Editing Martian meteorite

{{Short description|Meteorite made of rock originating from Mars}}
{{For|meteorites found on Mars|List of rocks on Mars}}
{{Infobox meteorite subdivision
|Subdivision               = Clan
|Name                      = Martian meteorite (SNC meteorites)
|Alternative_names         = 
|Image                     = EETA79001 S80-37631.jpg
|Image_caption             = Martian meteorite [[EETA79001]], [[shergottite]]
|Image_alt_text            = 
|Compositional_type        = <!-- Iron or blank -->
|Type                      = [[Achondrite]]
|Class                     = 
|Group                     =
|Subgroups                 = {{flatlist|
* [[Shergottite]]
* [[Nakhlite]]
* [[Chassignite]]
* [[Orthopyroxenite]]
* Basaltic Breccia
}}
|Structural_classification = 
|Parent_body               = [[Mars]]
|Composition               = 
|Petrologic_type           = 
|Number_of_specimens       = 277 {{as of|2020|September|15|lc=y}}<ref name=metbull>{{cite web |title=Search results for 'Martian meteorites' |url=https://www.lpi.usra.edu/meteor/metbull.php?sea=&sfor=names&ants=&nwas=&falls=&valids=&stype=contains&lrec=50&map=ge&browse=&country=All&srt=name&categ=Martian+meteorites&mblist=All&rect=&phot=&strewn=&snew=0&pnt=Normal%20table&dr=&page=1 |website=Meteoritical Bulletin |publisher=[[Meteoritical Society]] |access-date=27 April 2020}}</ref>
|TKW                       = <!-- {{Convert||kg}} -->
|Image2                    = MarsMeteorite-NWA7034-716969main black beauty full.jpg 
|Image2_caption            = Martian meteorite [[NWA 7034]], nicknamed "Black Beauty," weighs approximately {{convert|320|g|oz|abbr=on}}.<ref name="NASA-20130103">{{cite web |author=Staff |title=Researchers Identify Water Rich Meteorite Linked To Mars Crust |url=https://www.nasa.gov/mission_pages/mars/news/mars20130103.html |date=January 3, 2013 |publisher=[[NASA]] |access-date=January 3, 2013 |archive-date=May 29, 2018 |archive-url=https://web.archive.org/web/20180529095602/https://www.nasa.gov/mission_pages/mars/news/mars20130103.html |url-status=dead }}</ref> 
|Image2_alt_text           = 
}}
A '''Martian meteorite''' is a rock that formed on [[Mars]], was ejected from the planet by an [[impact event]], and traversed [[interplanetary space]] before landing on [[Earth]] as a [[meteorite]]. {{As of|2020|September}}, 277 meteorites had been classified as Martian, less than half a percent of the 72,000 meteorites that have been classified.<ref name="metbull"/> The largest complete, uncut Martian meteorite, Taoudenni 002,<ref>{{Cite web|first=Harry |last=Baker|date=2021-09-02|title=World's largest Martian meteorite goes on display|url=https://www.livescience.com/worlds-largest-martian-meteorite.html|access-date=2021-12-15|website=Lives Science|language=en}}</ref> was recovered in Mali in early 2021. It weighs 14.5 kilograms (32 pounds) and is on display at the [[Maine Mineral and Gem Museum]]. 

There are three [[meteorite group|groups]] of Martian meteorite: [[shergottites]], [[nakhlites]] and [[chassignites]], collectively known as '''SNC meteorites'''. Several other Martian meteorites are [[ungrouped meteorite|ungrouped]]. These meteorites are interpreted as Martian because they have [[chemical element|elemental]] and [[isotope|isotopic]] compositions that are similar to [[rock (geology)|rocks]] and [[Martian atmosphere|atmospheric gases on Mars]], which have been measured by [[List of Mars orbiters|orbiting spacecraft]], [[Mars lander|surface landers]] and [[Mars rover|rovers]].<ref name="pass48_12-14">{{cite journal|last=Treiman|first=A.H.|display-authors=etal|title=The SNC meteorites are from Mars|journal=Planetary and Space Science|volume=48|issue=12–14|date=October 2000 |pages=1213–1230|bibcode=2000P&SS...48.1213T|doi=10.1016/S0032-0633(00)00105-7}}</ref><ref name="NASA-20131017">{{cite web |last=Webster |first=Guy |title=NASA Rover Confirms Mars Origin of Some Meteorites |url=https://mars.jpl.nasa.gov/news/nasa-rover-confirms-mars-origin-of-some-meteorites/ |date=October 17, 2013 |work=[[NASA]] |access-date=October 29, 2013 }}</ref> The term does not include meteorites found on Mars, such as [[Heat Shield Rock]].

