Primordial heavy noble gases in the pristine Paris carbonaceous chondrite

The Paris carbonaceous chondrite represents the most pristine carbonaceous chondrite, providing a unique opportunity to investigate the composition of early solar system materials prior to the onset of significant aqueous alteration. A dual origin (namely from the inner and outer solar system) has been demonstrated for water in the Paris meteorite parent body (Piani et al. 2018 ). Here, we aim to evaluate the contribution of outer solar system (cometary‐like) water ice to the inner solar system water ice using Xe isotopes. We report Ar, Kr, and high‐precision Xe isotopic measurements within bulk CM 2.9 and CM 2.7 fragments, as well as Ne, Ar, Kr, and Xe isotope compositions of the insoluble organic matter (IOM). Noble gas signatures are similar to chondritic phase Q with no evidence for a cometary‐like Xe component. Small excesses in the heavy Xe isotopes relative to phase Q within bulk samples are attributed to contributions from presolar materials. CM 2.7 fragments have lower Ar/Xe relative to more pristine CM 2.9 fragments, with no systematic difference in Xe contents. We conclude that Kr and Xe were little affected by aqueous alteration, in agreement with (1) minor degrees of alteration and (2) no significant differences in the chemical signature of organic matter in CM 2.7 and CM 2.9 areas (Vinogradoff et al. 2017 ). Xenon contents in the IOM are larger than previously published data of Xe in chondritic IOM, in line with the Xe component in Paris being pristine and preserved from Xe loss during aqueous alteration/thermal metamorphism.     

Spatial distribution of organic matter in the Bells CM2 chondrite using near‐field infrared microspectroscopy

Abstract– Distributions of organic functional groups as well as inorganic features were analyzed in the Bells (CM2) carbonaceous chondrite using near‐field infrared (NFIR) spectroscopy. NFIR spectroscopy has recently been developed to enable infrared spectral mapping beyond the optical diffraction limit of conventional Fourier transform infrared microspectroscopy. NFIR spectral mapping of the Bells 300 nm thick sections on Al plates for 7.5 × 7.5 μm² areas showed some C‐H‐rich areas which were considered to represent the organic‐rich areas. Heterogeneous distributions of organic matter as well as those of inorganic phases such as silicates (Si‐O) were observed with 1 μm spatial resolution. The NFIR mappings of aliphatic C‐H (2960 and 2930 cm^?1) and structural OH (3650 cm^?1) confirm that organic matter is associated with phyllosilicates as previously suggested. The NFIR mapping method can provide 1 μm spatial distribution of organic functional groups and their association with minerals. High local sensitivity of NFIR enables us to find organic‐rich areas and to characterize them by their aliphatic CH₂/CH₃ ratios. The aliphatic CH₂/CH₃ ratio of Bells is slightly higher than Murchison, similar to Orgueil, and lower than literature values of IDPs and cometary dust particles.     

NanoSIMS analysis of organic carbon from the Tissint Martian meteorite: Evidence for the past existence of subsurface organic‐bearing fluids on Mars

Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock‐melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock‐melt veins and the deuterium enrichments (δD up to +1183‰) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen‐like, based on micro‐Raman spectra and multielemental ratios, and were probably deposited from fluids in shock‐induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (δ¹³C = ?12.8 to ?33.1‰) are significantly lighter than Martian atmospheric CO₂ and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic‐rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.     

