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The X-ray spectometer onboard the Near Earth Asteroid Rendezvous spacecraft will measure X-rays from the surface of 433 Eros in the energy region 0.7-10 keV. Detection of characteristic K[Alpha] line emissions from Mg, Al, Si, Ca, Ti, and Fe will allow the determination of surface abundances of these geologically important elements. Spatial resolution as fine as 3 km will be possible for those elements where counting statistics are not a limiting factor. These measurements will make it possible to relate Eros to known classes of meteorites and reveal geological processes that occurred on Eros. The calibration measurements and analysis procedures presented here are necessary for the reduction and analysis of the X-ray data to be collected during one year of orbital operations at Eros. [C] 2000 Academic Press Key Words: asteroids; instrumentation; X-rays; NEAR.

Introduction: Macromolecular organic matter in primitive small body materials is one of the reliable indicators to determine the chemical evolution in the early Solar System. JAXA's Hayabusa2 mission explored the carbonaceous asteroid Ryugu and collected its surface materials [1]. On December 6, 2020, the asteroid sample was returned to the Earth. Through the curatorial work at JAXA, it was reported that the Ryugu samples contain high abundances of hydrous minerals and organic matter [2, 3]. Afterward, the initial sample analysis has started from June 2021 to classify and characterize the Ryugu samples in the context of the Solar System formation. In order to uncover the significance of organic matter on C-type asteroid, the Initial Analysis Organic Macromolecule team unveiled the chemical, isotopic, and morphological compositions of macromolecular organic matter from the Ryugu samples. Samples and Methods: Chamber A aggregates (A0108) and Chamber C aggregates (C0109) collected at the first and second touchdown sites, respectively, have been analyzed. The individual intact grains from A0108 and C0109 range from 200 to 900 µm in size. Additional aggregates from Chamber A (A0106) and Chamber C (C0107) were transferred from the Soluble Organic Molecules team after their water and solvent extractions, and were treated with 6M HCl and 1M HCl/9M HF to yield insoluble organic matter (IOM) at Hiroshima University [4]. The main stream of the analytical procedures included a combination of µ-FTIR, µ-Raman spectroscopy, synchrotron-based STXMXANES, STEM-EELS-EDS, AFM-IR, NanoSIMS [4]. Additional protocols by Xe-PFIB, TXM, XRF, Solid-state 1H and 13C NMR, ToF-SIMS, Visible spectroscopy, and AFM have been included for the latter half of the initial analysis. EA-IRMS and noble gas isotope analysis of Ryugu IOM were also performed in collaboration with Soluble organic molecule (SOM) team [5] and Volatile team [6], respectively. Results and discussion: Macromolecular organic matter were abundant and has complex structures consisting of aromatic carbons, aliphatic carbons, ketones and carboxyls [7, 8]. The functional group compositions are typically seen in IOM from CI and CM chondrites. The functional group variations correlated with the morphologies of nanosized organic matter; organic nanoglobules and nanoparticles are aromatic-rich, while organic matter mixed with Mgrich phyllosilicate matrix and carbonates are IOM-like or diffuse carbon [8, 9]. The observed functional group diversity is likely influenced by aqueous evolution on the asteroid parent body without significant heating event. The dD distributions of Ryugu IOM from the Ryugu samples were within the dD range of CM, CI, and Tagish Lake chondrites [10]. The d15N of bulk C and insoluble organics from the Ryugu samples showed similar values to those from CI chondrites [10]. Extreme D and/or 15N enrichments or depletions in some carbonaceous grains could possibly have been derived from the solar nebula or protosolar molecular cloud. A very small fraction of carbonaceous particles show anomalous carbon isotopes including presolar SiC grains [11]. Ryugu organic matter likely resulted from heterogeneous aqueous processing that occurred on carbonaceous asteroids from the common primordial materials formed at an earlier stage of the solar nebula. These results proved the direct link between macromolecular organic matter in the carbonaceous asteroid and that in primitive carbonaceous chondrites. [ABSTRACT FROM AUTHOR]