== History ==
By the early 1980s, it was obvious that the SNC group of meteorites (Shergottites, Nakhlites, and Chassignites) were significantly different from most other meteorite types. Among these differences were younger formation ages, a different oxygen isotopic composition, the presence of aqueous weathering products, and some similarity in chemical composition to analyses of the Martian surface rocks in 1976 by the [[Viking program|Viking landers]]. Several scientists suggested these characteristics implied the origin of SNC meteorites from a relatively large parent body, possibly Mars.<ref name=Smith>{{cite journal |author=Smith, M.R. |author2=Laul, J. C. |author3=Ma, M. S. |author4=Huston, T. |author5=Verkouteren, R. M. |author6=Lipschutz, M. E. |author7=Schmitt, R. A. |bibcode=1984LPSC...14..612S |doi=10.1029/JB089iS02p0B612 |title=Petrogenesis of the SNC (Shergottites, Nakhlites, Chassignites) Meteorites: Implications for Their Origin From a Large Dynamic Planet, Possibly Mars. |journal=Journal of Geophysical Research |volume=89 |issue=S02 |pages=B612–B630 |date=February 15, 1984 }}</ref><ref>{{cite journal |author=Allan H. Treiman |author2=Michael J. Drake |author3=Marie-Josee Janssens |author4=Rainer Wolf |author5=Mitsuru Ebihara |doi=10.1016/0016-7037(86)90389-3 |title=Core formation in the Earth and Shergottite Parent Body (SPB):Chemical evidence from basalts |journal=Geochimica et Cosmochimica Acta |volume=50 |issue=6 |pages=1071–1091 |date=January 1986  |bibcode=1986GeCoA..50.1071T }}</ref> 

Then in 1983, various trapped gases were reported in impact-formed glass of the EET79001 shergottite, gases which closely resembled those in the Martian atmosphere as analyzed by Viking.<ref>{{cite journal|last=Bogard|first=D. D.|author2=Johnson, P.|title=Martian gases in an Antarctic meteorite|journal=Science|date=1983|volume=221|pages=651–654|bibcode = 1983Sci...221..651B |doi= 10.1126/science.221.4611.651|pmid=17787734|issue=4611|s2cid=32043880}}</ref> These trapped gases provided direct evidence for a Martian origin. In 2000, an article by Treiman, Gleason and Bogard gave a survey of all the arguments used to conclude the SNC meteorites (of which 14 had been found at the time) were from Mars. They wrote, "There seems little likelihood that the SNCs are not from Mars. If they were from another planetary body, it would have to be substantially identical to Mars as it now is understood."<ref name="pass48_12-14"/>

==Subdivision==
[[File:Martian meteorites subdivision.svg|thumbnail|right|The Martian meteorites are divided into three groups (orange) and two grouplets (yellow). SHE = [[Shergottite]], NAK = [[Nakhlite]], CHA = [[Chassignite]], OPX = Orthopyroxenite ([[ALH 84001]]), BBR = Basaltic Breccia ([[NWA 7034]]).]]

As of April 25, 2018, 192 of the 207 Martian meteorites are divided into three rare groups of [[Achondrite|achondritic]] (stony) [[meteorite]]s: ''shergottites'' (169), ''nakhlites'' (20), ''chassignites'' (3), and ones otherwise (15) (containing the orthopyroxenite (OPX) Allan Hills 84001, as well as 10 basaltic breccia meteorites).<ref name=metbull/> Consequently, Martian meteorites as a whole are sometimes referred to as the ''SNC group'' (pronounced {{IPAc-en|s|n|ɪ|k|}}).<ref>{{cite book |last1=Murdin |first1=P |title=Encyclopedia of Astronomy & Astrophysics |publisher=CRC Press |isbn=9781000523034 |chapter=SNC Meteorite |date=January 2001 |quote=The letters SNC (pronounced `snick') stand for the three main classes: shergottites, nakhlites and chassignites.}}</ref> They have [[isotope]] ratios that are consistent with each other and inconsistent with a terrestrial origin. The names derive from the location of where the first meteorite of their type was discovered.

