Search

Introduction: Regolith samples of the carbonaceous asteroid 162173 Ryugu were returned by the Hayabusa2 spacecraft in December 2020. Preliminary investigation of selected grains from each sampling site has revealed the occurrence of an abundant macromolecular insoluble material, similar to that of carbonaceous chondrites [1]. Understanding the origin of organic matter on carbonaceous asteroids and its subsequent evolution due to secondary processes as well as space weathering is one of the prime goals of the Hayabusa2 sample-return mission. Isotope composition of organic material found in extraterrestrial samples is a powerful proxy for tracking its origin and evolution during the solar system events [2]. To document the H- and N-isotope signatures of IOM contained in the Ryugu samples, we have used the NanoSIMS installed at the National Muséum of Natural History in Paris. We present here data acquired on the IOM isolated from grains of two touchdown sites. We have imaged between 2800 and 3200 ?m2 of the IOM of chamber A and C, respectively. The comparison with the IOM of carbonaceous chondrites allows for evaluating the influence of space weathering and aqueous alteration on the IOM in carbonaceous asteroids. Results: N-isotope distributions: the bulk δ15N is +17.4‰ and +30‰ for the IOM of chamber A and chamber C, respectively. These IOMs contain both 15N-enriched and depleted carbonaceous grains, with 180‰<δ15N< 800‰ for hotspots and -380‰ < δ15N < -180‰ for coldspots. Hotspots define a Poisson distribution with a mode value of +241‰ and +348‰ for chamber A and chamber C, respectively. Elemental ratios: Bulk N/C, O/C and S/C of Ryugu IOM are 0.035, 0.12, 0.032, respectively, for chamber A and 0.027, 0.04, 0.025 for chamber C. The N/C ratio of individual 15N-rich and depleted grains are comprised between 0.01 and 0.07, with those in the IOM of A0106 being slightly more N rich. Similarly, O/C and S/C ratios are also slightly higher in A0106. H-isotope distribution: Ryugu IOM exhibits bulk enrichments in D with δD = +306‰ and +440‰ for chamber A and chamber C, respectively. Numerous D-rich hotspots, are observed, with +600‰ < δD < +6000‰. They define a Poisson distribution, with a mode value of +1030‰ and +1374‰ for chamber A and chamber C, respectively. Of note, a few D-depleted organic grains are also observed (-200‰ < δD < 0‰). Discussion: Subtle differences are observed between the IOM of chamber A and chamber C: the IOM is less enriched in heavy isotopes in chamber A, and more enriched in N, O and S. This may reflect some heterogeneity at the scale of the asteroid, or the influence of sampling depth, hence the influence of space weathering. However, the elemental and isotope compositions of the IOM in Ryugu are comparable to those of hydrated carbonaceous chondrites. The bulk δ15N in Ryugu IOM is commensurable to levels reported in CI chondrites, despite the occurrence of hotspots being more 15N-rich in Ryugu [3]. The range of δ15N covered by these hotspots is, however, consistent with the IOM of CM chondrites and Tagish Lake, but remains in the lower end of the hotspots in CR chondrites. The most notable difference is the bulk δD which is lower than in the IOM of hydrated carbonaceous chondrites. The distribution of δD in Ryugu IOM is consistent with the IOMs in CI and CM chondrites. We did not observe enrichments as large as those reported in CR chondrites and in Tagish Lake [4,5]. The abundance of D- and 15N-rich hotspots appears similar in Ryugu and carbonaceous chondrites. Differences between Ryugu and carbonaceous chondrites may result from different intensity of aqueous alteration or the impact of space weathering, which could have induced a decrease of D/H in organic compounds by H implantation. Acknowledgments: The NanoSIMS facility at MNHN in Paris is supported by CNRS and MNHN. L. R. is grateful to the European Research Council (ERC consolidator grant HYDROMA). [ABSTRACT FROM AUTHOR]