Introduction: Due to their small sizes, analytical challenges have impeded fine-grained, extraterrestrial materials and their nanoscale components from being fully characterized. Presolar oxides can range in size from a few micrometers down to <30 nm and have been found to be the carriers of 54Cr isotopic anomalies, with the smallest grains carrying the largest anomalies [1-3]. Unfortunately, even with the spatial resolution afforded by NanoSIMS, measurements of the isotopic compositions of grains <100 nm across can suffer from significant dilution effects from nearby material and are, therefore, only lower limits and the amount of dilution must be modelled to obtain better estimates [3]. Although frequently used in materials science, atom probe tomography (APT) has only recently begun to be applied in planetary science and cosmochemistry (e.g., [4, 5]). While NanoSIMS has a much higher mass resolving power, APT generates quantitative atom-by-atom elemental and isotopic distributions in 3D with a high sensitivity (~80% detection efficiency) at near-atomic spatial resolution. APT also detects all mass/charge-state ratios <600 Da, allowing for the possibility of additional correlated anomalies to be discovered within a grain, which may have been previously missed. APT is therefore a powerful technique for studying fine-grained materials, such as presolar oxides by providing undiluted local elemental and isotopic compositions of each grain with nm-scale spatial resolution, so that subgrains, inclusions, and other compositional heterogeneities (e.g., gradients) can be detected. Samples and Methods: APT analyses require laborious sample preparation, particularly for site-specific sub-µm grains. For this study, we have developed protocols adapted from traditional APT sample preparation methods [6] for lifting out and preparing nano-tips that target sub-µm grains for APT analyses. Samples were prepared with the TESCAN LYRA3 FIB-SEM at the University of Chicago. The nano-tips were analyzed with the LEAP5000XS tomograph at Northwestern University. Prior to analyzing bona fide presolar oxides, we have analyzed a ~1.5 µm meteoritic chromite from the CI chondrite Orgueil. This grain was also analyzed by energy dispersive spectroscopy (EDS) prior to APT. Presolar oxides were previously identified in this residue by NanoSIMS [2]. We also analyzed three nanotips prepared from a natural chromite reference material, UWCr-3, from a South African chromitite [7]. Results and Discussion: APT confirms that the UWCr-3 chromite standard is homogenous in all elements at the nm-scale as confirmed by a nearest-neighbor statistical analysis. Cr2+, CrO+,2+, CrO2+,2+, and CrO3+ molecular ions were detected, but no peaks associated with Cr3O+ or Cr2O5+ were observed as seen in synthetic chromite [8]. In NanoSIMS, Cr isotopic ratios must be corrected for isobaric overlaps from Fe, where 54Fe+ overlaps with 54Cr+ can be corrected by assuming a fixed 54Fe/56Fe ratio. This can be mitigated in APT, where the formation of molecular ion species is element-dependent. While ion species with different isotopes of the same element will have the same field evaporation behavior (e.g., 53CrO vs 54CrO), ion species of the same mass but from different elements may not (e.g., 54CrO vs 54FeO). Notably, we found that the peaks due to CrO2+ ions in the 82-86 Da mass region of UWCr-3 correspond to the terrestrial abundances in all isotopes, allowing for measurements of 54Cr/52Cr ratios. Peaks due to CrO2+ ions in the 33-35 Da mass region also correspond to natural abundances in all peaks when areas with Ga ion implantation are removed from the mass spectrum. Some mass regions have isobaric overlaps in only one or two Cr peaks, so the remaining peak ratios can be used for verification. The meteoritic chromite from Orgueil is also homogenous in all elements at the nm-scale and has a nearly identical mass spectrum to the UWCr-3 chromite, sharing all peaks with only minor differences in relative peak intensities and peak shapes, likely due to their small differences in elemental abundances (UWCr-3 is more Cr- and Mg-rich and more Fe-, Al-, and Ti-poor) and different operating conditions, respectively. As with UWCr-3, the peaks due to CrO2+ and CrO2+ ions correspond to natural abundances in all peaks. We were also able to confirm the Orgueil chromite is isotopically normal in Mg, Ti, and Fe. This is not unexpected for a meteoritic chromite of this size. Preparations of meteoritic chromites <200 nm in size are currently underway. [ABSTRACT FROM AUTHOR]

Introduction: Given the long timespan between the stellar birth and recovery of presolar grains in the laboratory, presolar grains could have been chemically altered so that their measured isotopic signatures would reflect mixing between stellar, asteroidal, and terrestrial compositions. Potential asteroidal and terrestrial contaminations, therefore, complicate the interpretation of presolar grain data and thus limit the scientific value of presolar grains in constraining astrophysical processes. In particular, terrestrial and/or asteroidal N contamination is suspected to have caused the close-to-terrestrial 14N/15N ratios observed in the majority of presolar graphite. The substantial effect of N contamination has been confirmed for presolar silicon carbide (SiC) in the study of [1], in which the authors observed significantly increased 14N/15N ratios for mainstream (MS) SiC grains after an extended period of ion sputtering of the grain surfaces. Here, we report 14N/15N ratios for additional SiC grains of diverse groups following the study of [1]. Samples and Experiments: The SiC grains in this study were extracted from Murchison (CM2) using the CsF dissolution technique described in [3]. The C, N, and Si isotope ratios were measured with the WashU NanoSIMS 50 ion microprobe using standard analytical procedures. A Cs+ beam of ~9 pA and ~1 pA was used for presputtering and analysis, respectively. All the isotope data were collected in imaging mode at a spatial resolution of ~100 nm. After C and Si isotope analyses, we further presputtered the grains for a few minutes until the CN-/Si-ratio becomes steady prior to N isotope analyses. Results and Discussion: We have measured a total of 475 SiC grains (1.5 μm in size on average) for their C and Si isotopes, including 388 MS (81.7%), 26 AB (5.5%), 21 X (4.4%), 20 Z (4.2%), 17 Y (3.6%), and three putative nova (0.6%) grains. The overabundance of X grains in our sample results from a sample selection bias because we prioritized the analyses of Mg-rich SiC grains - X grain candidates (see [4] for details). We collected coordinated N isotope data for 42 of the grains, as shown in Fig. 1. MS, Y, and Z Grains: While it is a sample selection bias that our MS grains show lower 12C/13C ratios than the literature data, the higher 14N/15N ratios observed in our MS/Y/Z grains are consistent with the results of [1], pointing to a significant contribution of N contamination to the literature N isotope data. Although the literature data reveal a similar range of 14N/15N ratios for MS, Y, and Z grains [2], our four Z grains all exhibit high 14N/15N ratios, which differs significantly from the MS grains and implies different stellar origins. AB Grains: Recent statistical analyses [e.g., 5] of literature data pointed out a weak correlation between 13C and 15N for AB grains. This correlation is strengthened by our new AB grain data and points to the important role of hot CNO burning (at T > ~1' 108 K) in governing the C and N isotope ratios of AB grains. X Grains: Our new data show a clear separation of the X from MS/Y/Z grains in Fig. 1, in contrast to an overlap between these groups in the literature data that could have been caused by N contamination. Our X grains with 12C/13C <100 seem to show lowered 14N/15N ratios, pointing to the 'nova' grain region. This provides further support to the proposed supernova origin of 'nova' grains [6]. Conclusions: Our analytical procedure allowed suppressing sampling nitrogen contamination. The 'cleaner' N isotope ratios of our SiC grains are more representative of intrinsic stellar signatures and revealed several new trends and features. More data are on the way to increase the statistics prior to the start of the meeting. [ABSTRACT FROM AUTHOR]

Introduction: Mainstream (MS) grains - the dominant population (>90%) of presolar SiC - are believed to have originated from low-mass asymptotic giant branch (AGB) stars with close-to-solar metallicities. In comparison, presolar Y and Z grains are two minor populations (~1-5% each) of presolar SiC. The main difference between Y/Z and MS grains is that the former are generally more depleted in 29Si/28Si and enriched in 30Si/28Si than the latter. In addition, while MS and Z grains generally have lower-than-solar 12C/13C ratios, Y grains are defined as grains with 12C/13C = 100. In some Y and Z grains, large 30Si/28Si and 50Ti/48Ti excesses were observed, suggesting that these two minor types came from AGB stars with 1/3-1/2 Z8 [1]. However, the low-metallicity AGB stellar origins of Y and Z grains are challenged by the indistinguishable Mo isotopic compositions of MS, Y, and Z grains, in contrast to the varying Mo isotopic patterns predicted by AGB models for low-mass AGB stars of different metallicities [2]. Thus, the stellar origins of Y and Z grains remain enigmatic. Here, we provide the first piece of evidence that Y and Z grains show heavy-element isotopic compositions different than MS grains, namely higher 88Sr/87Sr and 138Ba/136Ba ratios. Results and Discussion: Light- and heavy-element isotopic data were collected with the Carnegie NanoSIMS 50L ion microprobe and the University of Chicago's CHILI instrument, respectively. Preliminary Sr and Ba data were reported in [3]. We obtained sufficiently precise Sr and Ba isotopic data for 11 Y and seven Z grains. We found that the Y and Z grains show higher 88Sr/87Sr (Fig. 1) and 138Ba/136Ba ratios when compared to MS grains data from the literature. The Si, Sr, and Ba isotopic compositions of our Y and Z grains can be consistently explained if the amount of 13C - the major neutron source for the s-process - is reduced by a factor of 1.0-7.8 (D6 -D1.5 cases) in FRANEC Torino AGB models for 0.15-0.50 Z8 AGB stars with respect to those (D1.5-U1.3 cases) required by MS grains for a 1.0 Z8 AGB star (Fig. 1). This scenario is in line with the previous finding based on Ti isotopes [2], but it fails to explain the indistinguishable Mo isotopic compositions of MS, Y, and Z grains. Also, our inferred amounts of 13C (D6-D1.5 cases) for the parent low-metallicity AGB stars of Y and Z grains, lie within those inferred for low-metallicity AGB stars based on stellar observations [4] but are, on average, relatively low. The unrepresentativeness of the parent stars of Y and Z grains may stem from the fact that the grains originated from a limited number of ancient low-metallicity stars, given that the abundance of Y and Z grains is more than an order of magnitude lower than the abundance of MS grains in primitive meteorites. Conclusions: The higher 88Sr/87Sr and 138Ba/136Ba ratios of our Y and Z grains provide strong support to the suggestion that these two minor types originated from low-metallicity AGB stars, which, however, is challenged by the indistinguishable Mo isotopic compositions of MS, Y, and Z grains. Since the varying Mo isotopic patterns predicted by AGB models for stars with different metallicities result mainly from the energy dependences of 95,96,97,98Mo(n,?) cross-sections [2], new cross-section measurements are needed. [ABSTRACT FROM AUTHOR]

Introduction: The JAXA Hayabusa2 spacecraft collected surface regolith from C-type asteroid (162173) Ryugu during two separate touchdown events (stored in sample chambers A and C, respectively). Preliminary examinations of these samples by JAXA Curation [1] and Hayabusa2 Initial Analysis Teams [2,3] indicate a strong connection to Ivuna-type (CI) carbonaceous chondrites, in agreement with orbital-based near-infrared spectroscopy of the asteroid surface [4]. Scanning-transmission X-ray microscopy (STXM) and X-ray absorption near-edge structure spectroscopy (XANES) of Ryugu insoluble organic matter (IOM) residues also indicates a strong similarity with other aqueously-altered carbonaceous chondrites, specifically CI, CM, and the C-ungrouped Tagish Lake [3,5]. However, these studies also reported the presence of carbonaceous sub-grains with functional group distributions previously unseen in these chondrite groups. Here we further investigate the differences in organic macromolecular material between Ryugu and CI chondrites using correlated XANES, transmission electron microscopy (TEM), and nanoscale secondary ion mass spectroscopy (NanoSIMS). Samples and Methods: Ryugu regolith grains were prepared from aggregate samples A0108 (from Chamber A) and C0109 (from Chamber C). Samples were either prepared by sulfur embedding and ultramicrotomy or by a focused ion beam (FIB) liftout procedure, and a corresponding suite of samples were prepared from fragments from the CI chondrite Orgueil. STXM/XANES data were acquired at beamline 5.3.2.2 and 5.3.2.1 at the Advanced Light Source, or beamline BL-19 at the Photon Factory. Subsequently, TEM characterization was performed with an aberration-corrected Nion UltraSTEM 200-X at the U.S. Naval Research Laboratory using a 60 keV beam. Nitrogen and carbon isotopes of FIB section A0108-3 were also measured with a Cameca NanoSIMS 50L at the Carnegie Institution for Science. Results and discussion: The functional chemistry distribution of carbonaceous grains in Ryugu samples can be categorized into three main groups based on their XANES spectral shapes. The first two, IOM-like and Highly Aromatic, match the functional group diversity typically observed in nanoglobules from carbonaceous chondrites [6]. Likewise, carbonaceous grains in the Orgeuil samples also produced XANES spectra that matched either of these spectral "fingerprints". In contrast, Ryugu samples contained carbonaceous grains with a third spectral shape, characterized by a large, narrow peak at 285 eV (due to C=C bonds), little to no peak at 286.7 eV (ketone C=O), and broad intensity at 288-289 eV (a combination of aliphatic C-C and carboxyl COOH). This Aromatic spectral shape could be consistent with a macromolecular structure composed of small, highly-modified, polyaromatic moieties connected by long aliphatic side chains, which could have been generated on the Ryugu parent body during aqueous alteration. By correlating NanoSIMS, TEM and XANES data from FIB section A0108-3, we hope to glean information regarding the origin(s) of these three XANES spectral shapes. 15N/14N isotope ratios of most of the IOM-like and Aromatic carbonaceous grains in this FIB section were all anomalous relative to the bulk value of the section (i.e., diffuse organic matter interspersed within the fine-grained matrix). The two Highly Aromatic grains in the section contained slightly negative d15N/14N values (-89±58 and -120±66), indicating these grains formed from distinct reservoirs of organic precursors, than the IOM-like and Aromatic grains. These data also suggest that the presence of the Aromatic functional chemistry profile is unlikely to come from addition of a separate population of organic precursor material, but rather was generated on the parent body in combination with IOM-like products. [ABSTRACT FROM AUTHOR]

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: Insoluble organic matter in carbonaceous chondrites has been studied extensively in order to constrain the history of the evolution of organic carbon in the solar system and the role of asteroids in delivery of prebiotic chemistry to the early Earth [1]. These studies have shown both that the organic matter can be considerably altered by hydrothermal processing on the asteroid, and that D and 15N isotopic composition indicators of outer nebula or molecular cloud origin can survive moderate levels of such parent body alteration. As revealing as the study of meteoritic organics has been, all such studies suffer from sampling biases associated with the factors necessary for meteorites to have reached Earth from the parent asteroid and survived atmospheric entry and the exposure to the terrestrial atmosphere. The direct laboratory study of organic matter in returned asteroid regolith, presently from Ctype asteroid Ryugu, and in future from asteroid Bennu, provides an unprecedented opportunity to examine asteroid organic matter with established provenance and minimal artifacts from terrestrial alteration. As part of the Hayabusa2 initial analysis of Ryugu samples, we have used to analytical transmission electron microscopy to study the microstructure, elemental composition, and functional chemistry of Ryugu insoluble organic matter, and the relationship to fine-grained minerals. Methods: The samples for these studies included whole particles, extracted focused ion beam (FIB) crosssections, microtomed slices of particles, and microtomed slice of insoluble organics isolates (IOM) from both the Chamber A and Chamber C collections. This range of samples and preparation methods allowed for investigation of a wide range of different aspects of the samples, such as the greatest preservation of mineral-organic textural relationships and possible soluble components in FIB sections, and observation of the few-nm to sub-nm features in the microtomed samples. Transmission electron microscopy studies were performed with two microscopes: a JEOL 2200FS operated at 200 kV for bright field imaging, and a Nion UltraSTEM-X operated at 60 kV and 200 kV for annular dark field imaging, energy dispersive x-ray spectroscopy (EDS) of the elemental composition and electron energy loss spectroscopy (EELS) of the C K-edge fine structure and plasmon regions. The EDS and EELS data were collected with Bruker Xflash 100 and Gatan Enfinium spectrometers attached to the UltraSTEM, respectively. Results: The results of the electron microscopy studies of the organic matter confirm a strong link between the Ryugu regolith samples and carbonaceous chondrites in general and are most similar to observations of organic matter in CI chondrites such as Orgueil that have undergone low temperature aqueous alteration. Diffuse organic carbon is abundant, intermixed with μm to sub-μm minerals, including Mg-rich phyllosilicates, magnetite, carbonates and sulfides. Solid and hollow nanoglobules are present as isolated particles, most commonly < 400 nm diameter, and in clusters, with a few individual nanoglobules extending to as large as 2 μm. Nanodiamonds are also present in clusters surrounded by amorphous carbon. Two FIB sections revealed secondary minerals with interior vesicles. One of these sections, sample A0108-3, transected vesicles in a calcite grain that contain diffuse organics and nanoscale silicates and sulfides. The other (AP002-g01T5) preserved closed vesicles in a pyrrhotite grain that contain C-rich fluids. The EELS observations of the C bonding indicate that the diffuse carbon interspersed in Mg-rich phyllosilicates has a strong absorption feature at 290.4 eV associated with CO3 groups, and varying amounts of other functional groups, including aromatic, ketone, aliphatic and carboxyl. The functional group chemistry of the nanoglobules includes particles that are dominated by aromatic groups (285 eV), and others with significant amounts of ketone (286.5) and carboxyl (288.5) groups. Finally, some aromatic carbon is present as coatings on nanoscale secondary minerals, including Fe and Cu-bearing sulfides. Taken together, the results demonstrate complex records of preaccretionary and parent body processing in the Hayabusa2 samples from Ryugu. [ABSTRACT FROM AUTHOR]

Introduction: Presolar grains are tiny (nm- to low μm-sized) and rare dust grains that formed around dying stars and were part of the original building blocks of the Solar System. They were trapped and preserved in primitive chondrite matrices and can be identified by their highly anomalous O or C isotopic compositions. Their study allows unique insights into galactic, stellar, interstellar, and asteroidal evolutionary processes. In 2020, JAXA's Hayabusa2 spacecraft returned over 5 g of material from C-type asteroid (162173) Ryugu. Preliminary chemical and isotopic data suggests that Ryugu samples experienced extensive aqueous alteration and closely resemble the CI chondrite group [1]. We aim to characterize and ascertain the inventory of preserved presolar grains in Ryugu samples, and compare their abundances and characteristics to carbonaceous chondrites. Methods: We used the Carnegie NanoSIMS 50L to search for presolar grains in thin sections of Ryugu (A0058- 2) and Ivuna (CI1). 12,13C-, 16,17,18O-, 28Si- and 27Al16O- ion images for contiguous 10Ã--10 μm2-sized frames were collected in multi-collection mode with a Cs+ primary beam (~0.7 pA), and analyzed via standard methods [2]. We further analyzed C isotopic compositions of microtomed Ryugu samples (A0108-8, -9, -11, -14; C0109-8, -11, -19) and Ryugu grains (A0108-13, C0109-2) that were pressed into Au foils, including grains from both touchdown sites (Chambers A and C). Presolar SiC grains were identified by their highly C-anomalous isotopic compositions, associated with 28Si [2]. Sixteen C-anomalous grains from all Ryugu samples were remeasured for N and Si isotopes. Results: In the Ryugu thin section, we mapped a total area of 18,400 μm2 and identified 1 presolar oxide (Fig. 1a), 8 SiC grains and 8 grains that may be SiC or graphite. Another 10 C-anomalous presolar grains were detected in the other Ryugu samples (~10,000 μm2 area). In the Ivuna thin section, a total area of 23,100 μm2 was analyzed, containing 12 SiCs and 5 grains that may be SiC or graphite. The abundances of all C-anomalous presolar grains with 1σ uncertainties is 32 !" #$ ppm in Ryugu (combined from all samples) and 35 !% #&& ppm in Ivuna (Fig. 1b). The Al-rich oxide (Fig. 1a) is a highly 17O-enriched Group 1 grain with a diameter of 0.26 μm. Most SiC grains have 12C/13C ratios between 13 and 69 and thus likely belong to the mainstream group, though contribution from nearby organics could dilute the extremely 13C-rich signatures of type AB grains. Discussion: Ryugu samples contain abundant C-anomalous presolar grains. Refractory O- and C-rich phases survived the pervasive aqueous alteration that Ryugu has experienced, whereas presolar silicates were probably destroyed. The identical SiC abundance found here for Ryugu and Ivuna, which also agrees with literature data acquired by different methods for Orgueil [3, 4], further supports a Ryugu-CI connection. No differences were observed between Chamber A and C grains, although statistical errors for Chamber C are large and no thin section has been analyzed thus far. [ABSTRACT FROM AUTHOR]