page_id=60|publisher=Meteoritical Society|access-date=26 February 2013}}</ref> The definition of the year is used because the year changes during the Austral summer season (December to March) and this avoids samples from one expedition having different years. This is the reason ALH A81005 has the year "81" in its name despite being found on 17 January 1982.<ref name="Antarctic Rules"/>

==Description==
ALH A81005 measures {{convert|3|xx|2.5|xx|3|cm|in}}. It has a dark fusion crust on the outside. The interior is made up of a black to dark grey groundmass ([[Earth:Matrix (geology)|matrix]]) with larger grey and white angular crystals (clasts). This appearance is typical for breccias, including those originating on Earth. The size of the larger crystals ranges from sub-millimeter to {{convert|8|mm}} in diameter.<ref name="MetDB ALH A81005" />

Thin section analysis revealed that the crystals are mostly [[Chemistry:Plagioclase|plagioclase]], with some [[Chemistry:Pyroxene|pyroxene]] and [[Chemistry:Olivine|olivine]]. It was also discovered that the meteorite had similarities to terrestrial gabbro or [[Earth:Basalt|basalt]]. Microprobe analysis showed that the [[Chemistry:Plagioclase|plagioclase]] was very calcium-rich. The crystals are a solid solution of 97% [[Chemistry:Anorthite|anorthite]] and 3% [[Chemistry:Albite|albite]]. The [[Chemistry:Pyroxene|pyroxene]]s have a variable composition lying between [[Chemistry:Enstatite|enstatite]], ferrosilite and [[Chemistry:Wollastonite|wollastonite]]. The [[Chemistry:Olivine|olivine]] is a solid solution of 11 to 40% [[Chemistry:Fayalite|fayalite]] with the rest being [[Chemistry:Forsterite|forsterite]].<ref name="MetDB ALH A81005" />  ALH A81005 is classified as a "lunar anorthosite breccia" and belongs to the group "lunar anorthosite" (abbreviated Lun-A).<ref name="MetDB ALH A81005" />

== History ==
The determination<!--conclusion?--> that ALH A81005 was of lunar origin was made<!--reached?--> by Robert Clayton and Toshiko Mayeda, researchers at the [[Organization:University of Chicago|University of Chicago]],<ref>{{cite web|url=https://news.google.com/newspapers?id=6JFVAAAAIBAJ&sjid=9D8NAAAAIBAJ&pg=1160,26557&dq=first+lunar+meteorite&hl=en|title=Meteorite came from moon|date=March 16, 1983|work=The Leader-Post|publisher=Regina, Saskatchewan|page=A5|access-date=27 February 2013}}</ref> following the determination by Smithsonian Institution scientist [[Biography:Brian Harold Mason|Brian Harold Mason]] that the meteorite was similar in chemical and isotopic composition to rocks returned by the [[Astronomy:Apollo program|Apollo program]] astronauts from lunar highland areas.<ref>{{cite web|url=https://news.google.com/newspapers?id=ULQSAAAAIBAJ&sjid=cfkDAAAAIBAJ&pg=7118,318836&dq=first+lunar+meteorite&hl=en|title=Scientists say meteorite is likely piece of the moon|date=March 16, 1983|work=Spokane Chronicle|page=A9|access-date=27 February 2013|location=Spokane, Washington}}</ref>  Evidence that ALHA 81005 is a lunar sample, was presented at the 18 March 1983 meeting of the [[Organization:Lunar and Planetary Institute|Lunar and Planetary Institute]].  The evidence included fabric data, mineralogical data, compositional data, oxygen isotope data, [[Chemistry:Noble gas|noble gas]] data, [[Astronomy:Cosmic ray|cosmic ray]] exposure history, magnetic properties, nuclear particle tracks, and [[Physics:Thermoluminescence|thermoluminescence]] data.<ref name="Cassidy">{{cite book |last1=Cassidy |first1=William |title=Meteorites, Ice, and Antarctica: A personal account |url=https://archive.org/details/meteoritesiceant00waca |url-access=limited |date=2003 |publisher=Cambridge University Press |location=Cambridge |isbn=9780521258722 |pages=[https://archive.org/details/meteoritesiceant00waca/page/n159 144]-185,320}}</ref>

==References==
{{Reflist}}



[[Category:Lunar meteorites]]

{{Sourceattribution|Allan Hills A81005}}