Carbonaceous chondrites or C chondrites are a class of

chondritic A chondrite is a stony (non-metallic) meteorite that has not been modified by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form primiti ...

meteorites comprising at least 8 known groups and many ungrouped

meteorite A meteorite is a rock (geology), rock that originated in outer space and has fallen to the surface of a planet or Natural satellite, moon. When the original object enters the atmosphere, various factors such as friction, pressure, and chemical ...

s. They include some of the most primitive known meteorites. The C chondrites represent only a small proportion (4.6%) of

meteorite fall A meteorite fall, also called an observed fall, is a meteorite collected after its fall from outer space, that was also observed by people or automated devices. Any other meteorite is called a "meteorite find, find". There are more than 1,300 d ...

s. Some famous carbonaceous chondrites are: Allende, Murchison,

Orgueil Orgueil (; ) is a commune in the Tarn-et-Garonne department in the Occitanie region in southern France. History Orgueil has existed for more than 1000 years. It was first mentioned in the 9th century, when Orgueil was part of Saint-Sernin Abb ...

, Ivuna,

Murray Murray may refer to: Businesses * Murray (bicycle company), an American bicycle manufacturer * Murray Motor Car Company, an American car manufacturer * Murrays, an Australian bus company * Murray International Trust, a Scottish investment trus ...

Tagish Lake Tagish Lake is a lake in Yukon and northern British Columbia, Canada. The lake is long and averages wide with an area of , about two thirds of which is in British Columbia. The average depth is and maximum depth is . It has two arms, the Ta ...

Sutter's Mill Sutter's Mill was a water-powered sawmill on the bank of the South Fork American River in the foothills of the Sierra Nevada in California. It was named after its owner John Sutter. A worker constructing the mill, James W. Marshall, found go ...

, and

Winchcombe Winchcombe () is a market town and civil parish in the Borough of Tewkesbury in the county of Gloucestershire, England, situated northeast of Cheltenham. The population was recorded as 4,538 in the 2011 United Kingdom census, 2011 census and ...

General description

C chondrites contain a relatively high proportion of carbon (up to 3%), which is in the form of

graphite Graphite () is a Crystallinity, crystalline allotrope (form) of the element carbon. It consists of many stacked Layered materials, layers of graphene, typically in excess of hundreds of layers. Graphite occurs naturally and is the most stable ...

carbonate A carbonate is a salt of carbonic acid, (), characterized by the presence of the carbonate ion, a polyatomic ion with the formula . The word "carbonate" may also refer to a carbonate ester, an organic compound containing the carbonate group ...

s and organic compounds, including

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although over 500 amino acids exist in nature, by far the most important are the 22 α-amino acids incorporated into proteins. Only these 22 a ...

s. In addition, they contain water and minerals that have been modified by the influence of water. The carbonaceous chondrites were not exposed to higher temperatures, so that they are hardly changed by thermal processes. Some carbonaceous chondrites, such as the

Allende meteorite The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01:05 on February 8, 1969, falling over the Mexican state of Chihuahua. After it broke up in the atmosphere, an extensive search for p ...

, contain calcium-aluminum-rich inclusions (CAIs). These are compounds that emerged early from the primeval

solar nebula There is evidence that the formation of the Solar System began about 4.6 bya, billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, whil ...

, condensed out and represent the oldest minerals formed in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

. Some primitive carbonaceous chondrites, such as the CM chondrite Murchison, contain presolar minerals, including

moissanite Moissanite () is naturally occurring silicon carbide and its various crystalline polymorphs. It has the chemical formula SiC and is a rare mineral, discovered by the French chemist Henri Moissan in 1893. Silicon carbide or moissanite is useful ...

(natural

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A wide bandgap semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder a ...

) and tiny nanometer-sized diamonds that apparently were not formed in the Solar System. These presolar minerals were probably formed during the explosion of a nearby

supernova A supernova (: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last stellar evolution, evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion ...

or in the vicinity of a pulsating

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The stellar atmosphere, outer atmosphere is inflated and tenuous, making the radius large and the surface t ...

(more precisely: a so-called

AGB star The asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) lat ...

) before they got into the cloud of matter from which the Solar System was formed. Such star explosions release pressure waves that can condense clouds of matter in their surroundings, leading to the formation of new ones, stars and

planetary systems A planetary system is a set of gravitationally bound non-stellar bodies in or out of orbit around a star or star system. Generally speaking, systems with one or more planets constitute a planetary system, although such systems may also consis ...

. Another carbonaceous chondrite, the Flensburg meteorite (2019), provides evidence of the earliest known occurrence of liquid water in the young Solar System to date.

