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In order to gain insights on the conditions of aqueous alteration on asteroid Ryugu and the origin of water in the outer solar system, we developed the measurement of water content in magnetite at the micrometer scale by secondary ion mass spectrometry (NanoSIMS) and determined the H and Si content of coarse‐grained euhedral magnetite grains (polyhedral magnetite) and coarse‐grained fibrous (spherulitic) magnetite from the Ryugu polished section A0058‐C1001. The hydrogen content in magnetite ranges between ~900 and ~3300 wt ppm equivalent water and is correlated with the Si content. Polyhedral magnetite has low and homogenous silicon and water content, whereas fibrous magnetite shows correlated Si and water excesses. These excesses can be explained by the presence of hydrous Si‐rich amorphous nanoinclusions trapped during the precipitation of fibrous magnetite away from equilibrium and testify that fibrous magnetite formed from a hydrous gel with possibly more than 20 wt% water. An attempt to determine the water content in sub‐μm framboids indicates that additional calibration and contamination issues must be addressed before a safe conclusion can be drawn, but hints at elevated water content as well. The high water content in fibrous magnetite, expected to be among the first minerals to crystallize at low water–rock ratio, points to the control of water content by local conditions of magnetite precipitation rather than large‐scale alteration conditions. Systematic lithological variations associated with water‐rich and water‐poor magnetite suggest that the global context of alteration may be better understood if local water concentrations are compared with millimeter‐scale distribution of the various morphologies of magnetite. Finally, the high water content in the magnetite precursor gel indicates that the initial O isotopic composition in alteration water must not have been very different from that of the earliest magnetite crystals. [ABSTRACT FROM AUTHOR]

Author(s): P. Beck (corresponding author) [1]; Ph. Gillet [1]; A. El Goresy [2]; S. Mostefaoui [2] The accretion of the terrestrial planets from asteroid collisions and the delivery to the [...]

