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NMR studies of chemical structural variation of insoluble organic matter from different carbonaceous chondrite groups
Abstract
Solid-state 1H and 13C Nuclear Magnetic Resonance (NMR) spectroscopic experiments have been performed on isolated meteoritic Insoluble Organic Matter (IOM) spanning four different carbonaceous chondrite meteorite groups; a CR2 (EET92042), a CI1 (Orgueil), a CM2 (Murchison), and the unique C2 meteorite, Tagish Lake. These solid state NMR experiments reveal considerable variation in bulk organic composition across the different meteorite group’s IOM. The fraction of aromatic carbon increases as CR2 < CI1 < CM2 < Tagish Lake. The increases in aromatic carbon are offset by reductions in aliphatic (sp3) carbon moieties, e.g., “CHx,” and “CHx(O,N).” Oxidized sp2 bonded carbon, e.g., carboxyls and ketones grouped as “CO,” are largely conservative across these meteorite groups. Single pulse (SP) 13C magic angle spinning (MAS) NMR experiments reveal the presence of nanodiamonds with an apparent concentration ranking in the IOM of CR2 < CI1 < CM2 < Tagish Lake. A pair of independent NMR experiments reveals that, on average, the aromatic moieties in the IOM of all four meteoritic IOM fractions are highly substituted. Fast spinning SP 1H MAS NMR spectral data combined with other NMR experimental data reveal that the average hydrogen content of sp3 bonded carbon functional groups is low, requiring a high degree of aliphatic chain branching in each IOM fraction. The variation in chemistry across the meteorite groups is consistent with alteration by low temperature chemical oxidation. It is concluded that such chemistry principally affected the aliphatic moieties whereas the aromatic moieties and nanodiamonds may have been largely unaffected.
... While the mineral phases of these meteorites provide information on the alteration history of their parent bodies, their organic matter, representing up to 5% of their weight (Glavin et al., 2018;Pearson et al., 2006;Pizzarello et al., 2006), gives invaluable information on the organic content that could have been delivered to the early Earth. This organic matter can be divided into two fractions: soluble organic matter (SOM), which represents up to 25% of the organic content, and the dominant insoluble organic matter (IOM) fraction, which contains the balance of organic carbon (Alexander et al., 2007;Cody & Alexander, 2005;Sephton, 2002). ...
... The isolation of the IOM fraction from meteorites requires a chemical treatment stronger than that for the soluble fraction, including a demineralization step. Due to the IOM fraction's insolubility, different analytical techniques are used for its study (Alexander et al., 1998(Alexander et al., , 2017Cody & Alexander, 2005). IOM is suggested to consist of aggregates of macromolecules composed of small condensed aromatic units linked by aliphatic bridges, including a small fraction of heteroatoms (Cody & Alexander, 2005;Derenne & Robert, 2010;Remusat et al., 2005) and fractions of small polyaromatic moieties with masses ranging from 200 to 1000 Da (Danger et al., 2020). ...
... Due to the IOM fraction's insolubility, different analytical techniques are used for its study (Alexander et al., 1998(Alexander et al., , 2017Cody & Alexander, 2005). IOM is suggested to consist of aggregates of macromolecules composed of small condensed aromatic units linked by aliphatic bridges, including a small fraction of heteroatoms (Cody & Alexander, 2005;Derenne & Robert, 2010;Remusat et al., 2005) and fractions of small polyaromatic moieties with masses ranging from 200 to 1000 Da (Danger et al., 2020). ...
Using high‐resolution atomic force microscopy (AFM) with CO‐functionalized tips, we atomically resolved individual molecules from Murchison meteorite samples. We analyzed powdered Murchison meteorite material directly, as well as processed extracts that we prepared to facilitate characterization by AFM. From the untreated Murchison sample, we resolved very few molecules, as the sample contained mostly small molecules that could not be identified by AFM. By contrast, using a procedure based on several trituration and extraction steps with organic solvents, we isolated a fraction enriched in larger organic compounds. The treatment increased the fraction of molecules that could be resolved by AFM, allowing us to identify organic constituents and molecular moieties, such as polycyclic aromatic hydrocarbons and aliphatic chains. The AFM measurements are complemented by high‐resolution mass spectrometry analysis of Murchison fractions. We provide a proof of principle that AFM can be used to image and identify individual organic molecules from meteorites and propose a method for extracting and preparing meteorite samples for their investigation by AFM. We discuss the challenges and prospects of this approach to study extraterrestrial samples based on single‐molecule identification.
... We report here the composition (n CHx /n C=O and n CHx /n C=C ) of the IOMs from the Orgueil, Murchison, EET 92042 and Tagish Lake chondrites derived from the spectra published by Orthous-Daunay et al. [33] (Fig. S-5). These compositions are compared with the NMR estimates of Cody & Alexander, [9] and Gardinier et al. [16] (Fig. 7). It is first necessary to discuss those NMR data, which display some inconsistencies between them. ...
... Cody and Alexander, [9] and Gardinier et al. [16] both report CP/ MAS NMR data that provide quantitative estimates of the composition of IOM from Orgueil and Murchison. In the case of the Murchison chondrite, the ratio of aliphatic to aromatic carbon atoms F ali /F aro estimated by Gardinier et al. [16] is slightly higher than that of Cody and Alexander [9], but it lies within the error bars (Fig. 8). ...
... Cody and Alexander, [9] and Gardinier et al. [16] both report CP/ MAS NMR data that provide quantitative estimates of the composition of IOM from Orgueil and Murchison. In the case of the Murchison chondrite, the ratio of aliphatic to aromatic carbon atoms F ali /F aro estimated by Gardinier et al. [16] is slightly higher than that of Cody and Alexander [9], but it lies within the error bars (Fig. 8). In the case of Orgueil, the F ali /F aro ratio is lower than that of Cody and Alexander [9], but the error bars also overlap (Fig. 8). ...
The determination of the abundances of the CHx, C=O and aromatic groups in chondritic Insoluble Organic Matter (IOM) and coals by Infrared (IR) spectroscopy is a challenging issue due to insufficient knowledge on the absorption cross-sections and their sensitivity to the molecular environment. Here, we report a calibration approach based on a 13C synthetic model material whose composition was unambiguously determined by Direct-Pulse/Magic Angle Spinning Nuclear Magnetic Resonance (DP/MAS NMR). Ratios of the cross-sections of the CHx, C=O and aromatic groups have been determined, and the method has been applied to IOM samples extracted from four chondrites as Orgueil (CI), Murchison (CM), Tagish Lake (C2-ungrouped) and EET 92042 (CR), and to a series of coals. The estimate of the aliphatic to aromatic carbon ratio (nCHx/nAro) in IOM samples from Orgueil, Murchison and Tagish Lake chondrites is in good agreement with Single-Pulse/NMR estimates earlier published, and is lower by a factor of 1.3 in the case of the CR chondrite EET 92042 (but the error bars overlap). In contrast, the aliphatic to carbonyl ratio (nCHx/nC=O) is overestimated for the four chondrites. These discrepancies are likely due to the control of the absorption cross-section of the C=O and C=C bonds by the local molecular environment. Regarding coals, the use of published NMR analyses has brought to light that the integrated cross-section ratio ACHx/AAro varies with the vitrinite reflectance over an order of magnitude. Here as well, the local oxygen speciation plays a critical control in AAro, which decreases with increasing the vitrinite reflectance. We provide an analytical law that links ACHx/AAro and vitrinite reflectance, which will allow the determination of nCHx/nAro for any coal sample, provided its vitrinite reflectance is known.
... Demineralized residue can be used for a non-destructive investigation by solid-state 1 H and 13 C NMR spectroscopy 24,25 . It was suggested that Murchison IOM is composed primarily of highly substituted single ring aromatics, substituted furan/pyran moieties, and highly branched oxygenated aliphatic groups. ...
... Based on chemical constraints to atomic compositions, the determined Murchison alkali-extracted IOM components can be conservatively assigned to aromatic molecules with functionalized aliphatic substituents (region I) and condensed aromatic compounds (region II) 37 . This corroborates well the NMR data on the demineralized Murchison IOM witnessing its substantial aromaticity along with abundant aliphatic substituents 24 ...
... Therefore, oxygen enrichment could not be explained exclusively by reactions of organic compounds with sulfates from inorganic matrices. Moreover, it was previously suggested that the Murchison OM was oxidized during hydrothermal alteration in the parent body 24,39 . The results in Fig. 7 might indicate occurrence of extensive oxidation during both CHO and CHOS species formation. ...
Despite broad application of different analytical techniques for studies on organic matter of chondrite meteorites, information about composition and structure of individual compounds is still very limited due to extreme molecular diversity of extraterrestrial organic matter. Here we present the first application of isotopic exchange assisted Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) for analysis of alkali extractable fraction of insoluble organic matter (IOM) of the Murchison and Allende meteorites. This allowed us to determine the individual S-containing ions with different types of sulfur atoms in IOM. Thiols, thiophenes, sulfoxides, sulfonyls and sulfonates were identified in both samples but with different proportions, which contribution corroborated with the hydrothermal and thermal history of the meteorites. The results were supported by XPS and thermogravimetric analysis coupled to FTICR MS. The latter was applied for the first time for analysis of chondritic IOM. To emphasize the peculiar extraterrestrial origin of IOM we have compared it with coal kerogen, which is characterized by the comparable complexity of molecular composition but its aromatic nature and low oxygen content can be ascribed almost exclusively to degradation of biomacromolecules.
... Micron to submicron organic particles (OPs) 19 consistent with the composition of IOM occur in primitive chondrite matrices. Insoluble organic matter is acid insoluble, solid macromolecular organic material 20 that is largely made up of small aromatic groups with short, highly branched aliphatic moieties forming side chains on and cross links between the aromatic moieties 21 . They are often individual rounded submicron objects, socalled nanoglobules 22 , but also occur as dendrites or veins in CC matrix, featuring sub-particle nanoglobule morphologies 23 when imaged by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). ...
... This work is a part of a research series funded by the grant no. 21 ...
The recent return of samples from asteroid 162173 Ryugu provides a first insight into early Solar System prebiotic evolution from known planetary bodies. Ryugu’s samples are CI chondrite-like, rich in water and organic material, and primarily composed of phyllosilicate. This phyllosilicate surrounds micron to submicron macromolecular organic particles known as insoluble organic matter. Using advanced microscopy techniques on Hayabusa-2 samples, we find that aqueous alteration on Ryugu produced organic particles richer in aromatics compared to less altered carbonaceous chondrites. This challenges the view that aromatic-rich organic matter formed pre-accretion. Additionally, widespread diffuse organic material occurs in phyllosilicate more aliphatic-, carboxylic-rich, and aromatic-poor than the discrete organic particles, likely preserving the soluble organic material. Some organic particles evolved to encapsulate phyllosilicate, indicating that aqueous alteration on Ryugu led to the containment of soluble organic matter within these particles. Earth therefore has been, and continues to be, delivered micron-sized polymeric organic objects containing biologically relevant molecules.
... radicals contained in primitive organic matter like the insoluble organic matter conserved in ancient sedimentary rocks and in carbonaceous meteorites 38,[41][42][43][44][45][46][47] , but it has never been applied to flame soot. This powerful diagnostic is based on the hyperfine interaction of nuclei with spin ½ such as 1 H, 13 C, 15 N, and 31 P, or with spin 1 such as 2 H and 14 N. ...
... This strongly suggests that in the soot samples, many aromatic hydrogens have been substituted with aliphatic side chains, the sources of benzylic and distant hydrogens. By analogy with insoluble organic matter constituted of highly branched aromatic clusters linked by short and branched aliphatic chains 43,46,47 , the elongated shape of the signal ridge of benzylic hydrogens and the dominant signal of distant hydrogens in the HYSCORE spectra are indicative of branched aromatic radicals. This analysis, therefore, supports previous FTIR 18 observations, showing a high number of aliphatic C-H bonds compared to that of aromatic C-H suggested to be mainly in the form of alkyl, alkenyl side chains or cross-linked aromatic units in the soot material 49 . ...
In order to tackle the climate emergency, it is imperative to advance cleaner technologies to reduce pollutant emission as soot particles. However, there is still a lack of complete understanding of the mechanisms responsible for their formation. In this work, we performed an investigation devoted to the study of persistent radicals potentially involved in the formation of soot particles, by continuous wave and pulsed electron paramagnetic resonance. This work provides experimental evidence of the presence in nascent soot of highly branched, resonance-stabilized aromatic radicals bearing aliphatic groups, linked together by short carbon chains, and reinforced by non-covalent π-π interactions. These radicals appear to be highly specific of nascent soot and quickly disappear with the increasing soot maturity. Their presence in nascent soot could represent an underestimated health risk factor in addition to the already well documented effect of the high specific surface and the presence of harmful adsorbates.