===Shergottites===
Roughly three-quarters of all Martian meteorites can be classified as shergottites. They are named after the [[Shergotty meteorite]], which fell at [[Sherghati]], [[India]] in 1865.<ref>[http://www2.jpl.nasa.gov/snc/shergotty.html Shergotty Meteorite - JPL, NASA]</ref> Shergottites are [[igneous rock]]s of [[mafic]] to [[ultramafic]] [[lithology]]. They fall into three main groups, the [[basaltic]], [[olivine]]-phyric (such as the [[Tissint]] group found in Morocco in 2011<ref>{{Cite web | url=http://www.space.com/18014-mars-meteorites-black-glass.html | title=Meteorite's Black Glass May Reveal Secrets of Mars| website=[[Space.com]]| date=11 October 2012 |first=Charles Q. |last=Choi}}</ref><ref>{{cite news|last=Morin|first=Monte|title=An unusually pristine piece of Mars|url=https://www.latimes.com/world/middleeast/la-xpm-2012-oct-12-la-sci-martian-meteorite-20121010-story.html|newspaper=Los Angeles Times|date=October 12, 2012}}</ref>) and [[lherzolite|lherzolitic]] shergottites, based on their crystal size and mineral content. They can be categorised alternatively into three or four groups based on their [[rare-earth element]] content.<ref name="Bridges Warren 2006 pp. 229–251">{{cite journal | last1=Bridges | first1=J.C. | last2=Warren | first2=P.H. | title=The SNC meteorites: basaltic igneous processes on Mars | journal=Journal of the Geological Society | publisher=Geological Society of London | volume=163 | issue=2 | year=2006 | issn=0016-7649 | doi=10.1144/0016-764904-501 | pages=229–251| bibcode=2006JGSoc.163..229B | s2cid=6815557 | url=http://oro.open.ac.uk/71/1/Bridges-Warren-revised._Jour_of_geo_soc_spec_iss.pdf }}</ref> These two classification systems do not line up with each other, hinting at complex relationships between the various source rocks and magmas from which the shergottites formed.
[[File:NWA 6963 full slice.jpg|thumb|left|NWA 6963,<ref>{{Cite web |url=http://www.lpi.usra.edu/meteor/metbull.php?code=54565 |title=Northwest Africa 6963 (NWA 6963)}}</ref> a shergottite found in Morocco, September 2011.]] 
The shergottites appear to have crystallised as recently as 180 million years ago,<ref name="Nyquist 2001 105–164"/> which is a surprisingly young age considering how ancient the majority of the surface of Mars appears to be, and the small size of Mars itself. Because of this, some have advocated the idea that the shergottites are much older than this.<ref>{{cite journal|title= Martian meteorite chronology and the evolution of the interior of Mars|journal=Earth and Planetary Science Letters|volume=280|issue=1–4|pages=285–295|doi=10.1016/j.epsl.2009.01.042|year=2009|last1=Bouvier|first1=Audrey|last2=Blichert-Toft|first2=Janne|author2-link=Janne Blichert-Toft|last3=Albarède|first3=Francis|bibcode=2009E&PSL.280..285B}}</ref> This "Shergottite Age Paradox" remains unsolved and is still an area of active research and debate.

It has been suggested the 3-million-year-old crater [[Mojave (crater)|Mojave]], 58.5&nbsp;km in diameter, was a potential source of these meteorites.<ref name="Werner2014">{{Cite journal | doi = 10.1126/science.1247282| title = The Source Crater of Martian Shergottite Meteorites| date = 2014-03-06| last1 = Werner | first1 = S. C.|author1-link= Stephanie C. Werner | journal = Science| volume = 343| issue = 6177| pages = 1343–6| last2 = Ody | first2 = A. | last3 = Poulet | first3 = F. | pmid=24603150| bibcode = 2014Sci...343.1343W| s2cid = 206553043| doi-access = free}}</ref> A paper published in 2021, however, disputes this, proposing instead the 28 km crater [[Tooting (crater)|Tooting]], or possibly the crater [[09-000015]] as the crater source of the depleted olivine-phyric shergottites ejected 1.1 Ma ago.<ref>{{Cite journal|last1=Lagain|first1=A.|last2=Benedix|first2=G. K.|last3=Servis|first3=K.|last4=Baratoux|first4=D.|last5=Doucet|first5=L. S.|last6=Rajšic|first6=A.|last7=Devillepoix|first7=H. a. R.|last8=Bland|first8=P. A.|last9=Towner|first9=M. C.|last10=Sansom|first10=E. K.|last11=Miljković|first11=K.|date=2021-11-03|title=The Tharsis mantle source of depleted shergottites revealed by 90 million impact craters|journal=Nature Communications|language=en|volume=12|issue=1|pages=6352|doi=10.1038/s41467-021-26648-3|pmid=34732704|pmc=8566585|bibcode=2021NatCo..12.6352L |issn=2041-1723}}</ref><ref>{{Cite web|last=Gough|first=Evan|date=2021-11-08|title=We Now Know Exactly Which Crater the Martian Meteorites Came From|url=https://www.universetoday.com/153207/we-now-know-exactly-which-crater-the-martian-meteorites-came-from/|access-date=2021-11-15|website=Universe Today|language=en-US}}</ref>

===Nakhlites===
[[File:Nakhla meteorite.jpg|thumb|200px|[[Nakhla meteorite]]'s two sides and its inner surfaces after breaking it]]
{{Main|Nakhlite}}
Nakhlites are named after the first of them, the [[Nakhla meteorite]], which fell in [[El-Nakhla]], [[Alexandria]], [[Egypt]] in 1911 and had an estimated weight of 10&nbsp;[[gram|kg]].

