Murchison meteorite 1886716 225829761 2008-07-15T16:22:14Z Basilicofresco 6579637 /* Classification and composition */ {{Meteorite |Name= Murchison |Image= Murchison crop.jpg |Image_caption= A Murchison meteorite specimen at the [[National Museum of Natural History]] (Washington) |Image_width= |Type= [[Chondrite]] |Class= [[Carbonaceous chondrite]] |Group= CM2 |Structural_classification= |Composition= 22.13% total [[iron]], 12% [[water]] |Shock= S1-2 |Weathering= |Country= [[Australia]] |Region= [[Victoria (Australia)|Victoria]] |Lat_Long= {{coord|36|37|S|145|12|E|display=inline,title}}<ref name=database>[http://tin.er.usgs.gov/meteor/metbull.php?code=16875 Meteoritical Bulletin Database: '''Murchison''']</ref> |Observed_fall= Yes |Fall_date= [[28 September]] [[1969]] |Found_date= |TKW= 100 kg |Image2= Murchison-meteorite-stardust.jpg |Image2_caption= Pair of grains from the Murchison meteorite }} The '''Murchison''' meteorite is named after [[Murchison, Victoria]], in [[Australia]]. It is one of the most studied [[meteorite]]s due to its large mass (>100 kg), the fact that it was an observed fall, and it belongs to a group of meteorites rich in [[organic compound]]s. ==History== On [[28 September]] [[1969]], near the village of [[Murchison, Victoria]] in [[Australia]], a bright [[fireball]] was observed to separate into three fragments before disappearing<ref name=database />. A cloud of smoke and, 30 seconds later, a tremor were observed. Many specimens were found over an area larger than 13 km², with individual masses up to 7 kg; one, weighing 680 g, broke through a roof and fell in hay<ref name=database />. The total collected mass exceeds 100 kg. ==Classification and composition== The meteorite belongs to the CM group of [[carbonaceous chondrite]]s (see [[meteorite classification]]). Like most [[Carbonaceous chondrite|CM chondrite]]s, Murchison is [[Chondrite#Petrologic types|petrologic type 2]], which means that it experienced extensive alteration by water-rich fluids on its parent body<ref>S. A. Airieau, J. Farquhar, M. H. Thiemens, L. A. Leshin, H. Bao, E. Young. [http://www.lpi.usra.edu/meetings/lpsc2007/pdf/1230.pdf ''Planetesimal sulfate and aqueous alteration in CM and CI carbonaceous chondrites'']. Geochimica et Cosmochimica Acta, Volume 69, Issue 16, p. 4167-4172.</ref> before falling to Earth. CM chondrites, together with the CI group, are rich in carbon and are among the most chemically primitive meteorites in our collections. Like other CM chondrites, Murchison contains abundant [[Calcium-aluminium-rich inclusion|CAI]]s. Over 100 [[amino acid]]s (the basic components of biological life) have been identified in the meteorite. ==Organic matter== [[Image:Murchison-meteorite-ANL.jpg|left|thumbnail|250px|Fragment of the Murchison meteorite (at right) and isolated individual particles (shown in the test tube).]] Murchison contains common [[amino acid]]s such as [[glycine]], [[alanine]] and [[glutamic acid]] as well as unusual ones like [[isovaline]] and [[pseudoleucine]].<ref>{{cite journal | title=Evidence for extraterrestrial amino-acids and hydrocarbons in the Murchison meteorite | last=Kvenvolden | first=Keith A. | coauthors=Lawless, James; Pering, Katherine; Peterson, Etta; Flores, Jose; Ponnamperuma, Cyril, Kaplan, Isaac R.; Moore, Carleton | journal=[[Nature (journal)|Nature]] | volume=228 | issue=5275 | pages=923–926 | year=1970|url=http://chemport.cas.org/cgi-bin/sdcgi?APP=ftslink&action=reflink&origin=npg&version=1.0&coi=1:CAS:528:DyaE3MXisVCnsg%3D%3D&pissn=0028-0836&pyear=1983&md5=cb8b015f54156458fa2be8cdca44789f | doi=10.1038/228923a0 }}</ref> The initial report stated that the amino acids were [[racemic]] (that is, the [[Chirality (chemistry)|chirality]] of their [[enantiomer]]s are equally left- and right-handed), indicating that they are not present due to terrestrial contamination. A complex mixture of [[alkane]]s was isolated as well, similar to that found in the [[Miller-Urey experiment]]. [[Serine]] and [[threonine]], usually considered to be earthly contaminants, were conspicuously absent in the samples. More research found that some amino acids were present in [[enantiomeric excess]].