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NASA NTRSDate not supplied

Preservation of Previously Unsampled Primordial Isotopic Components in Ryugu and Bennu Samples

Ivuna-type (CI) carbonaceous chondrites are primitive meteorites whose relative elemental abundances closely match the solar photosphere 1 , making them critical benchmarks for the bulk chemical and isotopic composition of the planet-forming disk. Recent sample-return missions to Ryugu 2 and Bennu 3 have enabled direct laboratory analysis of these rubble-pile CI-like asteroids 4 , formed from the reaccumulated fragments of once-larger parent bodies. As such, they may retain a broader spectrum of primordial nucleosynthetic components than is preserved in known meteorites. Here, we report the nucleosynthetic compositions of silicon (μ 30 Si), magnesium (μ 26 Mg*), and iron (μ 54 Fe), three of the four most abundant planet-building elements, in samples from Ryugu and Bennu, along with the newly discovered Oued Chebeika 002 CI chondrite 5 . In contrast to the isotopic homogeneity of CI chondrites, Ryugu and Bennu preserve resolvable μ 26 Mg* and μ 30 Si heterogeneity, revealing μ 26 Mg*- and μ 30 Si-rich nucleosynthetic components not sampled in meteorites. These components may reflect the preservation of previously unsampled primordial isotopic signals, prior to thermal processing 6,7 and late infall of primordial molecular cloud material to the outer disk 8,9 . Additionally, Ryugu particle C0002 exhibits a μ 26 Mg*-poor and μ 54 Cr-rich signature, consistent with incorporation of presolar material from massive supernovae 10,11 . Ryugu and Bennu samples define one end of a μ 54 Fe–μ 30 Si array among carbonaceous asteroid materials 9 , suggesting that the isotopic compositions of these asteroidal materials reflect mixing between early disk isotopic components identified in this study and material derived from the outermost disk 9 . This observation demonstrates that materials with solar chemical abundances can nonetheless exhibit markedly distinct nucleosynthetic signatures. Thus, Ryugu and Bennu samples are critical records of nucleosynthetic diversity among carbonaceous asteroids and underscore the value of sample-return missions in accessing primitive isotopic signatures absent from meteorite collections.

Martin Bizzarro↗
NASA NTRSDate not supplied

Anomalous and Ungrouped Carbonaceous Chondrites in the US Antarctic Meteorite Collection and their Potential Relevance to Ryugu and Bennu