Nakhlites are [[igneous rock]]s that are rich in [[augite]] and were formed from [[basalt]]ic [[magma]] from at least four eruptions, spanning around 90 million years, from 1416 ± 7 to 1322 ± 10 million years ago.<ref name=":0">{{Cite journal|last1=Cohen|first1=Benjamin E.|last2=Mark|first2=Darren F.|last3=Cassata|first3=William S.|last4=Lee|first4=Martin R.|last5=Tomkinson|first5=Tim|last6=Smith|first6=Caroline L.|date=2017-10-03|title=Taking the pulse of Mars via dating of a plume-fed volcano|journal=Nature Communications|language=En|volume=8|issue=1|pages=640|doi=10.1038/s41467-017-00513-8|pmid=28974682|pmc=5626741|issn=2041-1723|bibcode=2017NatCo...8..640C}}</ref> They contain [[augite]] and [[olivine]] [[crystal]]s. Their crystallization ages, compared to a crater count chronology of different regions on Mars, suggest the nakhlites formed on the large volcanic construct of either [[Tharsis]], [[Elysium Planitia|Elysium]], or [[Syrtis Major Planum]].<ref name=Nakhlites>{{cite journal |author=Treiman, A.H. |url=https://www.lpi.usra.edu/science/treiman/nakhlite_rev.pdf |title=The nakhlite meteorites: Augite-rich igneous rocks from Mars |volume=65 |issue=3 |journal=Chemie der Erde |pages=203–270 |year=2005 |access-date=July 30, 2011|bibcode=2005ChEG...65..203T |doi=10.1016/j.chemer.2005.01.004 }}</ref>

It has been shown that the nakhlites were suffused with liquid water around 620 million years ago and that they were ejected from Mars around 10.75 million years ago by an asteroid impact. They fell to Earth within the last 10,000 years.<ref name=Nakhlites/>

===Chassignites===
The first chassignite, the [[Chassigny (meteorite)|Chassigny meteorite]], fell at [[Chassigny, Haute-Marne]], [[France]] in 1815. There has been only one other chassignite recovered, named Northwest Africa (NWA) 2737. NWA 2737 was found in [[Morocco]] or [[Western Sahara]] in August 2000 by meteorite hunters Bruno Fectay and Carine Bidaut, who gave it the temporary name "Diderot." It was shown by Beck ''et al.''<ref>{{cite conference |author=Beck, P. |display-authors=etal |url=http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1326.pdf |title=The Diderot meteorite: The second chassignite |conference=36th Annual Lunar and Planetary Science Conference |date=March 14–18, 2005 |location=League City, Texas |id=abstract no.1326. |access-date=September 8, 2006 }}</ref> that its "[[mineralogy]], major and trace element chemistry as well as [[Isotopes of oxygen|oxygen isotope]]s revealed an unambiguous Martian origin and strong affinities with Chassigny."

===Ungrouped meteorites===
[[File:ALH84001.jpg|thumb|right|200px|[[Allan Hills 84001]] (ALH 84001)]]
Among these, the famous specimen [[Allan Hills 84001]] has a different rock type from other Martian meteorites: it is an [[pyroxenite|orthopyroxenite]] (an igneous rock dominantly composed of [[orthopyroxene]]). For this reason it is classified within its own group, the "OPX Martian meteorites". This meteorite received much attention after an electron microscope revealed structures that were considered to be the [[fossil]]ized remains of [[bacteria]]-like [[life]]forms. {{As of|2005}}, scientific consensus was that the [[Microfossil|microfossils]] were not indicative of Martian life, but of contamination by earthly [[biofilm]]s. ALH 84001 is as old as the basaltic and intermediate shergottite groups{{snd}} i.e., 4.1 billion years old.{{Citation needed|reason=No supporting information referenced|date=April 2017}}

In March 2004 it was suggested that the unique [[Kaidun meteorite]], which landed in [[Yemen]] on December 3, 1980,<ref>[https://www.lpi.usra.edu/meteor/metbull.php?code=12228 Meteoritical Bulletin Database]</ref> may have originated on the Martian moon of [[Phobos (moon)|Phobos]].<ref>{{cite journal|author=Zolensky, M. and Ivanov A.|title=The Kaidun Microbreccia Meteorite: A Harvest from the Inner and Outer Asteroid Belt|journal= Geochemistry|volume=63|issue=3|pages=185–246|date= 2003|doi=10.1078/0009-2819-00038|bibcode=2003ChEG...63..185Z |url=https://zenodo.org/record/1236062}}</ref> Because Phobos has similarities to [[C-type asteroid]]s and because the Kaidun meteorite is a [[carbonaceous chondrite]], Kaidun is not a Martian meteorite in the strict sense. However, it may contain small fragments of material from the Martian surface.