Composition and classification

Carbonaceous chondrites are grouped according to distinctive compositions thought to reflect the type of parent body from which they originated. These C chondrite groups are now each named with a standard two-letter CX designation, where C stands for "carbonaceous" (other types of

chondrites A chondrite is a stony (non-metallic) meteorite that has not been modified by either melting or planetary differentiation, differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar Syste ...

do not begin with this letter) plus a capital letter in the spot ''X'', which is very often the first letter of the name of a prominent meteorite—often the first to be discovered—in the group. Such meteorites are often named for the place where they fell, thus giving no clue as to the physical nature of the group. Group CH, where H is for "high metal" is so far the only exception. See below for name derivations of each group. Several groups of carbonaceous chondrites, notably the CM and CI groups, contain high percentages (3% to 22%) of

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

, as well as

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

s. They are composed mainly of

silicate A silicate is any member of a family of polyatomic anions consisting of silicon and oxygen, usually with the general formula , where . The family includes orthosilicate (), metasilicate (), and pyrosilicate (, ). The name is also used ...

oxide An oxide () is a chemical compound containing at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion (anion bearing a net charge of −2) of oxygen, an O2− ion with oxygen in the oxidation st ...

s and

sulfide Sulfide (also sulphide in British English) is an inorganic anion of sulfur with the chemical formula S2− or a compound containing one or more S2− ions. Solutions of sulfide salts are corrosive. ''Sulfide'' also refers to large families o ...

s, with the minerals

olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...

and serpentine being characteristic. The presence of volatile organic chemicals and water indicates that they have not undergone significant heating (>200 °C) since they were formed, and their compositions are considered to be close to that of the

from which the

condensed. Other groups of C chondrites, e.g., CO, CV, and CK chondrites, are relatively poor in volatile compounds, and some of these have experienced significant heating on their parent asteroids.

CI group

This group, named after the Ivuna meteorite (Tanzania), have chemical compositions that are close to that measured in the solar photosphere (aside from gaseous elements, and elements such as lithium which are underrepresented in the Sun's photosphere by comparison to their abundance in CI chondrites). In this sense, they are chemically the most primitive known meteorites. CI chondrites typically contain a high proportion of water (up to 22%), and organic matter in the form of

s and PAHs. Aqueous alteration promotes a composition of hydrous

phyllosilicate Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, the crystalline forms of silica (silicon dio ...

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...

, and

crystals occurring in a black matrix, and a possible lack of

chondrule A chondrule (from Ancient Greek χόνδρος ''chondros'', grain) is a round grain found in a chondrite. Chondrules form as molten or partially molten droplets in space before being Accretion (astrophysics), accreted to their parent asteroids ...

s. It is thought they have not been heated above , indicating that they condensed in the cooler outer portion of the solar nebula. Five CI chondrites have been observed to fall: Ivuna,

, Alais, Tonk, and Revelstoke. Four others have been found by Japanese field parties in Antarctica. In general, the extreme fragility of CI chondrites causes them to be highly susceptible to terrestrial weathering, and they do not survive on Earth's surface for long after they fall.

CV group

This group takes its name from Vigarano (Italy). Most of these chondrites belong to the

petrologic type A chondrite is a stony (non-metallic) meteorite that has not been modified by either melting or differentiation of the parent body. They are formed when various types of dust and small grains in the early Solar System accreted to form primiti ...

3. CV chondrites observed falls: * Allende *Bali *Bukhara *Grosnaja *Kaba *Mokoia *Vigarano

CM group

The group takes its name from Mighei (Ukraine), but the most famous member is the extensively studied Murchison meteorite. Many falls of this type have been observed and CM chondrites are known to contain a rich mix of complex organic compounds such as amino-acids and purine/pyrimidine nucleobases. CM chondrite famous falls: * Murchison *

*Aguas Zarcas * Jbilet Winselwan *

Winchcombe meteorite The Winchcombe meteorite is a carbonaceous chondrite meteorite that was observed entering the Earth's atmosphere as a fluorescent green fireball over Gloucestershire, England, at 21:54 on 28 February 2021. Due to a public appeal, fragments were ...

CR group

The group takes its name from Renazzo (Italy). The best

parent body A parent body in meteoritics is the celestial body from which originates a meteorite or a class of meteorites. Identification It is easiest to correlate a meteorite with a parent body when the parent body still exists. This is the case for Lun ...

candidate is

2 Pallas Pallas (minor-planet designation: 2 Pallas) is the List of largest asteroids, third-largest asteroid in the Solar System by volume and mass. It is the second asteroid to have been discovered, after 1 Ceres, Ceres, and is likely a remnant ...