With two different carbonaceous asteroid sample return missions in full swing, attention has focused on what connections can be made between the asteroid samples and the wide range of carbonaceous chondrite meteorites in worldwide collections. The US Antarctic meteorite collection contains nearly 1000 carbonaceous chondrites of various types including many in well-established groups as well as ungrouped, unusual or anomalous groups [1]. Some of the latter have been included in, or are possibly related to, recently proposed new carbonaceous chondrite classifications – CA and CY chondrites [2,3]. In addition to these, there are numerous ungrouped samples that have properties intermediate between established groups (like CM and CO; [4]), distinct from any other groups [5], or have anomalous properties that might be attributable to parent body processes such as heating, fluid interaction, or impacts [6]. Some CM anomalous or ungrouped chondrites share spectral features with Ryugu, which has a small hydration peak arguably due to hydrated minerals left after either impact heating or shock in carbonaceous chondrites [7]. PCA 91008, PCA 02012, GRO 95566, and LEW 85311 are all CMs that have experienced heating or metamorphism that may be due to impacts, solar radiation, or radiogenic decay [6]. These samples all have low H contents, C/H (bulk), and low 17O [6,8] and may hold clues to understanding the mineralogy of Ryugu, or interpretations of its spectral properties. WIS 91600, on the other hand, appears to be related to several other highly altered CM [6], and shares properties with the newly proposed CY chondrites [6]. An understanding of this grouplet will also aid in the interpretation of Bennu samples which have strong hydration features. In addition, ungrouped carbonaceous chondrites may provide valuable insights into the aqueous alteration potentially recorded in Bennu and Ryugu samples; such as the relatively moderate aqueous alteration recognized and dated at 4-5 myr after CAIs in MAC 88107 (C2-ungrouped) by [9] to the extensive aqueous alteration apparent in MIL 090292 (C1-ungrouped) [10]. Finally, LON 94101/94102 is a brecciated CM chondrite with numerous lithologies. Its appearance is similar to some of the brecciated lithologies visible at the surface of Bennu and Ryugu [11]. Although CM chondrites with multiple lithologies are common (e.g., [12]), the lithologies are often difficult to resolve at the hand specimen scale and only after some detailed e-beam characterization are the subtle lithologic differences evident (e.g., [13]). LON 94102 contains visibly distinct clasts at the hand specimen scale, relatively rare for CM breccias. The largest CM chondrites by mass from the U.S. Antarctic meteorite collection may provide insights into the extent of brecciation and heterogeneity within more typical CM chondrite-like source asteroids. For example, recent curation CT scans [14] show possible clasts within in a subsplit of ALH 83100 (CM1/2) which is the largest CM chondrite or CM chondrite pairing group in the U.S. Antarctic collection with an original mass of 3.019 kg. Similar work on additional subsplits or meteorites may aid our understanding of heterogeneity within CM chondrites from Antarctica. Initial classification of CM chondrites in U.S. Antarctic meteorite collection includes preliminary pairing when petrographically similar CM chondrites that have been previously found in the same field area. The two largest CM chondrite preliminary pairing groups by mass are the ALH 83102 (CM2) pairing group with an original mass of 2.554 kg and the EET 96005 (CM2) pairing group with an original mass of 1.125 kg. However, preliminary pairing groups assigned at classification—intrinsically— do not include stones that are petrographically distinct. Rigorous pairing group studies of CM chondrites from specific field sites are needed to investigate if there is unrecognized heterogeneity in CM chondrites from Antarctica that may represent common asteroid impactors (pre-atmospheric entry asteroids/meteoroids). Detailed pairing studies have the potential to recognize initial stones with multiple lithologies and investigate if there are stones that only sample one of those respective lithologies in the collection. These groups of heated CMs, extensively hydrated CMs, intermediate between CM and CO chondrites, and brecciated samples are all potentially relevant to Bennu and Ryugu samples, where heating, hydration, and brecciation have all come into play. These bodies might also be comprised of material intermediate to CM and CO chondrites, or at least distinct from the well-established CC groups. These small and unusual groups of carbonaceous chondrites may help to unlock new information about early solar system processes and aid in the understanding of the evolution of these carbonaceous asteroids.

meteorites↗
NASA NTRS2023

PAHs, Hydrocarbons, and Dimethylsulfides in Asteroid Ryugu Samples A0106 and C0107 and the Orgueil (CI1) Meteorite

Evaluating the molecular distribution of organic compounds in pristine extraterrestrial materials is cornerstone to understanding the abiotic synthesis of organics and allows us to better understand the molecular diversity available during the formation of our solar system and before the origins of life on Earth. In this work we identify multiple organic compounds in solvent extracts of asteroid Ryugu samples A0106 and C0107 and the Orgueil meteorite using two-dimensional gas chromatography and time-of-flight high resolution mass spectrometry (GC×GC-HRMS). Our analyses found similarities between the molecular distribution of organic compounds in Ryugu and the CI carbonaceous chondrite Orgueil. Specifically, several PAHs and organosulfides were found in Ryugu and Orgueil suggesting an interstellar and parent body origin for these compounds. We also evaluated the common relationship between Ryugu, Orgueil, and comets like Wild-2; however, until comprehensive compound-specific isotopic analyses for these organic species are undertaken, and until the effects of parent body processes and Earth’s weathering processes on meteoritic organics are better understood, their parent-daughter relationships will remain unanswered. Finally, the study of organic compounds in Ryugu samples and the curation practices for the future preservation of these unvaluable materials are also of special interest for future sample return missions, including NASA’s OSIRIS-REx asteroid sample return mission.

Hayabusa2↗
NASA NTRSDate not supplied

Aqueous Alteration on the Ryugu Parent Body Constrained by Chemical Equilibrium Models

The composition of solid samples returned from the asteroid 162173 Ryugu byHayabusa2 indicates aqueous alteration of rocks that formed a parent body of Ryugu [1, 2]. As on parent bodies of carbonaceous chondrites [3-5], Ryugu materials could have went through (1) accretion of anhydrous and reduced rocky grains together with water-rich ices, (2) melting of ices in the body’s interior through release of radiogenic heat [6], and (3)aqueous alteration of rocky and organic materials that produced secondary minerals, salt- and organic-bearing water solutions, gases, and altered organic matter. Although the bulk chemical composition and major mineralogy (phyllosilicates, magnetite, pyrrhotite, carbonates, phosphates, etc.) of Ryugu [1,2]are similar to those of CI carbonaceous chondrites [3-5, 7], the lack of sulfates and a deficiency of oxygen in the returned samples suggest a distinct alteration pathway. Chondritic materials [3-5] do not indicate complete chemical equilibration though low-temperature parent body processes. However, calculations of chemical equilibria in modeling rock-water-gas type systems[e.g., 8, 9], could assess deviations of chondritic materials from equilibrium conditions and constrain partitioning of chemical elements between solid, aqueous, and gas phase for different stages of alteration. Here we constrained speciation of solid, aqueous, and gaseous phases during aqueous alteration on the Ryugu parent body through chemical equilibrium calculations.