... The spectrum of acid-char S13.5 ( Figure 6a) consists of several overlapping located at approximately 10; 25; 34; 56; 75; 90; 118; 160; 190 and 290 ppm. Generally, signals in the range 0-90 ppm are assigned to sp 3 hybridization carbon, as well as between 0-45 ppm, this includes CH 3 ; CH 2 ; and CH-groups [39]. The peak at 34 ppm can be attributed to nanodiamond carbon [39]. ...
... Generally, signals in the range 0-90 ppm are assigned to sp 3 hybridization carbon, as well as between 0-45 ppm, this includes CH 3 ; CH 2 ; and CH-groups [39]. The peak at 34 ppm can be attributed to nanodiamond carbon [39]. The signal for carbon alkoxy groups appears at 56 ppm. ...
The present work aims to explore steam activation of sisal or glucose-derived acid-chars as an alternative to KOH activation to prepare superactivated carbons, and to assess the adsorption performance of acid-chars and derived activated carbons for pharmaceuticals removal. Acid-chars were prepared from two biomass precursors (sisal and glucose) using various H2SO4 concentrations (13.5 M, 12 M, and 9 M) and further steam-activated at increasing burn-off degrees. Selected materials were tested for the removal of ibuprofen and iopamidol from aqueous solution (kinetic and equilibrium assays) in single-solute conditions. Activated carbons prepared from acid-char carbonized with 13.5 M and 12 M H2SO4 are mainly microporous solids composed of compact rough particles, yielding a maximum surface area and a total pore volume of 1987 m2 g−1 and 0.96 cm3 g−1, respectively. Solid state NMR reveals that steam activation increased the aromaticity degree and amount of C=O functionalities. Steam activation improved the acid-chars adsorption capacity for ibuprofen from 20-65 mg g−1 to higher than 280 mg g−1, leading to fast adsorption kinetics (15–20 min). The maximum adsorption capacities of selected activated samples for ibuprofen and iopamidol were 323 and 1111 mg g−1, respectively.
... The CO, CV, and CK have almost only insoluble kerogen-like material, while in the CI, CM, and CR classes there are also numerous soluble organic compounds. Moreover, there are differences in the extracted organic materials between meteorites of the same class [42,43]. ...
... Soluble organics in CC meteorites include a various and complex suite of compounds that range from large species (i.e., polycyclic aromatic hydrocarbons (PAHs)) to small molecules (i.e., methane). Amino acids compounds are an important part of organics and are found in some specific CC meteorites, such as CI, CM, CR, and the ungrouped Tagish Lake [42][43][44] meteorite. It is interesting to note that there is a dependence of amino acid with alteration degree of the meteorite: the relative quantity of amino acids declines with a growing degree of alteration in the CC, indicating that aqueous alteration processes has an influence on the organic matter [45]. ...
Ceres is the largest object in the main belt and it is also the most water-rich body in the inner solar system besides the Earth. The discoveries made by the Dawn Mission revealed that the composition of Ceres includes organic material, with a component of carbon globally present and also a high quantity of localized aliphatic organics in specific areas. The inferred mineralogy of Ceres indicates the long-term activity of a large body of liquid water that produced the alteration minerals discovered on its surface, including ammonia-bearing minerals. To explain the presence of ammonium in the phyllosilicates, Ceres must have accreted organic matter, ammonia, water and carbon present in the protoplanetary formation region. It is conceivable that Ceres may have also processed and transformed its own original organic matter that could have been modified by the pervasive hydrothermal alteration. The coexistence of phyllosilicates, magnetite, carbonates, salts, organics and a high carbon content point to rock–water alteration playing an important role in promoting widespread carbon occurrence.
... IOM contains both labile aliphatic carbon and refractory aromatic carbon (37). The former is more enriched in 13 C, whereas the latter is depleted in 13 C (38,39). ...
... In the experimental simulations of the FTT reaction, 13 C-depleted long hydrocarbons and 13 C-enriched CO 2 were formed as a simulation of 13 C-depleted IOM and 13 C-enriched carbonate in meteorites. However, the produced aliphatic hydrocarbons were different from mostly aromatic IOM carbon (37). Furthermore, the isotope effect that is systematic of unreacted heavy CO and the produced light hydrocarbons from the FTT reaction is opposite to that of the light CO and heavy hydrocarbons found in the Murchison meteorite (29,53). ...
Solvent-soluble organic matter (SOM) in meteorites, which includes life’s building molecules, is suspected to originate from the cold region of the early solar system, on the basis of ¹³ C enrichment in the molecules. Here, we demonstrate that the isotopic characteristics are reproducible in amino acid synthesis associated with a formose-type reaction in a heated aqueous solution. Both thermochemically driven formose-type reaction and photochemically driven formose-type reaction likely occurred in asteroids and ice-dust grains in the early solar system. Thus, the present results suggest that the formation of ¹³ C-enriched SOM was not specific to the cold outer protosolar disk or the molecular cloud but occurred more widely in the early solar system.
... • The C=O/C=C ratio (carbonyl abundance) in IOM of C0057-9, A0106-4, A0106-6, A0108-60, A0108-61, and A0106-23-24-25 displays lower values than those in unheated chondrites (Figure 6a). Not all oxygen is present in carbonyl groups in chondritic IOM, and ether and alcohol groups are major functional groups (Cody & Alexander, 2005). Nevertheless, this low C=O abundance in some particles of Ryugu IOM is consistent with the O/C ratio estimated by NanoSIMS (0.12 and 0.04 for chambers A and C, respectively), and by STEM-EDS analyses (0.1 for both chambers A and C; Yabuta et al., 2023), which are both lower than O/C in Orgueil and Ivuna IOM samples, as 0.18 AE 0.02 and 0.158, respectively (Alexander et al., 2007). ...
We report a Fourier transform infrared analysis of functional groups in insoluble organic matter (IOM) extracted from a series of 100–500 μm Ryugu grains collected during the two touchdowns of February 22 and July 11, 2019. IOM extracted from most of the samples is very similar to IOM in primitive CI, CM, and CR chondrites, and shows that the extent of thermal metamorphism in Ryugu regolith was, at best, very limited. One sample displays chemical signatures consistent with a very mild heating, likely due to asteroidal collision impacts. We also report a lower carbonyl abundance in Ryugu IOM samples compared to primitive chondrites, which could reflect the accretion of a less oxygenated precursor by Ryugu. The possible effects of hydrothermal alteration and terrestrial weathering are also discussed. Last, no firm conclusions could be drawn on the origin of the soluble outlier phases, observed along with IOM in this study and in the preliminary analysis of Ryugu samples. However, it is clear that the HF/HCl residues presented in this publication are a mix between IOM and the nitrogen‐rich outlier phase.
... The Ryugu OM functional chemistry is dominated by four main groups: aromatic (C=C), ketone (C=O), carboxyl (COOH), and carbonate (CO 3 ), with lesser amounts of aliphatics (C-H n ). The aliphatic content of the Ryugu IOM observed by TEM EELS and STXM varies among particles, but appears to be higher than in Murchison IOM measured under similar conditions at NRL, which is consistent with bulk IOM measurements showing a greater aliphatic relative abundance for CIs than CMs (Cody & Alexander, 2005). Aliphatic-rich OM (c) Low-loss EELS of the pyrrhotite and closed vesicle after deconvolution of the zero loss peak. ...
Transmission electron microscopy analyses of Hayabusa2 samples show that Ryugu organic matter exhibits a range of morphologies, elemental compositions, and carbon functional chemistries consistent with those of carbonaceous chondrites that have experienced low‐temperature aqueous alteration. Both nanoglobules and diffuse organic matter are abundant. Non‐globular organic particles are also present, and including some that contain nanodiamond clusters. Diffuse organic matter is finely distributed in and around phyllosilicates, forms coatings on other minerals, and is also preserved in vesicles in secondary minerals such as carbonate and pyrrhotite. The average elemental compositions determined by energy‐dispersive spectroscopy of extracted, demineralized insoluble organic matter samples A0107 and C0106 are C 100 N 3 O 9 S 1 and C 100 N 3 O 7 S 1 , respectively, with the difference in O/C slightly outside the difference in the standard error of the mean. The functional chemistry of the nanoglobules varies from mostly aromatic C=C to mixtures of aromatic C=C, ketone C=O, aliphatic (CH n ), and carboxyl (COOH) groups. Diffuse organic matter associated with phyllosilicates has variable aromatic C, ketone and carboxyl groups, and some localized aliphatics, but is dominated by molecular carbonate (CO 3 ) absorption, comparable to prior observations of clay‐bound organic matter in CI meteorites.
... Another prominent application of MMC Raman spectroscopy is for the examination of the insoluble organic matter (IOM) in meteorites (Bower et al., 2013;Busemann et al., 2007;El Amri et al., 2005;Homma et al., 2015;Quirico et al., 2003) and other astromaterials (Busemann et al., 2009;Caro et al., 2008). The structure of meteorite MMC is a result of its original formation synthesis as well as secondary processes such as thermal and shock alteration (Bonal et al., 2006;Cody & Alexander, 2005;Ferroir et al., 2010;Nestola et al., 2020). With increased thermal alteration the MMC ordering increases and the structural differences are reflected in the MMC Raman spectrum. ...
Macromolecular carbon (MMC) is a polymeric solid form of carbon formed from numerous natural and anthropogenic processes. MMC is found in geologic samples, such as coals, meteorites, and metamorphic rocks, and the microstructure of the MMC provides details of the thermal history of the sample. Raman spectroscopy allows for a simple, quick examination of the MMC structure and thermal history of the rock. However, accurate Raman analysis necessitates that the Raman incident laser does not photodamage the MMC being measured. Here we examine, in detail, the effect of 532 and 488 nm laser irradiation on the structure of MMC in coals and meteorites. We show that photodegradation does affect the primary “G” and “D” Raman band peak positions, widths, absolute intensities, and relative intensities and we quantify changes with progressive irradiation. These results provide insight into the MMC structural changes that occur with photodegradation. We find that significant photodegradation occurs even with low laser powers (<200 μW). A literature survey of Raman MMC measurements shows that almost all publications use incident laser irradiances that would result in significant photodegradation of MMC within the accumulation time of a single Raman spectrum.
... Overall, CCs contain up to 5 wt% of organic matter dominated by an insoluble fraction (IOM -75 to 90 wt%) associated with a minor soluble fraction (SOM -10 to 25 wt%). While the IOM consists in high molecular weight molecules made of aromatic units and short aliphatic chains rich in hetero-elements (Cody and Alexander, 2005;Alexander et al., 2007;Derenne and Robert, 2010;Remusat et al., 2016Remusat et al., , 2019Vinogradoff et al., 2017;Danger et al., 2020), the SOM is composed of a diversity of small organic molecules (such as carboxylic acids, amino acids, nucleobases, sugars. . . -e.g., Pizzarello, 2006;Remusat, 2015;Martins et al., 2015) including polycyclic aromatic hydrocarbons (PAHs) (Oró et al., 1971;Pering and Ponnamperuma, 1971;Basile et al., 1984;Zenobi et al., 1989;Gilmour and Pillinger, 1994;Messenger et al., 1998;Sephton et al., 1998;Naraoka et al., 2000;Oba and Naraoka, 2003;Plows et al., 2003;Huang et al., 2015;Simkus et al., 2019;Kalpana et al., 2021). ...
Carbonaceous chondrites contain in a diverse suite of more or less soluble compounds, including polycyclic aromatic hydrocarbons (PAHs). These compounds are structured around two or more fused benzene rings, and have shown to be detected in various astrophysical environments. The origin of PAHs in carbonaceous chondrites is debated: they may originate from the interstellar medium (ISM) and thus potentially carry information on accretion processes. Alternatively, they may have formed or transformed during secondary processes on parent bodies and thus carry information about aqueous alteration conditions. Here, we investigate the nature, quantity, and isotopic composition of free PAHs in three recently recovered CM chondrites having experienced substantial and distinct degrees of alteration: the CM2.2 Aguas Zarcas, the CM2.0 Mukundpura and the CM1/2 Kolang. All the CMs investigated contain PAHs, with sizes ranging from 2 (naphthalene) to 5 cycles (benzopyrene). The concentration of PAHs is not correlated to the degree of alteration and larger PAHs are also the most depleted in ¹³C, suggesting an interstellar origin. Yet, the abundance of alkylated PAHs appears correlated to the degree of alteration and all the extracted PAHs are D-depleted, pointing towards hydrogen exchange with water having occurred during aqueous alteration. These combined results suggest that PAHs in CCs likely carry information on both accretion and alteration processes.
... One possibility to circumvent this issue in the case of organic compounds is to use chemical extraction and to perform IR spectroscopy on the extracted organics. This has been done and revealed for instance chemical variabilities between insoluble organic matter (IOM) of different carbonaceous chondrites (Alexander et al., 2007Cody & Alexander, 2005;Orthous-Daunay et al., 2013;Quirico et al., 2014Quirico et al., , 2018. In that case, however, information on the possibility of heterogeneities of organics within a sample is lost, as well as the petrographic relation with other constituents (silicates, metals, and so on). ...