Introduction: Ultra Carbonaceous Antarctic MicroMeteorites (UCAMMs) are sub-millimeter extraterrestrial particles with high abundance of organic matter and low abundance of minerals (C/Si ? 10 - 103), identified independently in the French and Japanese micrometeorite collections [1-6]. The organic matter in UCAMMs present high N/C ratios ranging from 0.02 to 0.2 [2, 7] and can present extreme D/H ratio. The characteristics of UCAMMs suggest that they were formed by irradiation by Galactic Cosmic Rays (GCRs) of nitrogen-rich ice mantles at the surface of small icy bodies [4, 8]. We investigated the isotopic signature of light elements in the organic matter of UCAMMs to study their links with organic matter from carbonaceous chondrites and interplanetary dust particles (IDPs). We present here a summary of our recent results, including sample analyses and ice irradiation experiments that aim at synthesizing analogs of the organic matter in UCAMMs. NanoSIMS analyses of UCAMMs: the H, C and N isotopic compositions of the 4 UCAMMs DC06-05-94 (DC94), DC06-07-18 (DC18), DC06-14-309 (DC309) and DC06-04-43 (DC43) were analyzed by nanoscale secondary ion mass spectrometry (NanoSIMS) at the Carnegie Earth and Planets Laboratory, the Museum National d'Histoire Naturelle and the Institut Curie [9]. The 4 UCAMMs do not exhibit similar isotopic compositions, with δD bulk values ranging from 1000‰ to 9000‰, δ13C from -90‰ to 30‰ and δ15N from -120‰ to 270‰. Each UCAMM is characterized by isotopic heterogeneities, typically at scales of a few μm [9]. Ice irradiation experiments: We performed ice irradiation experiments during 3 sessions in 2019, 2020 and 2021 at GANIL (Caen, France) [10], using the IGLIAS experimental setup connected to the IRRSUD ion beam (0.5-1 MeV/u). We formed 10μm - thick ice films by gas condensation on IR-transparent windows cooled down to 10K [8, 11]. The ice films consisted in one layer of isotopically labeled ice (with D, 15N and/or 13C-rich ice) between 2 layers of isotopically unlabeled ice (14N2-12CH4 or 14NH3-12CH4), forming an ice sandwich. The labeled layer accounted for 1% to 4% of the total thickness. Ice sandwiches were subsequently irradiated by heavy ions and slowly warmed up to the room temperature to obtain refractory organic residues. The residues, exhibiting an IR signature comparable to that of the organic matter in UCAMMs [8], were subsequently analyzed by NanoSIMS at the Institut Curie, to map the H, C and N isotopic heterogeneities. This study shows that the ion-processing of ice sandwiches made of N2-CH4 form an organic refractory residue that keeps the large isotopic heterogeneities of the initial ice sandwich, while that of NH3-CH4 ice sandwiches appears less favorable to the formation of isotopic heterogeneities. Extreme isotopic heterogeneities at low scale were observed in organic residues, indicating that local preservation of the initial ice sandwich composition can occur, maybe related to sporadic events during the annealing of the ice films. Results and discussion: These irradiation experiments demonstrate the possibility to form large micron-scale isotopic heterogeneities in organic residues from multilayer, isotopically heterogeneous, ice precursors. The organic matter of UCAMMs can thus have formed by irradiation by GCRs of isotopically heterogeneous ice mantles. Numerical models of the evolution of the early solar system predict the existence of gaseous reservoirs isotopically fractionated in H, C and N at different locations in the protoplanetary disk [12, 13]. The parent body/bodies of UCAMMs may have inherited from these fractionated reservoirs, condensed on its/their surface under the form of ice mantles. The diversity of isotopic signatures from one UCAMM to another also suggest that UCAMMs do not have anomalies inherited from one single parent gaseous reservoir. Further investigations on the correlation of elemental and isotopic ratios in the organic matter of UCAMMs will bring new insights to better constrain the characteristics of the parent reservoirs of UCAMMs. Acknowledgments: This work was funded by contract ANR-18-CE31-0011, CNES (MIAMI2), DIM-ACAV+ (C3E), CNRS-INSU/IN2P3 (PNP). The work at CONCORDIA Station (Projet#1120) was supported by IPEV and PNRA. [ABSTRACT FROM AUTHOR]

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: High pressure minerals from meteoritic shock melt veins are key to understand the collisional history of the Solar System. The L chondrites, the most shocked meteorites [1], present abundant shock melt veins from which we can retrace their history. To this day, their family of origin is still debated. The shock timescale of 7 chondrites was measured to deduce their parent body diameters. Moreover, we use tuite, a high pressure phosphate mineral to perform U-Pb datation by SIMS. We find a bimodal distribution of ages, which match closely the ages previously obtained for Creston and Novato, two other shocked L6 chondrites [2]. Samples and Methods: Seven samples were first studied by optical microscopy and Raman spectroscopy to identify high pressure (HP) polymorphs. Scanning Transmission Electron Microscopy (STEM) was then used to study microstructures and transformation/growth mechanisms. The EDX was used to locate eligible minerals for datation (phosphates). Combined STEM-EDX (UMET, Lille, France) and NanoSIMS (MNHN, Paris, France) chemical maps were finally collected on the same FIB sections in order to compare these two analytical approaches and produce chemical maps. The U and Pb isotope concentrations where then measured on the identified tuite grains with the help of a Cameca IMS 1280 LG SIMS (CRPG, Nancy France) for datation. Results: Multiple high pressure textures were observed in all seven samples. Polycristalline assemblages of ringwoodite are typically the dominant texture, but more exotic textures were also found. Some meteorites present ringwoodite as lamellae inside olivine crystals, whereas others seem to present an assemblage of MgSiO3 glass with akimotoite crystallites. Both these textures allowed us to investigate elemental diffusion induced by structural changes. We therefore calculated shock timescales following the methods described in [3,4]. For all our samples, assuming a temperature of 2400K [5], shock timescales ranging between 0.5 and 20 seconds were derived. The meteorites that do not contain ringwoodite lamellae have significantly higher shock timescales, between 11 and 16 seconds. These larger shock timescales were caused by an impact between larger bolides, including a parent body of at least 150km wide. This is significantly higher than parent-bodies with diameters around 70km required by the other group. In almost all meteorites, we find tuites inside the shock melt veins. The meteorites that do not contain tuite have at least shocked apatites and whitlockites, with shifted Raman spectra indicating a change in structure. We date both the host rock apatites and the shock vein phosphates. This allows us to obtain conclusive collision ages from a normal concordia diagram for two of our samples, one of each group. The tuites record collisions ages of 461+-57Ma for the group with the largest parent body, and 650+-160Ma for the group with the smaller parent body. The host rock minerals record upper intercepts of 4481Ma in both meteorites. Conclusion: Shocked L chondrites seem to define two groups, which are texturally different and appear to have a completely different history. A smaller, 70km-wide parent body exploded first (650 Ma ago) and yielded most of the shocked meteorites, and a larger one exploded in the cataclysmic collision known today as the "L chondrite parent body breakup" 470Ma ago. The upper intercept of 4481Ma could date the early separation of the original L chondrite parent body into different families. [ABSTRACT FROM AUTHOR]