M Yu Zolotov↗
NASA NTRSDate not supplied

Space weathering features of anhydrous minerals in fine grains from the C-type asteroid Ryugu

Materials exposed to the space environment are expected to show optically and chemically modified properties. This process is called as space weathering and is caused mainly by micrometeoroid bombardments and solar wind implantation [1]. Thus far, the space weathering of carbonaceous asteroids has not been well understood. Regolith samples were successfully recovered from C-type asteroid Ryugu by the Hayabusa mission [2]. Ryugu samples will provide insights into the ongoing space weathering of Ryugu [3]. In this study, we investigated the space weathering of anhydrous minerals including iron sulfides, magnetite, and carbonates, which are major reservoirs of volatiles including carbon, oxygen, and sulfur in Ryugu materials. We performed scanning electron microscopy (SEM) and transmission/scanning transmission electron microscopy (TEM/STEM) analysis for Ryugu samples.

Toru Matsumoto↗
NASA NTRSDate not supplied

Olivine Mineralogy of Asteroid Ryugu Samples and CI Chondrites: Further Evidence for their Common Origin

Initial analysis of asteroid Ryugu samples has revealed that they were mm-mm scale brecciamostly composed of aqueously altered phases (e.g., Mg-Fe phyllosilicates, carbonates) and showed remarkablesimilarities to CI chondrites in mineralogy and chemistry [e.g., 1,2]. Our detailed analysis of Ryugu samples hasdetected small amounts (<<1 vol.%) of unaltered silicates that would escape severe aqueous alteration [3]. Olivine isthe most abundant (>90 vol%) phase among such unaltered silicates. Although most Ryugu olivine grains aresmaller than 5 mm, they bear important information about the precursors of the parent Ryugu asteroid. In thisabstract we report additional results of olivine mineralogical study of Ryugu samples, and especially compare witholivine grains in CI chondrites (Ivuna and Orgueil) to further discuss their relationship and possible common origin.

T. Mikouchi↗
NASA NTRS2022

Lithological variation of asteroid Ryugu samples returned by the Hayabusa 2 spacecraft: Assessment from the 18 particles distributed to the initial analysis “Stone” team

JAXA’s Hayabusa2 spacecraft successfully returned~5.4g of C-type asteroid Ryugu materials on Dec. 2020 [e.g., 1] and the recovered samples were extensively analyzed by initial analysis teams and Phase2 curation teams. The reported results show that Ryugu samples are similar to CI chondritesin chemistry and mineralogy, showing evidence for aqueous alteration in the parent body [e.g., 2,3]. As a “stone” team of the initial analysis, we received 18coarse particles (>1 mm) of Ryugu samples to characterize their mineralogy and petrology. We found that the samples were breccias of mm-to-sub mm size clasts. All of the clasts are mainly composed of Mg-Fe phyllosilicates, but the alteration degree appears slightly different from one clast to another. Here we report a lithological variation of Ryugu samples to propose their reasonable lithological classification based upon different mineral assemblages and to discuss the formation and evolution of the Ryugu parent body.

Michael E Zolensky↗
NASA NTRSDate not supplied

Early Aqueous Alteration of Ryugu’s Parent Body – Insight from In-situ Isotopic Analyses

The Hayabusa2 mission returned approximately 5.4 g of highly aqueously-altered material resembling the CI (Ivuna-type) chondrites from the C-type asteroid Ryugu. To understand the timing and duration of aqueous alteration on Ryugu’s parent body, we measured the 53Mn-53Cr (t1/2 = 3.7 Myr) ages of dolomite, breunnerite, and Ca-carbonate minerals in Ryugu particles A0037 and C0009 using secondary ion mass spectrometry (SIMS) with the UCLA CAMECA ims-1290 instrument with Hyperion II oxygen plasma source. Using these carbonate formation ages, we estimate the accretion time and size of Ryugu’s parent body to have been within the first 1.8 million years of Solar System history in a planetesimal less than ~20 km in diameter, or within a larger body which was disrupted and reassembled. To further constrain the conditions of aqueous alteration, we measured the δ13C, δ18O, and Δ17O of Ryugu dolomite, Ca-carbonate, and magnetite using the UCLA CAMECA ims-1290. The results of our stable isotopic analyses show that the earliest stages of aqueous alteration occurred at low temperatures (between 0 and 20 °C), that the initial fluid was enriched in the heavy 13C, 17O and 18O isotopes, and that the fluid evolved towards lighter carbon and oxygen isotopic compositions as alteration proceeded.