... One possibility to circumvent this issue in the case of organic compounds is to use chemical extraction and to perform IR spectroscopy on the extracted organics. This has been done and revealed for instance chemical variabilities between insoluble organic matter (IOM) of different carbonaceous chondrites (Alexander et al., 2007Cody & Alexander, 2005;Orthous-Daunay et al., 2013;Quirico et al., 2014Quirico et al., , 2018. In that case, however, information on the possibility of heterogeneities of organics within a sample is lost, as well as the petrographic relation with other constituents (silicates, metals, and so on). ...
Meteorite matrices from primitive chondrites are an interplay of ingredients at the sub-μm scale, which requires analytical techniques with the nanometer spatial resolution to decipher the composition of individual components in their petrographic context. Infrared spectroscopy is an effective method that enables the probing of vibrations at the molecule atomic scale of organic and inorganic compounds but is often limited to a few micrometers in spatial resolution. To efficiently distinguish spectral signatures of the different constituents, we apply here nano-infrared spectroscopy (AFM-IR), based on the combination of infrared and atomic force microscopy, having a spatial resolution beyond the diffraction limits. Our study aims to characterize two chosen meteorite samples to investigate primitive material in terms of bulk chemistry (the CI chondrite Orgueil) and organic composition (the CR chondrite EET 92042). We confirm that this technique allows unmixing the IR signatures of organics and minerals to assess the variability of organic structure within these samples. We report an investigation of the impact of the widely used chemical HF/HCl (hydrogen fluoride/hydrochloric acid) extraction on the nature of refractory organics (insoluble organic matter [IOM]) and provide insights on the mineralogy of meteorite matrices from these two samples by comparing to reference (extra)terrestrial materials. These findings are discussed with a perspective toward understanding the impact of post-accretional aqueous alteration and thermal metamorphism on the composition of chondrites. Last, we highlight that the heterogeneity of organic matter within meteoritic materials extends down to the nanoscale, and by comparison with IOMs, oxygenated chemical groups are not affected by acid extractions.
... Molecules with permanent dipole moments are I.R. active, as shown in Fig. 3. NMR focuses on structural investigation of hydrocarbon molecules, while FT-IR is based on distinctive vibrational frequencies of bonds that include stretching and bending vibrations. NMR is an essential tool for group type analysis, i.e., it directly measures aromatic and aliphatic carbons ( 13 C NMR) and hydrogen distribution ( 1 H NMR). It also gives crucial information about a molecule's carbon and hydrogen structural grouping [14][15][16][17][18][19]. Integration of relevant portions of the 13 C and 1 H NMR spectra can be used to determine a quantitative assessment of oxygen-containing functions [20,21]. ...
Nuclear Magnetic Resonance (NMR) involves the study of nuclei immersed in a static magnetic field and exposed to a second oscillating field. Nuclei have two properties; spin properties and charge properties. Pyrolysis oil is created by dry heating biomass in a reactor without oxygen to around 500 degrees Celsius and then cooling it. Pyrolysis oil is a type of tar that includes too much oxygen to be classified as a pure hydrocarbon. One of the most fundamental methods in synthetic chemistry is using NMR to verify chemical structure. In the literature, little attention has been paid to the application of NMR in the authentication of chemical structures. In this study, we present a use case of NMR to characterize pyrolysis oil and authenticate chemical structures. Results show that the elucidation of chemical compositions of bio-oil is essential for the optimization of its processing technology and exploration of its potential application.
... Aqueous alteration processes resulted in an oxidized signature (that is, the loss of H) of the SOM, which is consistent with the previously observed linear correlation in H/C ratios and δD of Tagish Lake IOM (Cody & Alexander 2005;Alexander et al. 2007;Herd et al. 2011;Alexander et al. 2014) and inferences from previous IOM and SOM studies (Hilts et al. 2014;Quirico et al. 2018). The present measurement shows that the larger molecules were spared from removal throughout the alteration (Fig 3) This hypothesis can be tested by comparing the degree of H-loss between the IOM and the SOM. ...
Biologically relevant abiotic extraterrestrial soluble organic matter (SOM) has been widely investigated to study the origin of life and the chemical evolution of protoplanetary disks. Synthesis of biologically relevant organics, in particular, seems to require aqueous environments in the early solar system. However, SOM in primitive meteorites includes numerous chemical species besides the biologically relevant ones, and the reaction mechanisms that comprehensively explain the complex nature of SOM are unknown. Besides, the initial reactants, which formed before asteroid accretion, were uncharacterized. We examined the mass distribution of SOM extracted from three distinct Tagish Lake meteorite fragments, which exhibit different degrees of aqueous alteration though they originated from a single asteroid. We report that mass distributions of SOM in the primordial fragments are well fit by the SchulzZimm (SZ) model for the molecular weight distribution patterns found in chain growth polymerization experiments. Also, the distribution patterns diverge further from SZ with increasing degrees of aqueous alteration. These observations imply that the complex nature of the primordial SOM (1) was established before severe alteration on the asteroid, (2) possibly existed before parent-body accretion, and (3) later became simplified on the asteroid. Therefore, aqueous reactions on asteroids are not required conditions for cultivating complex SOM. Furthermore, we found that overall H over C ratios of SOM decrease with increasing aqueous alteration, and the estimate of H loss from the SOM is 10% to 30%. Organics seem to be a significant H2 source that may have caused subsequent chemical reactions in the Tagish Lake meteorite parent body.
... The IOM is dominated by highly cross-linked, small aromatic molecules with short aliphatic side chains (Sephton et al., 2004). Much has been discovered about the structure and composition of IOM from techniques such as nuclear magnetic resonance (NMR) spectroscopy, gas chromatography (GC or GC-MS), and transmission spectroscopy (Alexander et al., 2014;Cody & Alexander, 2005). X-ray absorption nearedge structure (XANES; Cody et al., 2008) and confocal Raman spectroscopy (Bonal et al., 2016) have been employed to estimate peak metamorphic temperatures based on observed organic compositions. ...
Carbonaceous chondrites (CCs) are important materials for understanding the early evolution of the solar system and delivery of organic material to the early Earth. Spectral analysis of CCs can establish the relationship between them and their possible parent asteroids, which helps to determine the surface composition of the asteroid. In this paper, the 0.3–26 μm reflectance spectra of a series of coals ranging from lignite to anthracite (Earth analogs of organic matter contained in CCs), a coal heated to various durations and temperatures, and reflectance spectra of CM2 meteorites were analyzed in conjunction with compositional information to derive spectral–compositional relationships. All types of coals have strong aromatic absorptions (3.28 and 5–6.5 μm) and aliphatic “triplet” absorptions (3.38, 3.41, and 3.48 μm). In contrast, CM2 meteorites have obvious aliphatic absorptions and lack aromatic absorptions. The reason is the weak absorption coefficients of aromatic materials and the overlap with strong OH/H2O absorption. Absorptions in the coal spectra are strongly related to elemental H/C ratio. When the H/C ratio is >0.55, the absorption intensity of an aliphatic increases linearly with the increase of H/C. For heated coal, increasing heating time above 1 h at 450 °C causes the disappearance of the aliphatic “triplet” absorptions. Similarly, heating Murchison meteorite to 400 °C for 1 week causes all the organic absorptions to disappear. This implies that in remote sensing detections, only asteroids (e.g., with CM and CI carbonaceous chondrites compositions) that experienced low thermal metamorphism (<400 °C) are suitable as potential targets for detecting organic compounds using features in the 3–4 µm region.
... provides the best quantitative picture of the main functional group in the bulk IOM [135][136][137][138][139][140]. 1 H-and 13 C-NMR also suggest that most of the PAUs in IOM is small and highly substituted, and that the aliphatic component be composed of short, highly branched units. There is considerable line broadening in the NMR spectra. ...
An interdisciplinary review of the chemical literature that points to a unifying scenario for the origin of life, referred to as the Primordial Multifunctional organic Entity (PriME) scenario, is provided herein. In the PriME scenario it is suggested that the Insoluble Organic Matter (IOM) in carbonaceous chondrites, as well as interplanetary dust particles from meteorites and comets may have played an important role in the three most critical processes involved in the origin of life, namely 1) metabolism, via a) the provision and accumulation of molecules that are the building blocks of life, b) catalysis (e.g., by templation), and c) protection of developing life molecules against radiation by excited state deactivation; 2) compartmentalization, via adsorption of compounds on the exposed organic surfaces in fractured meteorites, and 3) replication, via deaggregation, desorption and related physical phenomena. This scenario is based on the hitherto overlooked structural and physicochemical similarities between the IOM and the dark, insoluble, multifunctional melanin polymers found in bacteria and fungi and associated with the ability of these microorganisms to survive extreme conditions, including ionizing radiation. The underlying conceptual link between these two materials is strengthened by the fact that primary precursors of bacterial and fungal melanins (collectively referred to herein as allomelanins) are hydroxylated aromatic compounds like homogentisic acid and 1,8-dihydroxynaphthalene, and that similar hydroxylated aromatic compounds, including hydroxynaphthalenes, figure prominently among possible components of the organic materials on dust grains and ices in the interstellar matter, and may be involved in the formation of IOM in meteorites. Inspired by this rationale, a vis-à-vis review of the properties of IOM from various chondrites and non-nitrogenous allomelanin pigments from bacteria and fungi is provided herein. The unrecognized similarities between these materials may pave the way for a novel scenario at the origin of life, in which IOM-related complex organic polymers delivered to the early Earth are proposed to serve as PriME and were preserved and transformed in those primitive forms of life that shared the ability to synthesize melanin polymers playing an important role in the critical processes underlying the establishment of terrestrial eukaryotes.
... The same sample mounting protocol has been used to mount other small astromaterials such as interplanetary dust particles 56 . The meteorite insoluble organic matter (IOM) samples used in Raman analysis were prepared by demineralization of the bulk meteorites with CsF-HF dissolution according to the methods described in 57 . These residues have also previously been studied by Raman spectroscopy 6,29,56,58,59 . ...
Understanding the true nature of extra-terrestrial water and organic matter that were present at the birth of our solar system, and their subsequent evolution, necessitates the study of pristine astromaterials. In this study, we have studied both the water and organic contents from a dust particle recovered from the surface of near-Earth asteroid 25143 Itokawa by the Hayabusa mission, which was the first mission that brought pristine asteroidal materials to Earth’s astromaterial collection. The organic matter is presented as both nanocrystalline graphite and disordered polyaromatic carbon with high D/H and ¹⁵N/¹⁴N ratios (δD = + 4868 ± 2288‰; δ¹⁵N = + 344 ± 20‰) signifying an explicit extra-terrestrial origin. The contrasting organic feature (graphitic and disordered) substantiates the rubble-pile asteroid model of Itokawa, and offers support for material mixing in the asteroid belt that occurred in scales from small dust infall to catastrophic impacts of large asteroidal parent bodies. Our analysis of Itokawa water indicates that the asteroid has incorporated D-poor water ice at the abundance on par with inner solar system bodies. The asteroid was metamorphosed and dehydrated on the formerly large asteroid, and was subsequently evolved via late-stage hydration, modified by D-enriched exogenous organics and water derived from a carbonaceous parent body.
Tarda is an ungrouped, hydrated carbonaceous chondrite (C2‐ung) that was seen to fall in Morocco in 2020. Early studies showed that Tarda chemically resembles another ungrouped chondrite, Tagish Lake (C2‐ung), which has previously been linked to the dark D‐type asteroids. Samples of D‐type asteroids provide an important opportunity to investigate primitive conditions in the outer solar system. We show that Tarda contains few intact chondrules and refractory inclusions and that its composition is dominated by secondary Mg‐rich phyllosilicates (>70 vol%), carbonates, oxides, and Fe‐sulfides that formed during extensive water–rock reactions. Quantitative assessment of first‐order reversal curve (FORC) diagrams shows that Tarda's magnetic mineralogy (i.e., framboidal magnetite) is comparable to that of the CI chondrites and differs notably from that of most CM chondrites. These traits support a common formation process for magnetite in Tarda and the CI chondrites. Furthermore, Tarda's pre‐terrestrial paleomagnetic remanence is similar to that of Tagish Lake and samples returned from asteroid Ryugu, with a very weak paleointensity (<0.6 μT) suggesting that Tarda's parent body accreted more distally than that of the CM chondrites, possibly at a distance of >5.4–8.3 AU. An origin in the cold, outer regions of the solar system is further supported by the presence of distinct, porous clasts enriched in aliphatic‐rich organics that potentially retain a pristine interstellar composition. Together, our observations support a genetic relationship between Tarda and Tagish Lake.