Introduction: JAXA's Hayabusa2 mission returned the surface samples from the carbonaceous (C-type) asteroid Ryugu. The first touchdown samples and second touchdown samples were separately stored in the sample container chamber A and chamber C, respectively [1]. Fourier transform infrared (FTIR) spectroscopy is a nondestructive technique for functional group chemistry and structures which is suitable for both organic and inorganic compounds. As a part of the Hayabusa2-initial-analysis organic macromolecule team, infrared absorption spectra from the intact Ryugu particles and extracted insoluble organic matter (IOM) were obtained using FTIR microspectroscopy, to understand the nature of organic matter in Ryugu. Methods: Several samples were analyzed in parallel in the team, in Japan (Yokohama National Univ., YNU) and in France (IPAG, Grenoble and Orsay-lab teams) to increase the robustness of the analysis. The aggregates in chamber A (A0108 and A0106) and chamber C (C0109) were analyzed as intact Ryugu particles. IOM was obtained after solvent extraction followed by HF/HCl demineralization from the aggregates A0106 and C0107 (Hiroshima U) [2]. During drying, most IOM was precipitated, but there was a little left suspended (sticky phase). The samples were pressed between two diamond windows and then FTIR measurements were performed on the diamond windows in transmission mode. Results and Discussion: The organic features shown in the FTIR spectra of the Ryugu intact particles (Fig. 1) were aliphatic C-H stretching at 2960 cm-1 (CH3 asymmetric), 2930-2925 cm-1 (CH2 asymmetric), 2855-2850 cm-1 (CH3 and CH2 symmetric) and aromatic C=C stretching (~1600 cm-1). Carbonyl C=O stretching modes (~1700 cm-1) were not always visible. Extracted IOM displayed these organic peaks more clearly. In addition, C=O at 1660 cm-1 newly appeared, which may be assigned to unsaturated ketones/aldehydes or amides. There was no significant difference between the samples from surface and interior of a mm-sized grain (A0108-58) from the A0108 aggregate. Moreover, both in the case of intact particles and extracted IOM, the IR absorption spectra of chamber A and chamber C were almost identical, but some local heterogeneity exists. The Ryugu IOM had the highest CH2/CH3 with the highest aliphatic CH/aromatic C=C ratios compared to IOM from unheated carbonaceous chondrites [3], indicating that it is rich in long chain aliphatic moieties. We also observed possible N-H features at 3350 cm-1 and 3180 cm-1 in the Ryugu IOM. The N-H absorption was previously detected from reflectance IR measurements of intact Ryugu particles by JAXA curation [4,5], but the peak positions were ~80-90 cm-1 lower than the Ryugu IOM. Overall, the FTIR organic signatures of the Ryugu samples generally agree with CI chondrites but some differences do exist. The high CH2/CH3 ratios, aliphatic-rich, and N-rich nature of Ryugu organic matter might indicate primitiveness and freshness of the Ryugu particles. The differences between Ryugu and carbonaceous chondrites could be attributed to modification of organic matter in carbonaceous chondrites due to long preservation on the Earth, which Ryugu samples escaped. [ABSTRACT FROM AUTHOR]