. CR chondrites observed falls: * Al Rais * Kaidun * Renazzo Other famous CR chondrites: *Dar al Gani 574 * El Djouf 001 * Northwest Africa 801

CH group

"H" stands for "high metal" because CH chondrites may contain up to as much as 40% of metal. That makes them one of the most metal-rich of any of the chondrite groups, second only to the CB chondrites and some ungrouped chondrites such as NWA 12273. The first meteorite discovered was ALH 85085. Chemically, these chondrites are closely related to CR and CB groups. All specimens of this group belong only to petrologic types 2 or 3."Carbonaceous chondrite" Meteorite.fr: All About Meteorites: Classification

CB group

The group takes its name from the most representative member: Bencubbin (Australia). Although these chondrites contain over 50% nickel-iron metal, they are not classified as

mesosiderite Mesosiderites are a class of stony–iron meteorites consisting of about equal parts of metallic nickel-iron and silicate. They are breccias with an irregular texture; silicates and metal occur often in lumps or pebbles as well as in fine-grained ...

s because their mineralogical and chemical properties are strongly associated with CR chondrites.

CK group

This group takes its name from Karoonda (Australia). These chondrites are closely related to the CO and CV groups.

CO group

The group takes its name from

Ornans Ornans () is a commune in the Doubs department in the Bourgogne-Franche-Comté region in eastern France. On 1 January 2016 the former commune Bonnevaux-le-Prieuré was merged into Ornans.Ornans Ornans () is a commune in the Doubs department in the Bourgogne-Franche-Comté region in eastern France. On 1 January 2016 the former commune Bonnevaux-le-Prieuré was merged into Ornans.KainsazWarrenton
*

Moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...

Famous finds: * Dar al Gani 749

CL group

Officially recognized in 2022 after minimum specimens (five) described. CL chondrites, named after type specimen(s) Loongana, are chondrite-rich, metal-rich, and volatile-poor.

C ungrouped

The most famous members: *

*Tarda

Organic matter

Most of the

organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

in CI and CM carbonaceous chondrites is an insoluble complex material. That is similar to the description for

kerogen Kerogen is solid, insoluble organic matter in sedimentary rocks. It consists of a variety of organic materials, including dead plants, algae, and other microorganisms, that have been compressed and heated by geological processes. All the kero ...

. A kerogen-like material is also in the

ALH84001 Allan Hills 84001 (ALH84001) is a fragment of a Martian meteorite that was found in the Allan Hills in Antarctica on December 27, 1984, by a team of American meteorite hunters from the ANSMET project. Like other members of the shergottite– n ...

Martian meteorite 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. , 277 meteorites had been classified as Martian, less than half a perce ...

(an

achondrite An achondrite is a stony meteorite that does not contain chondrules. It consists of material similar to terrestrial basalts or plutonic rocks and has been differentiated and reprocessed to a lesser or greater degree due to melting and recrystalli ...

). The CM meteorite Murchison has over 96 extraterrestrial

s and other compounds including

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an Substituent, R-group. The general formula of a carboxylic acid is often written as or , sometimes as with R referring to an organyl ...

s, hydroxy carboxylic acids, sulphonic and phosphonic acids, aliphatic, aromatic and polar

hydrocarbon In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and Hydrophobe, hydrophobic; their odor is usually fain ...

fullerene A fullerene is an allotropes of carbon, allotrope of carbon whose molecules consist of carbon atoms connected by single and double bonds so as to form a closed or partially closed mesh, with fused rings of five to six atoms. The molecules may ...

heterocycle A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different elements as members of its ring(s). Heterocyclic organic chemistry is the branch of organic chemistry dealing with the synthesis, proper ...

carbonyl In organic chemistry, a carbonyl group is a functional group with the formula , composed of a carbon atom double bond, double-bonded to an oxygen atom, and it is divalent at the C atom. It is common to several classes of organic compounds (such a ...

compounds,

alcohol Alcohol may refer to: Common uses * Alcohol (chemistry), a class of compounds * Ethanol, one of several alcohols, commonly known as alcohol in everyday life ** Alcohol (drug), intoxicant found in alcoholic beverages ** Alcoholic beverage, an alco ...

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

s and

amide In organic chemistry, an amide, also known as an organic amide or a carboxamide, is a chemical compound, compound with the general formula , where R, R', and R″ represent any group, typically organyl functional group, groups or hydrogen at ...

Extraterrestrial amino acids

Amino acids in carbonaceous chondrites have important implications for theories describing the delivery of organic compounds to the early Earth and the subsequent development of life. Shortly after its fall and recovery in Australia in 1969, the Murchison meteorite was found to host five protein amino acids (

glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...

alanine Alanine (symbol Ala or A), or α-alanine, is an α-amino acid that is used in the biosynthesis of proteins. It contains an amine group and a carboxylic acid group, both attached to the central carbon atom which also carries a methyl group sid ...

valine Valine (symbol Val or V) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated −NH3+ form under biological conditions), an α- carboxylic acid group (which is in the deproton ...

proline Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid (used in the biosynthesis of proteins), although it does not contain the amino group but is rather a secondary amine. The secondary amine nitrogen is in the p ...

, and

glutamic acid Glutamic acid (symbol Glu or E; known as glutamate in its anionic form) is an α- amino acid that is used by almost all living beings in the biosynthesis of proteins. It is a non-essential nutrient for humans, meaning that the human body can ...

) in addition to 12 non-

proteinogenic Proteinogenic amino acids are amino acids that are incorporated biosynthetically into proteins during translation from RNA. The word "proteinogenic" means "protein creating". Throughout known life, there are 22 genetically encoded (proteinogenic) ...

amino acids including α-aminoisobutyric acid and

isovaline Isovaline is a rare amino acid transported to Earth by the Murchison meteorite, which landed in Australia in 1969. The discovery of isovaline in the biosphere demonstrates an extraterrestrial origin of amino acids and has been linked to the homo ...

, which are rare on Earth. Since then, the number of characterized amino acids in the Murchison meteorite has risen to 96, including 12 of the 20 common biological amino acids, along with hundreds more that have been detected, but remain uncharacterized. While the abundance of amino acids present in terrestrial soils presents a potential source of contamination, most of the amino acids characterized in Murchison are terrestrially rare or absent. Amino acids may be structurally

chiral Chirality () is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek language, Greek (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is dist ...

, meaning that they have two possible non-superimposable mirror image structures, termed

enantiomers In chemistry, an enantiomer (Help:IPA/English, /ɪˈnænti.əmər, ɛ-, -oʊ-/ Help:Pronunciation respelling key, ''ih-NAN-tee-ə-mər''), also known as an optical isomer, antipode, or optical antipode, is one of a pair of molecular entities whi ...

. Conventionally, these are referred to as left-handed (L) and right-handed (D) by analogy with

glyceraldehyde Glyceraldehyde (glyceral) is a triose monosaccharide with chemical formula C3 H6 O3. It is the simplest of all common aldoses. It is a sweet, colorless, crystalline solid that is an intermediate compound in carbohydrate metabolism. The word comes ...

. Living beings use L-amino acids, although there is no apparent reason why one enantiomer is favoured over the other as they behave equivalently in biological systems. In contrast with terrestrial biology, early laboratory studies, including the famous Miller-Urey Experiment, have shown that amino acids may form under a range of possible abiotic conditions with equal (racemic) mixtures of D- and L-enantiomers. Thus, the ratios between enantiomers for a given amino acid may discriminate between biotic and abiotic formation mechanisms. In the first characterization of amino acids in Murchison, all chiral examples were present in racemic mixtures indicating an abiotic origin. This is consistent with proposed sythetic pathways, as the formation of isovaline and other α-dialkyl amino acids in CM chondrites has been attributed to the Strecker synthesis which produces racemic mixtures of enantiomers. Ehrenfreund et al. (2001) found that amino acids in CI chondrites Ivuna and Orgueil were present at much lower concentrations than in CM chondrites (~30%), and that they had a distinct composition high in β-

, γ-

ABA ABA may refer to: Aviation * AB Aerotransport, former Scandinavian airline * IATA airport code for Abakan International Airport in Republic of Khakassia, Russia Businesses and organizations Broadcasting * Alabama Broadcasters Association, Uni ...

, and β-ABA but low in α-aminoisobutyric acid (AIB) and

. This implies that they had formed by a different synthetic pathway, and on a different parent body from the CM chondrites.