Astromaterials↗
NASA NTRS2024

Enantioselective Three-Dimensional High-Performance Liquid Chromatographic Determination of Amino Acids in the Hayabusa2 Returned Samples from the Asteroid Ryugu

The chirality of amino acids in extraterrestrial materials may provide an insight into the origin of the essential L-enantiopure amino acids in the terrestrial biosphere. In 2020, the Hayabusa2 mission succeeded in bringing back surface materials from the C-type asteroid (162173) Ryugu to the Earth. Amino acids were one of the targeted organic molecules to be studied in the Ryugu samples. To analyze the various structural isomers of amino acids, which were expected to be present, from the limited amount of the returned samples, the development of a highly-sensitive and selective analytical method was necessary. In the present study, a three-dimensional high-performance liquid chromatography (3D-HPLC) system has been developed for the enantioselective determination of five proteinogenic and three non-proteinogenic amino acids in the Ryugu samples, in which amino acids in the sample were separated by reversed-phase, anion-exchange and enantioselective columns after the fluorescence derivatization with 4-fluoro-7-nitro-2,1,3-benzoxadiozole. The applicability of the analytical system to the extraterrestrial samples was evaluated by analyzing several types of carbonaceous meteorites before applying the system to the Ryugu samples. In the analysis of the Ryugu samples, all of the target amino acids were successfully determined quantitatively. Non-proteinogenic amino acids including 2-amino-n-butyric acid, isovaline and norvaline, rarely present in the terrestrial environment, were found as almost racemic mixtures with 47.1 to 55.2%L.

Amino acids↗
NASA NTRS2023

Pervasive aqueous alteration in the early Solar System revealed by potassium isotopic variations in Ryugu samples and carbonaceous chondrites

C-type asteroids are the presumed home to carbonaceous chondrites, some of which contain abundant life-forming volatiles and organics. For the first time, samples from a C-type asteroid (162173 Ryugu) were successfully returned to Earth by JAXA’s Hayabusa2 mission. These pristine samples, uncontaminated by the terrestrial environment, allow a direct comparison with carbonaceous chondrites. This study reports the stable K isotopic compositions (expressed as δ 41 K) of Ryugu samples and seven carbonaceous chondrites to constrain the origin of K isotopic variations in the early Solar System. Three aliquots of Ryugu particles collected at two touchdown sites have identical δ 41 K values, averaged at -0.194 ± 0.038‰ (2SD). The K isotopic composition of Ryugu falls within the range of δ 41 K values measured on representative CI chondrites, and together, they define an average δ 41 K value of -0.185 ± 0.078‰ (2SE), which provides the current best estimate of the K isotopic composition of the bulk Solar System. Samples of CI chondrites with δ 41 K values that deviate from this range likely reflect terrestrial contaminations or compositional heterogeneities at sampled sizes. In addition to CI chondrites, substantial K isotopic variability is observed in other carbonaceous chondrites and within individual chondritic groups, with δ 41 K values inversely correlated with K abundances in many cases. These observations indicate widespread fluid activity occurred in chondrite parent bodies, which significantly altered the original K abundances and isotopic compositions of chondrules and matrices established at their accretion.

Asteroid Ryugu↗
NASA NTRSDate not supplied

Constraints on the surface materials of Ryugu from spectral and water analysis of experimentally-heated CI carbonaceous chondrite