Analytical SuperSTEM for extraterrestrial materials research

Abstract— Electron‐beam studies of extraterrestrial materials with significantly improved spatial resolution, energy resolution, and sensitivity are enabled using a 300 keV SuperSTEM scanning transmission electron microscope (STEM) with a monochromator and two spherical aberration correctors. The improved technical capabilities enable analyses previously not possible. Mineral structures can be directly imaged and analyzed with single‐atomic‐column resolution, liquids, and implanted gases can be detected, and UV‐VIS optical properties can be measured. Detection limits for minor/trace elements in thin (<100 nm thick) specimens are improved such that quantitative measurements of some extend to the sub‐500 ppm level. Electron energy‐loss spectroscopy (EELS) can be carried out with 0.10–0.20 eV energy resolution and atomic‐scale spatial resolution such that variations in oxidation state from one atomic column to another can be detected. Petrographic mapping is extended down to the atomic scale using energy‐dispersive X‐ray spectroscopy (EDS) and energy‐filtered transmission electron microscopy (EFTEM) imaging. Technical capabilities and examples of the applications of SuperSTEM to extraterrestrial materials are presented, including the UV spectral properties and organic carbon K‐edge fine structure of carbonaceous matter in interplanetary dust particles (IDPs), X‐ray elemental maps showing the nanometer‐scale distribution of carbon within GEMS (glass with embedded metal and sulfides), the first detection and quantification of trace Ti in GEMS using EDS, and detection of molecular H₂O in vesicles and implanted H₂ and He in irradiated mineral and glass grains.     

Fractionated matrix composition in CV3 Vigarano and alteration processes on the CV parent asteroid

Abstract— Although CV3 Vigarano is one of the most primitive CV chondrites, it has lost most of the S from the matrix; matrix Na is also depleted relative to the concentration in bulk CV chondrites. We used a matrix‐grid technique to study thirteen 50 × 50 μm regions in Vigarano; in each area, we used an electron microprobe to gather data with an electron beam 3 μm in width. We found two end‐member types of matrix textures. One is coarse and porous, has lower Fe contents and lower analytical totals; it appears to be contaminated with comminuted chondrule debris. The other is finer grained and appears smooth; its mean composition has higher Fe, but lower S and Al contents, than the coarse matrix areas. Our tentative interpretation is that the larger grain size of the coarse areas resulted from the admixing of comminuted chondrule materials, and thus that the initial fraction of nebular fines was higher in the fine matrix regions. Aside from volatiles, the overall composition of Vigarano matrix is similar to that observed in matrix‐grid studies of other carbonaceous chondrites: Al, Si, Fe, and Mn have high whole‐chondrite‐normalized abundance ratios; Ca concentrations are low and highly variable. Because asteroidal alteration effects are present in our sample, it is difficult to resolve nebular signatures in the compositions of the grid areas.     

Pristine stratospheric collection of interplanetary dust on an oil‐free polyurethane foam substrate

We performed chemical, mineralogical, and isotopic studies of the first interplanetary dust particles (IDPs) collected in the stratosphere without the use of silicone oil. The collection substrate, polyurethane foam, effectively traps impacting particles, but the lack of an embedding medium results in significant particle fragmentation. Two dust particles found on the collector exhibit the typical compositional and mineralogical properties of chondritic porous interplanetary dust particles (CP‐IDPs). Hydrogen and nitrogen isotopic imaging revealed isotopic anomalies of typical magnitude and spatial variability observed in previous CP‐IDP studies. Oxygen isotopic imaging shows that individual mineral grains and glass with embedded metal and sulfide (GEMS) grains are dominated by solar system materials. No systematic differences are observed in element abundance patterns of GEMS grains from the dry collection versus silicone oil‐collected IDPs. This initial study establishes the validity of a new IDP collection substrate that avoids the use of silicone oil as a collection medium, removing the need for this problematic contaminant and the organic solvents necessary to remove it. Additional silicone oil‐free collections of this type are needed to determine more accurate bulk element abundances of IDPs and to examine the indigenous soluble organic components of IDPs.     

Searching for the source regions of martian meteorites using MGS TES: Integrating martian meteorites into the global distribution of igneous materials on Mars