We analyzed the methanol extracts of six pristine specimens of the Tagish Lake meteorite (TL1, TL4, TL5A, TL6, TL7, and TL10a) and heated and unheated samples of Allende using high‐performance liquid chromatography coupled with high‐resolution, accurate mass–mass spectrometry (HPLC‐HRAM‐MS). All samples contained ppm levels of sulfate and methyl sulfate. The most abundant organosulfur compound in the methanol extracts of the Tagish Lake and Allende samples was methyl sulfate, which was likely formed primarily via an esterification reaction between intrinsic sources of methanol and sulfate. A homologous series of polythionic acids was also observed in the extracts of the Tagish Lake specimens and Allende. The polythionic acids were the most abundant soluble inorganic sulfur species found in the meteorites. Our results were confirmed using retention time, accurate mass, isotope matching, and tandem mass spectrometry (MS/MS). Hydroxymethanesulfonic acid, previously reported in Tagish Lake, was found only in an unheated Allende sample and in low abundance. Here, we propose possible sulfate formation pathways that begin with interstellar dimethyl sulfide, dimethyl disulfide, methyl sulfide, or methanethiol via cold, nebular processes within the interstellar medium and continue via MSA as an intermediary compound ending within planetary bodies with sulfate and methyl sulfate as the final products.
Organic compounds are a major component of dust in molecular clouds, alongside silicates and water ice, due to the high abundances of elements that make up these compounds in the Galaxy. The initial molecular inventory of the Solar System, inherited from the molecular cloud, was modified and new complex molecules were formed in the protoplanetary disk and planetesimals. Because astronomical observations mainly target gas, while cosmochemical evidence deals with solid phases, it is crucial to link discrepant knowledge on organic species through state-of-the-art modeling. This chapter reviews the latest understanding of surface reactions on inter-stellar dusts, gas–dust reactions in the protoplanetary disk, and alteration processes on planetesimals in the early Solar System.
The recent return of samples from carbonaceous asteroids provides first insight into early Solar System prebiotic evolution from known planetary bodies. Asteroid 162173 Ryugu samples are CI (Ivuna type), the most water- and organic-rich chondritic material, composing mostly of phyllosilicate. This phyllosilicate surrounds micron to submicron macromolecular organic particles - insoluble organic matter. Alteration on 162173Ryugu evolved insoluble organic material into organic particles aromatic-richer than what is found in the lesser altered carbonaceous chondrite matrices, consistent with CI and type 1 carbonaceous chondrites. Wider-spread diffuse organic material is also preserved within the phyllosilicate, aliphatic-, carboxylic-richer and aromatic-poorer than the organic particles. This diffuse organic material is probably a mixture of both acid insoluble and solvent soluble organic molecules. Carboxyl/aromatic ratios in the diffuse organic matter of Ryugu are also characteristic of CI and type 1 carbonaceous chondrites, indicating the role of aqueous alteration in its formation. Some organic particles additionally evolved to completely surround phyllosilicate itself, meaning that the soluble organic bearing diffuse organic matter is contained within some of the macromolecular organic particles by aqueous alteration on Ryugu. Earth therefore was, and currently is, delivered micron-sized polymeric organic objects encapsulating biologically relevant molecules.
This study analyzed samples of the Murchison and Sutter's Mill carbonaceous chondrite meteorites in support of the future analysis of samples returned from the asteroid (10155) Bennu by the OSIRIS‐REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission. Focusing specifically on the insoluble organic matter (IOM), this study establishes that a total of 1.3 g of bulk sample from a single chondritic meteorite are sufficient to obtain a wide range of cosmochemical information, including light element analysis (H, C, and N), isotopic analysis (D/H, ¹³ C/ ¹² C, and ¹⁵ N/ ¹⁴ N), and x‐ray fluorescence spectroscopy for major elemental abundances. IOM isolated from the bulk meteorite samples was analyzed by light element and isotopic analysis as described above, ¹ H and ¹³ C solid‐state nuclear magnetic resonance spectroscopy, Raman spectroscopy, and complete noble gas analyses (abundances and isotopes). The samples studied included a pair from Murchison (CM2), one of which had been irradiated with high‐energy x‐rays in the course of computed tomographic imaging. No differences between the irradiated and non‐irradiated Murchison samples were observed in the many different chemical and spectroscopic analyses, indicating that any x‐ray–derived sample damage is below levels of detection. Elemental, isotopic, and molecular spectroscopic data derived from IOM isolated from the Sutter's Mill sample reveals evidence that this meteorite falls into the class of heated CM chondrites.
Early stages of life likely employed catalytic RNAs (ribozymes) in many functions that are today filled by proteins. However, the earliest life forms must have emerged from heterogenous chemical mixtures, which included amino acids, short peptides, and many other compounds. Here we explored whether the presence of short peptides can help the emergence of catalytic RNAs. To do this, we conducted an in vitro selection for catalytic RNAs from randomized sequence in the presence of ten different peptides with a prebiotically plausible length of eight amino acids. This in vitro selection generated dozens of ribozymes, one of them with ∼900-fold higher activity in the presence of one specific peptide. Unexpectedly, the beneficial peptide had retained its N-terminal Fmoc protection group, and this group was required to benefit ribozyme activity. The same, or higher benefit resulted from peptide conjugates with prebiotically plausible polyaromatic hydrocarbons (PAHs) such as fluorene and naphthalene. This shows that PAH-peptide conjugates can act as potent cofactors to enhance ribozyme activity. The results are discussed in the context of the origin of life.
This review (in Japanese) highlights the results on the Stardust mission organics preliminary examination of the returned Comet 81P/Wild 2 particles, based on the Science article published in December 15, 2006. The recent developments of studies on organics in chondritic meteorites and/or interstellar dust particles using modern instruments are also described for seeking relations of organic characteristics among the three extraterrestrial samples. In addition, potential chemistry for which cometary and meteoritic organics were responsible as a source of exogenous delivery to the early Earth is discussed.
The Origins, Spectral Interpretation, Resource Identification, and Security Regolith Explorer (OSIRIS-REx) spacecraft arrived at its target, near-Earth asteroid 101955 Bennu, in December 2018. After one year of operating in proximity, the team selected a primary site for sample collection. In October 2020, the spacecraft descended to the surface of Bennu and collected a sample. The spacecraft departed Bennu in May 2021 and will return the sample to Earth in September 2023. The analysis of the returned sample will produce key data to determine the history of this B-type asteroid and that of its components and precursor objects. The main goal of the OSIRIS-REx Sample Analysis Plan is to provide a framework for the Sample Analysis Team to meet the Level 1 mission requirement to analyze the returned sample to determine presolar history, formation age, nebular and parent-body alteration history, relation to known meteorites, organic history, space weathering, resurfacing history, and energy balance in the regolith of Bennu. To achieve this goal, this plan establishes a hypothesis-driven framework for coordinated sample analyses, defines the analytical instrumentation and techniques to be applied to the returned sample, provides guidance on the analysis strategy for baseline, overguide, and threshold amounts of returned sample, including a rare or unique lithology, describes the data storage, management, retrieval, and archiving system, establishes a protocol for the implementation of a micro-geographical information system to facilitate co-registration and coordinated analysis of sample science data, outlines the plans for Sample Analysis Readiness Testing, and provides guidance for the transfer of samples from curation to the Sample Analysis Team.
Context. The current period is conducive to exploring our Solar System's origins with recent and future space sample return missions, which provide invaluable information from known Solar System asteroids and comets The Hayabusa2 mission of the Japan Aerospace Exploration Agency (JAXA) recently brought back samples from the surface of the Ryugu carbonaceous asteroid.
Aims. We aim to identify the different forms of chemical composition of organic matter and minerals that constitute these Solar System primitive objects, to shed light on the Solar System's origins.
Methods. In this work, we recorded infrared (IR) hyper-spectral maps of whole-rock Ryugu asteroid samples at the highest achievable spatial resolution with a synchrotron in the mid-IR (MIR). Additional global far-IR (FIR) spectra of each sample were also acquired.
Results. The hyper-spectral maps reveal the variability of the functional groups at small scales and the intimate association of phyl-losilicates with the aliphatic components of the organic matter present in Ryugu. The relative proportion of column densities of the identified IR functional groups (aliphatics, hydroxyl + interlayer and/or physisorbed water, carbonyl, carbonates, and silicates) giving access to the composition of the Ryugu samples is estimated from these IR hyper-spectral maps. Phyllosilicate spectra reveal the presence of mixtures of serpentine and saponite. We do not detect anhydrous silicates in the samples analysed, at the scales probed. The carbonates are dominated by dolomite. Aliphatics organics are distributed over the whole samples at the micron scale probed with the synchrotron, and intimately mixed with the phyllosilicates. The aromatic C=C contribution could not be safely deconvolved from OH in most spectra, due to the ubiquitous presence of hydrated minerals. The peak intensity ratios of the organics methylene to methyl (CH 2 /CH 3 ) of the Ryugu samples vary between about 1.5 and 2.5, and are compared to the ratios in chondrites from types 1 to 3. Overall, the mineralogical and organic characteristics of the Ryugu samples show similarities with those of CI chondrites, although with a noticeably higher CH 2 /CH 3 in Ryugu than generally measured in C1 chondrites collected on Earth, and possibly a higher carbonate content.
Cosmochemistry is a rapidly evolving field of planetary science and the second edition of this classic text reflects the exciting discoveries made over the past decade from new spacecraft missions. Topics covered include the synthesis of elements in stars, behaviour of elements and isotopes in the early solar nebula and planetary bodies, and compositions of extra-terrestrial materials. Radioisotope chronology of the early Solar System is also discussed, as well as geochemical exploration of planets by spacecraft, and cosmochemical constraints on the formation of solar systems. Thoroughly updated throughout, this new edition features significantly expanded coverage of chemical fractionation and isotopic analyses; focus boxes covering basic definitions and essential background material on mineralogy, organic chemistry and quantitative topics; and a comprehensive glossary. An appendix of analytical techniques and end-of-chapter review questions, with solutions available at www.cambridge.org/cosmochemistry2e, also contribute to making this the ideal teaching resource for courses on the Solar System's composition as well as a valuable reference for early career researchers.
Asteroids and comets are thought to form in the inner and outer solar systems, respectively. Chondritic porous and smooth interplanetary dust particles (CP IDPs and CS IDPs, respectively) in the stratosphere are regarded as dust grains from comets and hydrated asteroids, respectively. Here, we describe an Antarctic micrometeorite (AMM) composed of lithologies of both CP and CS IDPs. In addition to the CS IDP‐like compact lithology that experienced severe aqueous alteration, the CP IDP‐like porous lithology shows evidence of very weak aqueous alteration. The structure of the organic matter in the porous lithology varies from that in the CP IDPs to aromatic‐rich organic matter. In contrast, the structure of the organic matter in the compact lithology is homogenous, which is consistent with higher degrees of aqueous alteration. Its structure is more similar to that of CP IDPs and Wild 2 samples than that of meteoritic insoluble organic matter, suggesting that the compact lithology formed from the porous lithology. Some CP IDPs are related to cometary dust streams, such as those originating from 26P/Grigg‐Skjellerup. In addition, the presence of this AMM indicates an additional origin of the CP IDPs and their equivalent AMMs. The mineralogy and organic chemistry of this AMM suggest that its parent body was composed of the same building blocks as those of the comets, and later experienced incomplete aqueous alteration. The AMM probably formed as microbreccia in the regolith layer composed of materials from a CP IDP‐like crust and a hydrated interior.
On April 23rd, 2019, the Aguas Zarcas meteorite fall occurred in Costa Rica. Because the meteorite was quickly recovered, it contains valuable extraterrestrial materials that have not been contaminated by terrestrial processes. Our X-ray computed tomography (XCT) and scanning electron microscopy (SEM) results on various pre-rain fragments from earlier work (Kerraouch et al., 2020; 2021) revealed several distinct lithologies: Two distinct metal-rich lithologies (Met-1 and Met-2), a CM1/2 lithology, a C1 lithology, and a brecciated CM2 lithology consisting of different petrologic types. Here, we further examined these lithologies in the brecciated Aguas Zarcas meteorite and report new detailed mineralogical, chemical, isotopic, and organic matter characteristics. In addition to petrographic differences, the lithologies also display different chemical and isotopic compositions. The variations in their bulk oxygen isotopic compositions indicate that the various lithologies formed in different environments and/or under diverse conditions (e.g., water/rock ratios). Each lithology experienced a different hydration period during its evolution. Together, this suggests that multiple precursor parent bodies may have been involved in these processes of impact brecciation, mixing, and re-assembly. The Cr and Ti isotopic data for both the CM1/2 and Met-1 lithology are consistent with those of other CM chondrites, even though Met-1 displays a significantly lower ε⁵⁰Ti isotopic composition that may be attributable to sample heterogeneities on the bulk meteorite scale and may reflect variable abundances of refractory phases in the different lithologies of Aguas Zarcas. Finally, examination of the organic matter of the various lithologies also suggests no strong evidence of thermal events, but a short-term heating cannot completely be excluded. Raman parameters indicate that the peak temperature has been lower than that for Yamato-793321 (CM2, ∼400°C). Considering the new information presented in this study, we now better understand the origin and formation history of the Aguas Zarcas daughter body.