- We report the 53Mn-53Cr systematics of three dolomite grains from two different CI1 clasts contained within the Kaidun meteorite breccia. Three internal isochrones result in initial 53Mn/55Mn ratios of (4.2 ± 0.4) × 10−6, (4.6 ± 1.3) × 10−6, and (5.2 ± 1.1) × 10−6. These initial values are consistent with those measured for dolomite in the Orgueil CI1 chondrite (; ) but significantly lower than the initial ratio determined by from a combination of different carbonate types within various lithologies of the Kaidun meteorite. We construct an accretion scenario for the Kaidun breccia by comparing the mineralogy and formation time scales of carbonates in the Kaidun CI1 lithologies to the analogous ones of the CI1 chondrite Orgueil. In Orgueil, dolomite precipitation precedes the formation of the first bruennerite grains by a few million years (; ). As the CI1 clasts in Kaidun lack breunnerite grains, and considering that aqueous alteration occurred prior to reaccretion of the various clasts onto the Kaidun parent body (e.g., ), we hypothesize that after rapid accretion and early aqueous alteration occurring within the first approximately 4 Myr after solar system formation, impact disruption of several asteroids and their reassembly into the Kaidun parent asteroid was complete within an additional approximately 2 Myr. This confirms that aqueous alteration, impact, and reaccretion of material in the asteroid belt were early processes that began contemporaneously with chondrule formation. [ABSTRACT FROM AUTHOR]

Primordial carbon delivered to the early earth by asteroids and meteorites provided a diverse source of extraterrestrial organics from pre-existing simple organic compounds, complex solar-irradiated macromolecules, and macromolecules from extended hydrothermal processing. Surface regolith collected by the Hayabusa2 spacecraft from the carbon-rich asteroid 162173 Ryugu present a unique opportunity to untangle the sources and processing history of carbonaceous matter. Here we show carbonaceous grains in Ryugu can be classified into three main populations defined by spectral shape: Highly aromatic (HA), Alkyl-Aromatic (AA), and IOM-like (IL). These carbon populations may be related to primordial chemistry, since C and N isotopic compositions vary between the three groups. Diffuse carbon is occasionally dominated by molecular carbonate preferentially associated with coarse-grained phyllosilicate minerals. Compared to related carbonaceous meteorites, the greater diversity of organic functional chemistry in Ryugu indicate the pristine condition of these asteroid samples., (© 2024. This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply.)