Abstract— The objective of this study was to identify and map possible source regions for all 5 known martian meteorite lithologies (basalt, lherzolite, clinopyroxenite, orthopyroxenite, and dunite) using data from the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES). We deconvolved the TES data set using laboratory spectra of 6 martian meteorites (Los Angeles, Zagami, ALH A77005, Nakhla, ALH 84001, and Chassigny) as end members, along with atmospheric and surface spectra previously derived from TES data. Global maps (16 pixels/degree) of the distribution of each meteorite end member show that meteorite‐like compositions are not present at or above TES detectability limits over most of the planet's dust‐free regions. However, we have confidently identified local‐scale (100s‐1000s km²) concentrations of olivine‐ and orthopyroxene‐bearing materials similar to ALH A77005, Chassigny, and ALH 84001 in Nili Fossae, in and near Ganges Chasma, in the Argyre and Hellas basin rims, and in Eos Chasma. Nakhla‐like materials are identified near the detection limit throughout the eastern Valles Marineris region and portions of Syrtis Major. Basaltic shergottites were not detected in any spatially coherent areas at the scale of this study. Martian meteorite‐like lithologies represent only a minor portion of the dust‐free surface and, thus, are not representative of the bulk composition of the ancient crust. Meteorite‐like spectral signatures identified above TES detectability limits in more spatially restricted areas (<tens of km) are targets of ongoing analysis.     

Effect of a synchrotron X‐ray microtomography imaging experiment on the amino acid content of a CM chondrite

X‐ray microcomputed tomography and synchrotron X‐ray microcomputed tomography (μCT) are becoming popular tools for the reconnaissance imaging of chondrites. However, there are occasional concerns that the use of μCT may be detrimental to organic components of a chondrite. Soluble organic compounds represent ~2–10% of the total solvent extractable carbon in CI and CM carbonaceous chondrites and amino acids are among the most abundant compounds in the soluble organic fraction. We irradiated two samples of the Murchison CM2 carbonaceous chondrite under conditions slightly harsher (increased beam exposure time) than those typically used for x‐ray μCT imaging experiments to determine if detectable changes in the amino acid abundance and distribution relative to a nonexposed control sample occurred. After subjecting two meteorite portions to ionizing radiation dosages of 1.1 kiloGray (kGy) and 1.2 kGy with 48.6 and 46.6 keV monochromatic X‐rays, respectively, we analyzed the amino acid content of each sample. Within analytical errors, we found no differences in the amino acid abundances or enantiomeric ratios when comparing the control samples (nonexposed Murchison) and the irradiated samples. We show with calculations that any sample heating due to x‐ray exposure is negligible. We conclude that a monochromatic synchrotron X‐ray μCT experiment at beamline 13‐BM‐D of the Advanced Photon Source, which imparts ~1 kGy doses, has no detectable effect on the amino acid content of a carbonaceous chondrite. These results are important for the initial reconnaissance of returned samples from the OSIRIS‐REx and Hayabusa 2 asteroid sample return missions.     

Spectral properties and geologic processes on Eros from combined NEAR NIS and MSI data sets

Abstract— From April 24 to May 14, 2000, the Near Earth Asteroid Rendezvous (NEAR) Shoemaker mission's near infrared spectrometer (NIS) obtained its highest resolution data of 433 Eros. High signal‐to‐noise ratio NIS reflectance spectra cover a wavelength range of 800–2400 nm, with footprint sizes from 213 times 427 m to 394 times 788 m. This paper describes improvement in instrument calibration by remediation of internally scattered light; derivation of a “pseudo channel” for NIS at 754 nm using Multispectral Imager (MSI) Eros approach maps at 951 and 754 nm; synthesis of a 3127‐spectrum high‐resolution data set with the improved calibration and expanded wavelength coverage; and investigation of global and localized spectral variation with respect to mineralogy, composition, and space weathering of Eros, comparing the findings with previous analyses. Scattered light removal reduces the “red” slope of Eros spectra, though not to the level seen by telescopic observations. The pseudo channel completes sampling of Eros' 1 micron (Band I) absorption feature, enabling direct comparison of NIS data with other asteroid and meteorite spectra without additional scaling or correction. Following scattered light removal and wavelength range extension, the spectral parameters of average Eros plot well inside the S(IV) field of Gaffey et al. (1993) and are consistent with the L6 chondrite meteorite fields of Gaffey and Gilbert (1998). Although Eros shows no evidence of mineralogical heterogeneity, modest spectral variations correlate with morphologically and geographically distinct areas of the asteroid. Eros bright‐to‐dark spectral ratios are largely consistent with laboratory “space weathering” experiment results and modeling of space weathering effects. Eros brightness variation unaccompanied by significant spectral variation departs from “lunar‐type”—where band depths, slopes, and albedoes all correlate—and “Ida‐type”—where significant spectral variation is unaccompanied by corresponding brightness variation. The brightest areas on Eros—steep crater walls—have lesser spectral slope and deeper Band I, consistent with exposure of “fresher,” less space weathered materials. Bright crater slope materials have opx/(opx + olv) of 0.24–0.29 and may be more representative of the subsurface mineralogy than “average” Eros, which is probably affected by space weathering. The floors of the large craters Psyche and Himeros have lower albedo and contain the most degraded or altered looking materials. NIS spectra retain a “red” spectral slope at greater than 2 microns. The recalibrated and expanded NIS spectra show better agreements with mixing models based on space weathering of chondritic mixtures.     