We performed heating experiments of the Orgueil CI chondrite in vacuum conditions at fO2 around I/W to evaluate systematic changes in mineralogy, water contents, and visible to infrared spectral features. Our goal is to interpret the spectra of Ryugu, the target C asteroid of the Hayabusa2 mission, because Ryugu shows spectral features similar to partially dehydrated carbonaceous chondrites. However heated carbonaceous chondrites can be easily contaminated by terrestrial water, which makes it almost impossible for laboratory data to be compared with spectra of asteroids directly. Therefore, our heated samples were analyzed without exposure to the air after experimental heating to minimize the effects of terrestrial water. The depth of the 2.7-µm absorption band and the water content of the heated Orgueil form a positive correlation trend which follows the results of experimental heating of CM and Tagish Lake meteorites using our experimental procedures. It is found that 500-°C heated Orgueil sample shows the best spectral match with Ryugu in terms of the low reflectance (~2%) at visible wavelengths and a weak absorption (~10%) at around 2.72 µm owing to survival of Mg-rich phyllosilicates. We suggest that Ryugu might have experienced heating and dehydration at a temperature around 500 °C, after aqueous alteration, and presently contains a small quantity of hydrated minerals equivalent to 1-2 wt.% of water at the surface.

K. Amano↗
NASA NTRS2021

Thermally Altered Subsurface Material of Asteroid 162173 Ryugu

Studies of meteorite analysis and theoretical modeling have indicated the possibility that some carbonaceous near-Earth asteroids are thermally altered due to radiative heating during close approaches to the Sun in addition to parent body processes (Nakamura, 2005; Marchi et al., 2009; Chaumard et al., 2012). In April 2019, the Hayabusa2 mission successfully completed an artificial impact experiment on the carbonaceous near-Earth asteroid 162173 Ryugu (Arakawa et al., 2020), which provided an opportunity to investigate the effects of radiative heating through the exposed subsurface material. Here we report observations of the Ryugu’s subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Spectra of the subsurface material exhibit a slightly stronger and peak-shifted hydroxyl absorption feature compared to that observed for the surface, indicating that space weathering and/or radiative heating caused a subtle change in the spectrum of Ryugu surface. However, the shape of the absorption feature still suggests that the subsurface material experienced heating above 300 ˚C similar to the surface. In contrast, our thermal modeling shows that radiative heating does not increase the subsurface temperature at 1 m depth above 200 ˚C even if the semimajor axis is reduced down to 0.344 au. This supports that the Ryugu material would have been preferentially altered due to radiogenic and/or impact heating on the parent body rather than radiative heating.

Asteroids↗
NASA NTRS2021

Hydrothermal History of (162173) Ryugu’s Parent Body Inferred from Remote-Sensing Data

Small rubble pile asteroids record the thermal evolution of their much larger parent bodies. However, recent space weathering and/or solar heating create ambiguities between the uppermost layer observable by remote-sensing and the pristine material from the parent body. Hayabusa2 remote-sensing observations find that on the asteroid (162173) Ryugu both north and south pole regions preserve the least space-weathered material, which is spectrally blue carbonaceous chondritic material with a 0 – 3% deep 0.7-μm band absorption, indicative of Fe-bearing phyllosilicates . We report that spectrally blue Ryugu’s parent body experienced intensive aqueous alteration and subsequent thermal metamorphism at 570 – 670 K (300 – 400 ˚C), suggesting that Ryugu’s parent body was heated by radioactive decay of short-lived radionuclides possibly because of its early formation 2-2.5 Ma. The samples being brought to Earth by Hayabusa2 will give us our first insights into this epoch in solar system history. Moreover, we found the NUV-VIS spectral similarity between Ryugu and Polana–Eulalia family members, suggesting plausible origin from inner main belt predicted by the dynamical simulation.

Eri Tatsumi↗
NASA NTRS2021

Spectrally Blue Parent Body of Asteroid (162173) Ryugu and its Hydrothermal History

Small rubble pile asteroids record the thermal evolution of their much larger parent bodies. However, recent ‘space weathering’ and/or ‘solar heating’ create ambiguities between the uppermost layer observable by remote-sensing and the pristine material from the parent body. Hayabusa2 remote-sensing observations found that on the asteroid (162173) Ryugu both north and south pole regions preserve the material least processed by space weathering: spectrally blue carbonaceous chondritic material with a 0.7-μm band absorption, indicative of Fe-bearing phyllosilicates. This discovery suggests that Ryugu’s parent body experienced intensive aqueous alteration and subsequent thermal metamorphism at 670 – 970 K. Ryugu’s parent body was heated by radioactive decay of short-lived radionuclides possibly because of its early formation 2-2.5 Ma. Ryugu’s parent body which is spectrally blue represents some of the most ancient of carbonaceous chondritic compositions from the solar system. The samples being brought to Earth by Hayabusa2 will give us our first insights into this epoch in solar system history.