Abstract: Oxygen isotopes were measured in four chondritic hydrated interplanetary dust particles (IDPs) and five chondritic anhydrous IDPs including two GEMS-rich particles (Glass embedded with metal and sulfides) by a combination of high precision and high lateral resolution ion microprobe techniques. All IDPs have isotopic compositions tightly clustered around that of solar system planetary materials. Hydrated IDPs have mass-fractionated oxygen isotopic compositions similar to those of CI and CM carbonaceous chondrites, consistent with hydration of initially anhydrous protosolar dust. Anhydrous IDPs have small 16O excesses and depletions similar to those of carbonaceous chondrites, the largest 16O variations being hosted by the two GEMS-rich IDPs. Coarse-grained forsteritic olivine and enstatite in anhydrous IDPs are isotopically similar to their counterparts in comet Wild 2 and in chondrules suggesting a high temperature inner solar system origin. The small variations in the 16O content of GEMS-rich IDPs suggest that most GEMS either do not preserve a record of interstellar processes or the initial interstellar dust is not 16O-rich as expected by self-shielding models, although a larger dataset is required to verify these conclusions. Together with other chemical and mineralogical indicators, O isotopes show that the parent-bodies of carbonaceous chondrites, of chondritic IDPs, of most Antarctic micrometeorites, and comet Wild 2 belong to a single family of objects of carbonaceous chondrite chemical affinity as distinct from ordinary, enstatite, K- and R-chondrites. Comparison with astronomical observations thus suggests a chemical continuum of objects including main belt and outer solar system asteroids such as C-type, P-type and D-type asteroids, Trojans and Centaurs as well as short-period comets and other Kuiper Belt Objects. [Copyright &y& Elsevier]

We report detailed transmission electron microscope (TEM) observations of carbonates from one hydrated fine-grained Antarctic micrometeorite (H-FgMM). These carbonates show the occurrence of complex chemical variations and microstructures that provide important evidence regarding the formation and evolution of rarely analyzed H-FgMMs. The chemical variations were identified at both micrometer and nanometer scales, indicating that these carbonates formed under localized fluid conditions that suggest a variable chemical microenvironment. Individual carbonates grew from isolated reservoirs of fluid. Moreover, these carbonates contain manganese amounts almost twice as high as those measured in CM chondrites but similar to those identified in CI chondrites. Their particular compositions indicate reducing and progressively evolving conditions in the fluid from which these carbonates precipitated, probably due to water consumption during phyllosilicates formation. In addition to the compositional variability, microstructural features are pervasive in these carbonates, similar to those described in heavily shocked meteorites indicating that these carbonates were probably modified during shock processes after their formation. Since carbonates are highly susceptible to shock metamorphism, we suggest that it is essential to investigate their structure in detail before interpreting the isotopic measurements related to the time of their formation. Additionally, associated with carbonates, ubiquitous phosphates were identified in the micrometeorite analyzed. Future studies of these mineral associations will provide us further insight into the formation and evolution of asteroids, especially since they were both identified in the surface materials of Ryugu and Bennu. [ABSTRACT FROM AUTHOR]

This work presents a multi-analysis on 35 Antarctic micrometeorites (AMMs) (Concordia collection 2006) by coupled Raman and Infrared (IR) spectroscopies, in comparison with samples from type 1 and 2 carbonaceous CM, CR and CI chondrites. We identified the Raman G- and D -bands revealing the presence of polyaromatic carbonaceous material on raw particles in a subset of 16 particles. Thirteen AMMs (10 Fg + 1 Fg- Sc  + 1 Sc ) were selected from this first subset, and analyzed by infrared microscopy along with 4 AMMs (2 Fg + 1 Fg- Sc  + 1 Sc ) from a previous study by Dobrica et al. (2011). These analyses showed that scoriaceous, fine-grained scoriaceous and part of the fine-grained AMMs are not hydrated, with a weak abundance of carbonaceous matter. According to the Raman criterion defined by Dobrica et al. (2011), hydrous AMMs do not show structural modifications induced by heating through the atmospheric entry. In several hydrous AMMs, the carbonaceous matter abundance is found larger than in Orgueil (CI), Murchison (CM) and QUE 99177 (CR) chondrites and their mineral content exhibit differences reflected by the structure of the silicate 10 µm band. These observations suggest that part of the AMMs originates from one, or several, distinct parent bodies with respect to primitive carbonaceous chondrites. Each hydrous Fg-AMMS displays higher CH 2 /CH 3 ratio and a smaller carbonyl abundance than chondrites, which point toward a mild processing during atmospheric entry, possibly oxidation, which did not modify the carbon backbone and therefore do not induce differences in Raman spectroscopy. [ABSTRACT FROM AUTHOR]