Two refractory Wild 2 terminal particles from a carrot‐shaped track characterized combining MIR/FIR/Raman microspectroscopy and FE‐SEM/EDS analyses

We present the analyses results of two bulk Terminal Particles, C2112,7,171,0,0 and C2112,9,171,0,0, derived from the Jupiter‐family comet 81P/Wild 2 returned by the Stardust mission. Each particle embedded in a slab of silica aerogel was pressed in a diamond cell. This preparation, as expected, made it difficult to identify the minerals and organic materials present in these particles. This problem was overcome using a combination of three different analytical techniques, viz. FE‐SEM/EDS, IR, and Raman microspectroscopy that allowed identifying the minerals and small amounts of amorphous carbon present in both particles. TP2 and TP3 were dominated by Ca‐free and low‐Ca, Mg‐rich, Mg,Fe‐olivine. The presence of melilite in both particles is supported by IR microspectroscopy, but is not confirmed by Raman microspectroscopy, possibly because the amounts are too small to be detected. TP2 and TP3 show similar silicate mineral compositions, but Ni‐free and low‐Ni, subsulfur (Fe,Ni)S grains are present in TP2 only. TP2 contains indigenous amorphous carbon hot spots; no indigenous carbon was identified in TP3. These nonchondritic particles probably originated in a differentiated body. This work found an unanticipated carbon contamination following the FE‐SEM/EDS analyses. It is suggested that organic materials in the embedding silica aerogel are irradiated during FE‐SEM/EDS analyses creating a carbon gas that develops a strong fluorescence continuum. The combination of the selected analytical techniques can be used to characterize bulk Wild 2 particles without the need of extraction and removal of the encapsulating aerogel. This approach offers a relatively fast sample preparation procedure, but compressing the samples can cause spurious artifacts, viz. silica contamination. Because of the combination of techniques, we account for these artifacts.     

Northwest Africa 1950: Mineralogy and comparison with Antarctic lherzolitic shergottites

Abstract— NWA 1950 is a new lherzolitic shergottite recently recovered from Morocco and is the first sample of this group found outside Antarctica. Major constituent phases of NWA 1950 are olivine, pyroxenes, and plagioclase glass (“maskelynite”) and the rock shows a two distinct textures: poikilitic and non‐poikilitic typical of lherzolitic shergottites. In poikilitic areas, several‐millimeter‐sized pyroxene oikocrysts enclose cumulus olivine and chromite. In contrast, pyroxenes are much smaller in non‐poikilitic areas, and olivine and plagioclase glass are more abundant. Olivine in non‐poikilitic areas is more Fe‐rich (Fa_29–31) and shows a narrower distribution than that in poikilitic areas (Fa_23–29). Pyroxenes in non‐poikilitic areas are also more Fe‐rich than those in poikilitic areas that show continuous chemical zoning suggesting fractional crystallization under a closed system. These observations indicate that pyroxene in non‐poikilitic areas crystallized from evolved interstitial melts and olivine was re‐equilibrated with such melts. NWA 1950 shows similar mineralogy and petrology to previously known lherzolitic shergottites (ALH 77005, LEW 88516, Y‐793605 and GRV 99027) that are considered to have originated from the same igneous body on Mars. Olivine composition of NWA 1950 is intermediate between those of ALH 77005‐GRV 99027 and those of LEW 88516‐Y‐793605, but is rather similar to ALH 77005 and GRV 99027. The subtle difference of mineral chemistry (especially, olivine composition) can be explained by different degrees of re‐equilibration compared to other lherzolitic shergottites, perhaps due to different location in the same igneous body. Thus, NWA 1950 experienced a high degree of re‐equilibration, similar to ALH 77005 and GRV 99027.     