Eri Tatsumi↗
NASA NTRSDate not supplied

Ultraviolet/Visible Reflectance Spectra of Returned Samples of (162173) Ryugu Unexposed to Earth’s Atmosphere

Following the successful return of JAXA’s Hayabusa2 sample capsule, the material from asteroid (162173) Ryugu retrieved from the spacecraft retrieval container has been the subject of multi-pronged analyses [e.g., 1]. We undertook an effort to acquire reflectance spectra covering 200- to- 1100 nm of particles from Ryugu. This region probes the near-ultraviolet (NUV) to acquire reflectance spectra that cover the 250-nm Fresnel peak that can result from increased graphitization (reduced H content) of carbon-bearing materials. Laboratory tests show that increased graphitization could result from the effects of increased temperature, an effect of space weathering of materials closer to the Sun. Some ground-based reflectance spectra and space-based photometry of Ryugu show that reflectance is increasing with decreasing wavelength, suggesting the beginning of a UV upturn [2]. We sought evidence for space weathering (graphitization) of the Ryugu material at NUV wavelengths, by acquiring reflectance spectra of surface samples.

F Vilas↗
NASA NTRSDate not supplied

Isotopic Compositions of Noble Gases and Nitrogen in the Ryugu Samples Returned by Hayabusa2

In December 2014, the hayabusa2 spacecraft launched to visit the C-type asteroid (162173) Ryugu to bring back surface and subsurface materials to the Earth. The spacecraft arrived at Ryugu on June 27, 2018, and subsequently carried out two touchdowns (TDs) and sample collections. The 1st TD was carried out and collected surface samples, while the 2nd TD was done to collect the impact melt ejecta near the artificial crater made by the small carry-on Impactor operation in April 2019. Samples collected during the 1st and 2nd TDs were stored in Chamber A and C of the Hayabusa2 sample catcher, respectively. Our principal objective is to quantify the indigenous compositions of the Ryugu samples with as little terrestrial contamination as possible. Here we report the isotopic ratios and concentrations of noble gases and nitrogen in the Ryugu samples allocated to the Hayabusa2-initial-analysis-volatile team.

noble gas↗
NASA NTRS2022

Oxygen Isotopes of Anhydrous Primary Minerals Show Kinship Between Asteroid Ryugu and Comet 81P/Wild2

The extraterrestrial materials returned from asteroid (162173) Ryugu consist predominantly of low-temperature aqueously formed secondary minerals and are chemically and mineralogically similar to CI (Ivuna-type) carbonaceous chondrites. Here we show that high-temperature anhydrous primary minerals in Ryugu and CI chondrites exhibit a bimodal distribution of oxygen isotopic compositions: 16 O-rich (associated with refractory inclusions) and 16 O-poor (associated with chondrules). Both the 16 O-rich and 16 O-poor minerals probably formed in the inner solar protoplanetary disk and were subsequently transported outwards. The abundance ratios of the 16 O-rich to 16 O-poor minerals in Ryugu and CI chondrites are higher than in other carbonaceous chondrite groups, but are similar to that of comet 81P/Wild2, suggesting that Ryugu and CI chondrites accreted in the outer Solar System closer to the accretion region of comets.

Noriyuki Kawasaki↗
NASA NTRSDate not supplied

Ryugu and the Quest for Unaltered CI-Like Materials From the Early Solar System

Samples of C-type asteroid (162173) Ryugu returned by the Hayabusa2 mission of JAXA [1-3] have been found to be mineralogically, chemically, and isotopically similar to CI carbonaceous chondrites [3-6]. The rare CI meteorites have bulk chemical compositions closely matching the solar photosphere in all but the most volatile elements, and so are considered to represent the starting composition of the solar system. Paradoxically, however, all known CI have been extensively altered by aqueous fluids (i.e., they are CI1), so that their primary mineralogy, textures, and oxygen isotope compositions have been obscured. Thus, one of the most exciting discoveries from Ryugu samples is that they contain “less-altered” (CI2) areas, which have substantial abundances of anhydrous silicates (olivine and pyroxene) and Ca-Al-rich phases that may be remnants of primordial CI3 materials [4-11]. This discovery has motivated new investigations of CIs that show higher abundances of anhydrous silicate grains than previously recognized [9,12,13]. Such studies are an important step in the search for unaltered CI-like material, a so-called “holy grail” of meteoriticists [14]. To further this goal, we are studying Ryugu samples in the context of a previously unrecognized, potentially Ryugu-like, population of C2 materials that occur as xenoliths in polymict ureilites.

C A Goodrich↗