Carbonaceous chondrites contain both soluble and insoluble organic materials (SOM and IOM) which may have been produced in different environments via different processes or share possible genetic relationships. The SOM may have been produced from IOM during hydrothermal episodes on asteroids, and vice versa. The potential role played by the mineral matrix during these episodes (clay minerals of variable crystallinity) remains to be constrained. Here, we exposed a mixture of formaldehyde and glycolaldehyde with ammonia-bearing liquid water together with Fe-rich smectitic minerals to hydrothermal conditions mimicking asteroidal conditions. We used both amorphous gel of smectite or crystalline smectites in order to understand the influence of the crystallinity on the evolution of OM. The organo-mineral experimental residues were characterized at a multiple length scales using X-ray diffraction and microscopy/spectroscopic tools. Results evidence that some IOM polymerizes/condenses in the absence of Fe-rich smectites. Yet, the presence of Fe-rich smectites inhibits this production of IOM. Indeed, the interactions between the SOM and clay surfaces (interlayers or edges) reduce the concentration of SOM available for polymerization/condensation reactions, a necessary step for the production of IOM. In addition, the presence of OM disorganizes the crystallization of the Fe-rich amorphous silicates, leading to smaller crystal sized particles exhibiting a lower permanent charge. This might suggests that the smectite permanent charge distribution may help better constraining the origin and evolution of chondritic clay minerals. Altogether, the present study sheds new light on the organo-mineral interactions having occurred during hydrothermal episodes onto/within chondritic asteroids. Indeed, IOM formation from OM-rich aqueous fluids does not occur during the alteration of amorphous silicates. This would mean that IOM is either produced within pockets free of clay minerals or initially accreted as IOM-rich grain. Last, about ∼50 wt.% of the initial C could not be removed from the clay minerals at the end of the experiments using classical solvent extraction protocols, demonstrating that a high fraction of the SOM in carbonaceous chondrites may have been overlooked.
Meteorite matrices from primitive chondrites are an interplay of ingredients at the sub-µm scale, which requires analytical techniques with the nanometer spatial resolution to decipher the composition of individual components in their petrographic context. Infrared spectroscopy is an effective method that enables to probe of vibrations at the molecule-atomic scale of organic and inorganic compounds but is often limited to a few micrometers in spatial resolution. To efficiently distinguish spectral signatures of the different constituents, we apply here nano-IR spectroscopy (AFM-IR), based on the combination of infrared and atomic force microscopy, having a spatial resolution beyond the diffraction limits. Our study aims to characterize two chosen meteorite samples to investigate primitive material in terms of bulk chemistry (the CI chondrite Orgueil) and organic composition (the CR chondrite EET 92042). We confirm that this technique allows unmixing the IR signatures of organics and minerals to assess the variability of organic structure within these samples. We report an investigation of the impact of the widely used chemical HF/HCl (Hydrogen Fluoride/Hydrochloric) extraction on the nature of refractory organics (Insoluble Organic Matter, IOM) and provide insights on the mineralogy of meteorites matrices from these two samples by comparing to reference (extra)terrestrial materials. These findings are discussed with a perspective toward understanding the impact of post-accretional aqueous alteration and thermal metamorphism on the composition of chondrites. Last, we highlight that the heterogeneity of organic matter within meteoritic materials extends down to the nanoscale, and by comparison with IOMs, oxygenated chemical groups are not affected by acid extractions.
The insoluble organic material (IOM) in primitive chondritic meteorites is very enriched in D (up to δD≈3500 ‰ in bulk). Based largely on a series of electron paramagnetic resonance (EPR) studies of IOM from three meteorites (Orgueil, Murchison and Tagish Lake), it has been suggested that these enrichments are the result of exchange with H2D⁺ in the solar nebula and that exchange with radicals in the IOM was particularly facile so that they are enormously enriched in D (δD≥95000 ‰). To try to test whether radicals are largely responsible for the D enrichments in IOM, we have used EPR to measure the radical concentrations (spins/g) and g-factors of 18 IOM separates from C1-2 chondrites of varying petrologic type and chemical group that have a much wider range of H isotopic compositions (δD≈600-3500 ‰) than in previous studies. We confirm the previous studies findings that IOM exhibits non-Curie law behavior and that it does not completely saturate even at microwave excitation powers of 200 mW. We also have obtained similar g-factor values. However, our IOM samples typically exhibit a lower and more limited range of spin concentrations, and smaller deviations from Curie law behavior than in previous studies. Nor do we observe correlations between bulk δD and either spins/g or non-Curie law behavior that would be expected if exchange between H2D⁺ and radicals, as previously proposed, was the cause of the D-enrichments in IOM. Indeed, in general the radical concentrations and the degree of non-Curie law behavior do not seem to correlate with any of the measured IOM properties, with chondrite group or parent body history (e.g., degree of aqueous alteration). The only exceptions are the IOM in four Tagish Lake lithologies whose spin concentrations increase with increasing degree of thermal processing as indicated by decreasing H/C and δD, and increasing aromaticity.
Biologically relevant abiotic extraterrestrial soluble organic matter (SOM) has been widely investigated to study the origin of life and the chemical evolution of protoplanetary disks. Synthesis of biologically relevant organics, in particular, seems to require aqueous environments in the early solar system. However, SOM in primitive meteorites includes numerous chemical species besides the biologically relevant ones, and the reaction mechanisms that comprehensively explain the complex nature of SOM are unknown. Besides, the initial reactants, which formed before asteroid accretion, were uncharacterized. We examined the mass distribution of SOM extracted from three distinct Tagish Lake meteorite fragments, which exhibit different degrees of aqueous alteration though they originated from a single asteroid. We report that mass distributions of SOM in the primordial fragments are well fit by the Schulz-Zimm (SZ) model for the molecular weight distribution patterns found in chain-growth polymerization experiments. Also, the distribution patterns diverge further from SZ with increasing degrees of aqueous alteration. These observations imply that the complex nature of the primordial SOM (1) was established before severe alteration on the asteroid, (2) possibly existed before parent-body accretion, and (3) later became simplified on the asteroid. Therefore, aqueous reactions on asteroids are not required conditions for cultivating complex SOM. Furthermore, we found that overall H/C ratios of SOM decrease with increasing aqueous alteration, and the estimate of H loss from the SOM is 10%-30%. Organics seem to be a significant H2 source that may have caused subsequent chemical reactions in the Tagish Lake meteorite parent body. © 2021. The American Astronomical Society. All rights reserved.
Biochar application to soils has become a focus of research during the last decade due to its high potential for C sequestration. Nevertheless, there is no exhaustive information on the long-term effects of biochar application in soils contaminated with trace elements. In this work, a 2-year field experiment was conducted comprising the application of different types of biochar to acidic and moderately acidic soils with high concentrations of As, Cu, Pb, Ba and Zn. In addition, representative samples of each biochar were buried in permeable bags that allowed the flow of water and microorganisms but not their physical interaction with soil aggregates. The biochars significantly adsorbed trace elements from polluted soils. However, given the high total concentration of these persistent trace elements in the soils, the application of biochars did not succeed in reducing the concentration of available metals (CaCl2 extractable fraction). After 2 years of ageing under field conditions, some degradation of the biochars from olive pit, rice husk and wood were observed. This study provides novel information concerning the biochar alterations during ageing in polluted soils, as the decrease of aryl C signal observed by ¹³C nuclear magnetic resonance (NMR) spectroscopy and the presence of O-containing groups shown by Fourier Transform mid-Infrared Spectroscopy (FT-IR) in aged biochar which enhanced trace elements adsorption. Scanning electron microscopy (SEM) revealed slight changes on surface morphology of aged biochar particles.
Context. The Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission detected an infrared absorption at 3.4 μm on near-Earth asteroid (101955) Bennu. This absorption is indicative of carbon species, including organics, on the surface.
Aims. We aim to describe the composition of the organic matter on Bennu by investigating the spectral features in detail.
Methods. We use a curated set of spectra acquired by the OSIRIS-REx Visible and InfraRed Spectrometer that have features near 3.4 μm (3.2 to 3.6 μm) attributed to organics. We assess the shapes and strengths of these absorptions in the context of laboratory spectra of extraterrestrial organics and analogs.
Results. We find spectral evidence of aromatic and aliphatic CH bonds. The absorptions are broadly consistent in shape and depth with those associated with insoluble organic matter in meteorites. Given the thermal and space weathering environments on Bennu, it is likely that the organics have not been exposed for long enough to substantially decrease the H/C and destroy all aliphatic molecules.
Context. Carbonaceous chondrites have undergone alteration in their parent bodies and display oxidized secondary phases, including sulfates in CI and CM chondrites. The cause of the formation of these sulfates is yet to be determined.
Aims. This study investigates the potential of endogenous radiolysis of water (i.e., radiolysis caused by radionuclides present in the rock) on the parent bodies of carbonaceous chondrites. Radiolysis may have contributed to the enhanced degree of oxidation of CI and CM chondrites, and we also examined CV chondrites as a case with no measured sulfates.
Methods. We quantified the oxidants produced by radiolysis and how much of the sulfur content could be oxidized to form sulfates by this method. The amount of oxidants was calculated using a radiolytic production model developed and used for Earth and planetary applications that takes into account relevant physical parameters (water-to-rock ratio, grain density) and composition (amount of radionuclides, sulfur content).
Results. For CM and CI parent bodies, even using a very favorable set of assumptions, only slightly more than 1% of the available sulfur can be oxidized into sulfates by this process, significantly below the amount of sulfates observed in these chondrites.
Conclusions. Endogenous radiolysis is unlikely to have significantly contributed to the abundance of sulfate in CI and CM meteorites. The hypothesis of oxidation of sulfur by large quantities of O 2 accreted with primitive ice, on the other hand, is quantitatively supported by measurements of O 2 in comet 67P/Churyumov-Gerasimenko.
Meteorites contain organic matter that may have contributed to the origin of life on Earth. Carbonyl compounds such as aldehydes and carboxylic acids, which occur in meteorites, may be precursors of biologically necessary organic materials in the solar system. Therefore, such organic matter is of astrobiological importance and their detection and characterization can contribute to the understanding of the early solar system as well as the origin of life. Most organic matter is typically sub-micrometer in size, and organic nanoglobules are even smaller (50–300 nm). Novel analytical techniques with nanoscale spatial resolution are required to detect and characterize organic matter within extraterrestrial materials. Most techniques require powdered samples, consume the material, and lose petrographic context of organics. Here, we report the detection of nanoglobular aldehyde and carboxylic acids in a highly primitive carbonaceous chondrite (DOM 08006) with ~ 20 nm spatial resolution using nano-FTIR spectroscopy. Such organic matter is found within the matrix of DOM 08006 and is typically 50–300 nm in size. We also show petrographic context and nanoscale morphologic/topographic features of the organic matter. Our results indicate that prebiotic carbonyl nanoglobules can form in a less aqueous and relatively elevated temperature-environment (220–230 °C) in a carbonaceous parent body.
We question here the radiolytic origin of (i) polyaromatic insoluble organic matter (IOM) recovered from primitive chondrites, and (ii) organics at the surface of reddish Trans-Neptunian Objects (TNOs), some minor planets and icy satellites. Organic synthesis by ion irradiation was investigated through experiments on a variety of targets: Polyethylene glycol 1450, lignin, cellulose and sucrose, exposed to low (C 40 keV and Ne 170 keV) and high energy (C 12 MeV, Ni 17 MeV, ⁷⁸Kr 59 MeV) ions. These experiments show that all carbonaceous precursors evolve towards a sp²-rich amorphous carbon (a-C) above a critical nuclear dose of 10−7⁺¹⁰ eV.atom⁻¹. A thorough review of the literature shows that this value applies for a large range of carbonaceous materials, including C-rich simple ices. Below this critical dose, irradiated targets are carbonized and transformed into cross-linked polymeric disordered solids, with abundant olefinic and acetylenic bonds, but devoid of aromatic or polyaromatic species. Ion irradiation of simple compounds, e.g. ices, is thereby not a viable process to synthesize IOM. However, in the case of aromatic-rich precursors, swift heavy ions irradiation leads to polyaromatic materials, by bridging existing aromatic or polyaromatic units. In the context of Early Solar System, i.e. Galactic Cosmic Rays (GCR) irradiation during 10–20 Myr, the formation of chondritic IOM from simple ices mixed with interstellar Polycyclic Aromatic Hydrocarbons (PAHs) appears as a plausible mechanism. This scenario, based on the recycling of existing carbonaceous interstellar grains under low-temperature conditions, would account for the heterogeneity of the D, ¹⁵N and ¹³C isotopic fractionations at the molecular scale, and the preservation of deuterium hot spots that are highly sensitive to high-temperature conditions (> 300 °C). At the surface of TNOs, sp²-rich amorphous carbons are formed by the implantation of GCRs and Solar wind ions. The electronic dose is also very high for an irradiation time of several Gyr (> 100 eV.atom⁻¹), leading to the formation of reddish disordered solids, provided that the surface contains a minimum abundance of carbonaceous species. Finally, sp²-rich amorphous carbons produced in the laboratory (e.g. the ACAR compound from Zubko et al., 1996) are fair analogues of the darkening agent produced by radiolysis.