Concentration and variability of the AIB amino acid in polar micrometeorites: Implications for the exogenous delivery of amino acids to the primitive Earth

Abstract— Micrometeorites (MMs) are extraterrestrial particles ranging in size from 25 μm to 2 mm that survive atmospheric entry and are collected on the Earth's surface. They represent the largest mass flux (MF) of extraterrestrial material (30,000 ± 20,000 t/yr) to the present‐day Earth. Studies of large collections of MMs suggest that about 20% have not been heated to high temperatures and that they contain organic carbon. Since non‐protein amino acids have been found in some carbonaceous meteorites, they might also be found in unmelted MMs. However, previous searches for amino acids in MMs were inconclusive. We combined a new extraction method for amino acids with a highly sensitive analytical method to detect and quantitate amino acids in MMs collected at the South Pole. We found the non‐protein amino acid α‐amino isobutyric acid (AIB) in one of our samples. The non‐detection of this amino acid in the other samples analyzed suggests that there are amino acid‐containing and amino acid‐free MMs, with ?14% of the MMs containing AIB. Since the MF of MMs is much higher than that of carbonaceous chondrites (CMs), amino acids in these small particles would represent an important source of exogenous delivery of organic molecules. Therefore, the results are discussed on the basis of their implications for astrobiology.     

The effects of disk building on the distributions of refractory materials in the solar nebula

Abstract– Refractory materials, such as calcium‐aluminum‐rich inclusions (CAIs) and crystalline silicates, are widely found in chondritic meteorites as well as comets, taken as evidence for large‐scale mixing in the solar nebula. Most models for mixing in the solar nebula begin with a well‐formed protoplanetary disk. Here, we relax this assumption by modeling the formation and evolution of the solar nebula during and after the period when it accreted material from its parent molecular cloud. We consider how disk building impacts the long‐term evolution of the disk and the implications for grain transport and mixing within it. Our model shows that materials that formed before infall was complete could be preserved in primitive bodies, especially those that accreted in the outer disk. This potentially explains the discovery of refractory objects with low initial ²⁶Al/²⁷Al ratios in comets. Our model also shows that the highest fraction of refractory materials in meteorites formed around the time that infall stopped. Thus, we suggest that the calcium‐aluminum‐rich inclusions in chondrites would be dominated by the population that formed during the transition from class I to class II stage of young stellar objects. This helps us to understand the meaning of t = 0 in solar system chronology. Moreover, our model offers a possible explanation for the existence of isotopic variations observed among refractory materials—that the anomalous materials formed before the collapse of the parent molecular cloud was complete.     

Carbon isotopic fractionation in Fischer‐Tropsch‐type reactions and relevance to meteorite organics

Abstract— Fischer‐Tropsch‐type (FTT) reactions have been hypothesized to contribute to the formation of organic compounds in the early solar system, but it has been difficult to identify a signature of such reactions in meteoritic organics. The work reported here examined whether temperature‐dependent carbon isotopic fractionation of FTT reactions might provide such a signature. Analyses of bulk organic deposits resulting from FTT experiments show a slight trend toward lighter carbon isotopic ratios with increasing temperature. It is unlikely, however, that these carbon isotopic signatures could provide definitive provenance for organic compounds in solar system materials produced through FTT reactions, because of the small scale of the observed fractionations and the possibility that signatures from many different temperatures may be present in any specific grain.     