The Martian meteorite [[NWA 7034]] (nicknamed "Black Beauty"), found in the [[Sahara desert]] during 2011, has ten times the [[Asteroidal water|water content]] of other Mars meteorites found on Earth.<ref name="NASA-20130103" /> The meteorite contains components as old as 4.42 ± 0.07 Ga (billion years),<ref>{{Cite journal|last1=Nyquist|first1=Laurence E.|last2=Shih|first2=Chi-Yu|last3=McCubbin|first3=Francis M.|last4=Santos|first4=Alison R.|last5=Shearer|first5=Charles K.|last6=Peng|first6=Zhan X.|last7=Burger|first7=Paul V.|last8=Agee|first8=Carl B.|date=2016-02-17|title=Rb-Sr and Sm-Nd isotopic and REE studies of igneous components in the bulk matrix domain of Martian breccia Northwest Africa 7034|journal=Meteoritics & Planetary Science|language=en|volume=51|issue=3|pages=483–498|doi=10.1111/maps.12606|issn=1086-9379|bibcode=2016M&PS...51..483N|s2cid=131565237 |doi-access=free}}</ref> and was heated during the [[Geological history of Mars#Crater density timescale|Amazonian geologic period]] on Mars.<ref>{{Cite journal|last1=Cassata|first1=William S.|last2=Cohen|first2=Benjamin E.|last3=Mark|first3=Darren F.|last4=Trappitsch|first4=Reto|last5=Crow|first5=Carolyn A.|last6=Wimpenny|first6=Joshua|last7=Lee|first7=Martin R.|last8=Smith|first8=Caroline L.|date=2018-05-01|title=Chronology of martian breccia NWA 7034 and the formation of the martian crustal dichotomy|journal=Science Advances|language=en|volume=4|issue=5|pages=eaap8306|doi=10.1126/sciadv.aap8306|pmid=29806017|pmc=5966191|issn=2375-2548|bibcode=2018SciA....4.8306C}}</ref>

A meteorite that fell in 1986 in Dayanpo, China contained a magnesium silicate mineral called "[[Elgoresyite|Elgoresyte]]", a mineral not found on Earth.<ref>{{Cite web|title=A Mineral Unknown On Earth Could Be The Most Abundant Mineral On Mars|url=https://www.geologyin.com/2021/08/a-mineral-unknown-on-earth-could-be.html |date=2021-08-09 |work=Geology In |access-date=2021-08-18|language=en}}</ref>

==Origin==
The majority of SNC meteorites are quite young compared to most other meteorites and seem to imply that [[volcano|volcanic]] activity was present on Mars only a few hundred million years ago. The young formation ages of Martian meteorites was one of the early recognized characteristics that suggested their origin from a planetary body such as Mars. Among Martian meteorites, only ALH 84001 and NWA 7034 have radiometric ages older than about 1400&nbsp;Ma (Ma&nbsp;= million years). All nakhlites, as well as Chassigny and NWA 2737, give similar if not identical formation ages around 1300&nbsp;Ma, as determined by various radiometric dating techniques.<ref name="Nyquist 2001 105–164">{{cite journal|last=Nyquist|first=L.E.|display-authors=etal|title=Ages and geologic histories of martian meteorites|journal=Space Science Reviews|date=2001|volume=96|pages=105–164|bibcode = 2001SSRv...96..105N |doi=10.1023/A:1011993105172|citeseerx=10.1.1.117.1954|s2cid=10850454}}</ref><ref>{{cite journal|last=Park|first=J.|display-authors=etal|title=39Ar-40Ar ages of martian nakhlites|journal=Geochim. Cosmochim. Acta|date=2009|volume=73|issue=7|pages=2177–2189|bibcode = 2009GeCoA..73.2177P |doi=10.1016/j.gca.2008.12.027|url=https://zenodo.org/record/1258979}}</ref> Formation ages determined for many shergottites are variable and much younger, mostly ~150–575&nbsp;Ma.<ref name="Nyquist 2001 105–164"/><ref>{{cite journal|last=Borg|first=L.E.|display-authors=etal|title=Constraints on the U-Pbisotopic systematics of Mars inferred from a combined U-Pb, Rb-Sr, and Sm-Nd isotopic study of the martian meteorite Zagami|journal=Geochim. Cosmochim. Acta|date=2005|volume=69|issue=24|pages=5819–5830|bibcode=2005GeCoA..69.5819B|doi=10.1016/j.gca.2005.08.007}}</ref><ref>{{cite journal|last=Shih|first=C-Y|display-authors=etal|title=Rb-Sr and Sm-Nd dating of olivine-phyric shergottite Yamato 980459: Petrogenesis of depleted shergottites|journal=Antarctic Meteorite Research|date=2005|volume=18|pages=46–65|bibcode= 2005AMR....18...46S }}</ref><ref>{{cite journal|last=Nyquist|first=L.E.|display-authors=etal|title=Concordant Rb-Sr, Sm-Nd, and Ar-Ar ages for Northwest Africa 1460: A 446 Ma old basaltic shergottite related to "lherzolitic" shergottites|journal=Geochim. Cosmochim. Acta|date=2009|volume=73|issue=14|pages=4288–4309|bibcode=2009GeCoA..73.4288N|doi=10.1016/j.gca.2009.04.008|url=https://zenodo.org/record/1258981}}</ref>

