Martian meteorite

Source: Wikipedia, the free encyclopedia.
For meteorites found on Mars, see List of rocks on Mars.
Martian meteorite (SNC meteorites)
— 
shergottite
TypeAchondrite
Subgroups
NWA 7034, nicknamed "Black Beauty," weighs approximately 320 g (11 oz).[2]

A Martian meteorite is a rock that formed on

interplanetary space before landing on Earth as a meteorite. As of September 2020, 277 meteorites had been classified as Martian, less than half a percent of the 72,000 meteorites that have been classified.[1] The largest complete, uncut Martian meteorite, Taoudenni 002,[3] 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

surface landers and rovers.[4][5] 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 landers. Several scientists suggested these characteristics implied the origin of SNC meteorites from a relatively large parent body, possibly Mars.[6][7]

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.[8] 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."[4]

Subdivision

NWA 7034
).

As of April 25, 2018, 192 of the 207 Martian meteorites are divided into three rare groups of achondritic (stony) meteorites: shergottites (169), nakhlites (20), chassignites (3), and ones otherwise (15) (containing the orthopyroxenite (OPX) Allan Hills 84001, as well as 10 basaltic breccia meteorites).[1] Consequently, Martian meteorites as a whole are sometimes referred to as the SNC group. They have isotope ratios that are said to be consistent with each other and inconsistent with the Earth. 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

basaltic, olivine-phyric (such as the Tissint group found in Morocco in 2011[10][11]) and 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.[12]
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.

NWA 6963,[13] a shergottite found in Morocco, September 2011.

The shergottites appear to have crystallised as recently as 180 million years ago,[14] 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.[15] 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, 58.5 km in diameter, was a potential source of these meteorites.[16] A paper published in 2021, however, disputes this, proposing instead the 28 km crater Tooting, or possibly the crater 09-000015 as the crater source of the depleted olivine-phyric shergottites ejected 1.1 Ma ago.[17][18]

Nakhlites

Nakhla meteorite's two sides and its inner surfaces after breaking it
Main article: Nakhlite

Nakhlites are named after the first of them, the

El-Nakhla, Alexandria, Egypt in 1911 and had an estimated weight of 10 kg
.

Nakhlites are igneous rocks that are rich in augite and were formed from basaltic magma from at least four eruptions, spanning around 90 million years, from 1416 ± 7 to 1322 ± 10 million years ago.[19] They contain augite and olivine crystals. 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, or Syrtis Major Planum.[20]

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.[20]

Chassignites

The first chassignite, the 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.[21] that its "mineralogy, major and trace element chemistry as well as oxygen isotopes revealed an unambiguous Martian origin and strong affinities with Chassigny."

Ungrouped meteorites

Allan Hills 84001 (ALH 84001)

Among these, the famous specimen

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 fossilized remains of bacteria-like lifeforms. As of 2005, scientific consensus was that the microfossils were not indicative of Martian life, but of contamination by earthly biofilms. ALH 84001 is as old as the basaltic and intermediate shergottite groups – i.e., 4.1 billion years old.[citation needed
]

In March 2004 it was suggested that the unique Kaidun meteorite, which landed in Yemen on December 3, 1980,[22] may have originated on the Martian moon of Phobos.[23] Because Phobos has similarities to C-type asteroids 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

Sahara desert during 2011, has ten times the water content of other Mars meteorites found on Earth.[2] The meteorite contains components as old as 4.42 ± 0.07 Ga (billion years),[24] and was heated during the Amazonian geologic period on Mars.[25]

A meteorite that fell in 1986 in Dayanpo, China contained a magnesium silicate mineral called "Elgoresyte", a mineral not found on Earth.[26]

Origin

The majority of SNC meteorites are quite young compared to most other meteorites and seem to imply that 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 Ma (Ma = million years). All nakhlites, as well as Chassigny and NWA 2737, give similar if not identical formation ages around 1300 Ma, as determined by various radiometric dating techniques.[14][27] Formation ages determined for many shergottites are variable and much younger, mostly ~150–575 Ma.[14][28][29][30]

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,[31] 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.[14] 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 Ma),[14] 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 ALH 84001,[32] and a possible source for other shergottites.[33]

In a 2014 paper, several researchers claimed that all shergottites meteorites come from the Mojave Crater on Mars.[16]

Age estimates based on cosmic ray exposure

A Martian meteorite crafted into a small pendant and suspended from a silver 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 gases. 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.[34]

Ages since impact determined so far include[35][36]

Type Age (mya)
Dhofar 019, olivine-phyric shergottite 19.8 ± 2.3[34]
ALH 84001, orthopyroxenite 15.0 ± 0.8[34]
Dunite (Chassigny) 11.1 ± 1.6[34]
Six nakhlites 10.8 ± 0.8[19][34]
Lherzolites 3.8–4.7[34]
Six basaltic shergottites 2.4–3.0[34]
Five olivine-phyric shergottites 1.2 ± 0.1[34]
EET 79001 0.73 ± 0.15[34]

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

nanobacteria", but the existence of nanobacteria itself has been largely discredited.[38][39]

Many studies disputed the validity of the fossils.[40][41] For example, it was found that most of the organic matter in the meteorite was of terrestrial origin.[42] 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.[43] 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.[44]

While water is no indication of life, many of the meteorites found on Earth have shown water, including NWA 7034 which formed during the

recurring slope lineae[46]
) 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

References

  1. ^
    Meteoritical Society
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  2. ^ a b Staff (January 3, 2013). "Researchers Identify Water Rich Meteorite Linked To Mars Crust". NASA. Archived from the original on May 29, 2018. Retrieved January 3, 2013.
  3. ^ Baker, Harry (2021-09-02). "World's largest Martian meteorite goes on display". Lives Science. Retrieved 2021-12-15.
  4. ^
    doi:10.1016/S0032-0633(00)00105-7
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  5. ^ Webster, Guy (October 17, 2013). "NASA Rover Confirms Mars Origin of Some Meteorites". NASA. Retrieved October 29, 2013.
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  9. ^ Shergotty Meteorite - JPL, NASA
  10. ^ Choi, Charles Q. (11 October 2012). "Meteorite's Black Glass May Reveal Secrets of Mars". Space.com.
  11. ^ Morin, Monte (October 12, 2012). "An unusually pristine piece of Mars". Los Angeles Times.
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  13. ^ "Northwest Africa 6963 (NWA 6963)".
  14. ^
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  18. ^ Gough, Evan (2021-11-08). "We Now Know Exactly Which Crater the Martian Meteorites Came From". Universe Today. Retrieved 2021-11-15.
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    doi:10.1016/j.chemer.2005.01.004
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  21. ^ Beck, P.; et al. (March 14–18, 2005). The Diderot meteorite: The second chassignite (PDF). 36th Annual Lunar and Planetary Science Conference. League City, Texas. abstract no.1326. Retrieved September 8, 2006.
  22. ^ Meteoritical Bulletin Database
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  26. ^ "A Mineral Unknown On Earth Could Be The Most Abundant Mineral On Mars". Geology In. 2021-08-09. Retrieved 2021-08-18.
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  34. ^ a b c d e f g h i O. Eugster, G. F. Herzog, K. Marti, M. W. Caffee Irradiation Records, Cosmic-Ray Exposure Ages, and Transfer Times of Meteorites, see section 4.5 Martian Meteorites LPI, 2006
  35. ^ L.E. NYQUIST, D.D. BOGARD1, C.-Y. SHIH, A. GRESHAKE, D. STÖFFLER AGES AND GEOLOGIC HISTORIES OF MARTIAN METEORITES 2001
  36. ^ Tony Irving Martian Meteorites – has graphs of ejection ages – site maintained by Tony Irving for up to date information on Martian meteorites
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  38. ^ Young, John D.; Martel, Jan (January 1, 2010). "The Truth about Nanobacteria". Scientific American. Retrieved 2024-01-22.
  39. PMC 4176054
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  41. ^ David, Leonard (20 March 2002). "Controversy Continues: Mars Meteorite Clings to Life - Or Does It?]". Space.com. Archived from the original on 2002-04-04.
  42. S2CID 32301715
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  43. doi:10.1016/j.gca.2009.05.064
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  44. PMID 12011420
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  45. S2CID 206544554
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  46. ISSN 1752-0894
    .
General

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