Enantiomeric excesses observed in extraterrestrial amino acids

More recently, amino acids from several carbonaceous chondrites have been identified with significant L-enantiomeric excesses. L-excesses from 3 – 15% in several non-protein α-dialkyl amino acids have been found in the Murchison and Murray meteorites. Their extraterrestrial origin is indicated by their absence in biological systems and significant heavy

isotope Isotopes are distinct nuclear species (or ''nuclides'') of the same chemical element. They have the same atomic number (number of protons in their Atomic nucleus, nuclei) and position in the periodic table (and hence belong to the same chemica ...

enrichments in ¹³C and deuterium compared to terrestrial values. Further characterization of L-isovaline excesses up to 20.5% in a range of carbonaceous chondrite groups have supported a hypothesis that increasing

hydrothermal alteration Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a Rock (geology), rock by hydrothermal and other fluids. It is traditionally defined as metamorphism which involves a change in t ...

of the host meteorite correlates with increasing observed L-enantiomeric excess. Large L-excesses for α-H amino acids have also been reported, but these are more problematic due to the potential for terrestrial contamination. The ungrouped C2 chondrite

has L-

aspartic acid Aspartic acid (symbol Asp or D; the ionic form is known as aspartate), is an α-amino acid that is used in the biosynthesis of proteins. The L-isomer of aspartic acid is one of the 22 proteinogenic amino acids, i.e., the building blocks of protei ...

excesses up to ~60%, with carbon isotope measurements indicating an extraterrestrial origin due to significant enrichments in ¹³C. In Tagish Lake, proteinogenic amino acids show both significant L-excesses, and racemic mixtures: glutamic acid, serine, and threonine were found to have ~50 – 99% L-excesses, while alanine was racemic. It has been proposed that extraterrestrial amino acid L-excesses observed in carbonaceous chondrites are a result of differences in the crystallization behaviour of the enantiomers.

Circularly polarized In electrodynamics, circular polarization of an electromagnetic wave is a polarization state in which, at each point, the electromagnetic field of the wave has a constant magnitude and is rotating at a constant rate in a plane perpendicular to th ...

ultraviolet light has been shown to generate L-excesses in crystallizing amino acids for experimental conditions mimicking alteration on asteroids, and this is thought to be the dominant extraterrestrial source of chiral symmetry breaking (i.e., the favouring of one enantiomer over another). It is notable that only excesses of the L-enantiomer have been observed in extraterrestrial amino acids, suggesting that the abiotic process responsible for enantiomeric enrichments may be the original source of the L-amino acid selectivity currently observed in terrestrial life.

Implications for extraterrestrial biosignatures

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

have proposed a "Ladder of Life Detection" threshold of >20%

enantiomeric excess In stereochemistry, enantiomeric excess (ee) is a measurement of purity used for chiral substances. It reflects the degree to which a sample contains one enantiomer in greater amounts than the other. A racemic mixture has an ee of 0%, while a sing ...

in amino acids to distinguish extraterrestrial biosignatures. But, as previously mentioned, recent studies of carbonaceous chondrites and complementary experimental investigations have demonstrated that even larger enantiomeric excesses may be produced by abiotic pathways. To identify chiral asymmetry (enantiomeric excess) of biological origin, Glavin et al. (2020) emphasize three criteria that must be met: chiral asymmetry, light ¹³C isotopic composition, and simplified distribution of

structural isomers In chemistry, a structural isomer (or constitutional isomer in the IUPAC nomenclature) of a chemical compound, compound is a compound that contains the same number and type of atoms, but with a different connectivity (i.e. arrangement of chemica ...

. If a distribution of amino acids in an extraterrestrial sample is found to be chirally asymmetric, display structural isomeric preference, and carry ¹³C, ¹⁵N, and D depletions relative to associated inorganic material, a compelling case may be made for its biological origin. With the current interest in

sample return missions Sample or samples may refer to: * Sample (graphics), an intersection of a color channel and a pixel * Sample (material), a specimen or small quantity of something * Sample (signal), a digital discrete sample of a continuous analog signal * Sampl ...

from carbonaceous asteroids (e.g.,

OSIRIS-REx OSIRIS-REx was a NASA asteroid-study and sample-return mission that visited and collected samples from 101955 Bennu, a C-type asteroid, carbonaceous near-Earth object, near-Earth asteroid. The material, returned in September 2023, is expected ...

) and Mars headed by NASA and other space agencies, the subsequent analysis of returned samples devoid of terrestrial contamination will provide the best opportunity to discover potential biosignatures in our Solar System.

References

Carbonaceous chondrites at ''The Encyclopedia of Astrobiology, Astronomy, and Spaceflight''
*

External links

from Meteorites Australia - Meteorites.com.au {{Authority control Carbon compounds

General description

Composition and classification

CI group

CV group

CM group

CR group

CH group

CB group

CK group

CO group

CL group

C ungrouped

Organic matter

Extraterrestrial amino acids

Enantiomeric excesses observed in extraterrestrial amino acids

Implications for extraterrestrial biosignatures

See also

References

External links