Enrichment or depletion ranging from -40 to +100% in the major isotopes 16 O and 24 Mg were observed experimentally in solids condensed from carbonaceous plasma composed of CO 2 /MgCl 2 /Pentanol or N 2 O/Pentanol for O and MgCl 2 /Pentanol for Mg. In NanoSims imaging, isotope effects appear as micrometer-size hotspots embedded in a carbonaceous matrix showing no isotope fractionation. For Mg, these hotspots are localized in carbonaceous grains, which show positive and negative isotopic effects so that the whole grain has a standard isotope composition. For O, no specific structure was observed at hotspot locations. These results suggest that MIF (mass-independent fractionation) effects can be induced by chemical reactions taking place in plasma. The close agreement between the slopes of the linear correlations observed between δ 25 Mg versus δ 26 Mg and between δ 17 O versus δ 18 O and the slopes calculated using the empirical MIF factor η discovered in ozone [M. H. Thiemens, J. E. Heidenreich, III. Science 219, 1073-1075; C. Janssen, J. Guenther, K. Mauersberger, D. Krankowsky. Phys. Chem. Chem. Phys 3, 4718-4721] attests to the ubiquity of this process. Although the chemical reactants used in the present experiments cannot be directly transposed to the protosolar nebula, a similar MIF mechanism is proposed for oxygen isotopes: at high temperature, at the surface of grains, a mass-independent isotope exchange could have taken place between condensing oxides and oxygen atoms originated form the dissociation of CO or H 2 O gas., Competing Interests: The authors declare no competing interest., (Copyright © 2021 the Author(s). Published by PNAS.)

Pristine meteoritic materials carry light element isotopic fractionations that constrain physiochemical conditions during solar system formation. Here we report the discovery of a unique xenolith in the metal-rich chondrite Isheyevo. Its fine-grained, highly pristine mineralogy has similarity with interplanetary dust particles (IDPs), but the volume of the xenolith is more than 30,000 times that of a typical IDP. Furthermore, an extreme continuum of N isotopic variation is present in this xenolith: from very light N isotopic composition (delta(15)N(AIR) = -310 +/- 20 per thousand), similar to that inferred for the solar nebula, to the heaviest ratios measured in any solar system material (delta(15)N(AIR) = 4,900 +/- 300 per thousand). At the same time, its hydrogen and carbon isotopic compositions exhibit very little variation. This object poses serious challenges for existing models for the origin of light element isotopic anomalies.

The bulk of the comet 81P/Wild 2 (hereafter Wild 2) samples returned to Earth by the Stardust spacecraft appear to be weakly constructed mixtures of nanometer-scale grains, with occasional much larger (over 1 micrometer) ferromagnesian silicates, Fe-Ni sulfides, Fe-Ni metal, and accessory phases. The very wide range of olivine and low-Ca pyroxene compositions in comet Wild 2 requires a wide range of formation conditions, probably reflecting very different formation locations in the protoplanetary disk. The restricted compositional ranges of Fe-Ni sulfides, the wide range for silicates, and the absence of hydrous phases indicate that comet Wild 2 experienced little or no aqueous alteration. Less abundant Wild 2 materials include a refractory particle, whose presence appears to require radial transport in the early protoplanetary disk.

The Stardust spacecraft collected thousands of particles from comet 81P/Wild 2 and returned them to Earth for laboratory study. The preliminary examination of these samples shows that the nonvolatile portion of the comet is an unequilibrated assortment of materials that have both presolar and solar system origin. The comet contains an abundance of silicate grains that are much larger than predictions of interstellar grain models, and many of these are high-temperature minerals that appear to have formed in the inner regions of the solar nebula. Their presence in a comet proves that the formation of the solar system included mixing on the grandest scales.

Hydrogen, carbon, nitrogen, and oxygen isotopic compositions are heterogeneous among comet 81P/Wild 2 particle fragments; however, extreme isotopic anomalies are rare, indicating that the comet is not a pristine aggregate of presolar materials. Nonterrestrial nitrogen and neon isotope ratios suggest that indigenous organic matter and highly volatile materials were successfully collected. Except for a single (17)O-enriched circumstellar stardust grain, silicate and oxide minerals have oxygen isotopic compositions consistent with solar system origin. One refractory grain is (16)O-enriched, like refractory inclusions in meteorites, suggesting that Wild 2 contains material formed at high temperature in the inner solar system and transported to the Kuiper belt before comet accretion.

Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples.