Language：English  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1111/j.1945-5100.2010.01025.x

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/35090520

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1111/maps.14312

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DOI： 10.1111/maps.14279

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DOI： 10.1111/maps.14304

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DOI： 10.1111/maps.14271

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Language：English  

DOI： 10.1126/sciadv.adp2426

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PubMed

Language：English   Publisher：Springer Nature  

Returned samples from the carbonaceous asteroid (162173) Ryugu provide pristine information on the original aqueous alteration history of the Solar System. Secondary precipitates, such as carbonates and phyllosilicates, reveal elemental partitioning of the major component ions linked to the primordial brine composition of the asteroid. Here, we report on the elemental partitioning and Mg isotopic composition (²⁵Mg/²⁴Mg) of breunnerite [(Mg, Fe, Mn)CO₃] from the Ryugu C0002 sample and the A0106 and C0107 aggregates by sequential leaching extraction of salts, exchangeable ions, carbonates, and silicates. Breunnerite was the sample most enriched in light Mg isotopes, and the ²⁵Mg/²⁴Mg value of the fluid had shifted lower by ~0.38‰ than the initial value (set to 0‰) before dolomite precipitation. As a simple model, the Mg²⁺ first precipitated in phyllosilicates, followed by dolomite precipitation, at which time ~76−87% of Mg²⁺ had been removed from the primordial brine. A minor amount of phyllosilicate precipitation continued after dolomite precipitation. The element composition profiles of the latest solution that interacted with the cation exchange pool of Ryugu were predominantly Na-rich. Na⁺ acts as a bulk electrolyte and contributes to the stabilization of the negative surface charge of phyllosilicates and organic matter on Ryugu.

CiNii Research

Language：English  

DOI： 10.1038/s41467-024-50814-y

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PubMed

Language：English  

DOI： 10.1038/s41467-024-51731-w

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PubMed

Publisher：Geochimica et Cosmochimica Acta  

The surface chemistry of pyrrhotites from intact particles directly collected from asteroid (162173) Ryugu was investigated by micro-Raman spectroscopy. The Raman peak characteristic to pyrrhotite was observed at around 115 cm−1 in Ryugu pyrrhotites, similar to freshly cleaved surfaces of terrestrial pyrrhotites. Additional Raman bands centered at around 220, 275, and 313 cm−1 with broadened features were also detected from the Ryugu pyrrhotites. The set of Raman bands at 220 and 275 cm−1 was assigned to typical Fe-S stretching vibrations of ν2 (225 cm−1) and ν1 (275 cm−1). These bands are not clearly observed in bulk crystals of pyrrhotite but appear in its nanoparticulate phase. These bands are ordinarily seen in amorphous monosulfides that formed under low oxygen fugacity (fO2) conditions in nature, indicating that the structural alteration of pyrrhotite surfaces occurred heterogeneously on the nanoscale under low fO2 conditions. Further, the Raman band at 313 cm−1 was attributed to a characteristic tetrahedral bonding of Fe(III) in the lattice of FeII1-3xFeIII1-2xS, followed by the local breakdown of the crystal lattice structures from planar bonding with Fe(II). In addition, some areas of the Ryugu pyrrhotite grains showed corroded structures with iridescence. Furthermore, assemblages of magnetite particles were also preferentially observed on small areas of the likely-dissolved pyrrhotite crystals in phyllosilicate matrices. These characteristic features in the Raman spectra and in corroded structures of Ryugu pyrrhotites record changes in the local environmental conditions via aqueous alteration. The corrosion of pyrrhotite crystals followed by the preferential formation of magnetite particles by asteroidal water is the likely product of dissolution of Fe(II) from the pyrrhotite surface and its oxidative precipitation in microchemical environments on the Ryugu parent body.

DOI： 10.1016/j.gca.2024.06.016

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Scopus

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Publisher：Meteoritics and Planetary Science  

Transmission electron microscopy analyses of Hayabusa2 samples show that Ryugu organic matter exhibits a range of morphologies, elemental compositions, and carbon functional chemistries consistent with those of carbonaceous chondrites that have experienced low-temperature aqueous alteration. Both nanoglobules and diffuse organic matter are abundant. Non-globular organic particles are also present, and including some that contain nanodiamond clusters. Diffuse organic matter is finely distributed in and around phyllosilicates, forms coatings on other minerals, and is also preserved in vesicles in secondary minerals such as carbonate and pyrrhotite. The average elemental compositions determined by energy-dispersive spectroscopy of extracted, demineralized insoluble organic matter samples A0107 and C0106 are C100N3O9S1 and C100N3O7S1, respectively, with the difference in O/C slightly outside the difference in the standard error of the mean. The functional chemistry of the nanoglobules varies from mostly aromatic C=C to mixtures of aromatic C=C, ketone C=O, aliphatic (CHn), and carboxyl (COOH) groups. Diffuse organic matter associated with phyllosilicates has variable aromatic C, ketone and carboxyl groups, and some localized aliphatics, but is dominated by molecular carbonate (CO3) absorption, comparable to prior observations of clay-bound organic matter in CI meteorites.

DOI： 10.1111/maps.14128

Scopus

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Web of Science

Publisher：Meteoritics and Planetary Science  

Samples from asteroid Ryugu, brought back by asteroid explorer Hayabusa2, are important for investigating the origin and evolution of the solar system. Here, we report the elemental compositions of a 123-mg Ryugu sample determined with a nondestructive muon elemental analysis method. This method is a powerful tool for determining bulk chemical composition, including light elements such as C, N, and O. From the muonic x-ray spectra with three carbonaceous chondrites, the relationship between the elemental composition and muonic x-ray intensity was determined for each element. Calibration curves showed linearity, and the elemental composition of Ryugu was quantitatively determined. The results reflect the average bulk elemental composition of asteroid Ryugu owing to the large amount of samples. Ryugu has an elemental composition similar to that of Orgueil (CI1) and should be classified as CI1. However, the O/Si ratio of Ryugu is 25% lower than that of Orgueil, indicating that Orgueil may have been seriously contaminated by terrestrial materials after its fall to Earth. These results indicate that the Ryugu sample is more representative than the CI chondrites as a solid material of the solar system.

DOI： 10.1111/maps.14135

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Scopus

Publisher：Meteoritics and Planetary Science  

Samples were recently collected from the carbonaceous asteroid (162173) Ryugu, by the Japan Aerospace Exploration Agency (JAXA) Hayabusa2 mission. They resemble CI chondrites material, thus showing clear evidence of extensive aqueous alteration attested by the widespread presence of a mixture of serpentine and saponite. We present here a scanning transmission electron microscopy study of the Ryugu dominant lithology of the phyllosilicate matrix at the nanometer scale, which we compare with that of the Orgueil CI chondrite. In both objects, the phyllosilicates are of comparable nature and texture, consisting of a mixture of small-sized crystallites of serpentine and saponite. At the micrometer scale or less, the texture is an alternation of fine and coarse domains. The fine-grained regions are dominated by saponite. In Ryugu, they enclose numerous Fe,Ni nanosulfides, whereas in Orgueil, S- and Ni-rich ferrihydrite is abundant. The coarse-grained regions contain more serpentine and no or little Fe,Ni sulfides or ferrihydrite. Scanning transmission x-ray microscopy at the Fe-L3 edge also reveals that iron valency of phyllosilicates is higher and more homogeneous in Orgueil (~70% Fe3+) than in Ryugu (<50% Fe3+). We interpret the observed textures as being mostly a consequence of aqueous alteration, likely resulting from the replacement by phyllosilicates of submicrometric components, initially agglomerated by a primary accretion. The fine-grained domains may result from the replacement of GEMS (GEMS—glass with embedded metal and sulfides) objects or from other types of nanometric assemblages of silicate and Fe-based nanophases. On the other hand, the coarse-grained regions may correspond to the replacement of anhydrous crystalline silicates of the olivine and pyroxene type. The major difference is the presence of Fe,Ni sulfides in Ryugu and of ferrihydrite and higher iron valency of phyllosilicates in Orgueil. This might be due to long-term terrestrial weathering that would have destabilized the nanosulfides. We also explore an alternative scenario involving more oxidizing hydrothermal conditions on the Orgueil parent body.

DOI： 10.1111/maps.14101

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Language：English   Publisher：Nature Communications  

We report primordial aqueous alteration signatures in water-soluble organic molecules from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 spacecraft of JAXA. Newly identified low-molecular-weight hydroxy acids (HO-R-COOH) and dicarboxylic acids (HOOC-R-COOH), such as glycolic acid, lactic acid, glyceric acid, oxalic acid, and succinic acid, are predominant in samples from the two touchdown locations at Ryugu. The quantitative and qualitative profiles for the hydrophilic molecules between the two sampling locations shows similar trends within the order of ppb (parts per billion) to ppm (parts per million). A wide variety of structural isomers, including α- and β-hydroxy acids, are observed among the hydrophilic molecules. We also identify pyruvic acid and dihydroxy and tricarboxylic acids, which are biochemically important intermediates relevant to molecular evolution, such as the primordial TCA (tricarboxylic acid) cycle. Here, we find evidence that the asteroid Ryugu samples underwent substantial aqueous alteration, as revealed by the presence of malonic acid during keto–enol tautomerism in the dicarboxylic acid profile. The comprehensive data suggest the presence of a series for water-soluble organic molecules in the regolith of Ryugu and evidence of signatures in coevolutionary aqueous alteration between water and organics in this carbonaceous asteroid.

DOI： 10.1038/s41467-024-49237-6

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PubMed

Publisher：Meteoritics and Planetary Science  

We present here an investigation of Ryugu particles recovered by the Hayabusa2 space mission and their extracted carbonaceous acid residues using Raman spectroscopy. Raman parameters of Ryugu intact grains and their acid residues are characterized by broad D (defect induced) and G (graphite) band widths, indicating the presence of polyaromatic carbonaceous matter with low thermal maturity. Raman spectra of Ryugu particles and CI (type 1) chondrites exhibit stronger laser-induced fluorescence backgrounds compared to Type 2 and Type 3 carbonaceous chondrites. The high fluorescence signatures and wide bandwidths of the D and G bands of Ryugu intact grains are similar to the Raman spectra observed in CI chondrites, reflecting the low structural order of their aromatic carbonaceous matter, and strengthening the link between Ryugu particles and CI chondrites. The high fluorescence background intensity of the Ryugu particles is due to multiple causes, but it is likely that the relative abundance of geometry-bearing macromolecular organic matter in total organic carbon contents makes a large contribution to the fluorescence intensities. Locally observed high fluorescence in the acid-extracted residues of Ryugu is due to nitrogen-bearing outlier phase. The high fluorescence signature is one consequence of the low degree of thermal maturity of the organic matter and supports evidence that the Ryugu particles have escaped significant parent body thermal metamorphism.

DOI： 10.1111/maps.14234

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Scopus

Publisher：Earth and Planetary Science Letters  

We report the H, C, and N isotopic compositions of microscale (0.2 to 2 µm) organic matter in samples of asteroid Ryugu and the Orgueil CI carbonaceous chondrite. Three regolith particles of asteroid Ryugu, returned by the Hayabusa2 spacecraft, and several fragments of Orgueil were analyzed by NanoSIMS isotopic imaging. The isotopic distributions of the Ryugu samples from two different collection spots are closely similar to each other and to the Orgueil samples, strengthening the proposed Ryugu-CI chondrite connection. Most individual sub-μm organic grains have isotopic compositions within error of bulk values, but 2–10 % of them are outliers exhibiting large isotopic enrichments or depletions in D, 15N, and/or 13C. The H, C and N isotopic compositions of the outliers are not correlated with each other: while some organic grains are both D- and 15N-enriched, many are enriched or depleted in one or the other system. This most likely points to a diversity in isotopic fractionation pathways and thus diversity in the local formation environments for the individual outlier grains. The observation of a relatively small population of isotopic outlier grains can be explained either by escape from nebular and/or parent body homogenization of carbonaceous precursor material or addition of later isotopic outlier grains. The strong chemical similarity of isotopically typical and isotopically outlying grains, as reflected by synchrotron x-ray absorption spectra, suggests a genetic connection and thus favors the former, homogenization scenario. However, the fact that even the least altered meteorites show the same pattern of a small population of outliers on top of a larger population of homogenized grains indicates that some or most of the homogenization occurred prior to accretion of the macromolecular organic grains into asteroidal parent bodies.

DOI： 10.1016/j.epsl.2024.118719

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Scopus

Publisher：Geochimica et Cosmochimica Acta  

Samples collected from the surface/subsurface of C-type asteroid 162173 Ryugu by the Hayabusa2 mission were nondestructively analyzed in three dimensions (3D). Seventy-three small particles (approximately 10–180 µm in size) were observed using X-ray nanotomography, with an effective spatial resolution of approximately 200 nm. Detailed descriptions of these samples in terms of mineralogy, petrology, and variations among particles were reported. The 57 most common particles consisted of a phyllosilicate matrix containing mineral grains, mainly magnetite, pyrrhotite, dolomite and apatite. The remaining particles were mostly monomineralic particles (pyrrhotite, dolomite, breunnerite, apatite, and Mg-Na phosphate) with two unique particles (calcite in a Al2Si2O5(OH)4 matrix, and CaCO3, phyllosilicate, and tochilinite-chronstedtite inclusions in a carbonaceous material matrix). The results confirmed that the samples correspond to Ivuna-type carbonaceous chondrites (CI chondrites) or related materials. Many small inclusions of voids and carbonaceous materials were detected in pyrrhotite, dolomite, breunnerite, and apatite. However, no fluid inclusions were observed, except for those in pyrrhotite that have already been reported. Magnetite exhibited a wide variety of morphologies, from irregular shapes (spherulites, framboids, plaquettes, and whiskers) to euhedral shapes (equants, rods, and cubes), along with transitional shapes. In contrast, the other minerals exhibit predominantly euhedral shapes (pyrrhotite: pseudo-hexagonal plates, dolomite: flattened rhombohedrons, breunnerite: largely flattened rhombohedrons, and apatite: hexagonal prisms) or aggregates of faceted crystals, except for Mg-Na phosphate. The matrices were heterogeneous with variable phyllosilicate particle sizes, Mg/Fe ratios, density (1.7 ± 0.2 g/cm3), nanoporosities (36 ± 9 %), and abundances of nanograins of Fe(-Ni) sulfides. The macroporosity of the particles was estimated as 12 ± 4 %. The observed textural relationships among the minerals suggest a precipitation sequence of: magnetite (spherulite → plaquette/framboid → rod/equant) → pyrrhotite (pentlandite → pyrrhotite) → apatite → dolomite → breunnerite → coarse phyllosilicates. Fe-bearing olivine (or low-Ca pyroxene) might have precipitated later than dolomite, indicating a high Mg activity in the aqueous solution. This precipitation sequence corresponds to a transition from irregular crystal forms (as seen in some magnetite) to regular forms of euhedral crystals (observed in some magnetite and other minerals). Based on the precipitation sequence and mineral morphologies, together with previously reported observations, a model for aqueous alteration in the Ryugu parent body was proposed as follows: CO2-H2O ice, amorphous silicates (GEMS-like material), and some minerals (mostly metal, sulfides, and anhydrous silicates) accumulated to form the parent body of Ryugu. Amorphous silicates and Fe-Ni metal quickly dissolved into the melted ice to form a highly supersaturated aqueous solution. Poorly-crystalized phyllosilicate and spherulitic magnetite precipitated first, followed by plaquette/framboidal magnetites with decreasing degree of supersaturation due to precipitation. Pseudo-hexagonal pyrrhotite plates were formed by dissolution and reprecipitation under relatively low supersaturation. Subsequently, apatite, dolomite, and breunnerite precipitated in this order in response to decreasing supersaturation.

DOI： 10.1016/j.gca.2024.03.032

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Scopus

Publisher：Meteoritics and Planetary Science  

Regolith samples returned from asteroid 162173 Ryugu by the Hayabusa2 mission provide direct means to study how space weathering operates on the surfaces of hydrous asteroids. The mechanisms of space weathering, its effects on mineral surfaces, and the characteristic time scales on which alteration occurs are central to understanding the spectroscopic properties and the taxonomy of asteroids in the solar system. Here, we investigate the behavior of the iron monosulfides mineral pyrrhotite (Fe1−xS) at the earliest stages of space weathering. Using electron microscopy methods, we identified a partially exposed pyrrhotite crystal that morphologically shows evidence for mass loss due to exposure to solar wind ion irradiation. We find that crystallographic changes to the pyrrhotite can be related to sulfur loss from its space-exposed surface and the diffusive redistribution of resulting excess iron into the interior of the crystal. Diffusion profiles allow us to estimate an order of magnitude of the exposure time of a few thousand years consistent with previous estimates of space exposure. During this interval, the adjacent phyllosilicates did not acquire discernable damage, suggesting that they are less susceptible to alteration by ion irradiation than pyrrhotite.

DOI： 10.1111/maps.14176

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Scopus

Publisher：Meteoritics and Planetary Science  

Apatite is present as an accessory phase in many meteorites and is often formed as a secondary product of aqueous alteration. Its propensity to incorporate rare earth elements (REE) results in apatite usually being the main REE-bearing phase in hydrously altered meteorites. Asteroid Ryugu is thought to have experienced pervasive aqueous alteration and material collected from the surface of Ryugu is expected to provide insight into asteroidal aqueous alteration processes without influence by terrestrial weathering. Morphologies and mineral associations of apatite grains from five rock fragments collected from the asteroid Ryugu by the Hayabusa2 spacecraft were examined and their REE concentrations were measured by synchrotron X-ray fluorescence (SXRF) spectroscopy. The main minerals associated with apatite are dolomite, magnetite, and pyrrhotite. Grain boundary corrosion of the interfaces between apatite assemblages and the surrounding matrix suggest that paragenetic formation on the asteroid was followed by a later episode of hydrous alteration. Light REE (LREE) concentration levels recorded at 20–150 times those of bulk CI levels together with a steady increase from LREE toward enrichment of medium REE (MREE, up to Er) at 50–400 times bulk CI levels may suggest postgenetic removal of LREE from Ryugu apatite grains by late-stage circulation of a hydrothermal fluid.

DOI： 10.1111/maps.14177

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Publisher：Journal of Chromatography Open  

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.

DOI： 10.1016/j.jcoa.2024.100134

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Publisher：Meteoritics and Planetary Science  

The nitrogen isotope compositions of two samples returned from the asteroid Ryugu were determined using a stepwise combustion method, along with Ivuna (CI) and Y-980115, a CI-like Antarctic meteorite, as references. The two Ryugu samples A0105-07 and C0106-07 showed bulk δ15N values of +1.7 ± 0.5‰ and +0.2 ± 0.6‰, respectively, significantly lower than Ivuna with +36.4 ± 0.4‰, but close to Y-980115 with +4.0 ± 0.3‰. The Ryugu samples are further characterized by C/N and 36Ar/N ratios up to 3.4× and 4.9× the value of Ivuna, respectively. Among all Ryugu samples and CI chondrites, a positive correlation was observed between nitrogen concentrations and δ15N values, with samples with lower nitrogen concentrations exhibiting lower δ15N. This trend is explained by a two-component mixing model. One component is present at a constant abundance among all CI-related samples, with a δ15N value around 0‰ or lower. The other varies in abundance between different samples, and exhibits a δ15N value of +56 ± 4‰. The first 15N-poor endmember is seemingly tightly incorporated into a carbonaceous host phase, whereas the 15N-rich endmember can be mobilized and decoupled from carbon, potentially because it is in the form of ammonia. Asteroid materials with volatile compositions that are similar to those reported here for the Ryugu samples are attractive candidates for the volatile sources among Earth's building blocks.

DOI： 10.1111/maps.14175

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Scopus

Language：English   Publisher：Springer Nature  

Extraterrestrial minerals on the surface of airless Solar System bodies undergo gradual alteration processes known as space weathering over long periods of time. The signatures of space weathering help us understand the phenomena occurring in the Solar System. However, meteorites rarely retain the signatures, making it impossible to study the space weathering processes precisely. Here, we examine samples retrieved from the asteroid Ryugu by the Hayabusa2 spacecraft and discover the presence of nonmagnetic framboids through electron holography measurements that can visualize magnetic flux. Magnetite particles, which normally provide a record of the nebular magnetic field, have lost their magnetic properties by reduction via a high-velocity (>5 km s⁻¹) impact of a micrometeoroid with a diameter ranging from 2 to 20 μm after destruction of the parent body of Ryugu. Around these particles, thousands of metallic-iron nanoparticles with a vortex magnetic domain structure, which could have recorded a magnetic field in the impact event, are found. Through measuring the remanent magnetization of the iron nanoparticles, future studies are expected to elucidate the nature of the nebular/interplanetary magnetic fields after the termination of aqueous alteration in an asteroid.

CiNii Research

Language：English   Publisher：Nature Communications  

Extraterrestrial minerals on the surface of airless Solar System bodies undergo gradual alteration processes known as space weathering over long periods of time. The signatures of space weathering help us understand the phenomena occurring in the Solar System. However, meteorites rarely retain the signatures, making it impossible to study the space weathering processes precisely. Here, we examine samples retrieved from the asteroid Ryugu by the Hayabusa2 spacecraft and discover the presence of nonmagnetic framboids through electron holography measurements that can visualize magnetic flux. Magnetite particles, which normally provide a record of the nebular magnetic field, have lost their magnetic properties by reduction via a high-velocity (>5 km s–1) impact of a micrometeoroid with a diameter ranging from 2 to 20 μm after destruction of the parent body of Ryugu. Around these particles, thousands of metallic-iron nanoparticles with a vortex magnetic domain structure, which could have recorded a magnetic field in the impact event, are found. Through measuring the remanent magnetization of the iron nanoparticles, future studies are expected to elucidate the nature of the nebular/interplanetary magnetic fields after the termination of aqueous alteration in an asteroid.

DOI： 10.1038/s41467-024-47798-0

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PubMed

Publisher：Astronomy and Astrophysics  

Context. The JAXA Hayabusa2 mission returned well-preserved samples collected from the carbonaceous asteroid Ryugu, providing unique non-terrestrially weathered samples from a known parent body. Aims. This work aims to provide a better understanding of the formation and evolution of primitive asteroidal matter by studying the fine scale association of organic matter and minerals in Ryugu samples. We characterized the samples by IR nanospectroscopy using infrared photothermal nanospectroscopy (AFM-IR) technique. This technique overcomes the diffraction limit (of several microns) of conventional infrared microspectroscopy (μ-FTIR). The samples were mapped in the mid-IR range at a lateral spatial resolution about a hundred times better than with μ-FTIR. This provided us with unique in situ access to the distribution of the different infrared signatures of organic components at the sub-micron scale present in the Ryugu whole-rock samples as well as to the characterization of the compositional variability of Ryugu in the insoluble organic matter (IOM) chemically extracted from the Ryugu samples. Methods. The AFM-IR maps of whole-rock particles and IOM residues from Ryugu samples were recorded with a lateral resolution of tens of nanometers. Spectra were recorded in the 1900-900 cm-1 spectral range by AFM-IR (Icon-IR) for all samples, and additional spectra were recorded from 2700 to 4000 cm-1 for one IOM sample by an optical photothermal IR (O-PTIR) technique using a mIRage® IR microscope. Results. Organic matter is present in two forms in the whole-rock samples: as a diffuse phase intermixed with the phyllosilicate matrix and as individual organic nanoparticles. We identify the Ryugu organic nanoparticles as nanoglobule-like inclusions texturally resembling nanoglobules present in primitive meteorites. Using AFM-IR, we record for the first time the infrared spectra of Ryugu organic nanoparticles that clearly show enhanced carbonyl (C=O) and CH contributions with respect to the diffuse organic matter in Ryugu whole-rock and IOM residue.

DOI： 10.1051/0004-6361/202347435

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Publisher：Meteoritics and Planetary Science  

We analyzed an asteroid Ryugu sample returned to Earth by JAXA's Hayabusa2 mission using nanoIR, SEM, and TEM microscopy. We identified multiple distinct carbon reservoirs within the phyllosilicate matrix and demonstrate infrared spectral affinities for some of the carbon to insoluble organic matter (IOM). TEM studies of Ryugu samples have allowed us to better understand the interrelationship between the crystallographic orientations of phyllosilicates and the secondary minerals such as carbonate, sulfide, and apatite. Transport of elements provides a unifying theme for understanding these interrelationships.

DOI： 10.1111/maps.14161

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Publisher：Geochimica et Cosmochimica Acta  

In order to better constrain the alteration history of the Ryugu parent body, we performed a multi-analytical study combining scanning electron microscopy, transmission electron microscopy and infrared spectroscopy on sections extracted from the three fragments A0064-FO019, A0064-FO021 and C0002-FO019 returned from Ryugu by the Hayabusa2 space mission. The three sections show large differences in terms of structure, mineralogy and infrared signature. Section A0064-FO019 resembles the major Ryugu lithology with the presence of both fine-grained phyllosilicates (fg-phyllos) with embedded nanosulfides and coarse-grained phyllosilicates (cg-phyllos), whereas section C0002-FO019 belongs to the group of the less altered lithologies with the presence of anhydrous minerals embedded in a partially amorphous matrix. Section A0064-FO021 also belongs to this group but shows two different lithologies, a compact amorphous one and a more porous and very fractured one showing the presence of Na-rich phosphate, calcite and olivine. The two less altered lithologies (sections A0064-FO021 and C0002-FO019) show the presence of numerous mineralogical features similar to those observed in cometary interplanetary dust particles, ultra-carbonaceous Antarctic micrometeorites or in the CM Paris meteorite, i.e. amorphous and partially crystallized matrix with GEMS-like ghosts objects, whisker olivine, phosphide, or FeNi metal. This supports an outer solar system origin common with that of cometary material for the Ryugu parent body. Combined with the results of Nakamura et al. (2022b) reporting the presence of a lithology showing the presence of GEMS-like objects, we propose that section C0002-FO019 represents the onset of aqueous alteration of such primitive materials. The cg-phyllos and fg-phyllos of section A0064-FO019, i.e. of the major Ryugu lithology, representing the advanced stage of alteration, exhibit distinctive IR signatures with a higher abundance of oxygen-rich functional groups in the organic matter (OM) from the cg-phyllos. We thus suggest the following chronology of formation and evolution for Ryugu: (1) accretion of highly porous aggregate of GEMS-like units with fine-grained high-temperature anhydrous silicates, (2) onset of alteration with the dissolution of primary nanosulfides and development of amorphous/partially crystallized material in the pores, (3) crystallization of fg-phyllos with a second generation of sulfides, (4) later formation of cg-phyllos devoid of nanosulfides and their associated oxygen-rich OM in a more water-rich environment.

DOI： 10.1016/j.gca.2024.02.006

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Publisher：Meteoritics and Planetary Science  

Oxygen 3-isotope ratios of magnetite and carbonates in aqueously altered carbonaceous chondrites provide important clues to understanding the evolution of the fluid in the asteroidal parent bodies. We conducted oxygen 3-isotope analyses of magnetite, dolomite, and breunnerite in two sections of asteroid Ryugu returned samples, A0058 and C0002, using a secondary ion mass spectrometer (SIMS). Magnetite was analyzed by using a lower primary ion energy that reduced instrumental biases due to the crystal orientation effect. We found two groups of magnetite data identified from the SIMS pit morphologies: (1) higher δ18O (from 3‰ to 7‰) and ∆17O (~2‰) with porous SIMS pits mostly from spherulitic magnetite, and (2) lower δ18O (~ −3‰) and variable ∆17O (0‰–2‰) mostly from euhedral magnetite. Dolomite and breunnerite analyses were conducted using multi-collection Faraday cup detectors with precisions ≤0.3‰. The instrumental bias correction was applied based on carbonate compositions in two ways, using Fe and (Fe + Mn) contents, respectively, because Ryugu dolomite contains higher amounts of Mn than the terrestrial standard. Results of dolomite and breunnerite analyses show a narrow range of ∆17O; 0.0‰–0.3‰ for dolomite in A0058 and 0.2‰–0.8‰ for dolomite and breunnerite in C0002. The majority of breunnerite, including large ≥100 μm grains, show systematically lower δ18O (~21‰) than dolomite (25‰–30‰ and 23‰–27‰ depending on the instrumental bias corrections). The equilibrium temperatures between magnetite and dolomite from the coarse-grained lithology in A0058 are calculated to be 51 ± 11°C and 78 ± 14°C, depending on the instrumental bias correction scheme for dolomite; a reliable temperature estimate would require a Mn-bearing dolomite standard to evaluate the instrumental bias corrections, which is not currently available. These results indicate that the oxygen isotope ratios of aqueous fluids in the Ryugu parent asteroid were isotopically heterogeneous, either spatially, or temporary. Initial water ice accreted to the Ryugu parent body might have ∆17O > 2‰ that was melted and interacted with anhydrous solids with the initial ∆17O < 0‰. In the early stage of aqueous alteration, spherulitic magnetite and calcite formed from aqueous fluid with ∆17O ~ 2‰ that was produced by isotope exchange between water (∆17O > 2‰) and anhydrous solids (∆17O < 0‰). Dolomite and breunnerite, along with some magnetite, formed at the later stage of aqueous alteration under higher water-to-rock ratios where the oxygen isotope ratios were nearly at equilibrium between fluid and solid phases. Including literature data, δ18O of carbonates decreased in the order calcite, dolomite, and breunnerite, suggesting that the temperature of alteration might have increased with the degree of aqueous alteration.

DOI： 10.1111/maps.14163

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Scopus

Publisher：Meteoritics and Planetary Science  

Japan Aerospace Exploration Agency's Martian Moons eXploration (MMX) mission will launch a spacecraft in 2024 to return samples from Phobos in 2029. Curatorial work for the returned Phobos samples is critical for the sample allocation without degrading the sample integrity and subsequent sample analysis that will provide new constraints on the origin of Phobos and the evolution of the circum-Mars environment. The Sample Analysis Working Team of the MMX is designing the sample curation protocol. The curation protocol consists of three phases: (1) quick analysis (extraction and mass spectrometry for gases), (2) pre-basic characterization (bulk-scale observation), and (3) basic characterization (grain-by-grain observation and allocation of the sample aliquots). Nondestructive analyses within the clean chamber (e.g., visible and near-infrared spectral imaging) and outside the chamber (e.g., gas mass spectrometry) are incorporated into the curation flow in coordination with the MMX mission instrument teams for ground-truthing the remote-sensing data sets. The MMX curation/sample analysis flow enables the seamless integration between the sample and remote-sensing data sets to maximize the scientific value of the collected Phobos samples.

DOI： 10.1111/maps.14121

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Scopus

Publisher：Nature Astronomy  

Large amounts of nitrogen compounds, such as ammonium salts, may be stored in icy bodies and comets, but the transport of these nitrogen-bearing solids into the near-Earth region is not well understood. Here, we report the discovery of iron nitride on magnetite grains from the surface of the near-Earth C-type carbonaceous asteroid Ryugu, suggesting inorganic nitrogen fixation. Micrometeoroid impacts and solar wind irradiation may have caused the selective loss of volatile species from major iron-bearing minerals to form the metallic iron. Iron nitride is a product of nitridation of the iron metal by impacts of micrometeoroids that have higher nitrogen contents than the CI chondrites. The impactors are probably primitive materials with origins in the nitrogen-rich reservoirs in the outer Solar System. Our observation implies that the amount of nitrogen available for planetary formation and prebiotic reactions in the inner Solar System is greater than previously recognized.

DOI： 10.1038/s41550-023-02137-z

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Language：English   Publisher：Springer Nature  

Large amounts of nitrogen compounds, such as ammonium salts, may be stored in icy bodies and comets, but the transport of these nitrogen-bearing solids into the near-Earth region is not well understood. Here, we report the discovery of iron nitride on magnetite grains from the surface of the near-Earth C-type carbonaceous asteroid Ryugu, suggesting inorganic nitrogen fixation. Micrometeoroid impacts and solar wind irradiation may have caused the selective loss of volatile species from major iron-bearing minerals to form the metallic iron. Iron nitride is a product of nitridation of the iron metal by impacts of micrometeoroids that have higher nitrogen contents than the CI chondrites. The impactors are probably primitive materials with origins in the nitrogen-rich reservoirs in the outer Solar System. Our observation implies that the amount of nitrogen available for planetary formation and prebiotic reactions in the inner Solar System is greater than previously recognized.

CiNii Research

Publisher：Icarus  

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 δ41K) 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 δ41K values, averaged at −0.194 ± 0.038‰ (2SD). The K isotopic composition of Ryugu falls within the range of δ41K values measured on representative CI chondrites, and together, they define an average δ41K 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 δ41K 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 δ41K 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.

DOI： 10.1016/j.icarus.2023.115884

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Scopus

Publisher：Meteoritics and Planetary Science  

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.

DOI： 10.1111/maps.14139

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Scopus

Language：English   Publisher：Science Advances  

The Hayabusa2 spacecraft delivered samples of the carbonaceous asteroid Ryugu to Earth. Some of the sample particles show evidence of micrometeoroid impacts, which occurred on the asteroid surface. Among those, particles A0067 and A0094 have flat surfaces on which a large number of microcraters and impact melt splashes are observed. Two impact melt splashes and one microcrater were analyzed to unveil the nature of the objects that impacted the asteroid surface. The melt splashes consist mainly of Mg-Fe–rich glassy silicates and Fe-Ni sulfides. The microcrater trapped an impact melt consisting mainly of Mg-Fe–rich glassy silicate, Fe-Ni sulfides, and minor silica-rich glass. These impact melts show a single compositional trend indicating mixing of Ryugu surface materials and impactors having chondritic chemical compositions. The relict impactor in one of the melt splashes shows mineralogical similarity with anhydrous chondritic interplanetary dust particles having a probable cometary origin. The chondritic micrometeoroids probably impacted the Ryugu surface during its residence in a near-Earth orbit.

DOI： 10.1126/sciadv.adi7203

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PubMed

Publisher：Icarus  

This paper is focused on the characterization of the thermal history of C-type asteroid Ryugu through the structure of the polyaromatic carbonaceous matter in the returned samples determined by Raman spectroscopy. Both intact particles and extracted Insoluble Organic Matter (IOM) from the two sampling sites on Ryugu have been characterized. The main conclusions are that (i) there is no structural difference of the polyaromatic component probed by Raman spectroscopy between the two sampling sites, (ii) in a manner similar to type 1 and 2 chondrites, the characterized Ryugu particles did not experience significant long-duration thermal metamorphism related to the radioactive decay of elements such as 26Al; (iii) some structural variability is nevertheless observed within our particle set. It can be interpreted as some particles having experienced some short-duration and weak heating (R3 in the scale defined by Quirico et al. 2018 and TII or lower according to the scale defined by Nakamura, 2005).

DOI： 10.1016/j.icarus.2023.115826

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Scopus

Publisher：Meteoritics and Planetary Science  

The Hayabusa2 mission from the Japan Aerospace Exploration Agency (JAXA) returned to the Earth samples of carbonaceous asteroid (162173) Ryugu. This mission offers a unique opportunity to investigate in the laboratory samples from a C-type asteroid, without physical or chemical alteration by the terrestrial atmosphere. Here, we report on an investigation of the mineralogy and the organo-chemistry of Hayabusa2 samples using a combination of micro- and nano-infrared spectroscopy. Particles investigated with conventional FTIR spectroscopy have spectra dominated by phyllosilicate-related absorption, as observed for samples of CI-chondrites, selected ungrouped carbonaceous chondrites, and selected hydrated micrometeorites. Ryugu samples show smaller sulfate-related absorption than CI-chondrites. Our samples that were only briefly exposed to the Earth atmosphere show absorptions related to molecular water, revealing fast terrestrial contamination of the spectral signature at 3 μm. Overall, our FTIR data are in agreement with other work done on Ryugu samples, revealing a low degree of mineralogical variability across Ryugu samples. AFM-IR mapping of the grains shows the presence of a micrometer-sized organic globule in one of our analyzed grains. The AFM-IR spectra obtained on this globule are similar to IR spectra obtained on IOM suggesting that it is constituted of refractory organic matter. This globule may host silicate in its interior, with a different mineralogy than bulk Ryugu phyllosilicate. The shape, presence of peculiar silicate, and the nature of organic constituting the globule point toward a pre-accretionary origin of this globule and that at least part of Ryugu organics were inherited from the protosolar nebulae or the interstellar media. Altogether, our results show the similarities between Ryugu samples and CI chondrites.

DOI： 10.1111/maps.14122

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Scopus

Publisher：Meteoritics and Planetary Science  

Ryugu asteroid grains brought back to the Earth by the Hayabusa2 space mission are pristine samples containing hydrated minerals and organic compounds. Here, we investigate the mineralogy of their phyllosilicate-rich matrix with four-dimensional scanning transmission electron microscopy (4D-STEM). We have identified and mapped the mineral phases at the nanometer scale (serpentine, smectite, pyrrhotite), observed the presence of Ni-bearing pyrrhotite, and identified the serpentine polymorph as lizardite, in agreement with the reported aqueous alteration history of Ryugu. Furthermore, we have mapped the d-spacings of smectite and observed a broad distribution of values, ranging from 1 to 2 nm, with an average d-spacing of 1.24 nm, indicating significant heterogeneity within the sample. Such d-spacing variability could be the result of either the presence of organic matter trapped in the interlayers or the influence of various geochemical conditions at the submicrometer scale, suggestive of a range of organic compounds and/or changes in smectite crystal chemistry.

DOI： 10.1111/maps.14124

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Scopus

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

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DOI： 10.14862/geochemproc.71.0_160

CiNii Research

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

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DOI： 10.14862/geochemproc.71.0_148

CiNii Research

Language：English   Publisher：Analytical Chemistry  

Characterization of the elemental distribution of samples with rough surfaces has been strongly desired for the analysis of various natural and artificial materials. Particularly for pristine and rare analytes with micrometer sizes embedded on specimen surfaces, non-invasive and matrix effect-free analysis is required without surface polishing treatment. To satisfy these requirements, we proposed a new method employing the sequential combination of two imaging modalities, i.e., microenergy-dispersive X-ray fluorescence (micro-XRF) and Raman micro-spectroscopy. The applicability of the developed method is tested by the quantitative analysis of cation composition in micrometer-sized carbonate grains on the surfaces of intact particles sampled directly from the asteroid Ryugu. The first step of micro-XRF imaging enabled a quick search for the sparsely scattered and micrometer-sized carbonates by the codistributions of Ca2+ and Mn2+ on the Mg2+- and Fe2+-rich phyllosilicate matrix. The following step of Raman micro-spectroscopy probed the carbonate grains and analyzed their cation composition (Ca2+, Mg2+, and Fe2+ + Mn2+) in a matrix effect-free manner via the systematic Raman shifts of the lattice modes. The carbonates were basically assigned to ferroan dolomite bearing a considerable amount of Fe2+ + Mn2+ at around 10 atom %. These results are in good accordance with the assignments reported by scanning electron microscopy-energy-dispersive X-ray spectroscopy, where the thin-sectioned and surface-polished Ryugu particles were applicable. The proposed method requires neither sectioning nor surface polishing; hence, it can be applied to the remote sensing apparatus on spacecrafts and planetary rovers. Furthermore, the non-invasive and matrix effect-free characterization will provide a reliable analytical tool for quantitative analysis of the elemental distribution on the samples with surface roughness and chemical heterogeneity at a micrometer scale, such as art paintings, traditional crafts with decorated shapes, as well as sands and rocks with complex morphologies in nature.

DOI： 10.1021/acs.analchem.3c03463

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PubMed

Language：English   Publisher：Science  

Polycyclic aromatic hydrocarbons (PAHs) contain ≲20% of the carbon in the interstellar medium. They are potentially produced in circumstellar environments (at temperatures ≳1000 kelvin), by reactions within cold (~10 kelvin) interstellar clouds, or by processing of carbon-rich dust grains. We report isotopic properties of PAHs extracted from samples of the asteroid Ryugu and the meteorite Murchison. The doubly-13C substituted compositions (D2×13C values) of the PAHs naphthalene, fluoranthene, and pyrene are 9 to 51% higher than values expected for a stochastic distribution of isotopes. The D2×13C values are higher than expected if the PAHs formed in a circumstellar environment, but consistent with formation in the interstellar medium. By contrast, the PAHs phenanthrene and anthracene in Ryugu samples have D2×13C values consistent with formation by higher-temperature reactions.

DOI： 10.1126/science.adg6304

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PubMed

Publisher：Geochemical Perspectives Letters  

Initial analyses of samples collected from two locations on the asteroid Ryugu indicated that the mineralogical, chemical, and isotopic characteristics of the Ryugu samples show similarities to carbonaceous chondrites, particularly the Ivuna-type (CI) group. In this study, we analysed a composite sample of four bulk Ryugu samples (A0106, A0106-A0107, C0107, and C0108) collected from both sampling locations that were combined in order to determine its mass independent Mo isotopic composition and reveal contributions from diverse nucleosynthetic sources. The ε94Mo and ε95Mo values for the Ryugu sample are characterised by the carbonaceous chondrite (CC)-type, which is consistent with the nucleosynthetic isotope compositions observed for other elements (Cr, Ti, Fe, and Zn). The Ryugu composite sample, however, is characterised by greater s-process depletion of Mo isotopes compared with any known bulk carbonaceous chondrite, even including CI chondrites. The observed Mo isotopic signature in the Ryugu composite was most likely caused by either incomplete digestion of s-process-rich presolar SiC, or biased sampling of materials enriched in aqueously-formed secondary minerals characterised by s-process-poor Mo isotopes, resulting from the physicochemical separation between s-process-rich presolar grains and a complementary s-process-poor aqueous fluid in the Ryugu parent body.

DOI： 10.7185/geochemlet.2341

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Language：English   Publisher：Science Advances  

The carbonaceous asteroid Ryugu has been explored by the Hayabusa2 spacecraft to elucidate the actual nature of hydrous asteroids. Laboratory analyses revealed that the samples from Ryugu are comparable to unheated CI carbonaceous chondrites; however, reflectance spectra of Ryugu samples and CIs do not coincide. Here, we demonstrate that Ryugu sample spectra are reproduced by heating Orgueil CI chondrite at 300°C under reducing conditions, which caused dehydration of terrestrial weathering products and reduction of iron in phyllosilicates. Terrestrial weathering of CIs accounts for the spectral differences between Ryugu sample and CIs, which is more severe than space weathering that likely explains those between asteroid Ryugu and the collected samples. Previous assignments of CI chondrite parent bodies, i.e., chemically most primitive objects in the solar system, are based on the spectra of CI chondrites. This study indicates that actual spectra of CI parent bodies are much darker and flatter at ultraviolet to visible wavelengths than the spectra of CI chondrites.

DOI： 10.1126/sciadv.adi3789

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PubMed

Publisher：Meteoritics and Planetary Science  

We report Nd and Sm isotopic compositions of four samples of Ryugu returned by the Hayabusa2 mission, including “A” (first touchdown) and “C” (second touchdown) samples, and several carbonaceous chondrites to evaluate potential genetic relationships between Ryugu and known chondrite groups and track the cosmic ray exposure history of Ryugu. We resolved Nd and Sm isotopic anomalies in small (<20 ng Nd and Sm) sample sizes via thermal ionization mass spectrometer using 1013 Ω amplifiers. Ryugu samples exhibit resolvable negative μ142Nd values consistent with carbonaceous chondrite values, suggesting that Ryugu is related to the parent bodies of carbonaceous chondrites. Ryugu's negative μ149Sm values are the result of exposure to galactic cosmic rays, as demonstrated by the correlation between 150Sm/152Sm and 149Sm/152Sm ratios that fall along the expected neutron capture correlation line. The neutron fluence calculated in the “A” samples (2.75 ± 1.94 × 1015 n cm−2) is slightly higher compared to the “C” samples (0.95 ± 2.04 × 1015 n cm−2), though overlapping within measurement uncertainty. The Sm results for Ryugu, at this level of precision, thus are consistent with a well-mixed surface layer at least to the depths from which the “A” and “C” samples derive.

DOI： 10.1111/maps.14109

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Publisher：Astrophysical Journal Letters  

The nucleosynthetic isotope composition of planetary materials provides a record of the heterogeneous distribution of stardust within the early solar system. In 2020 December, the Japan Aerospace Exploration Agency Hayabusa2 spacecraft returned to Earth the first samples of a primitive asteroid, namely, the Cb-type asteroid Ryugu. This provides a unique opportunity to explore the kinship between primitive asteroids and carbonaceous chondrites. We report high-precision μ 26Mg* and μ 25Mg values of Ryugu samples together with those of CI, CM, CV, and ungrouped carbonaceous chondrites. The stable Mg isotope composition of Ryugu aliquots defines μ 25Mg values ranging from -160 ± 20 ppm to -272 ± 30 ppm, which extends to lighter compositions relative to Ivuna-type (CI) and other carbonaceous chondrite groups. We interpret the μ 25Mg variability as reflecting heterogeneous sampling of a carbonate phase hosting isotopically light Mg (μ 25Mg ∼ -1400 ppm) formed by low temperature equilibrium processes. After correcting for this effect, Ryugu samples return homogeneous μ 26Mg* values corresponding to a weighted mean of 7.1 ± 0.8 ppm. Thus, Ryugu defines a μ 26Mg* excess relative to the CI and CR chondrite reservoirs corresponding to 3.8 ± 1.1 and 11.9 ± 0.8 ppm, respectively. These variations cannot be accounted for by in situ decay of 26Al given their respective 27Al/24Mg ratios. Instead, it requires that Ryugu and the CI and CR parent bodies formed from material with a different initial 26Al/27Al ratio or that they are sourced from material with distinct Mg isotope compositions. Thus, our new Mg isotope data challenge the notion that Ryugu and CI chondrites share a common nucleosynthetic heritage.

DOI： 10.3847/2041-8213/ad09d9

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Publisher：Icarus  

Reflectance spectra (0.3–4 μm) of powder samples of the third largest stone C0002 returned from the asteroid Ryugu by JAXA Hayabusa2 mission were measured and compared with proximity observation data taken by the Optical Navigation Camera - Telescopic (ONC-T) and the Near-Infrared Spectrometer (NIRS3) onboard the Hayabusa2 spacecraft. Although the characteristics of the 2.7 μm absorption band due to structural hydroxyl of the Ryugu powder samples are consistent with CI1 chondrite meteorites, NIRS3 spectra of the global surface of Ryugu exhibit a wavelength shift of +6 nm in the 2.7 μm absorption band center in comparison with those of both the powder samples and an artificial crater on the asteroid formed by the Small Carry-on Impactor (SCI). This is consistent with effects of solar wind-induced space weathering being present across the global surface of asteroid Ryugu. The darkness of the Ryugu surface in comparison with the returned samples and an upturn in reflectance observed in the average ONC-T spectrum at ultraviolet wavelengths may also be due to space weathering.

DOI： 10.1016/j.icarus.2023.115755

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Scopus

Publisher：Meteoritics and Planetary Science  

Samples returned from the carbonaceous asteroid (162173) Ryugu by the Hayabusa2 mission revealed that Ryugu is composed of materials consistent with CI chondrites and some types of space weathering. We report detailed mineralogy of the fine-grained Ryugu samples allocated to our “Sand” team and report additional space weathering features found on the grains. The dominant mineralogy is composed of a fine-grained mixture of Mg-rich saponite and serpentine, magnetite, pyrrhotite, pentlandite, dolomite, and Fe-bearing magnesite. These grains have mineralogy comparable to that of CI chondrites, showing severe aqueous alteration but lacking ferrihydrite and sulfate. These results are similar to previous works on large Ryugu grains. In addition to the major minerals, we also find many minerals that are rare or have not been reported among CI chondrites. Accessory minerals identified are hydroxyapatite, Mg-Na phosphate, olivine, low-Ca pyroxene, Mg-Al spinel, chromite, manganochromite, eskolaite, ilmenite, cubanite, polydymite, transjordanite, schreibersite, calcite, moissanite, and poorly crystalline phyllosilicate. We also show scanning transmission electron microscope and scanning electron microscope compositional maps and images of some space-weathered grains and severely heated and melted grains. Although our mineralogical results are consistent with that of millimeter-sized grains, the fine-grained fraction is best suited to investigate impact-induced space weathering.

DOI： 10.1111/maps.14093

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Publisher：Meteoritics and Planetary Science  

The Hayabusa2 mission sampled Ryugu, an asteroid that did not suffer extensive thermal metamorphism, and returned rocks to the Earth with no significant air exposure. It therefore offers a unique opportunity to study the redox state of carbonaceous Cb-type asteroids and evaluate the overall redox state of the most primitive rocks of the solar system. An analytical framework was developed to investigate the iron mineralogy and valence state in extraterrestrial material at the micron scale by combining x-ray diffraction, conventional Mössbauer (MS), and nuclear forward scattering (NFS) spectroscopies. An array of standard minerals was analyzed and cross-calibrated between MS and NFS. Then, MS and NFS spectra on three Ryugu grains were collected at the bulk and the micron scales. In Ryugu samples, iron is essentially accommodated in magnetite, clay minerals (serpentine–smectite), and sulfides. Only a single set of Mössbauer parameters was necessary to account for the entire variability observed in MS and NFS spectra, at all spatial scales investigated. These parameters therefore make up a fully consistent iron mineralogical model for the Ryugu samples. As far as MS and NFS spectroscopies are concerned, Ryugu grains are overall similar to each other and share most of their mineralogical features with CI-type chondrites. In detail however, no ferrihydrite is found in Ryugu particles even at the very sensitive scale of Mössbauer spectroscopy. The typical Fe3+/Fetot of clay minerals is much lower than typical redox ratios measured in CI chondrites (Fe3+/Fetot = 85%–90%). Furthermore, magnetite from Ryugu is stoichiometric with no significant maghemite component, whereas up to 12% of maghemite was previously identified in the Orgueil's so-called magnetite. These differences suggest that most CI meteorites suffered terrestrial alteration and that the preterrestrial composition of these carbon-rich samples was less oxidized than previously measured. However, it is not clear yet whether or not the parent bodies of CI chondrites were as reduced as Ryugu. Finally, the high spatial resolution of NFS allows to disentangle the redox state and the crystal chemistry of iron accommodated in serpentine and smectite. The most likely polytype of serpentine is lizardite, containing <35% of Fe3+, a fraction of which being tetrahedrally coordinated. Smectite is more oxidized (Fe3+/Fetot > 65%) and mainly contains octahedral ferric iron. This finding implies that these clays formed from highly alkaline fluids and the spatial variability highlighted here may suggest a temporal evolution or a spatial variability of the nature of this fluid.

DOI： 10.1111/maps.14098

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Publisher：Earth, Planets and Space  

Developing a cleanroom and clean chambers (CCs) for Hayabusa2 returned samples has been discussed with the committee for Hayabusa2 sample curation facility since 2015. One major difference from the specifications of the CCs used for Itokawa samples is that a part of samples was decided to be handled and preserved in vacuum to avoid terrestrial nitrogen contamination with organics or unknown materials that might easily react with the samples. Thus, the CCs for Hayabusa2 samples were divided into two CCs for vacuum processes and three CCs for purified nitrogen conditions. The cleanroom was built in summer 2017, while the CCs were installed in the summer of 2018. After the installation of the CCs, instruments for initial descriptions, sample containers, handling tools for powder and particle samples, and jigs to assist handling samples were developed in parallel with functional checks and repeated rehearsals between the fall of 2018 and the fall of 2020. The curatorial works on Hayabusa2-retuned samples were conducted as previously planned. Simultaneously, contaminations and influences of inorganics, organics, microbial, and magnetic constructs have been assessed to evaluate their potential effects on the analysis of the returned samples. Additionally, the tools used to touch samples directly have been demagnetized to avoid sample magnetization during their handling and the tool magnetization was measured before and after their usages. The series of developments and experiences from the curatorial works of Hayabusa2-returned samples represent valuable implications for future sample return missions. Graphical Abstract: [Figure not available: see fulltext.].

DOI： 10.1186/s40623-023-01924-2

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Publisher：Meteoritics and Planetary Science  

We report a Fourier transform infrared analysis of functional groups in insoluble organic matter (IOM) extracted from a series of 100–500 μm Ryugu grains collected during the two touchdowns of February 22 and July 11, 2019. IOM extracted from most of the samples is very similar to IOM in primitive CI, CM, and CR chondrites, and shows that the extent of thermal metamorphism in Ryugu regolith was, at best, very limited. One sample displays chemical signatures consistent with a very mild heating, likely due to asteroidal collision impacts. We also report a lower carbonyl abundance in Ryugu IOM samples compared to primitive chondrites, which could reflect the accretion of a less oxygenated precursor by Ryugu. The possible effects of hydrothermal alteration and terrestrial weathering are also discussed. Last, no firm conclusions could be drawn on the origin of the soluble outlier phases, observed along with IOM in this study and in the preliminary analysis of Ryugu samples. However, it is clear that the HF/HCl residues presented in this publication are a mix between IOM and the nitrogen-rich outlier phase.

DOI： 10.1111/maps.14097

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Language：English   Publisher：Science Advances  

Studies of material returned from Cb asteroid Ryugu have revealed considerable mineralogical and chemical heterogeneity, stemming primarily from brecciation and aqueous alteration. Isotopic anomalies could have also been affected by delivery of exogenous clasts and aqueous mobilization of soluble elements. Here, we show that isotopic anomalies for mildly soluble Cr are highly variable in Ryugu and CI chondrites, whereas those of Ti are relatively uniform. This variation in Cr isotope ratios is most likely due to physicochemical fractionation between 54Cr-rich presolar nanoparticles and Cr-bearing secondary minerals at the millimeter-scale in the bulk samples, likely due to extensive aqueous alteration in their parent bodies that occurred 5:2þ11::84 Ma after Solar System birth. In contrast, Ti isotopes were marginally affected by this process. Our results show that isotopic heterogeneities in asteroids are not all nebular or accretionary in nature but can also reflect element redistribution by water.

DOI： 10.1126/sciadv.adi7048

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PubMed

Language：English   Publisher：Nature Communications  

The sample from the near-Earth carbonaceous asteroid (162173) Ryugu is analyzed in the context of carbonaceous meteorites soluble organic matter. The analysis of soluble molecules of samples collected by the Hayabusa2 spacecraft shines light on an extremely high molecular diversity on the C-type asteroid. Sequential solvent extracts of increasing polarity of Ryugu samples are analyzed using mass spectrometry with complementary ionization methods and structural information confirmed by nuclear magnetic resonance spectroscopy. Here we show a continuum in the molecular size and polarity, and no organomagnesium molecules are detected, reflecting a low temperature and water-rich environment on the parent body approving earlier mineralogical and chemical data. High abundance of sulfidic and nitrogen rich compounds as well as high abundance of ammonium ions confirm the water processing. Polycyclic aromatic hydrocarbons are also detected in a structural continuum of carbon saturations and oxidations, implying multiple origins of the observed organic complexity, thus involving generic processes such as earlier carbonization and serpentinization with successive low temperature aqueous alteration.

DOI： 10.1038/s41467-023-42075-y

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PubMed

Publisher：Communications Earth and Environment  

Returned samples from Cb-type asteroid (162173) Ryugu exhibit very dark spectra in visible and near-infrared ranges, generally consistent with the Hayabusa2 observations. A critical difference is that a structural water absorption of hydrous silicates is around twice as deep in the returned samples compared with those of Ryugu’s surface, suggesting Ryugu surface is more dehydrated. Here we use laboratory experiments data to indicate the spectral differences between returned samples and asteroid surface are best explained if Ryugu surface has (1) higher porosity, (2) larger particle size, and (3) more space-weathered condition, with the last being the most effective. On Ryugu, space weathering by micrometeoroid bombardments promoting dehydration seem to be more effective than that by solar-wind implantation. Extremely homogeneous spectra of the Ryugu’s global surface is in contrast with the heterogeneous S-type asteroid (25143) Itokawa’s spectra, which suggests space weathering has proceeded more rapidly on Cb-type asteroids than S-type asteroids.

DOI： 10.1038/s43247-023-00991-3

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Language：English   Publisher：Nature Communications  

Samples from the carbonaceous asteroid (162173) Ryugu provide information on the chemical evolution of organic molecules in the early solar system. Here we show the element partitioning of the major component ions by sequential extractions of salts, carbonates, and phyllosilicate-bearing fractions to reveal primordial brine composition of the primitive asteroid. Sodium is the dominant electrolyte of the salt fraction extract. Anions and NH4+ are more abundant in the salt fraction than in the carbonate and phyllosilicate fractions, with molar concentrations in the order SO42−> Cl−> S2O32−> NO3−> NH4+. The salt fraction extracts contain anionic soluble sulfur-bearing species such as S n-polythionic acids (n < 6), C n-alkylsulfonates, alkylthiosulfonates, hydroxyalkylsulfonates, and hydroxyalkylthiosulfonates (n < 7). The sulfur-bearing soluble compounds may have driven the molecular evolution of prebiotic organic material transforming simple organic molecules into hydrophilic, amphiphilic, and refractory S allotropes.

DOI： 10.1038/s41467-023-40871-0

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PubMed

Publisher：Meteoritics and Planetary Science  

We report μm-scale nondestructive infrared (IR) hyperspectral results (IR computed tomography, IR-CT) in 3-D and IR surface imaging, IR-S) in 2-D, at SOLEIL) combined with X-ray nano-computed tomography analyses (at SPring-8) performed on eight small Ryugu fragments extracted from mm-sized grains coming both from touchdown first and second sites. We describe the multiscale assembly of phyllosilicates, carbonates, sulfides, oxides, and organics. Two types of silicates, as well as diverse kinds of organic matter, were detected inside Ryugu material. Their spatial correlations are described to discuss the role of the mineralogical microenvironments in the formation/evolution of organic matter. In particular, we have shown that there is a redistribution of the organic matter diffuse component during aqueous alteration on the parent body, with a preferential circulation among fine-grained phyllosilicates.

DOI： 10.1111/maps.14068

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Publisher：Journal of Analytical Atomic Spectrometry  

Mass spectrometry of noble gas isotopes extracted from limited amounts of extraterrestrial materials delivered by robotic space missions requires high sensitivity, high ion transmission, low detection limit, and several other characteristics not readily available in commercial instruments. We compared two different configurations of electron impact ionisation. We concluded that the ion source with cylindrical symmetry and without a magnetic field in the ionisation region is better for analyzing all stable noble gas isotopes extracted from sub-milligram extraterrestrial samples. Isotopic analyses of noble gases retrieved using multi-step heating of sub-mg samples delivered from near-Earth (162 173) asteroid Ryugu support this conclusion.

DOI： 10.1039/d3ja00125c

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Language：English   Publisher：Scientific Reports  

In the samples collected from the asteroid Ryugu, magnetite displays natural remanent magnetization due to nebular magnetic field, whereas contemporaneously grown iron sulfide does not display stable remanent magnetization. To clarify this counterintuitive feature, we observed their nanoscale magnetic domain structures using electron holography and found that framboidal magnetites have an external magnetic field of 300 A m−1, similar to the bulk value, and its magnetic stability was enhanced by interactions with neighboring magnetites, permitting a disk magnetic field to be recorded. Micrometer-sized pyrrhotite showed a multidomain magnetic structure that was unable to retain natural remanent magnetization over a long time due to short relaxation time of magnetic-domain-wall movement, whereas submicron-sized sulfides formed a nonmagnetic phase. These results show that both magnetite and sulfide could have formed simultaneously during the aqueous alteration in the parent body of the asteroid Ryugu.

DOI： 10.1038/s41598-023-41242-x

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PubMed

Publisher：Meteoritics and Planetary Science  

The infrared spectral characteristics of organic-rich acid residues prepared from Ryugu samples returned by the JAXA Hayabusa2 mission generally match those from unheated carbonaceous chondrite meteorites, but the residues from Ryugu are richer in methyl and methylene functional groups and have higher CH2/CH3 ratios. Moreover, two distinct outlier carbonaceous phases are found; one with spectral characteristics of N-H functional groups, likely amides, and a second phase containing less nitrogen. Such infrared characteristics of Ryugu organic matter might indicate the pristine nature of the freshly collected samples and reflect the near-surface chemistry in the parent asteroid.

DOI： 10.1111/maps.14064

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Scopus

Publisher：Planetary Science Journal  

We present oxygen isotopic analyses of fragments of the near-Earth Cb-type asteroid Ryugu returned by the Hayabusa2 spacecraft that reinforce the close correspondence between Ryugu and CI chondrites. Small differences between Ryugu samples and CI chondrites in D¢17O can be explained at least in part by contamination of the latter by terrestrial water. The discovery that a randomly sampled C-complex asteroid is composed of CI-chondrite-like rock, combined with thermal models for formation prior to significant decay of the short-lived radioisotope 26Al, suggests that if lithified at the time of alteration, the parent body was small (=50 km radius). If the parent planetesimal was large (>50 km in radius), it was likely composed of high-permeability, poorly lithified sediment rather than consolidated rock.

DOI： 10.3847/PSJ/acea62

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Publisher：Nature Geoscience  

The Hayabusa2 spacecraft explored asteroid Ryugu and brought its surface materials to Earth. Ryugu samples resemble Ivuna-type (CI) chondrites—the most chemically primitive meteorites—and contain secondary phyllosilicates and carbonates, which are indicative of aqueous alteration. Understanding the conditions (such as temperature, redox state and fluid composition) during aqueous alteration is crucial to elucidating how Ryugu evolved to its present state, but little is known about the temporal changes in these conditions. Here we show that calcium carbonate (calcite) grains in Ryugu and Ivuna samples have variable 18O/16O and 13C/12C ratios that are, respectively, 24–46‰ and 65–108‰ greater than terrestrial standard values, whereas those of calcium–magnesium carbonate (dolomite) grains are much more homogeneous, ranging within 31–36‰ for oxygen and 67–75‰ for carbon. We infer that the calcite precipitated first over a wide range of temperatures and oxygen partial pressures, and that the proportion of gaseous CO2/CO/CH4 molecules changed temporally. By contrast, the dolomite formed later in a more oxygen-rich and thus CO2-dominated environment when the system was approaching equilibrium. The characteristic isotopic compositions of secondary carbonates in Ryugu and Ivuna are not observed for other hydrous meteorites, suggesting a unique evolutionary pathway for their parent asteroid(s).

DOI： 10.1038/s41561-023-01226-y

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Web of Science

Publisher：Astrophysical Journal Letters  

Ryugu is a second-generation C-type asteroid formed by the reassembly of fragments of a previous larger body in the main asteroid belt. While the majority of Ryugu samples returned by Hayabusa2 are composed of a lithology dominated by aqueously altered minerals, clasts of pristine olivine and pyroxene remain in the least-altered lithologies. These clasts are objects of great interest for revealing the composition of the dust from which the original building blocks of Ryugu's parent asteroid formed. Here we show that some grains rich in olivine, pyroxene, and amorphous silicates discovered in one millimeter-sized stone of Ryugu have infrared spectra similar to the D-type asteroid Hektor (a Jupiter Trojan), to comet Hale-Bopp, and to some anhydrous interplanetary dust particles of probable cometary origin. This result indicates that Ryugu's primary parent body incorporated anhydrous ingredients similar to the building blocks of asteroids (and possibly some comets) formed in the outer solar system, and that Ryugu retained valuable information on the formation and evolution of planetesimals at different epochs of our solar system's history.

DOI： 10.3847/2041-8213/acdf5c

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Language：English   Publisher：Science Advances  

Preliminary analyses of asteroid Ryugu samples show kinship to aqueously altered CI (Ivuna-type) chondrites, suggesting similar origins. We report identification of C-rich, particularly primitive clasts in Ryugu samples that contain preserved presolar silicate grains and exceptional abundances of presolar SiC and isotopically anomalous organic matter. The high presolar silicate abundance (104 ppm) indicates that the clast escaped extensive alteration. The 5 to 10 times higher abundances of presolar SiC (~235 ppm), N-rich organic matter, organics with N isotopic anomalies (1.2%), and organics with C isotopic anomalies (0.2%) in the primitive clasts compared to bulk Ryugu suggest that the clasts formed in a unique part of the protoplanetary disk enriched in presolar materials. These clasts likely represent previously unsampled outer solar system material that accreted onto Ryugu after aqueous alteration ceased, consistent with Ryugu’s rubble pile origin.

DOI： 10.1126/sciadv.adh1003

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Language：Japanese   Publisher：The Japanese Society for Planetary Sciences  

<p>小惑星リュウグウの物質が2020年12月に探査機はやぶさ2によって地球に持ち帰られた．その後，1年間の初期分析期間を経て，様々な科学的成果が得られている．著者は初期分析の一つである揮発性成分分析に携わった．再突入カプセル回収時のサンプルコンテナのガス採取・分析，リュウグウ固体試料の揮発性成分分析により，リュウグウ試料の経験した出来事の物理化学情報や年代学的情報が得られた．本稿では揮発性成分分析チームの活動について紹介する．</p>

DOI： 10.14909/yuseijin.32.2_133

CiNii Research

Publisher：Earth, Planets and Space  

We performed in-situ analysis on a ~ 1 mm-sized grain A0080 returned by the Hayabusa2 spacecraft from near-Earth asteroid (162173) Ryugu to investigate the relationship of soluble organic matter (SOM) to minerals. Desorption electrospray ionization-high resolution mass spectrometry (DESI-HRMS) imaging mapped more than 200 CHN, CHO, CHO–Na (sodium adducted), and CHNO soluble organic compounds. A heterogeneous spatial distribution was observed for different compound classes of SOM as well as among alkylated homologues on the sample surface. The A0080 sample showed mineralogy more like an Ivuna-type (CI) carbonaceous chondrite than other meteorites. It contained two different lithologies, which are either rich (lithology 1) or poor (lithology 2) in magnetite, pyrrhotite, and dolomite. CHN compounds were more concentrated in lithology 1 than in lithology 2; on the other hand, CHO, CHO–Na, and CHNO compounds were distributed in both lithologies. Such different spatial distribution of SOM is likely the result of interaction of the SOM with minerals, during precipitation of the SOM via fluid activity, or could be due to difference in transportation efficiencies of SOMs in aqueous fluid. Organic-related ions measured by time-of-flight secondary ion mass spectrometry (ToF–SIMS) did not coincide with the spatial distribution revealed by DESI-HRMS imaging. This result may be because the different ionization mechanism between DESI and SIMS, or indicate that the ToF–SIMS data would be mainly derived from methanol-insoluble organic matter in A0080. In the Orgueil meteorite, such relationship between altered minerals and SOM distributions was not observed by DESI-HRMS analysis and field-emission scanning electron microscopy, which would result from differences of SOM formation processes and sequent alteration process on the parent bodies or even on the Earth. Alkylated homologues of CHN compounds were identified in A0080 by DESI-HRMS imaging as observed in the Murchison meteorite, but not from the Orgueil meteorite. These compounds with a large C number were enriched in Murchison fragments with abundant carbonate grains. In contrast, such relationship was not observed in A0080, implying different formation or growth mechanisms for the alkylated CHN compounds by interaction with fluid and minerals on the Murchison parent body and asteroid Ryugu. Graphical Abstract: [Figure not available: see fulltext.]

DOI： 10.1186/s40623-023-01792-w

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Publisher：Geochimica et Cosmochimica Acta  

The hot water and acid extracts of two different Ryugu samples collected by the Hayabusa2 mission were analyzed for the presence of aliphatic amines and amino acids. The abundances and relative distributions of both classes of molecules were determined, as well as the enantiomeric compositions of the chiral amino acids. The Ryugu samples studied here were recovered from sample chambers A and C, which were composed of surface material, and a combination of surface and possible subsurface material, respectively. A total of thirteen amino acids were detected and quantitated in these samples, with an additional five amino acids that were tentatively identified but not quantitated. The abundances of four aliphatic amines identified in the Ryugu samples were also determined in the current work. Amino acids were observed in the acid hydrolyzed and unhydrolyzed hot water extracts of asteroid Ryugu regolith using liquid chromatography with UV fluorescence detection and high-resolution mass spectrometry. Conversely, aliphatic amines were only analyzed in the unhydrolyzed hot water Ryugu extracts. Two- to six-carbon (C2-C6) amino acids with individual abundances ranging from 0.02 to 15.8 nmol g−1, and one- to three-carbon (C1-C3) aliphatic amines with individual abundances from 0.05 to 34.14 nmol g−1, were found in the hot water extracts. Several non-protein amino acids that are rare in biology, including β-amino-n-butyric acid (β-ABA) and β-aminoisobuytric acid (β-AIB), were racemic or very nearly racemic, thus indicating their likely abiotic origins. Trace amounts of select protein amino acids that were enriched in the L-enantiomer may indicate low levels of terrestrial amino acid contamination in the samples. However, the presence of elevated abundances of free and racemic alanine, a common protein amino acid in terrestrial biology, and elevated abundances of the predominately free and racemic non-protein amino acids, β-ABA and β-AIB, indicate that many of the amino acids detected in the Ryugu water extracts were indigenous to the samples. Although the Ryugu samples have been found to be chemically similar to CI type carbonaceous chondrites, the measured concentrations and relative distributions of amino acids and aliphatic amines in Ryugu samples were notably different from those previously observed for the CI1.1 carbonaceous chondrite, Orgueil. This discrepancy could be the result of differences in the original chemical compositions of the parent bodies and/or alteration conditions, such as space weathering. In addition to α-amino acids that could have been formed by Strecker cyanohydrin synthesis during a low temperature aqueous alteration phase, β-, γ-, and δ-amino acids, including C3 – C5 straight-chain n-ω-amino acids that are not formed by Strecker synthesis, were also observed in the Ryugu extracts. The suite of amino acids measured in the Ryugu samples indicates that multiple amino acid formation mechanisms were active on the Ryugu parent body. The analytical techniques used here are well-suited to search for similar analytes in asteroid Bennu material collected by the NASA OSIRIS-REx mission scheduled for Earth return in September 2023.

DOI： 10.1016/j.gca.2023.02.017

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Publisher：Astrophysical Journal Letters  

Rock fragments of the Cb-type asteroid Ryugu returned to Earth by the JAXA Hayabusa2 mission share mineralogical, chemical, and isotopic properties with the Ivuna-type (CI) carbonaceous chondrites. Similar to CI chondrites, these fragments underwent extensive aqueous alteration and consist predominantly of hydrous minerals likely formed in the presence of liquid water on the Ryugu parent asteroid. Here we present an in situ analytical survey performed by secondary ion mass spectrometry from which we have estimated the D/H ratio of Ryugu’s hydrous minerals, D/HRyugu, to be [165 ± 19] × 10−6, which corresponds to δDRyugu = +59 ± 121‰ (2σ). The hydrous mineral D/HRyugu’s values for the two sampling sites on Ryugu are similar; they are also similar to the estimated D/H ratio of hydrous minerals in the CI chondrites Orgueil and Alais. This result reinforces a link between Ryugu and CI chondrites and an inference that Ryugu’s samples, which avoided terrestrial contamination, are our best proxy to estimate the composition of water at the origin of hydrous minerals in CI-like material. Based on this data and recent literature studies, the contribution of CI chondrites to the hydrogen of Earth’s surficial reservoirs is evaluated to be ∼3%. We conclude that the water responsible for the alteration of Ryugu’s rocks was derived from water ice precursors inherited from the interstellar medium; the ice partially re-equilibrated its hydrogen with the nebular H2 before being accreted on the Ryugu’s parent asteroid.

DOI： 10.3847/2041-8213/acc393

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Publisher：Geochimica et Cosmochimica Acta  

We have investigated several particles collected during each of two touchdowns of the Hayabusa2 spacecraft at the surface of the C-type asteroid 162173 Ryugu using various electron microscope techniques. Our detailed transmission electron microscopy study shows the presence of magnetite with various morphologies coexisting in close proximity. This is characteristic of CI chondrite-like materials and consistent with the mineral assemblages and compositions in the Ryugu parent body. We describe the microstructural characteristics of magnetite with different morphologies, which could have resulted from the chemical conditions (growth vs. diffusion rate) during their formation. Furthermore, we describe the presence of magnetites with a spherulitic structure composed of individual radiating fibers that are characterized by pervasive, homogeneously distributed euhedral to subhedral pores that have not been described in previous chondrite studies. This particular spherulitic structure is consistent with crystallization under nonequilibrium conditions. Additionally, the presence of a high density of defects within the magnetite fibers, the high surface/volume ratio of this morphology, and the presence of amorphous materials in several pores and at the edges of the acicular fibers further support their formation under nonequilibrium conditions. We suggest that the growth processes that lead to this structure result from the solution reaching a supersaturated state, resulting in an adjustment to a lower free energy condition via nucleation and rapid growth.

DOI： 10.1016/j.gca.2023.02.003

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Publisher：International Journal of Thermophysics  

The thermophysical properties of small Solar System bodies are essential to be determined, on which the thermal evolution of small bodies largely depends. The carbonaceous asteroid Ryugu is one of the small undifferentiated bodies formed in the early Solar System. Hayabusa2 explored the asteroid Ryugu and returned the surface samples in 2020 for detailed on-ground investigation, including measurements of thermal properties. Because the available sample amount was limited, this study developed a novel method to measure the thermal diffusivity of small and irregularly shaped samples of about 1 mm in diameter by combining lock-in thermography and periodic heating methods on the microscale. This method enables us to measure the thermal diffusivity of both flat-plate and granular shape samples by selecting the suitable detecting direction of the temperature response. Especially, when the sample has a flat-plate shape, the anisotropic distribution of the in-plane thermal diffusivity can be evaluated. This method was applied to six Ryugu samples, and the detailed anisotropic distribution of the thermal diffusivity was obtained. The measurement results showed that the samples show local thermal anisotropy caused by cracks and voids. The average thermal diffusivity among all samples was (2.8 to 5.8) × 10−7 m2·s. Based on the density and specific heat of the samples obtained independently, the thermal effusivity was estimated to be 791 J·(s1/2·m2·K) to 1253 J·(s1/2·m2·K), which is defined as the resistance of surface temperature to the change of thermal input. The determined thermal effusivity, often called thermal inertia in planetary science, is larger than the observed value of 225 ± 45 J· (s1/2·m2·K) of the asteroid Ryugu's surface, obtained from the diurnal temperature change of the rotating asteroid by a thermal infrared camera onboard Hayabuas2. This difference is likely to be attributed to the difference in the analytical scale between the sample and the surface boulders compared with the thermal diffusion length. Consequently, it was found that the present result is more representative of the thermal diffusivity and thermal inertia of local part of individual Ryugu particles.

DOI： 10.1007/s10765-023-03158-6

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Language：English   Publisher：Nature Communications  

The pristine sample from the near-Earth carbonaceous asteroid (162173) Ryugu collected by the Hayabusa2 spacecraft enabled us to analyze the pristine extraterrestrial material without uncontrolled exposure to the Earth’s atmosphere and biosphere. The initial analysis team for the soluble organic matter reported the detection of wide variety of organic molecules including racemic amino acids in the Ryugu samples. Here we report the detection of uracil, one of the four nucleobases in ribonucleic acid, in aqueous extracts from Ryugu samples. In addition, nicotinic acid (niacin, a B3 vitamer), its derivatives, and imidazoles were detected in search for nitrogen heterocyclic molecules. The observed difference in the concentration of uracil between A0106 and C0107 may be related to the possible differences in the degree of alteration induced by energetic particles such as ultraviolet photons and cosmic rays. The present study strongly suggests that such molecules of prebiotic interest commonly formed in carbonaceous asteroids including Ryugu and were delivered to the early Earth.

DOI： 10.1038/s41467-023-36904-3

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PubMed

Publisher：Geochimica et Cosmochimica Acta  

Carbonaceous chondrites are considered to have originated from C-type asteroids and represent some of the most primitive material in our solar system. Furthermore, since carbonaceous chondrites can contain significant quantities of volatile elements, they may have played a crucial role in supplying volatiles and organic material to Earth and other inner solar system bodies. However, a major challenge of unravelling the volatile composition of chondritic meteorites is distinguishing between which features were inherited from the parent body, and what may be a secondary feature attributable to terrestrial weathering. In December 2020, the Hayabusa2 mission of the Japan Aerospace Exploration Agency (JAXA) successfully returned surface material from the C-type asteroid (162173) Ryugu to Earth. This material has now been classified as closely resembling CI-type chondrites, which are the most chemically pristine meteorites. The analysis of material from the surface of Ryugu therefore provides a unique opportunity to analyse the volatile composition of material that originated from a CI-type asteroid without the complications arising from terrestrial contamination. Given their highly volatile nature, the noble gas and nitrogen inventories of chondrites are highly sensitive to different alteration processes on the asteroid parent body, and to terrestrial contamination. Here, we investigate the nitrogen and noble gas signature of two pelletized grains collected from the first and second touchdown sites (Okazaki et al., 2022a), to provide an insight into the formation and alteration history of Ryugu. The concentration of trapped noble gas in the Ryugu samples is greater than the average composition of previously measured CI chondrites and are primarily derived from phase Q, although a significant contribution of presolar nanodiamond Xe-HL is noted. The large noble gas concentrations coupled with a significant contribution of presolar nanodiamonds suggests that the Ryugu samples may represent some of the most primitive unprocessed material from the early solar system. In contrast to the noble gases, the abundance of nitrogen and δ15N composition of the two Ryugu pellets are lower than the average CI chondrite value. We attribute the lower nitrogen abundances and δ15N measured in this study to the preferential loss of a 15N-rich phase from our samples during aqueous alteration on the parent planetesimal. The analyses of other grains returned from Ryugu have shown large variations in nitrogen concentrations and δ15N indicating that alteration fluids heterogeneously interacted with material now present on the surface of Ryugu. Finally, the ratio of trapped noble gases to nitrogen is higher than CI chondrites, and is closer to refractory phase Q and nanodiamonds. This indicates that Ryugu experienced aqueous alteration that led to the significant and variable loss of nitrogen, likely from soluble organic matter, without modification of the noble gas budget, which is primarily hosted in insoluble organic matter and presolar diamonds and is therefore more resistant to aqueous alteration.

DOI： 10.1016/j.gca.2023.01.020

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Publisher：Geochemical Perspectives Letters  

The Hayabusa 2 spacecraft brought back to Earth grains of the carbonaceous asteroid Ryugu. Such grains represent the pristine state of CI chondritic materials and have been preserved from exposure to Earth's atmosphere. Here, we show evidence of the presence of organics trapped within the interlayer space of smectite layers in Ryugu grains. No such organics are found in theOrgueil CI meteorite. We put forward that the organics within the interlayer space of smectite inOrgueil CI meteorite were lost during their oxidation on Earth.Also, we propose that the presence of organics within the interlayers space of smectite might be responsible for the possible NH infrared signature observed in Ryugu particles and potentially to a few large C-type asteroids including Ceres.

DOI： 10.7185/geochemlet.2307

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41550-023-01938-6

Language：English   Publisher：(一社)日本放射線影響学会  

2011年に発生した福島第一原子力発電所(FDNPP)事故時に従事していた東京電力(TEPCO)作業員を対象とし、検出された放射線量と検診データとの相関性を検討した。2006年3月～2013年1月までの期間内に、定期健康診断を受診したTEPCO男性作業員2164例を調査対象とし、始めに、緊急作業員585例の血液学的データと交絡因子により対数線形回帰分析を行い、2011年3月時に受けた内部被曝の影響を調べた。次に、緊急作業員1801例に対しては、原発事故前後の内部/外部被曝線量と血液学的データおよび交絡因子との相関性について検討した。その結果、作業員585例に関しては2011年3月での内部被曝は主に甲状腺線量に起因し、骨髄線量への影響はみられなかった。また、事故後では事故前に比べ、単球、好酸球および好塩基球が僅かに増加した一方、喫煙や飲酒の頻度は大幅に減少していた。外部線量ではヘモグロビン(Hb)、赤血球および好酸球との正相関が示され、年齢、ヘマトクリットおよび飲酒の頻度では負の相関性が認められた。さらに、これらの変数のうち、Hbでは外部線量と最も高い相関性が示された。以上より、本研究で得られた知見は今後、原子力関連事故に際し、緊急作業員の健康状態の評価に有用な参照値となり得ることが示唆された。

Publisher：Astronomy and Astrophysics  

Context. The current period is conducive to exploring our Solar System's origins with recent and future space sample return missions, which provide invaluable information from known Solar System asteroids and comets The Hayabusa2 mission of the Japan Aerospace Exploration Agency (JAXA) recently brought back samples from the surface of the Ryugu carbonaceous asteroid. Aims. We aim to identify the different forms of chemical composition of organic matter and minerals that constitute these Solar System primitive objects, to shed light on the Solar System's origins. Methods. In this work, we recorded infrared (IR) hyper-spectral maps of whole-rock Ryugu asteroid samples at the highest achievable spatial resolution with a synchrotron in the mid-IR (MIR). Additional global far-IR (FIR) spectra of each sample were also acquired. Results. The hyper-spectral maps reveal the variability of the functional groups at small scales and the intimate association of phyl-losilicates with the aliphatic components of the organic matter present in Ryugu. The relative proportion of column densities of the identified IR functional groups (aliphatics, hydroxyl + interlayer and/or physisorbed water, carbonyl, carbonates, and silicates) giving access to the composition of the Ryugu samples is estimated from these IR hyper-spectral maps. Phyllosilicate spectra reveal the presence of mixtures of serpentine and saponite. We do not detect anhydrous silicates in the samples analysed, at the scales probed. The carbonates are dominated by dolomite. Aliphatics organics are distributed over the whole samples at the micron scale probed with the synchrotron, and intimately mixed with the phyllosilicates. The aromatic C=C contribution could not be safely deconvolved from OH in most spectra, due to the ubiquitous presence of hydrated minerals. The peak intensity ratios of the organics methylene to methyl (CH2/CH3) of the Ryugu samples vary between about 1.5 and 2.5, and are compared to the ratios in chondrites from types 1 to 3. Overall, the mineralogical and organic characteristics of the Ryugu samples show similarities with those of CI chondrites, although with a noticeably higher CH2/CH3 in Ryugu than generally measured in C1 chondrites collected on Earth, and possibly a higher carbonate content.

DOI： 10.1051/0004-6361/202244702

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Publisher：Earth, Planets and Space  

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, such as 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. Graphical Abstract: [Figure not available: see fulltext.].

DOI： 10.1186/s40623-022-01758-4

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Language：English   Publisher：Science  

Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed 17 Ryugu samples measuring 1 to 8 millimeters. Carbon dioxide-bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu's parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and calcium- and aluminum-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed through aqueous alteration reactions at low temperature, high pH, and water/rock ratios of <1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate that Ryugu's parent body formed ~2 million years after the beginning of Solar System formation.

DOI： 10.1126/science.abn8671

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PubMed

Language：English   Publisher：Science  

Samples of the carbonaceous asteroid (162173) Ryugu were collected and brought to Earth by the Hayabusa2 spacecraft. We investigated the macromolecular organic matter in Ryugu samples and found that it contains aromatic and aliphatic carbon, ketone, and carboxyl functional groups. The spectroscopic features of the organic matter are consistent with those in chemically primitive carbonaceous chondrite meteorites that experienced parent-body aqueous alteration (reactions with liquid water). The morphology of the organic carbon includes nanoglobules and diffuse carbon associated with phyllosilicate and carbonate minerals. Deuterium and/or nitrogen-15 enrichments indicate that the organic matter formed in a cold molecular cloud or the presolar nebula. The diversity of the organic matter indicates variable levels of aqueous alteration on Ryugu’s parent body.

DOI： 10.1126/science.abn9057

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Language：English   Publisher：Science  

The Hayabusa2 spacecraft collected samples from the surface of the carbonaceous near-Earth asteroid (162173) Ryugu and brought them to Earth. The samples were expected to contain organic molecules, which record processes that occurred in the early Solar System. We analyzed organic molecules extracted from the Ryugu surface samples. We identified a variety of molecules containing the atoms CHNOS, formed by methylation, hydration, hydroxylation, and sulfurization reactions. Amino acids, aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-heterocyclic compounds were detected, which had properties consistent with an abiotic origin. These compounds likely arose from an aqueous reaction on Ryugu’s parent body and are similar to the organics in Ivuna-type meteorites. These molecules can survive on the surfaces of asteroids and be transported throughout the Solar System.

DOI： 10.1126/science.abn9033

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Language：English   Publisher：Science  

Carbonaceous meteorites are thought to be fragments of C-type (carbonaceous) asteroids. Samples of the C-type asteroid (162173) Ryugu were retrieved by the Hayabusa2 spacecraft. We measured the mineralogy and bulk chemical and isotopic compositions of Ryugu samples. The samples are mainly composed of materials similar to those of carbonaceous chondrite meteorites, particularly the CI (Ivuna-type) group. The samples consist predominantly of minerals formed in aqueous fluid on a parent planetesimal. The primary minerals were altered by fluids at a temperature of 37° ± 10°C, about 5:2+0.8-0.7 million (statistical) or 5:2+1.6-2.1 million (systematic) years after the formation of the first solids in the Solar System. After aqueous alteration, the Ryugu samples were likely never heated above ~100°C. The samples have a chemical composition that more closely resembles that of the Sun's photosphere than other natural samples do.

DOI： 10.1126/science.abn7850

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Language：English   Publisher：Science  

The near-Earth carbonaceous asteroid (162173) Ryugu is expected to contain volatile chemical species that could provide information on the origin of Earth’s volatiles. Samples of Ryugu were retrieved by the Hayabusa2 spacecraft. We measured noble gas and nitrogen isotopes in Ryugu samples and found that they are dominated by presolar and primordial components, incorporated during Solar System formation. Noble gas concentrations are higher than those in Ivuna-type carbonaceous (CI) chondrite meteorites. Several host phases of isotopically distinct nitrogen have different abundances among the samples. Our measurements support a close relationship between Ryugu and CI chondrites. Noble gases produced by galactic cosmic rays, indicating a ~5 million year exposure, and from implanted solar wind record the recent irradiation history of Ryugu after it migrated to its current orbit.

DOI： 10.1126/science.abo0431

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Language：English   Publisher：Nature Communications  

Chondrule-like objects and Ca-Al-rich inclusions (CAIs) are discovered in the retuned samples from asteroid Ryugu. Here we report results of oxygen isotope, mineralogical, and compositional analysis of the chondrule-like objects and CAIs. Three chondrule-like objects dominated by Mg-rich olivine are 16O-rich and -poor with Δ17O (=δ17O – 0.52 × δ18O) values of ~ –23‰ and ~ –3‰, resembling what has been proposed as early generations of chondrules. The 16O-rich objects are likely to be melted amoeboid olivine aggregates that escaped from incorporation into 16O-poor chondrule precursor dust. Two CAIs composed of refractory minerals are 16O-rich with Δ17O of ~ –23‰ and possibly as old as the oldest CAIs. The discovered objects (<30 µm) are as small as those from comets, suggesting radial transport favoring smaller objects from the inner solar nebula to the formation location of the Ryugu original parent body, which is farther from the Sun and scarce in chondrules. The transported objects may have been mostly destroyed during aqueous alteration in the Ryugu parent body.

DOI： 10.1038/s41467-023-36268-8

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Language：English   Publisher：Nature Astronomy  

Initial analyses showed that asteroid Ryugu’s composition is close to CI (Ivuna-like) carbonaceous chondrites (CCs) – the chemically most primitive meteorites, characterized by near-solar abundances for most elements. However, some isotopic signatures (for example, Ti, Cr) overlap with other CC groups, so the details of the link between Ryugu and the CI chondrites are not yet fully clear. Here we show that Ryugu and CI chondrites have the same zinc and copper isotopic composition. As the various chondrite groups have very distinct Zn and Cu isotopic signatures, our results point at a common genetic heritage between Ryugu and CI chondrites, ruling out any affinity with other CC groups. Since Ryugu’s pristine samples match the solar elemental composition for many elements, their Zn and Cu isotopic compositions likely represent the best estimates of the solar composition. Earth’s mass-independent Zn isotopic composition is intermediate between Ryugu/CC and non-carbonaceous chondrites (NCs), suggesting a contribution of Ryugu-like material to Earth’s budgets of Zn and other moderately volatile elements.

DOI： 10.1038/s41550-022-01846-1

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Language：English   Publisher：Springer Nature  

Without a protective atmosphere, space-exposed surfaces of airless Solar System bodies gradually experience an alteration in composition, structure and optical properties through a collective process called space weathering. The return of samples from near-Earth asteroid (162173) Ryugu by Hayabusa2 provides the first opportunity for laboratory study of space-weathering signatures on the most abundant type of inner solar system body: a C-type asteroid, composed of materials largely unchanged since the formation of the Solar System. Weathered Ryugu grains show areas of surface amorphization and partial melting of phyllosilicates, in which reduction from Fe³⁺ to Fe²⁺ and dehydration developed. Space weathering probably contributed to dehydration by dehydroxylation of Ryugu surface phyllosilicates that had already lost interlayer water molecules and to weakening of the 2.7 µm hydroxyl (–OH) band in reflectance spectra. For C-type asteroids in general, this indicates that a weak 2.7 µm band can signify space-weathering-induced surface dehydration, rather than bulk volatile loss.

DOI： 10.1038/s41550-022-01841-6

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Publisher：ACS Earth and Space Chemistry  

Sulfur comprises various compound forms in natural environments and could have played important roles in chemical evolution in the universe. Various soluble organosulfur compounds and inorganic sulfur oxides were identified in the methanol extracts of three carbonaceous chondrites (Murchison, Tagish Lake, and Allende) using high-performance liquid chromatography coupled with high-resolution mass spectrometry. The most abundant S-bearing organic compound was hydroxymethane sulfonic acid (HMSA, HOCH2SO3H), which is reported from a meteorite for the first time, at a concentration of 201 nmol/g in the Murchison meteorite. Because HMSA is known to be produced by the reaction of formaldehyde (HCHO) and bisulfite (HSO3-), this result indicates that formaldehyde should be abundant prior to the reaction with HSO3- in the meteorite parent bodies. The bisulfite derivatives of glycolaldehyde and glyceraldehyde were further identified in the methanol extract, suggesting that the formose reaction had proceeded during the aqueous alteration. The finding of these sugar-HSO3- adducts suggests that the formose reaction might have been controlled by the presence of sulfur species in the body. Furthermore, alkylated sulfonic acids (CnH2n+1SO3H) were also present as a series of homologous compounds up to C14 in the Murchison meteorite, even though previous studies found only C1-C4 sulfonic acids. In addition to organosulfur compounds, variable inorganic polysulfur oxides and acids were detected. The abundant S-bearing compounds in the meteorites imply important roles of sulfur in the organic reactions in carbonaceous asteroids.

DOI： 10.1021/acsearthspacechem.2c00157

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Publisher：Earth, Planets and Space  

Sample-return missions allow the study of materials collected directly from celestial bodies, unbiased by atmospheric entry effects and/or terrestrial alteration and contamination phenomena, using state-of-the-art techniques which are available only in a laboratory environment—but only if the collected material stays pristine. The scarcity of outer-space unaltered material recovered until now makes this material extremely precious for the potential scientific insight it can bring. To maximize the scientific output of current and future sample-return missions, the scientific community needs to plan for ways of storing, handling, and measuring this precious material while preserving their pristine state for as long as the ‘invasiveness’ of measurements allows. In July 2021, as part of the Hayabusa2 (JAXA) “Stone” preliminary examination team, we received several microscopic particles from the asteroid Ryugu, with the goal of performing IR hyper-spectral imaging and IR micro-tomography studies. Here, we describe the sample transfer, handling methods and analytical pipeline we implemented to study this very precious material while minimizing and surveilling their alteration history on Earth. Graphical Abstract: [Figure not available: see fulltext.]

DOI： 10.1186/s40623-022-01762-8

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Publisher：Earth, Planets and Space  

The Hayabusa2 spacecraft succeeded in sampling and returning materials from the C-type, near-Earth asteroid (162173) Ryugu. As part of the Hayabusa2 Initial Analyses, chemical and isotopic compositions of volatile species were measured. The samples analyzed were grains of about 1 mm in diameter and were individually treated without exposure to Earth’s atmosphere throughout the entire analytical/experimental processes to minimize alteration and contamination effects by adsorption of Earth’s atmosphere or chemical reactions with reactive species such as oxygen and water in Earth’s atmosphere. In order to perform spectroscopic and electron-microscopic observations in advance of a series of the isotopic measurements, the sample surface needed to be smoothed. We employed a pelletization method to obtain the required flatness for the returned samples because pelletization is a less sample-consuming method compared to mechanical polishing, microtomy, or ion milling. In order to perform the subsequent analyses, the samples must undergo minimal contamination during the pelletization procedure and be easy to remove from the pelletization tools. Therefore, embedding with resins or low-melting-point metals was not employed. Under these constraints, tools and methods for sample pelletization, handling, and transportation were developed. The tools developed for pelletization and housing also contributed to easier handling of small (less than about 1 mm in diameter) samples. Here we describe the methods and the tools that enable treatment of pristine asteroidal samples under non-atmospheric exposure conditions throughout transportation, weighing, pelletization, and installation into the instruments for chemical and isotopic measurements. The methods and tools we developed can be applied to other small samples including meteorites, cosmic dust, and future returned samples. Graphical Abstract: [Figure not available: see fulltext.].

DOI： 10.1186/s40623-022-01747-7

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Language：English   Publisher：Science Advances  

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: 16O-rich (associated with refractory inclusions) and 16O-poor (associated with chondrules). Both the 16O-rich and 16O-poor minerals probably formed in the inner solar protoplanetary disk and were subsequently transported outward. The abundance ratios of the 16O-rich to 16O-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.

DOI： 10.1126/sciadv.ade2067

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Language：English   Publisher：Science Advances  

Little is known about the origin of the spectral diversity of asteroids and what it says about conditions in the protoplanetary disk. Here, we show that samples returned from Cb-type asteroid Ryugu have Fe isotopic anomalies indistinguishable from Ivuna-type (CI) chondrites, which are distinct from all other carbonaceous chondrites. Iron isotopes, therefore, demonstrate that Ryugu and CI chondrites formed in a reservoir that was different from the source regions of other carbonaceous asteroids. Growth and migration of the giant planets destabilized nearby planetesimals and ejected some inward to be implanted into the Main Belt. In this framework, most carbonaceous chondrites may have originated from regions around the birthplaces of Jupiter and Saturn, while the distinct isotopic composition of CI chondrites and Ryugu may reflect their formation further away in the disk, owing their presence in the inner Solar System to excitation by Uranus and Neptune.

DOI： 10.1126/sciadv.add8141

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Publisher：Earth, Planets and Space  

A fundamental parameter-based quantification scheme for confocal XRF was applied to sub-micron synchrotron radiation X-ray fluorescence (SR-XRF) data obtained at the beamline P06 of the Deutsches Elektronen-Synchrotron (DESY, Hamburg, Germany) from two sections C0033-01 and C0033-04 that were wet cut from rock fragment C0033 collected from Cb-type asteroid (162173) Ryugu by JAXA’s Hayabusa2 mission. Trace-element quantifications show that C0033 bulk matrix is CI-like, whereas individual mineral grains (i.e., magnetite, pyrrhotite, dolomite, apatite and breunnerite) show, depending on the respective phase, minor to strong deviations. The non-destructive nature of SR-XRF coupled with a new PyMca (a Python toolkit for XRF data analysis)-based quantification approach, performed in parallel with the synchrotron experiments, proves to be an attractive tool for the initial analysis of samples from return missions, such as Hayabusa2 and OSIRIS-REx, the latter returning material from a B-type asteroid (101955) Bennu in 2023.

DOI： 10.1186/s40623-022-01726-y

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Language：English   Publisher：American Association for the Advancement of Science (AAAS)  

The Hayabusa2 spacecraft returned to Earth from the asteroid 162173 Ryugu on 6 December 2020. One day after the recovery, the gas species retained in the sample container were extracted and measured on-site and stored in gas collection bottles. The container gas consists of helium and neon with an extraterrestrial ³He/⁴He and ²⁰Ne/²²Ne ratios, along with some contaminant terrestrial atmospheric gases. A mixture of solar and Earth’s atmospheric gas is the best explanation for the container gas composition. Fragmentation of Ryugu grains within the sample container is discussed on the basis of the estimated amount of indigenous He and the size distribution of the recovered Ryugu grains. This is the first successful return of gas species from a near-Earth asteroid.

DOI： 10.1126/sciadv.abo7239

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CiNii Research

Publisher：Meteoritics and Planetary Science  

Asteroids and comets are thought to form in the inner and outer solar systems, respectively. Chondritic porous and smooth interplanetary dust particles (CP IDPs and CS IDPs, respectively) in the stratosphere are regarded as dust grains from comets and hydrated asteroids, respectively. Here, we describe an Antarctic micrometeorite (AMM) composed of lithologies of both CP and CS IDPs. In addition to the CS IDP-like compact lithology that experienced severe aqueous alteration, the CP IDP-like porous lithology shows evidence of very weak aqueous alteration. The structure of the organic matter in the porous lithology varies from that in the CP IDPs to aromatic-rich organic matter. In contrast, the structure of the organic matter in the compact lithology is homogenous, which is consistent with higher degrees of aqueous alteration. Its structure is more similar to that of CP IDPs and Wild 2 samples than that of meteoritic insoluble organic matter, suggesting that the compact lithology formed from the porous lithology. Some CP IDPs are related to cometary dust streams, such as those originating from 26P/Grigg-Skjellerup. In addition, the presence of this AMM indicates an additional origin of the CP IDPs and their equivalent AMMs. The mineralogy and organic chemistry of this AMM suggest that its parent body was composed of the same building blocks as those of the comets, and later experienced incomplete aqueous alteration. The AMM probably formed as microbreccia in the regolith layer composed of materials from a CP IDP-like crust and a hydrated interior.

DOI： 10.1111/maps.13919

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Publisher：Journal of Geophysical Research: Planets  

In this study, systematic rock magnetic measurements and saturation isothermal remanent magnetization (SIRM) paleointensity calibration experiments were conducted for the returned samples from C-type asteroid (162173) Ryugu and two carbonaceous chondrites (Orgueil and Tagish Lake) to evaluate the remanence carriers of the Ryugu sample and its ability as a paleomagnetic recorder. Our magnetic measurements show that Ryugu samples exhibit signatures for framboidal magnetite, coarse-grained magnetite, and pyrrhotite, and that framboidal magnetite is the dominant remanence carrier of Ryugu samples in the middle-coercivity range. The SIRM paleointensity constant was obtained for two Ryugu samples, and the median value was 3,318 ± 1,038 μT, which is close to the literature's value based on the average among magnetite, titanomagnetite, pyrrhotite, and FeNi alloys and is widely used for SIRM paleointensity experiments. The paleointensity values estimated using the obtained SIRM paleointensity constant indicate a strong magnetic field of the protoplanetary disk, suggesting that Sun's protoplanetary disk existed at the disk location of Ryugu's parent planetesimal when framboidal magnetite precipitated from the aqueous fluid.

DOI： 10.1029/2022JE007405

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Publisher：Geochemical Perspectives Letters  

The Hayabusa2 spacecraft has returned samples from the Cb-type asteroid (162173) Ryugu to Earth. Previous petrological and chemical analyses support a close link between Ryugu and CI chondrites that are presumed to be chemically the most primitive meteorites with a solar-like composition. However, Ryugu samples are highly enriched in Ca compared to typical CI chondrites. To identify the cause of this discrepancy, here we report stable Ca isotopic data (expressed as δ44/40CaSRM915a) for returned Ryugu samples collected from two sites. We found that samples from both sites have similar δ44/40CaSRM915a (0.58 ± 0.03 % and 0.55 ± 0.08 %, 2 s.d.) that fall within the range defined by CIs. This isotopic similarity suggests that the Ca budget of CIs and Ryugu samples is dominated by carbonates, and the variably higher Ca contents in Ryugu samples are due to the abundant carbonates. Precipitation of carbonates on Ryugu likely coincided with a major episode of aqueous activity dated to have occurred ∼5 Myr after Solar System formation. Based on the pristine Ryugu samples, the average δ44/40CaSRM915a of the Solar System is defined to be 0.57 ± 0.04 % (2 s.d.).

DOI： 10.7185/geochemlet.2238

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Language：English   Publisher：Earth, Planets and Space  

Millimetre-sized primordial rock fragments originating from asteroid Ryugu were investigated using high energy X-ray fluorescence spectroscopy, providing 2D and 3D elemental distribution and quantitative composition information on the microscopic level. Samples were collected in two phases from two sites on asteroid Ryugu and safely returned to Earth by JAXA’s asteroid explorer Hayabusa2, during which time the collected material was stored and maintained free from terrestrial influences, including exposure to Earth’s atmosphere. Several grains of interest were identified and further characterised to obtain quantitative information on the rare earth element (REE) content within said grains, following a reference-based and computed-tomography-assisted fundamental parameters quantification approach. Several orders of magnitude REE enrichments compared to the mean CI chondrite composition were found within grains that could be identified as apatite phase. Small enrichment of LREE was found for dolomite grains and slight enrichment or depletion for the general matrices within the Ryugu rock fragments A0055 and C0076, respectively. Graphical Abstract: [Figure not available: see fulltext.]

DOI： 10.1186/s40623-022-01705-3

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Publisher：Astrophysical Journal Letters  

We have conducted a NanoSIMS-based search for presolar material in samples recently returned from C-type asteroid Ryugu as part of JAXA's Hayabusa2 mission. We report the detection of all major presolar grain types with O- and C-anomalous isotopic compositions typically identified in carbonaceous chondrite meteorites: 1 silicate, 1 oxide, 1 O-anomalous supernova grain of ambiguous phase, 38 SiC, and 16 carbonaceous grains. At least two of the carbonaceous grains are presolar graphites, whereas several grains with moderate C isotopic anomalies are probably organics. The presolar silicate was located in a clast with a less altered lithology than the typical extensively aqueously altered Ryugu matrix. The matrix-normalized presolar grain abundances in Ryugu are 4.8 − 2.6 + 4.7 ppm for O-anomalous grains, 25 − 5 + 6 ppm for SiC grains, and 11 − 3 + 5 ppm for carbonaceous grains. Ryugu is isotopically and petrologically similar to carbonaceous Ivuna-type (CI) chondrites. To compare the in situ presolar grain abundances of Ryugu with CI chondrites, we also mapped Ivuna and Orgueil samples and found a total of 15 SiC grains and 6 carbonaceous grains. No O-anomalous grains were detected. The matrix-normalized presolar grain abundances in the CI chondrites are similar to those in Ryugu: 23 − 6 + 7 ppm SiC and 9.0 − 3.6 + 5.4 ppm carbonaceous grains. Thus, our results provide further evidence in support of the Ryugu-CI connection. They also reveal intriguing hints of small-scale heterogeneities in the Ryugu samples, such as locally distinct degrees of alteration that allowed the preservation of delicate presolar material.