The chronological history of shergottites is not totally understood, and a few scientists have suggested that some may actually have formed prior to the times given by their radiometric ages,<ref>{{cite journal|last=Bouvier|first=A.|display-authors=etal|title= The case for old basaltic shergottites|journal=Earth Planet. Sci. Lett.|date=2008|volume=266|issue=1–2|pages=105–124|bibcode= 2008E&PSL.266..105B|doi=10.1016/j.epsl.2007.11.006}}</ref> a suggestion not accepted by most scientists. Formation ages of SNC meteorites are often linked to their cosmic-ray exposure (CRE) ages, as measured from the nuclear products of interactions of the meteorite in space with energetic [[cosmic ray]] particles. Thus, all measured nakhlites give essentially identical CRE ages of approximately 11 Ma, which when combined with their possible identical formation ages indicates ejection of nakhlites into space from a single location on Mars by a single impact event.<ref name="Nyquist 2001 105–164" /> Some of the shergottites also seem to form distinct groups according to their CRE ages and formation ages, again indicating ejection of several different shergottites from Mars by a single impact. However, CRE ages of shergottites vary considerably (~0.5–19&nbsp;Ma),<ref name="Nyquist 2001 105–164" /> and several impact events are required to eject all the known shergottites. It had been asserted that there are no large young craters on Mars that are candidates as sources for the Martian meteorites, but subsequent studies claimed to have a likely source for [[Allan Hills 84001|ALH 84001]],<ref>{{Cite news |url=https://www.newscientist.com/article.ns?id=dn8004 |title=Birthplace of famous Mars meteorite pinpointed |date=September 16, 2005 |work=New Scientist |first=David L. |last=Chandler |accessdate=September 8, 2006 |url-status=dead |archiveurl=https://web.archive.org/web/20060113195930/https://www.newscientist.com/article.ns/?id=dn8004 |archivedate=2006-01-13}}</ref> and a possible source for other shergottites.<ref>{{cite journal|author=McEwen, A.S.|url=http://www.mars.asu.edu/christensen/classdocs/mcewen_zunil_Icarus_2005.pdf|title=The rayed crater Zunil and interpretations of small impact craters on Mars|journal=[[Icarus (journal)|Icarus]]|volume=176|issue=2|pages=351–381|date=2005|access-date=2006-09-08|doi= 10.1016/j.icarus.2005.02.009|bibcode=2005Icar..176..351M|last2=Preblich|first2=B|last3=Turtle|first3=E|last4=Artemieva|first4=N|author4-link=Natalia Artemieva|last5=Golombek|first5=M|last6=Hurst|first6=M|last7=Kirk|first7=R|last8=Burr|first8=D|last9=Christensen|first9=P}}.</ref>

In a 2014 paper, several researchers claimed that all shergottites meteorites come from the [[Mojave (crater)|Mojave Crater]] on Mars.<ref name="Werner2014"/>

===Age estimates based on cosmic ray exposure===
[[File:Martian meteorite crafted into a small pendant.jpg|thumb|right|A Martian meteorite crafted into a small pendant and suspended from a gold necklace.]]
The amount of time spent in transit from Mars to Earth can be estimated by measurements of the effect of cosmic radiation on the meteorites, particularly on isotope ratios of [[noble gas]]es. The meteorites cluster in families that seem to correspond to distinct impact events on Mars. It is thought that the meteorites all originate in relatively few impacts every few million years on  Mars. The impactors would be kilometers in diameter and the craters they form on Mars tens of kilometers in diameter. Models of impacts on Mars are consistent with these findings.<ref name="Eugster">O. Eugster, G. F. Herzog, K. Marti, M. W. Caffee [http://www.lpi.usra.edu/books/MESSII/9004.pdf Irradiation Records, Cosmic-Ray Exposure Ages, and Transfer Times of Meteorites, see section 4.5 Martian Meteorites] LPI, 2006</ref>

Ages since impact determined so far include<ref>L.E. NYQUIST, D.D. BOGARD1, C.-Y. SHIH, A. GRESHAKE, D. STÖFFLER [http://seismo.berkeley.edu/~manga/nyquist.pdf AGES AND GEOLOGIC HISTORIES OF MARTIAN METEORITES] 2001</ref><ref>Tony Irving [http://www.imca.cc/mars/martian-meteorites.htm Martian Meteorites – has graphs of ejection ages] – site maintained by Tony Irving for up to date information on Martian meteorites</ref>
{| class="wikitable"
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! Type !! Age ([[Year#mya|mya]])
|-
| Dhofar 019, olivine-phyric shergottite|| 19.8 ± 2.3<ref name=Eugster/>
|-
|  ALH 84001, orthopyroxenite||15.0 ± 0.8<ref name=Eugster/>
|-
| Dunite (Chassigny) || 11.1 ± 1.6<ref name=Eugster/>
|-
| Six nakhlites || 10.8 ± 0.8<ref name=":0" /><ref name=Eugster/>
|-
| Lherzolites  || 3.8–4.7<ref name=Eugster/>
|-
| Six basaltic shergottites || 2.4–3.0<ref name=Eugster/>
|-
| Five olivine-phyric shergottites || 1.2 ± 0.1<ref name=Eugster/>
|- 
| EET 79001 || 0.73 ± 0.15<ref name=Eugster/>
|}

==Possible evidence of life==
Several Martian meteorites have been found to contain what some think is evidence for fossilized Martian life forms. The most significant of these is a meteorite found in the [[Allan Hills]] of [[Antarctica]] ([[Allan Hills 84001|ALH 84001]]). Ejection from Mars seems to have taken place about 16 million years ago. Arrival on Earth was about 13 000 years ago. Cracks in the rock appear to have filled with carbonate materials (implying groundwater was present) between 4 and 3.6 billion-years-ago. Evidence of [[polycyclic aromatic hydrocarbons]] (PAHs) have been identified with the levels increasing away from the surface. Other Antarctic meteorites do not contain PAHs. Earthly contamination should presumably be highest at the surface. Several minerals in the crack fill are deposited in phases, specifically, [[iron]] deposited as [[magnetite]], that are claimed to be typical of biodepositation on Earth.  There are also small ovoid and tubular structures that might be [[nanobacteria]] [[fossil]]s in carbonate material in crack fills (investigators McKay, Gibson, Thomas-Keprta, Zare).<ref>{{cite journal|doi= 10.1126/science.273.5277.924|last1=McKay|first1=D.|last2=Gibson Jr|date=1996|first2=EK|last3=Thomas-Keprta|first3=KL|last4= Vali|first4=H|last5=Romanek|first5=CS|last6=Clemett|first6=SJ|last7=Chillier|first7=XD|last8=Maechling|first8=CR|last9=Zare| first9 = RN|title=Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite AL84001|journal= Science|volume=273|issue=5277|pages=924–930|pmid=8688069|bibcode=1996Sci...273..924M|s2cid=40690489}}</ref> [[micropaleontology|Micropaleontologist]] Schopf, who described several important terrestrial bacterial assemblages, examined ALH 84001 and opined that the structures are too small to be Earthly bacteria and don't look especially like lifeforms to him. The size of the objects is consistent with Earthly "[[nanobacteria]]", but the existence of nanobacteria itself has been largely discredited.<ref>{{cite news |last1=Young |first1=John D. |last2=Martel |first2=Jan |date=January 1, 2010 |title=The Truth about Nanobacteria |url=https://www.scientificamerican.com/article/the-rise-and-fall-of-nanobacteria/ |work=Scientific American |access-date=2024-01-22}}</ref><ref>{{cite journal |last1=Schlieper |first1=Georg |last2=KrÜger |first2=Thilo |last3=Heiss |first3=Alexander |last4=Jahnen-Dechent |first4=Willi |date=November 2011 |title=A red herring in vascular calcification: 'nanobacteria' are protein–mineral complexes involved in biomineralization |journal=Nephrology Dialysis Transplantation |volume=26 |issue=11 |pages=3436–3439 |doi=10.1093/ndt/gfr521 |pmid=21965584 |pmc=4176054 }}</ref>

Many studies disputed the validity of the fossils.<ref>{{Cite magazine |first1=Corey S. |last1=Powell and |first2=W. Wayt |last2=Gibbs |date=October 1996 |title=Bugs in the Data? |magazine=Scientific American |volume=275 |number=4 |pages=20–22 |url=https://www.scientificamerican.com/article/bugs-in-the-data/ |jstor=24993389}}</ref><ref>{{Cite web |url=http://www.space.com/scienceastronomy/solarsystem/mars_meteorite_020320.html |title=Controversy Continues: Mars Meteorite Clings to Life - Or Does It?] |url-status=dead |archiveurl=https://web.archive.org/web/20020404034759/http://www.space.com/scienceastronomy/solarsystem/mars_meteorite_020320.html |archivedate=2002-04-04 |first=Leonard |last=David |date=20 March 2002 |work=Space.com}}</ref> For example, it was found that most of the organic matter in the meteorite was of terrestrial origin.<ref>{{cite journal|doi=10.1126/science.279.5349.362|title=A Search for Endogenous Amino Acids in Martian Meteorite ALH84001| date=1998|last1=Bada|first1=J. L.|journal=Science|volume=279|issue=5349|pages=362–5|pmid=9430583|last2=Glavin|first2=DP|last3= McDonald|first3=GD|last4=Becker|first4=L|bibcode=1998Sci...279..362B |s2cid=32301715}}</ref> But, a recent study suggests that [[magnetite]] in the meteorite could have been produced by Martian microbes. The study, published in the journal of the Geochemical and Meteoritic Society, used more advanced high resolution electron microscopy than was possible in 1996.<ref>{{cite journal|doi=10.1016/j.gca.2009.05.064|title=Origins of magnetite nanocrystals in Martian meteorite ALH84001|date=2009|last1=Thomas-Keprta|first1=K.L.|last2=Clemett|first2=S.J.|last3=McKay|first3=D.S.|last4=Gibson| first4 = E.K.|last5=Wentworth|first5=S.J.|journal=Geochimica et Cosmochimica Acta|volume=73|issue=21|pages=6631|bibcode= 2009GeCoA..73.6631T|url=https://zenodo.org/record/1258983}}</ref> A serious difficulty with the claims for a biogenic origin of the magnetites is that the majority of them exhibit topotactic crystallographic relationships with the host carbonates (i.e., there are 3D orientation relationships between the magnetite and carbonate lattices), which is strongly indicative that the magnetites have grown in-situ by a physico-chemical mechanism.<ref>{{cite journal | last1 = Barber | first1 = D.J. | last2 = Scott | first2 = E.R.D. | year = 2002 | title = Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills ALH84001 | journal = Proc. Natl. Acad. Sci. USA | volume = 99 | issue = 10| pages = 6556–61 | doi=10.1073/pnas.102045799| pmc = 124441 | bibcode = 2002PNAS...99.6556B | pmid=12011420| doi-access = free }}</ref>