The large variations in hydrogen isotope ratios found in insoluble organic matter (IOM) in chondritic meteorites may be attributed to hydrogen isotopic exchange between IOM and water during aqueous alteration. We conducted D–H exchange experiments (1) during synthesis of IOM simulant (hereafter called chondritic organic analog, COA) from formaldehyde, glycolaldehyde, and ammonia with water, and (2) with the synthesized COA with a secondary reservoir of water. The changes in the D/H ratios obtained by infrared spectra of the COA suggest that most of the hydrogen in the COA is derived from water during synthesis. We further investigated the kinetics of D–H exchange between D‐rich COA and D‐poor water, as well as the opposite case, D‐poor COA and D‐rich water. To help assess understanding exchange kinetics, two‐dimensional isotope imaging obtained using isotope microscope revealed that no gradient D–H exchange profiles were present in the COA grains, indicating that the rate‐limiting step for D–H exchange is not diffusion. Thus, the changes in D/(D + H) ratios were fit by the first‐order reaction rate law. Apparent kinetic parameters—the rate constants, the activation energies, and the frequency factors—were obtained with the Arrhenius equation. Using these kinetic expressions, hydrogen isotopic exchange profiles were estimated for time and temperature behavior. The D–H exchange between organic matter and water is apparently relatively fast and this implies that the aqueous alteration temperatures should have been very low, likely close to 0 °C to maintain hydrogen isotopic disequilibrium between organic matter and liquid water for millions of years.
A series of experiments was performed to constrain the chemical and isotope evolution of insoluble organic material (IOM) during hydrothermal alteration at temperatures ranging from 250 °C to 450 °C at 50 MPa. Experiments involved IOM that was extracted from the Murchison (CM2) meteorite or synthesized by aqueous carbonization of dextrose. Flash (dry) pyrolysis experiments at 400 – 1000 °C were also conducted with Murchison-IOM to distinguish between the effects of hydrothermal and thermal degradation. Extended reaction times (up to 3905 h) were employed to establish D/H equilibria between IOM and H2O. The H isotope compositions of the H2O used in the experiments ranged from δD = -447 ‰ to 3259 ‰. Results revealed that the extent of the IOM H isotope evolution strongly depends on the δD composition of the coexisting H2O with minimal temperature effects. The empirical relationship that describes the isotope exchange between IOM and H2O is as follows:
δDIOM (‰) = 0.643 (± 0.007) * δDH2O (‰) – 86 (± 8) (‰)
Based on this empirical relationship, two models are proposed for the H2O-IOM H exchange. The first assumes that all H in IOM is exchangeable and that the redistribution of H-bearing moieties with experiment temperature results in an “apparent” εorganics-H2O= -357 ‰. The second model considers a higher εorganics-H2O (-131 ‰), in accordance with theoretical studies, and assumes the presence of two H reservoirs, one that undergoes H isotope exchange with H2O and one that does not. In this case, 74 % of the H in IOM is exchangeable with H2O.
In our experiments, the hydrothermally altered Murchison-IOM lost labile ¹⁵N enriched N-H moieties. Experiments that included ¹⁵N-labelled NH3(aq) found that there was only minor N exchange with IOM. Furthermore, the experimental data show that the extent of H and N loss is temperature and process dependent. This results in the decoupling of N/C and H/C atomic ratio systematics between hydrothermal alteration and flash (dry) pyrolysis, with much more limited changes in H/C and N/C after flash pyrolysis.
In the light of the experiments, two models for the range of bulk and IOM H isotope compositions of the aqueously altered CI, CM, and CR chondrites are explored. The very D-rich IOM compositions, relative to the bulk compositions, cannot be explained by a fully exchangeable IOM with a reasonable value for εorganics-H2O (i.e., <0 ‰). Instead, a two-component IOM model is invoked in which the initial bulk and non-exchangeable IOM have δD = 3650 ‰. The estimated ranges of Fexchange, including uncertainties in εorganics-H2O, are 0.59-0.75 and 0.13-0.30 for CMs and CRs, respectively. Most values of Fexchange are significantly lower than in the experiments, perhaps because the alteration temperatures in the chondrites were << 250 °C. An apparent relationship between Fexchange and the IOM δ¹⁵N suggests an endmember composition of ∼ 300 ‰. For the CMs, alone, however, the initial δ¹⁵N is projected to ∼ 137 ‰.
Molecular structures and chemical compositions of organic matter in primitive meteorites reflect the conditions of the parent bodies, as well as the preaccretional history. During the parent body processing, co-existing minerals could have effects on structural changes of organics, in addition to temperature and redox state. Here, we performed heating experiments of a primordial organic matter analog with and without minerals to understand the effects of minerals on organic matter in conditions simulating metamorphism in thermally metamorphosed type 3 chondrites. The primordial analog materials were heated up to 400 °C, and the experimental products were analyzed using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and gas chromatography mass spectrometry (GC/MS). Montmorillonite and olivine, particularly montmorillonite, enhanced decomposition of oxygen containing species due to decarboxylation and/or cracking, while olivine enhanced esterification at lower temperature. Our results further imply that the variations of insoluble organic matter in CV, CO, and type 3 ordinary chondrites could be partially due to different mineral compositions. We also tested the effects of pressure on the degradation of the organic matter at 400 °C up to 268 atm, however no significant pressure effects were observed by FTIR and GC/MS.
The NMR signals of isotopically or chemically dilute nuclear spins S in solids can be enhanced by repeatedly transferring polarization from a more abundant species I of high abundance (usually protons) to which they are coupled. The gain in power sensitivity as compared with conventional observation of the rare spins approaches NII(I+1)γI2/NSS(S+1)γS2, or ∼ 103 for S = 13C, I = 1H in organic solids. The transfer of polarization is accomplished by any of a number of double resonance methods. High‐frequency resolution of the S ‐spin signal is obtained by decoupling of the abundant spins. The experimental requirements of the technique are discussed and a brief comparison of its sensitivity with other procedures is made. Representative applications and experimental results are mentioned.
The preatmospheric mass of the Tagish Lake meteoroid was about 200,000 kilograms. Its calculated orbit indicates affinity
to the Apollo asteroids with a semimajor axis in the middle of the asteroid belt, consistent with a linkage to low-albedo
C, D, and P type asteroids. The mineralogy, oxygen isotope, and bulk chemical composition of recovered samples of the Tagish
Lake meteorite are intermediate between CM and CI meteorites. These data suggest that the Tagish Lake meteorite may be one
of the most primitive solar system materials yet studied.
General integral and series expressions are derived for the intensities of sidebands observed in the magic angle spectra of inhomogeneously broadened I=1/2 systems. The expressions are evaluated for a wide range of shift parameters and the results used to construct graphical and numerical methods for extracting the principal values of chemical shift tensors from the intensities of just a few sidebands. The methods are illustrated by application to 31P spectra of barium diethyl phosphate. The results agree well with previous single crystal measurements.
Interstellar ices are chemically processed by ultraviolet (UV) radiation
to form complex products, and models of UV photochemistry provide
powerful tools for the interpretation of astronomical observations. We
have performed UV photolysis experiments on pure 10K samples of nine
ices of molecules of astrophysical interest: H_2_O, NH_3_, CH_4_, CO,
CO_2_, O_2_, N_2_, H_2_CO, and CH_3_OH. Destruction of these species by
photochemical processes is discussed, and the cross-sections for
destruction are estimated for use in chemical models. New molecules
produced during photolysis are identified on the basis of their
characteristic infrared features, and their chemical origins and
astrophysical implications are discussed. Rates of formation are also
estimated for first-order products. In experiments with CH_4_ and with
H_2_CO, molecules with as many as 7-8C atoms are produced. Such results
may indicate how and why very complex organic molecules are formed in
molecular mixtures characteristic of interstellar ice mantles.
Primitive meteorites contain up to 400 p.p.m. of a very fine-grained type of carbon, noncommittally called Cδ1. It apparently conies from outside the Solar System, as it carries isotopically anomalous krypton and xenon ('Xe-HL' or 'CCFXe', enriched twofold in the lightest and heaviest isotopes2) and nitrogen (δ15N =- 330‰3; that is, depleted in 15N by -330‰ relative to atmospheric nitrogen), although the carbon itself is within the terrestrial range (δ13C =-38‰1). Expanding on a preliminary report4, we now present evidence that part or all of Cδ is diamond - Not shock-produced but primary, formed by stellar condensation as a metastable phase. It appears that interstellar dust contains diamond.
The carbonaceous chondrite meteorites contain a record of the formation of the solar system, part of which is present within organic matter. This organic matter is predominantly aromatic, and its sources remain controversial. The δ13C values for individual free and macromolecular aromatic moieties from Cold Bokkeveld and Murchison suggest that these units originate from radiation-induced "circle" reactions involving simultaneous bond synthesis and cracking. Large carbon isotope fractionations and a deuterium enrichment for these entities suggest that these reactions occurred in a dense interstellar cloud. The juxtaposition of the synthesis and cracking products implies that the reactions occurred in a restricting medium, the most likely candidate for which is the icy organic mantles of interstellar grains. In contrast, the δ13C record in aromatic moieties from Orgueil is mostly obscured, possibly due to the increased levels of parent body aqueous alteration experienced by this meteorite. These novel observations are consistent with the interstellar-parent body hypothesis, where the final form of meteoritic organic matter results from the transfiguration of interstellar organic precursors by aqueous reactions on the meteorite parent body.
The methods available in NMR spectroscopy to obtain the principal values of the chemical-shift tensor are discussed. Applications to coal and to compounds with model structures that might be important in coal are presented. The composition of aromatic carbons in coal as determined by chemical-shift powder patterns is compared to results obtained by cross-polarization with magic-angle spinning and dipolar dephasing.
This chapter provides an overview of the fundamental issues concerning quantitation in ¹³C NMR spectroscopy of carbonaceous solids. General factors governing quantitation in solid-state ¹³C NMR spectroscopy (such as sample heterogeneity, the presence of unpaired electron spins, interference of proton decoupling by molecular motion, magic-angle spinning (MAS) effects, and implementation of the proper recycle-delay time) are discussed together with those factors that play a major role in cross-polarization (CP) experiments (Hartmann—Hahn match, proton spin-locking, cross-polarization spin dynamics, and interference of cross-polarization from MAS). Technical aspects and requirements of the solid-state ¹³C NMR experiment are outlined, and effective strategies to obtain the most reliable results are presented.
Radiolytic salt enrichment through the decomposition of water molecules owing to the natural irradiation of water-rock systems during spans of geological time is discussed on the basis of experimental data and geochemical evidence.-from Author
Polycyclic aromatic hydrocarbons (PAHs) in water ice were exposed to ultraviolet (UV) radiation under astrophysical conditions, and the products were analyzed by infrared spectroscopy and mass spectrometry. Peripheral carbon atoms were oxidized, producing aromatic alcohols, ketones, and ethers, and reduced, producing partially hydrogenated aromatic hydrocarbons, molecules that account for the interstellar 3.4-micrometer emission feature. These classes of compounds are all present in carbonaceous meteorites. Hydrogen and deuterium atoms exchange readily between the PAHs and the ice, which may explain the deuterium enrichments found in certain meteoritic molecules. This work has important implications for extraterrestrial organics in biogenesis.
Hydrous pyrolysis, supercritical fluid extraction (SFE), gas
chromatography-mass-spectrometry (GC-MS) and isotope ratio
monitoring-gas chromatography-mass spectrometry (irm-GC-MS) were used to
investigate the constitution of macromolecular materials in meteorites.
Results from the carbonaceous chondrites Orgueil (CI1) and Cold
Bokkeveld (CM2) were compared with those obtained previously from
Murchison (CM2). Fragments of meteoritic macromolecular materials were
produced by hydrous pyrolysis, extracted by SFE, and identified by
GC-MS. The CI1 and CM2 hydrous pyrolysates all contain volatile aromatic
compounds, some of which have aliphatic side chains, hydroxyl groups,
and thiophene rings attached. The results indicate that the
macromolecular materials in these meteorites are qualitatively similar.
However, the pyrolysates show significant quantitative differences, with
the products of ether linkages and condensed aromatic networks being
less abundant in the more aqueously altered meteorites. In addition, the
methylnaphthalene maturity parameter negatively correlates with aqueous
alteration. These features are interpreted as the result of chemical
reactions favored under hydrous conditions. Hence, the extent of aqueous
alteration on the meteorite parent body appears to be the most important
evolutionary stage in determining the final structure of macromolecular
materials in the CI1 and CM2 meteorites. The carbon isotopic
compositions of the fragments of macromolecular materials were
determined by irm-GC-MS. δ 13C values for the hydrous
pyrolysis products range from -25.5 to -10.2‰ for Orgueil and
-22.9 to +4.0‰ for Cold Bokkeveld. These values can be compared
to the -24.6 to -5.6‰ range obtained previously for Murchison.