Characterizing organic particle impacts on inert metal surfaces: Foundations for capturing organic molecules during hypervelocity transits of Enceladus plumes

The presence and accessibility of a sub‐ice‐surface saline ocean at Enceladus, together with geothermal activity and a rocky core, make it a compelling location to conduct further, in‐depth, astrobiological investigations to probe for organic molecules indicative of extraterrestrial life. Cryovolcanic plumes in the south polar region of Enceladus enable the use of remote in situ sampling and analysis techniques. However, efficient plume sampling and the transportation of captured organic materials to an organic analyzer present unique challenges for an Enceladus mission. A systematic study, accelerating organic ice‐particle simulants into soft inert metal targets at velocities ranging 0.5–3.0 km s⁻¹, was carried out using a light gas gun to explore the efficacy of a plume capture instrument. Capture efficiency varied for different metal targets as a function of impact velocity and particle size. Importantly, organic chemical compounds remained chemically intact in particles captured at speeds up to ~2 km s⁻¹. Calibration plots relating the velocity, crater, and particle diameter were established to facilitate future ice‐particle impact experiments where the size of individual ice particles is unknown.     

Space weathering on Eros: Constraints from albedo and spectral measurements of Psyche crater

Abstract— We present combined multi‐spectral imager (MSI) (0.95 μm) and near‐infrared spectrometer (NIS) (0.8–2.4 μm) observations of Psyche crater on S‐type asteroid 433 Eros obtained by the Near‐Earth Asteroid Rendezvous (NEAR)—Shoemaker spacecraft. At 5.3 km in diameter, Psyche is one of the largest craters on Eros which exhibit distinctive brightness patterns consistent with downslope motion of dark regolith material overlying a substrate of brighter material. At spatial scales of 620 m/ spectrum, Psyche crater wall materials exhibit albedo contrasts of 32–40% at 0.946 μm. Associated spectral variations occur at a much lower level of 4–8% (±2–4%). We report results of scattering model and lunar analogy investigations into several possible causes for these albedo and spectral trends: grain size differences, olivine, pyroxene, and troilite variations, and optical surface maturation. We find that the albedo contrasts in Psyche crater are not consistent with a cause due solely to variations in grain size, olivine, pyroxene or lunar‐like optical maturation. A grain size change sufficient to explain the observed albedo contrasts would result in strong color variations that are not observed. Olivine and pyroxene variations would produce strong band‐correlated variations that are not observed. A simple lunar‐like optical maturation effect would produce strong reddening that is not observed. The contrasts and associated spectral variation trends are most consistent with a combination of enhanced troilite (a dark spectrally neutral component simulating optical effects of shock) and lunar‐like optical maturation. These results suggest that space weathering processes may affect the spectral properties of Eros materials, causing surface exposures to differ optically from subsurface bedrock. However, there are significant spectral differences between Eros' proposed analog meteorites (ordinary chondrites and/or primitive achondrites), and Eros' freshest exposures of subsurface bright materials. After accounting for all differences in the measurement units of our reflectance comparisons, we have found that the bright materials on Eros have reflectance values at 0.946 μm consistent with meteorites, but spectral continua that are much redder than meteorites from 1.5 to 2.4 μm. Most importantly, we calculate that average Eros surface materials are 30–40% darker than meteorites.     

A potentially new type of nonchondritic interplanetary dust particle with hematite,organic carbon,amorphous Na,Ca‐aluminosilicate,and FeO‐spheres

Abstract– We used a combination of different analytical techniques to study particle W7190‐D12 using microinfrared spectroscopy, micro‐Raman spectroscopy, and field emission scanning electron microscopy (FESEM) energy dispersive X‐ray spectroscopy (EDS). The particle consists mainly of hematite (α‐Fe₂O₃) with considerable variations in structural disorder. It further contains amorphous (Na,K)‐bearing Ca,Al‐silicate and organic carbon. Iron‐bearing spherules (<150 nm in diameter) cover the surface of this particle. At local sites of structural disorder at the hematite surface, the hematite spheres were reduced to FeO in the presence of organic carbons forming FeO‐spheres. However, metallic Fe spheres cannot be excluded based on the available data. To the best of our knowledge, this particle is the first detection of such spherules at the surface of a stratospheric dust particle. Although there is no definitive evidence for an extraterrestrial origin of particle W7190‐D12, we suggest that it could be an IDP that had moved away from the asteroid‐forming region of the early solar system into the outer solar system of the accreting Kuiper Belt objects. After it was released from a Jupiter family comet, this particle became part of the zodiacal cloud. Atmospheric entry flash‐heating caused (1) the formation of microenvironments of reduced iron oxide when indigenous carbon materials reacted with hematite covering its surface resulting in the formation of FeO‐spheres and (2) Na‐loss from Na,Al‐plagioclase. The particle of this study, and other similar particles on this collector, may represent a potentially new type of nonchondritic IDPs associated with Jupiter family comets, although an origin in the asteroid belt cannot be ignored.     