While water is no indication of life, many of the meteorites found on Earth have shown water, including NWA 7034 which formed during the [[Amazonian (Mars)|Amazonian period]] of Martian geological history.<ref>{{Cite journal|last1=Agee|first1=Carl B.|last2=Wilson|first2=Nicole V.|last3=McCubbin|first3=Francis M.|last4=Ziegler|first4=Karen|last5=Polyak|first5=Victor J.|last6=Sharp|first6=Zachary D.|last7=Asmerom|first7=Yemane|last8=Nunn|first8=Morgan H.|last9=Shaheen|first9=Robina|date=2013-02-15|title=Unique Meteorite from Early Amazonian Mars: Water-Rich Basaltic Breccia Northwest Africa 7034|journal=Science|language=en|volume=339|issue=6121|pages=780–785|doi=10.1126/science.1228858|issn=0036-8075|pmid=23287721|bibcode=2013Sci...339..780A|s2cid=206544554|doi-access=free}}</ref> Other signs of surface liquid [[water on Mars]] (such as [[recurring slope lineae]]<ref>{{Cite journal|last1=Ojha|first1=Lujendra|last2=Wilhelm|first2=Mary Beth|last3=Murchie|first3=Scott L.|last4=McEwen|first4=Alfred S.|last5=Wray|first5=James J.|last6=Hanley|first6=Jennifer|last7=Massé|first7=Marion|last8=Chojnacki|first8=Matt|date=2015-11-01|title=Spectral evidence for hydrated salts in recurring slope lineae on Mars|journal=Nature Geoscience|language=en|volume=8|issue=11|pages=829–832|doi=10.1038/ngeo2546|issn=1752-0894|bibcode=2015NatGe...8..829O}}</ref>) are a topic of debate among planetary scientists, but generally consistent with the earlier evidence provided by Martian meteorites. Any liquid water present is likely too minimal to support life.

==See also==
* [[Colin Pillinger]] 
* [[Glossary of meteoritics]]
* [[List of Martian meteorites|List of Martian meteorites (on Earth)]]
* [[List of meteorites on Mars]]
* [[Panspermia#Lithopanspermia|Lithopanspermia]], which includes the speculation that life on Earth may have arrived as microbes on Martian meteorites
* [[Mars sample-return mission]]

==References==
{{Reflist|30em}}
;General
{{Refbegin}}
* {{cite journal |last= Lodders |first= K|author-link=Katharina Lodders |title= A survey of shergottite, nakhlite and chassigny meteorites whole-rock compositions |journal= Meteoritics & Planetary Science |volume= 33 |pages= A183–A190 |date= 1998 |quote= Note: at the time of this article 12 SNC meteorites had been found |bibcode= 1998M&PSA..33..183L |doi=10.1111/j.1945-5100.1998.tb01331.x|doi-access= free }}
{{Refend}}

==External links==
{{commons category|Martian meteorites}}
* [https://imca.cc/mars/martian-meteorites-list.htm List of Martian Meteorites]
* [https://www2.jpl.nasa.gov/snc/ Mars Meteorite Home Page (JPL)]
* [https://web.archive.org/web/20041018203431/http://lpi.usra.edu/expmars/poster/poster.html Anatomy of A Martian Meteorite Poster and Information Packet]
* [https://www.lpi.usra.edu/lpi/meteorites/mars_meteorite.html On the Question of the Mars Meteorite]
* [http://www.psrd.hawaii.edu/Archive/Contents.html Archive for Planetary Science Research Discoveries | PSRD]
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