The low molecular weight components in each hydrous pyrolysate display
shifts to increased 13C contents with carbon number. This
indicates the production of simple organic entities by the preferential
cracking of 12C- 12C bonds in more complex
starting materials. The shifts extend from C 7 to C
8 for Orgueil and Cold Bokkeveld but from C 7 to C
10 for Murchison. Higher molecular weight components for all
of the hydrous pyrolysates show a general trend of decreasing
13C content with carbon number. The higher molecular weight
features can be explained by the preferential addition of 12C
during the primary synthesis of the macromolecular materials. In
addition, δ 13C values for the methylnaphthalenes are
consistent with the addition of 12C to the most reactive site
on the naphthalene parent molecule providing supporting evidence for
synthesis. Hence, the macromolecular materials are composed of organic
units created by both synthesis and cracking. Therefore, secondary
processing by liquid water on the meteorite parent body exerts a strong
control on the final molecular architecture of meteoritic macromolecular
materials. Yet, the carbon isotopic compositions of some individual
moieties may retain a record of primary synthesis.
The ranges of delta18O and delta17O in components of the Murchison (C2) chondrite exceed those in all other meteorites analyzed. Previous authors have proposed that C2 chondrites are the products of aqueous alteration of anhydrous silicates. A model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes. The minimum number (two) of initial isotopic reservoirs is assumed. Two major stages of reservoir interaction are required: one at high temperature to produce the 16O-mixing line observed for the anhydrous minerals, and another at low temperature to produce the matrix minerals. The isotopic compositions severely constrain the conditions of the low-temperature process, requiring temperatures 44%. Extension of the model to the data on C1 chondrites requires aqueous alteration in a warmer, wetter environment.
We argue and illustrate numerically that profound oxidation that led to formations of sulfates in parent bodies of carbonaceous chondrites and Galilean satellites could have been driven by hydrothermal alteration followed by H2 escape into space.
Ivuna, a CI carbonaceous chondrite, has been found to contain abundant amounts of the three-ring polycyclic aromatic hydrocarbons (PAHs) phenanthrene/anthracene, but no detectable levels of the two- and four-ring PAHs naphthalene and pyrene/fluoranthene. Either the three-ring PAHs in Ivuna were synthesized in a process that did not produce the two- or four-ring PAHs, or all these compounds were synthesized together and subsequently separated. Thermodynamical considerations and studies of hydrocarbon pyrolysis and combustion do not support the former possibility. Ivuna and other CI carbonaceous chondrites are known to have been extensively altered by water. The aqueous solubilities suggest that some PAHs would have been mobilized during the aqueous alteration phase in carbonaceous meteorite parent bodies. In a model geochromatography experiment, naphthalene, phenanthrene, and pyrene were partially resolved at a low pressure and flow rate utilizing columns containing crushed serpentine or beach sand, and water for elution. This laboratory geochromatography experiment suggests that complete separation of PAHs could be expected to occur in the parent body of CI carbonaceous chondrites. Such processes on Earth are known to lead to the formation of hydrothermal PAH minerals such as pendletonite. It is proposed that aqueous fluids driven by heat in the parent body of Ivuna migrated from the interior to the surface, in the process transporting, separating, and concentrating PAHs at various zones in the parent body.
The Tagish Lake meteorite soluble organic suite has a general composition that differs from those of both CI and CM chondrites. These differences suggest that distinct processes may have been involved in the formation of different groups of organics in meteorites. Tagish Lake alkyl dicarboxylic acids have a varied, abundant distribution and are, with carboxylated pyridines, the only compounds to have an occurence comparable to that of the Murchison meteorite. This study has undertaken their molecular and isotopic characterization, with the aim to understand their origin and to gain insights into the evolutionary history of the meteorite parent body. Tagish Lake alkyl dicarboxylic acids are present as a homologous series of saturated and unsaturated species with three-through ten-carbon atom chain length. Linear saturated acids are predominant and show decreasing amounts with increasing chain length. A total of 44 of these compounds were detected with the most abundant, succinic acid, present at ~40 nmol/g meteorite. Overall the molecular distribution of Tagish Lake dicarboxylic acids shows a remarkable compound-to-compound correspondence with those observed in the Murchison and Murray meteorites. In both Tagish Lake and Murchison, the imides of the more abundant dicarboxylic acids were also observed. The hydrogen and carbon isotopic compositions of individual Tagish Lake dicarboxylic acids were determined and compared to those of the corresponding acids in the Murchison meteorite. All δD and δ13C values for Tagish Lake acids are positive and show a substantial isotopic enrichment. δD values vary from, approximately, +1120‰ for succinic acid to +1530‰ for methyl glutaric acid. δ13C values ranged from +12.6‰ for methyl glutaric acid to +22.9‰ for glutaric acid, with adipic acid having a significantly lower value (+5.5‰). Murchison dicarboxylic acid showed similar isotopic values: their δ13C values were generally higher by an average 17% and δD values were lower for succinic and glutaric acids, possibly due to contamination. The molecular and isotopic data collected for these compounds restrict their possible origin to processes, either interstellar or of very cold nebular regions, that produced significant isotopic enrichments. Saturated or partially unsaturated nitriles and dinitriles appear to be good precursor candidates as their hydrolysis, upon water exposure, would produce dicarboxylic acids and other carboxylated species found in Tagish Lake. This evolutionary course could possibly include preaccretionary processes.
Carbon-13 NMR studies involving conventional cross polarization and dipolar dephasing techniques at a variety of contact and delay times, respectively, provide valuable information on the magnitude of 13C-1H dipole-dipole interactions. In solids whose spectra have overlapping resonances, such techniques discriminate between protonated and nonprotonated carbons. In dipolar dephased spectra, dipolar and rotational modulation of the resonances can occur for methine and methylene carbons, which are strongly coupled to the directly bonded protons. Methyl carbons exhibit a very wide range of effective dipolar couplings because of rapid methyl rotation that varies depending upon the structural environment. Dipolar modulation in methyl groups is not observed. Carbon atoms in tert-butyl methyl groups experience even weaker effective dipolar interactions than other methyl carbon atoms. These motionally decreased dipolar interactions are similar to those experienced by the quaternary aliphatic carbon atom. Steric crowding of a tert-butyl group on an aromatic ring causes (on the average) one of its methyl groups to differ in mobility from the other two. A biexponential decay not evident in any of the other functional groups studied results for both the quaternary and methyl carbons in the tert-butyl group. Nonprotonated sp2-hybridized carbon atoms also exhibit weak dipolar couplings because of the remoteness of protons. The magnitude of the coupling varies substantially as a result of variations in motional freedom and structure.
A survey of /sup 13/C chemical shifts of aromatic hydrocarbons is used to derive an assignment scheme which should be applicable to the majority of coal-derived materials and also to other hydrocarbons such as crude oils and aromatic resins. This scheme is used to derive structural information on four extracts prepared from low-rank British coals. 4 figures, 3 tables.
We report here on the use of solid-state 13C nuclear magnetic resonance (NMR) spectroscopy to contrast the average chemical composition of modern degraded gymnosperm woods with fossil gymnosperm woods from Australian brown coals (Miocene). We first established the quantitative nature of the NMR techniques for these samples so that the conventional solid-state 13C NMR spectra and the dipolar dephasing NMR spectra could be used with a high degree of reliability to depict average chemical compositions. The NMR results provide some valuable insights about the early coalification of xylem tissue from gymnosperms. Though the cellulosic components of wood are degraded to varying degrees during peatification and ensuing coalification, it is unlikely that they play a major role in the formation of aromatic structures in coalified woods. The NMR data show that gynmosperm lignin, the primary aromatic contribution to the coal, is altered in part by demethylation of guaiacyl-units to catechol-like structures. The dipolar dephasing NMR data indicate that the lignin also becomes more cross-linked or condensed.
An electron paramagnetic resonance (EPR) investigation was performed on the insoluble organic matter from the Orgueil and Murchison meteorites and on terrestrial coals with similar elemental composition. A complementary electron nuclear double resonance (ENDOR) study was also carried out. The measured g-factors of the observed paramagnetic radicals in the meteoritic organic matter exhibit a similar correlation with the chemical composition as for the type III (i.e., hydrogen-poor) terrestrial coals. The main result, obtained from EPR saturation and 1H ENDOR enhancement measurements, showed that the effective local concentration in radicals of about 3 to 4 × 1019 spin.g−1 in the meteoritic organic matter is much higher than the average concentration, hence the occurrence of radical-rich regions accounting for 5% and 20% of the total volume for Murchison and Orgueil, respectively. This heterogeneity of concentration seems to be unique among natural organic macromolecules. It is proposed that these radical-rich regions correspond to pristine parts of the organic matter synthesized in conditions close to those prevailing in the interstellar medium, and which have survived the hydrothermal process on the parent body.
Abstract— The Tagish Lake meteorite soluble organic suite has a general composition that differs from those of both CI and CM chondrites. These differences suggest that distinct processes may have been involved in the formation of different groups of organics in meteorites. Tagish Lake alkyl dicarboxylic acids have a varied, abundant distribution and are, with carboxylated pyridines, the only compounds to have an occurrence comparable to that of the Murchison meteorite. This study has undertaken their molecular and isotopic characterization, with the aim to understand their origin and to gain insights into the evolutionary history of the meteorite parent body.
Tagish Lake alkyl dicarboxylic acids are present as a homologous series of saturated and unsaturated species with three- through ten-carbon atom chain length. Linear saturated acids are predominant and show decreasing amounts with increasing chain length. A total of 44 of these compounds were detected with the most abundant, succinic acid, present at ˜40 nmol/g meteorite. Overall the molecular distribution of Tagish Lake dicarboxylic acids shows a remarkable compound-to-compound correspondence with those observed in the Murchison and Murray meteorites. In both Tagish Lake and Murchison, the imides of the more abundant dicarboxylic acids were also observed.
The hydrogen and carbon isotopic compositions of individual Tagish Lake dicarboxylic acids were determined and compared to those of the corresponding acids in the Murchison meteorite. All δD and δ13C values for Tagish Lake acids are positive and show a substantial isotopic enrichment. δD values vary from, approximately, +1120%o for succinic acid to +1530%o for methyl glutaric acid. δ13C values ranged from +12.6%o for methyl glutaric acid to +22.9%o for glutaric acid, with adipic acid having a significantly lower value (+5.5%o). Murchison dicarboxylic acid showed similar isotopic values: their δ513C values were generally higher by an average 17% and δD values were lower for succinic and glutaric acids, possibly due to contamination.
The molecular and isotopic data collected for these compounds restrict their possible origin to processes, either interstellar or of very cold nebular regions, that produced significant isotopic enrichments. Saturated or partially unsaturated nitriles and dinitriles appear to be good precursor candidates as their hydrolysis, upon water exposure, would produce dicarboxylic acids and other carboxylated species found in Tagish Lake. This evolutionary course could possibly include pre-accretionary processes.
Many organic compounds or their precursorsfound in meteorites originated in the interstellar or circumstellarmedium and were later incorporated intoplanetesimals during the formation of thesolar system. There they either survivedintact or underwent further processing tosynthesize secondary products on themeteorite parent body.The most distinct feature of CI and CM carbonaceouschondrites, two typesof stony meteorites, is their high carbon content(up to 3% of weight), either in theform of carbonates or of organic compounds. The bulkof the organic carbon consistsof an insoluble macromolecular material with a complexstructure. Also present is asoluble organic fraction, which has been analyzedby several separation and analyticalprocedures. Low detection limits can be achievedby derivatization of the organicmolecules with reagents that allow for analysisby gas chromatography/massspectroscopy and high performance liquidchromatography. The CM meteoriteMurchison has been found to contain more than70 extraterrestrial amino acids andseveral other classes of compounds includingcarboxylic acids, hydroxy carboxylicacids, sulphonic and phosphonic acids, aliphatic,aromatic and polar hydrocarbons,fullerenes, heterocycles as well as carbonylcompounds, alcohols, amines and amides.The organic matter was found to be enriched indeuterium, and distinct organiccompounds show isotopic enrichments of carbon andnitrogen relative to terrestrialmatter.
C1 and C2 carbonaceous chondrites contain several percent of organic matter, mainly as a bridged aromatic polymer containing
COOH, OH, and CO groups, as well as heterocyclic rings containing N, O, and S. The remaining 5–30% includes the following
compound classes, either present initially or generated by solvolysis: alkanes (mainly normal), alkenes, arenes, alicyclics,
alcohols, aliphatic carboxylic acids, purines, pyrimidines, and other basic N-compounds, amino acids, porphyrin-like pigments,
carbynes, etc.