<ref>{{cite journal | title=Distribution and enantiomeric composition of amino acids in the Murchison meteorite | last=Engel | first=Michael H. | coauthors=Nagy, Bartholomew | journal=[[Nature (journal)|Nature]] | volume=296 | pages=837–840 | date=April 29, 1982 | doi=10.1038/296837a0 }}</ref> [[Homochirality]] is considered a unique biological property. The claims were challenged on the grounds that the protein amino acids were non-racemic but the other amino acids were.<ref>{{cite journal | title=On the reported optical activity of amino acids in the Murchison meteorite | last=Bada | first=Jeffrey L. | coauthors=Cronin, John R.; Ho, Ming-Shan, Kvenvolden, Keith A.; Lawless, James G.; Miller, Stanley L.; Oro, J.; Steinberg, Spencer | journal=[[Nature (journal)|Nature]] | volume=301 | pages=494–496 | date=February 10, 1983 | doi=10.1038/301494a0 }}</ref> In 1997 research showed that individual amino-acid [[enantiomers]] from Murchison were enriched in the nitrogen [[isotope]] <sup>15</sup>N relative to their terrestrial counterparts, which confirmed an extraterrestrial source for an <small>L</small>-enantiomer excess in the Solar System.<ref>{{cite journal | title=Isotopic evidence for extraterrestrial non-racemic amino acids in the Murchison meteorite | last=Engel | first=Michael H. | coauthors=Macko, S. A. | journal=[[Nature (journal)|Nature]] | volume=389 | pages=265–268 | date=September 1, 1997 | doi=10.1038/38460 }}</ref> The list of organic materials identified in the meteorite was extended to [[polyol]]s by 2001.<ref>{{cite journal | title=Carbonaceous meteorites as a source of sugar-related organic compounds for the early Earth | last=Cooper | first=George | coauthors=Kimmich, Novelle; Belisle, Warren; Sarinana, Josh; Brabham, Katrina; Garrel, Laurence|journal=[[Nature (journal)|Nature]] | volume=414 | pages=879–883 | date=December 20, 2001 | doi=10.1038/414879a }}</ref> Building on the idea that homochirality (existence of only left handed amino acids and right handed sugars) is triggered by deposition of chiral molecules on meteorites, research in 2005 demonstrated that an amino acid like <small>L</small>-[[proline]] is capable of catalyzing the formation of chiral sugars. The [[catalysis]] is non-linear, that is proline with an [[enantiomeric excess]] of 20% yields an [[allose]] with enantiomeric excess of 55% starting from a benzyloxy acetaldehyde in a sequential [[aldol reaction|aldol]] type reaction in an organic solvent like [[Dimethylformamide|DMF]].<ref>{{cite journal | title=Plausible origins of homochirality in the amino acid catalyzed neogenesis of carbohydrates | last=Córdova | first=Armando | coauthors=Engqvist, Magnus; Ibrahem, Ismail; Casas, Jesús; Sundén, Henrik|journal=[[Chem. Commun.]] | pages=2047–2049 | year=2005 | doi=10.1039/b500589b }}</ref> In other words a small amount of chiral amino acids may explain the evolution of right-handedness of sugars. According to Engel, several lines of evidence indicate that the interior portions of well-preserved fragments from Murchison are pristine. Engel points to the array of amino acids Murchison contains and to isotope studies to bolster his position. Other scientists are equally convinced that the evidence proves the opposite: that Murchison is now thoroughly contaminated by terrestrial organic material. A 2008 study showed that the Murchison meteorite contains [[nucleobases]]. Measured carbon isotope ratios indicate a non-terrestrial origin for these compounds.<ref>{{cite journal |last=Martins |first=Zita |authorlink= |coauthors=''et al.'' |year=2008 |month= |title=Extraterrestrial nucleobases in the Murchison meteorite |journal=Earth and Planetary Science Letters |volume=270 |issue=1&ndash;2 |pages=130&ndash;136 |doi=10.1016/j.epsl.2008.03.026 |url= |accessdate= |quote= }}</ref> ==References== {{Reflist|2}} ==External links== * {{cite web |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=375 |title=Murchison's Amino Acids: Tainted Evidence? |first=Anne M. |last=Rosenthal |date=2003-02-12 |publisher=Astrobiology Magazine}} [[Category:Origin of life]] [[Category:Astrobiology]] [[de:Murchison (Meteorit)]] [[es:Meteorito Murchison]] [[fr:Météorite de Murchison]] [[it:Meteorite di Murchison]] [[he:מטאוריט מורצ'יסון]] [[ja:マーチソン隕石]] [[pl:Murchison (meteoryt)]] [[ru:Murchison (метеорит)]] [[sl:Murchison (meteorit)]] [[tr:Murchison Göktaşı]]