Amino acid photostability on the Martian surface

Abstract— In the framework of international planetary exploration programs, several space missions are planned to search for organics and bio‐signatures on Mars. Previous attempts have not detected any organic compounds in the Martian regolith. It is therefore critical to investigate the processes that may affect organic molecules on and below the planet's surface. Laboratory simulations can provide useful data about the reaction pathways of organic material at Mars' surface. We have studied the stability of amino acid thin films against ultraviolet (UV) irradiation and use those data to predict the survival time of these compounds on and in the Martian regolith. We show that thin films of glycine and D‐alanine are expected to have half‐lives of 22 ± 5 hr and of 3 ± 1 hr, respectively, when irradiated with Mars‐like UV flux levels. Modelling shows that the half‐lives of the amino acids are extended to the order of 10⁷ years when embedded in regolith. These data suggest that subsurface sampling must be a key component of future missions to Mars dedicated to organic detection.     

Carbonaceous materials in the acid residue from the Orgueil carbonaceous chondrite meteorite

Abstract— Insoluble organic matter (IOM) dominates the HF/HCl residue of the Orgueil (CI) carbonaceous chondrite meteorite. The IOM is composed primarily of two C‐rich particle types. The first has a fluffy texture similar to crumpled tissue paper, and the second type occurs as solid or hollow nanospheres. High‐resolution transmission electron microscope (HRTEM) images of the fluffy material show it is poorly ordered, with small, irregularly shaped regions having fringes with 0.34–0.38 nm spacings and locally 0.21 nm cross‐fringes. Nanodiamonds occur in the fluffy material. The rounded C‐rich particles are common in the residue and their HRTEM images show neither fringes nor nanodiamonds. Both types of carbonaceous materials have a high aromatic component, as revealed by electron energy‐loss spectroscopy (EELS), with up to 10 at% substitution by S, N, and O. The average compositions of the fluffy material and nanospheres are C₁₀₀S_1.9N_3.7O_4.9 and C₁₀₀S_2.4N_5.0O_3.9, respectively. The structural and chemical heterogeneity of the carbonaceous materials may represent material from multiple sources.     

Structure,composition, and location of organic matter in the enstatite chondrite Sahara 97096 (EH3)

Abstract– The insoluble organic matter (IOM) of an unequilibrated enstatite chondrite Sahara (SAH) 97096 has been investigated using a battery of analytical techniques. As the enstatite chondrites are thought to have formed in a reduced environment at higher temperatures than carbonaceous chondrites, they constitute an interesting comparative material to test the heterogeneities of the IOM in the solar system and to constrain the processes that could affect IOM during solar system evolution. The SAH 97096 IOM is found in situ: as submicrometer grains in the network of fine‐grained matrix occurring mostly around chondrules and as inclusions in metallic nodules, where the carbonaceous matter appears to be more graphitized. IOM in these two settings has very similar δ¹⁵N and δ¹³C; this supports the idea that graphitized inclusions in metal could be formed by metal catalytic graphitization of matrix IOM. A detailed comparison between the IOM extracted from a fresh part and a terrestrially weathered part of SAH 97096 shows the similarity between both IOM samples in spite of the high degree of mineral alteration in the latter. The isolated IOM exhibits a heterogeneous polyaromatic macromolecular structure, sometimes highly graphitized, without any detectable free radicals and deuterium‐heterogeneity and having mean H‐ and N‐isotopic compositions in the range of values observed for carbonaceous chondrites. It contains some submicrometer‐sized areas highly enriched in ¹⁵N (δ¹⁵N up to 1600‰). These observations reinforce the idea that the IOM found in carbonaceous chondrites is a common component widespread in the solar system. Most of the features of SAH 97096 IOM could be explained by the thermal modification of this main component.