On the basis of laboratory experiments, it appears that these compounds formed in the solar nebula, by catalytic (Fischer-Tropsch)
reactions of CO, H2, and NH3 at 360–400 K, ∼ 10−5 atm. The onset of these reactions was triggered by the formation of suitable catalysts (magnetite, hydrated silicates) at
these temperatures. Such reactions may be a source of prebiotic carbon compounds on the inner planets, and interstellar molecules.
All meteoritic organic chemical analyses published since 1900 are critically reviewed. Inactive during the first half of the century, this field has been revived by the modern realities of spaceflight and exploration, but work has been concentrated on searching the organic constituents of the carbonaceous chondrites for compounds possibly indicative of extraterrestrial life. It is one theme of this paper that this is a poorly focussed effort. A second theme is that many compound identifications reported in the literature are, by present standards, insufficiently supported.The characteristics and thermal histories of the various classes of chondrites are very briefly reviewed. It is shown that certain classes other than carbonaceous chondrites might reasonably be expected to contain organic material. The distribution of carbon among these classes is discussed, and the forms which carbon takes in each case are noted. It is shown that significant amounts of extractable organic material may be expected not only in the carbonaceous chondrites but also in the unequilibrated ordinary chondrites and in the ureilites. Evidence indicating that volatile materials, possibly including carbon and its compounds, are heterogeneously distributed in chondrite specimens is considered. Amounts of organic material extracted or volatilized from various meteorite specimens are tabulated.Various crude but informative studies undertaken using unfractionated extracts are discussed. Data indicating the elemental composition and general chemical nature of meteorite extracts are tabulated and the infrared and ultraviolet absorption spectra of meteorite extracts and crude fractions are described and discussed. Isotope ratio analyses of extracts, volatilized and combusted materials, and whole stones are discussed and the carbon and hydrogen isotope ratios found in carbonaceous chondrite analyses are tabulated. Analytical studies proving or claiming to prove the presence in meteorites of particular organic compounds are discussed critically and in detail. Evidence indicating that certain analytical studies of hydrocarbons and of amino acids have been crucially affected by the presence of contaminating materials is considered. It is concluded that optically active compounds have not been proven to be present in meteorites.Possible origins of meteorite organic compounds and the relations of these origins to theories of meteorite origin are briefly discussed.
Solid state CP/MAS 13C nuclear magnetic resonance (NMR) study of the insoluble organic fraction isolated by HF/HCl treatment under an inert atmosphere from the Orgueil and Murchison carbonaceous meteorites is reported. Based on these spectra, eight different types of carbons (aro- and ali-linked CH3, CH2, aliphatic C-linked to heteroelements, protonated and non-protonated aromatic C, carboxyls and carbonyls) were identified, their relative amounts were determined and theoretical NMR-derived H/C atomic ratios were calculated. Comparison of these H/C ratios with those obtained from elemental analysis revealed that a large part of the carbons of the insoluble fraction of both meteorites are not detected by CP/MAS 13C NMR. Taking into account these undetected carbons, the relative abundance of aromatic carbons (as % of the total carbons) was calculated as between 69 and 78% in Orgueil and 61 and 67% in Murchison and thus shown to be much higher than previously thought. In addition, the NMR data allowed to calculate the ratio of non-protonated and protonated aromatic carbons. Based on previous studies on chemical and thermal degradation, the present NMR data were interpreted as reflecting the occurrence of highly substituted rather small aromatic moieties in these insoluble organic materials. Along with FTIR data, NMR results also pointed to a relatively high branching level in the aliphatic chains, especially for Murchison. According to the above results, the insoluble organic matter in these meteorites did not suffer a marked thermal maturation during the late hydrothermalism of the parent body. Its synthesis involved a statistical combination of all the possible bonds between -CH3, -CH2 and -CH radicals, producing both the aliphatic and the aromatic moieties. This model explains not only the chemical features of the chondritic insoluble organic material but also the typical FTIR signature of the interstellar medium. Therefore, organic material found in the interstellar medium and that incorporated in the most primitive objects of the solar system seem to share a common organosynthesis.
The degrees of thermal metamorphism of 10 CM chondrites and of the Allende CV3 chondrite were evaluated from the viewpoint of “graphitization” of the carbonaceous macromolecular matter by means of flash pyrolysis-gas chromatography (GC). The unheated chondrites, Yamato- (Y-) 791198, Murray and Cold Bokkeveld, yielded larger amounts and wider varieties of pyrolyzates than the chondrites strongly heated in the parent asteroids, Y-82054, Y-86695, and Belgica- (B-) 7904, and Asuka- (A-) 881334 (more strongly heated than Y-793321, which has been weakly heated, but lesser than the other strongly heated meteorites). The weakly heated chondrites, Y-793321 and A-881458, showed intermediate features. The data indicate that graphitization of the carbonaceous matter is most extreme in the strongly heated chondrites and that during graphitization, the matter has lost its labile portion, which can generate pyrolyzates such as naphthalene. In order to establish a new method for the evaluation of the degree of graphitization of chondritic carbonaceous matter, a diagram was developed to show the relationship between the total amounts of pyrolyzates with retention times later than 5 min (=SRT>5) and the ratio of the amount of naphthalene, a pyrolysis product, to SRT>5 (=SN/SRT>5). The diagram indicates a possible evolutionary pathway of graphitization of the carbonaceous matter in carbonaceous chondrites.
Acid-resistant residues were prepared for eighteen meteorites from seven chondrite classes, using improved procedures designed to minimize loss of presolar grains. Noble gases were measured by stepped pyrolysis, and the abundances of five exotic noble-gas components were used to determine abundances of diamond, SiC, and graphite. Diamond separates were prepared to check diamond abundances determined from noble gases. Diamond and SiC were found in unmetamorphosed members of all seven chondrite classes and evidence for graphite was found in Orgued (CI) and LL3.0–3.1 chondrites. Our data and noble-gas and stable-isotope data in the literature show that presolar grains were incorporated into all chondrite classes. The grains are sited in the fine-grained matrix, and their abundances within the matrix reflect mainly the degree of metamorphism suffered by the host meteorite. The pattern of metamorphic destruction differs from class to class. In unequilibrated ordinary chondrites (UOCs), graphite is most easily destroyed, followed by SiC and then diamond. No presolar grains remain in UOCs of petrologic type > 3.8, whose matrices have been completely recrystallized. In EH chondrites, diamond and SiC survive much more severe metamorphism than in UOCs, with SiC apparently more stable than diamond. Presolar graphite was not detected. In CV3 and C03 chondrites, diamond appears to be more stable than SiC and graphite again is missing.
13C-1H heteronuclear dipolar dephasing n.m.r. techniques allow discrimination between different chemical species contributing to the 13C n.m.r. spectra of complex hydrocarbons. Model compound studies show significantly different effective transverse relaxation constants for carboxyl and quaternary carbon atoms (≈200 μs), secondary and tertiary (≈20 μs), and primary carbon atoms (≈80 μs). Use of these effective relaxation data, together with appropriately timed windows in the continuous wave decoupling applied in standard cross-polarization-magic-angle spinning experiments on anthracite coal allow discrimination between aromatic tertiary and aromatic quaternary ring carbon atoms in this coal. Within the accuracy of experimental error, and of the structural modelling experiments herein reported, the use of the dipolar dephasing technique together with results of X-ray diffraction on coals allows a reasonable estimate to be made of the average number of condensed polynuclear rings in an ‘average molecule’ in the anthracite studied. Based on a model of pericondensed aromatic rings, this number lies between 33 and 45.
The carbonaceous chondrites display the widest range of oxygen isotopic composition of any meteorite group, as a consequence of the interaction of primordial isotopic reservoirs in the solar nebula. These isotopic variations can be used to identify the reservoirs and to determine conditions and loci of their interactions. We present a comprehensive set of whole-rock analyses of CV, CO, CK, CM, CR, CH, and CI chondrites, as well as selected components of some of these meteorites. A simple model is developed which describes the isotopic behavior during parent-body aqueous alteration processes. The process of thermal dehydration also produces a recognizable effect in the oxygen isotopic composition.
Complementary, double- and single-resonance solid-state (1H and 13C) nuclear magnetic resonance (NMR) experiments were performed on a solvent extracted and demineralized sample of Murchison meteorite organic macromolecule. These NMR data provide a consistent picture of a complex organic solid composed of a wide range of organic (aromatic and aliphatic) functional groups, including numerous oxygen-containing functional groups. The fraction of aromatic carbon within the Murchison organic residue (constrained by three independent experiments) lies between 0.61 and 0.66. The close similarity in cross-polarized and single-pulse spectra suggests that both methods detect the same distribution of carbon. With the exception of interstellar diamond (readily detected in slow magic angle spinning single-pulse NMR experiments), there is no evidence in the solid-state NMR data for a significant abundance of large laterally condensed aromatic molecules in the Murchison organic insoluble residue. Given the most optimistic estimation, such carbon would not exceed 10% and more likely is a fraction of this maximum estimate. The fraction of aromatic carbon directly bonded to hydrogen is low (∼30%), indicating that the aromatic molecules in the Murchison organic residue are highly substituted. The bulk hydrogen content, H/C, derived from NMR data, ranges from a low of 0.53 ± 0.06 and a high of 0.63 ± 0.06. The hydrogen content (H/C) determined via elemental analysis is 0.53. The range of oxygen-containing organic functionality in the Murchison is substantial. Depending on whether various oxygen-containing organic functional groups exist as free acids and hydroxyls or are linked as esters and ethers results in a wide range in O/C (0.22 to 0.37). The lowest values are more consistent with elemental analyses, requiring that oxygen-containing functional groups in the Murchison macromolecule are highly linked. The combined 1H and 13C NMR data reveal a high proportion of methine carbon, which requires that carbon chains within the Murchison organic macromolecule are highly branched.
The critical Rayleigh number for convective flow of pore water through a permeable spherical body is derived. The result affords constraints on carbonaceous chondrite planetesimal sizes and rates of heat production. If the chemical compositions of carbonaceous chondrites are taken as evidence against flow of pore water, then the present calculations suggest that the parent bodies were less than ∼80 km in diameter. The maximum diameter for absence of flow depends in part on the high permeabilities required by estimates of high water/rock ratios in altered carbonaceous chondrites. Pore water would have flowed through parent bodies larger than ∼120 km in diameter with typical rock-like permeabilities. Convective flow and isochemical alteration are not compatible and our calculations can be used to identify the combinations of parent body size and heat generation consistent with one or the other.
The CI chondrites are taken to represent average solar system material based on the similarity of their elemental compositions to that of the solar photosphere. However, their oxygen isotope geochemistry is dominated by secondary minerals that formed during aqueous alteration on the CI parent body. Precursors to this alteration, namely olivine and pyroxene, are extremely rare in CI chondrites, precluding previous measurements of their oxygen isotopic composition. We report ion microprobe analyses of oxygen isotopes in single olivine and pyroxene grains separated from CI chondrites Orgueil and Ivuna.
Organic material in meteorites provides insight into the cosmochemistry of the early solar system. The distribution of polycyclic aromatic hydrocarbons (PAHs) in the Allende and Murchison carbonaceous chondrites was investigated by use of a technique called microprobe laser-desorption laser-ionization mass spectrometry, which permits spatial resolution with approximately a 40-μm spot size. Sharp chemical gradients of PAHs are associated with specific meteorite features. The ratios of various PAH intensities relative to the smallest PAH, naphthalene, are nearly constant across the sample. These findings suggest a common origin for PAHs dating before or during the formation of the parent body, consistent with proposed interstellar formation mechanisms.
The identification of the mechanism(s) responsible for heating asteroids is among the major problems in planetary science. Because of difficulties with models of electromagnetic induction and the decay of short-lived radionuclides, it is worthwhile to evaluate the evidence for collisional heating. Localized impact heating is responsible for forming shock veins, melt pockets, metal-sulfide mixtures, vugs, agglutinates and a wide variety of melt-rock clasts. New evidence for localized impact heating comes from the high proportion of relict type-6 material among impact-melt-bearing ordinary chondrites (OC). This relict material was probably metamorphosed by residual heat within large craters. Olivine aggregates composed of faceted crystals with 120° triple junctions occur within the melted regions of the Chico and Rose City OC melt rocks; the olivine aggregates formed from shocked, mosaicized olivine grains that underwent contact metamorphism. Large-scale collisional heating is supported by the correlation in OC between petrologic type and shock stage; no other heating mechanism can readily account for this correlation. The occurrence of impact-melt-rock clasts in OC that have been metamorphosed along with their whole rocks indicates that some impact events preceded or accompanied thermal metamorphism. Such impact events, occurring during or shortly after accretion, are probably responsible for substantially melting ∼0.5% of OC. These events most have heated a larger percentage of OC to subsolidus temperatures sufficient to have caused significant metamorphism. If collisional heating is viable, then OC parent asteroids must have been large; large OC asteroids in the main belt may include those of the S(IV) spectral subtype. Collisional heating is inconsistent with layered ("onion-shell") structures in OC asteroids (wherein t