DOI： 10.3847/2041-8213/ac83bd

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Language：Japanese   Publisher：The Japanese Society for Planetary Sciences  

<p>2020年12月6日に小惑星探査機「はやぶさ2」はC型小惑星リュウグウ表層物質を収めた再突入カ プセルを地球に帰還させた．回収された再突入カプセルに収められた試料コンテナは，オーストラリア現地でのガス採取を実施した後，JAXA相模原キャンパスの惑星物質試料受入設備に搬入され，チェンバー導入前の部品取り外し・洗浄等のプロセスを経てクリーンチェンバー内で真空中での開封・高純度窒素環境下での帰還試料の取り出し・初期記載が行われた．これらのリュウグウ帰還試料の初期記載の結果，これまでに回収されたどの隕石よりも反射率が低く，全体密度が小さい事が判明した．また，赤外反射スペクトルの吸収特性から水酸基を含む含水鉱物と炭酸塩鉱物，及びCH結合に富む有機物が試料中に含まれることが明らかになった．これらの情報を既知の隕石と比較すると，CIコンドライト隕石に最も似ていると言える．また探査機搭載機器によって得られた可視・近赤外スペクトルと比較した結果，帰還試料はリュウグウ表層全体を代表している事が分かった．取り出された試料の一部は既に初期分析チーム，2次キュレーションチーム，NASAへ配分され，更に国際公募研究による配布が予定されている．本稿では一連の試料取り扱いプロセス・初期記載内容について述べる．</p>

DOI： 10.14909/yuseijin.31.2_153

CiNii Research

Publisher：Earth, Planets and Space  

We report ground-based environmental assessments performed during development of the sampler system until the launch of the Hayabusa2 spacecraft. We conducted static monitoring of potential contaminants to assess the environmental cleanliness during (1) laboratory work performed throughout the development and manufacturing processes of the sampler devices, (2) installation of the sampler system on the spacecraft, and (3) transportation to the launch site at the Japan Aerospace Exploration Agency’s (JAXA’s) Tanegashima Space Center. Major elements and ions detected in our inorganic analyses were sodium (Na), potassium (K), and ionized chloride (Cl–); those elements and ions were positively correlated with the total organic content and with exposure duration in the range from 101 to 103 nanograms per monitor coupon within an ~ 30-mm diameter scale. We confirmed that total deposits on the coupon were below the microgram-scale order during manufacturing, installation, and transportation in the prelaunch phase. The present assessment yields a nominal safety declaration for analysis of the pristine sample (> 5.4 g) returned from asteroid (162173) Ryugu combined with a highly clean environmental background level. We expect that the sample returned from Ryugu by Hayabusa2 will be free of severe and/or unknown contamination and will allow us to provide native profiles recorded for the carbonaceous asteroid history. Graphical Abstract: [Figure not available: see fulltext.].

DOI： 10.1186/s40623-022-01628-z

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Publisher：Earth, Planets and Space  

Hayabusa2 returned surface samples from the C-type near-Earth asteroid (162173) Ryugu to Woomera, South Australia, in December 2020. The samples returned from Ryugu are expected to contain not only volatile components reflecting its primitive nature, but also solar wind components due to exposure to space. Such volatiles may partly be released inside the sealed sample container enclosing Ryugu samples due to particle destruction or container heating in a contingency case. In order to collect and analyze volatiles released in the container prior to the container-opening, we set up a gas extraction and analyses system (GAEA: GAs Extraction and Analyses system). The system requires ultra-high vacuum conditions, small vacuum line volume to minimize dead volume and simple configuration as well as having an interface to connect the container. The system includes gas bottles for passive collection of volatiles at room temperature and bottles for active collection at liquid nitrogen temperature. A quadrupole mass spectrometer is installed to analyze gases in the vacuum line, and a non-evaporative getter pump is also used when noble gases are analyzed. The rehearsal operation of the GAEA was made at ISAS/JAXA as well as transportation tests in Japan. In November 2020, it was transported safely to the Quick Look Facility (QLF) in Woomera. It was set up at the QLF and worked as planned for collection and analysis of gas components from the returned sample container. Here we report the concept, design and calibration results for the GAEA and an outline of analytical protocols applied in Woomera. Graphical Abstract: [Figure not available: see fulltext.]

DOI： 10.1186/s40623-022-01638-x

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Language：English   Publisher：Science  

The Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. The mission performed two landing operations to collect samples of surface and subsurface material, the latter exposed by an artificial impact. We present images of the second touchdown site, finding that ejecta from the impact crater was present at the sample location. Surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to Ryugu’s boulders, and shapes from quasi-spherical to flattened. The samples were returned to Earth on 6 December 2020. We describe the morphology of >5 grams of returned pebbles and sand. Their diverse color, shape, and structure are consistent with the observed materials of Ryugu; we conclude that they are a representative sample of the asteroid.

DOI： 10.1126/science.abj8624

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Publisher：Nature Astronomy  

C-type asteroids1 are considered to be primitive small Solar System bodies enriched in water and organics, providing clues to the origin and evolution of the Solar System and the building blocks of life. C-type asteroid 162173 Ryugu has been characterized by remote sensing2–7 and on-asteroid measurements8,9 with Hayabusa2 (ref. 10). However, the ground truth provided by laboratory analysis of returned samples is invaluable to determine the fine properties of asteroids and other planetary bodies. We report preliminary results of analyses on returned samples from Ryugu of the particle size distribution, density and porosity, spectral properties and textural properties, and the results of a search for Ca–Al-rich inclusions (CAIs) and chondrules. The bulk sample mainly consists of rugged and smooth particles of millimetre to submillimetre size, confirming that the physical and chemical properties were not altered during the return from the asteroid. The power index of its size distribution is shallower than that of the surface boulder observed on Ryugu11, indicating differences in the returned Ryugu samples. The average of the estimated bulk densities of Ryugu sample particles is 1,282 ± 231 kg m−3, which is lower than that of meteorites12, suggesting a high microporosity down to the millimetre scale, extending centimetre-scale estimates from thermal measurements5,9. The extremely dark optical to near-infrared reflectance and spectral profile with weak absorptions at 2.7 and 3.4 μm imply a carbonaceous composition with indigenous aqueous alteration, matching the global average of Ryugu3,4 and confirming that the sample is representative of the asteroid. Together with the absence of submillimetre CAIs and chondrules, these features indicate that Ryugu is most similar to CI chondrites but has lower albedo, higher porosity and more fragile characteristics.

DOI： 10.1038/s41550-021-01550-6

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Language：English   Publisher：(一社)日本放射線影響学会  

福島第1原子力発電所(FDNPP)の労働者を対象として、放射線教育を受けた頻度、放射線の知識、作業現場での不安について調査した。2016年11月にアンケート調査を行い、テキストマイニング法により、アンケートの自由記入欄から不安に関連する語彙を抽出した。その結果、アンケートは1135名(男性1120名、女性6名、無記入9名、年齢18～70歳)の労働者から回収された(回収率70.8%)。また、3カテゴリ(放射線教育を受けた頻度、放射線の知識、作業不安)間では、放射線の知識と作業不安、放射線教育を受けた頻度と放射線の知識において有意な関連性が認められた。さらに、労働者が放射線教育を受けることにより、放射線に関する知識が増え、結果として、放射線への不安を低減する一助となっていたことも明らかにされた。なお、本調査では自由記述式による回答数127件のうち、有効回答数が92件得られ、テキストマイニング法により頻出語が71語抽出され、使用語彙が、不安度に依存して異なることも明らかにされた。以上より、テキストマイニング法を用いることで、放射線に対する不安の有無や、対象者の労働環境等に関する情報が得られた。

Language：English   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p>The Hayabusa2 spacecraft explored C-type near-Earth asteroid (162173) Ryugu and returned asteroidal materials, collected during two touchdown operations, to the Earth as the first sample from carbonaceous-type asteroid. The sample container, in which ~5 g of Ryugu sample was enclosed, was safely opened in the clean chamber system with no severe exposure to the terrestrial atmosphere. In the course of preparation operation of the sample container, two dark-colored millimeter- to sub-millimeter-sized particles were found outside the sealing part of the sample container. Because they look similar to the Ryugu particles inside the sample container, the particles were named as Q particles (Q from <i>questionable</i>). In this study, we investigated Q particles (Q001 and Q002) mineralogically and petrographically to compare them with potential contaminants (the ablator material of the reentry capsule and fine sand particles at the capsule landing site), Ryugu sample, and CI chondrites. The Q particles show close resemblance to Ryugu sample and CI chondrites, but have no evidence of terrestrial weathering that CI chondrites experienced. We therefore conclude that the Q particles are originated from Ryugu and were expelled from the sample catcher (sample storage canister) in space prior to the enclosure operation of the sample catcher in the sample container. The most likely scenario is that the Q particles escaped from the sample catcher during the retrieval of the sample collection reflector, which was the necessary operation for the sample container closing.</p>

DOI： 10.2343/geochemj.gj22017

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Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p>In mineral alteration processes in reducing hydrothermal environments such as the Central Ridge and subduction zones, much work has been done on the generation of hydrogen associated with the oxidation of divalent iron (Fe(II)) (e.g., McCollom and Bach, 2009), and the Fischer-Tropsch type reaction (carbon dioxide and hydrogen to produce aliphatic organic carbons such as methane) as a nonbiological organic matter formation process (e.g., Sforna et al., 2018). Similar arguments have been made for carbonaceous chondrites with similar mineral compositions, for example (e.g., Glein and Zolotov). As for the Fe(II)-associated reactions, the formation of magnetite from olivine has been considered important from the beginning, but it has been noted that oxidation reactions that Fe(II) undergoes at lower temperatures in the structure of layered silicates (serpentinite, saponite), once formed, contribute to the same extent (Andreani et al. 2013). On the other hand, the Fe(II)/Fetotal ratio in the structure of 2:1-type layered silicates (e.g., smectite) decreases with increasing Eh over a wide Eh range, but the changing Eh range has been shown to be mineral dependent (Gorski et al., 2013). Samples from the C-type asteroid Ryuguu brought back by Hayabusa2 indicate that Ryuguu experienced water alteration in the early solar system and that there was coevolution of minerals and organic matter associated with water alteration. Quantifying the Fe(II)/Fe(III) ratio in layered silicates from Ryuguu, which, unlike carbonaceous chondrites, are unaffected by terrestrial weathering, will provide important information for studying the reducing effects of layered silicates within the asteroid. In this study, the Fe(II)/Fe(III) ratios of layered silicates in Ryuguu were investigated by analyzing them with a scanning transmission X-ray microscope (STXM) without the influence of the oxidative Earth atmosphere.</p>

DOI： 10.14862/geochemproc.69.0_106

CiNii Research

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

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DOI： 10.14862/geochemproc.69.0_107

CiNii Research

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p></p>

DOI： 10.14862/geochemproc.69.0_104

CiNii Research

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

<p>As a part of the organic macromolecule subteam, infrared absorption spectra from the intact Ryugu particles and extracted insoluble organic matter (IOM) were obtained using Fourier transform infrared (FTIR) microspectroscopy, to understand the nature of organic matter in Ryugu. 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 unheated chondritic IOM. We also observed possible N-H features in the Ryugu IOM. Such characteristics of Ryugu organic matter might indicate freshness of the Ryugu particles, which is not preserved in carbonaceous chondrites.</p>

DOI： 10.14862/geochemproc.69.0_103

CiNii Research

Language：English  

Mass spectrometry has been widely used in lander missions to characterize the volatiles in rocks and soils on planetary surfaces. A good vacuum seal is very important for introducing such solid samples to a vacuum chamber and ejecting them. However, multiple measurements require many metal gaskets, leading to extra weight and complexity for the instruments. In this study, we investigate the capability of three kinds of elastomeric O-rings (Viton, Nexus-SLT, and Nexus-FV) as vacuum seals for mass spectrometric measurements, particularly for in situ K–Ar dating on Mars. First, thermal cycle tests revealed that low-temperature-resistant O-rings can maintain pressure <10⁻⁵ Pa at −60 °C under 1 bar ambient pressure, whereas Viton O-rings leaked at −25 °C. Then, the amount of ⁴⁰Ar due to outgassing from the O-rings and permeation under the ambient pressure of 650 Pa or 3 Pa was measured and compared with the amounts of ⁴⁰Ar that a flight-equivalent laser would liberate from potential target Martian rocks. The measured amounts were <1% of that a target rock with 5000 ppm K₂O and an age of 4.2 Ga would yield. These results suggest that a Viton O-ring can maintain the Ar blank low under the Mars atmospheric pressure when temperatures are higher than −25 °C. A double O-ring seal using the low-temperature-resistant elastomers would be an alternative approach at lower temperatures. The elastomeric O-rings would be useful for constructing a small and light-weighted mass spectrometric instrument for in situ K–Ar dating on Mars.

DOI： 10.1016/j.asr.2017.07.002

Language：English   Publishing type：Research paper (scientific journal)  

A comprehensive study of the organic chemistry and mineralogy of an ultracarbonaceous micrometeorite (UCAMM D05IB80) collected from near the Dome Fuji Station, Antarctica, was carried out to understand the genetic relationship among organic materials, silicates, and water. The micrometeorite is composed of a dense aggregate of ∼5 µm-sized hollow ellipsoidal organic material containing submicrometer-sized phases such as glass with embedded metal and sulfides (GEMS) and mineral grains. There is a wide area of organic material (∼15 × 15 μm) in its interior. Low-Ca pyroxene is much more abundant than olivine and shows various Mg/(Mg + Fe) ratios ranging from ∼1.0 to 0.78, which is common to previous works on UCAMMs. By contrast, GEMS grains in this UCAMM have unusual chemical compositions. They are depleted in both Mg and S, which suggests that these elements were leached out from the GEMS grains during very weak aqueous alteration, without the formation of phyllosilicates. The organic materials have two textures—smooth and globular with an irregular outline—and these are composed of imine, nitrile and/or aromatic nitrogen heterocycles, and amide. The ratio of nitrogen to carbon (N/C) in the smooth region of the organics is ∼0.15, which is five times higher than that of insoluble organic macromolecules in types 1 and 2 carbonaceous chondritic meteorites. In addition, the UCAMM organic materials are soluble in epoxy and are thus hydrophilic; this polar nature indicates that they are very primitive. The surface of the material is coated with an inorganic layer, a few nanometers thick, that consists of C, O, Si, S, and Fe. Sulfur is also contained in the interior, implying the presence of organosulfur moieties. There are no isotopic anomalies of D, ¹³C, or ¹⁵N in the organic material. Interstellar photochemistry alone would not be sufficient to explain the N/C ratio of the UCAMM organics; therefore, we suggest that a very small amount of fluid on a comet must have been necessary for the formation of the UCAMM. The GEMS grains depleted in Mg and S in the UCAMM prove a very weak degree of aqueous alteration; weaker than that of carbonaceous chondrites. Short-duration weak alteration probably caused by planetesimal shock locally melted cometary ice grains and released water that dissolved the organics; the fluid would likely have not mobilized because of the very low thermal conductivity of the porous icy body. This event allowed the formation of the large organic puddle of the UCAMM, as well as organic matter sulfurization, formation of thin membrane-like layers of minerals, and deformation of organic nanoglobules.

DOI： 10.1016/j.gca.2017.06.047

Language：English   Publishing type：Research paper (scientific journal)  

The spacecraft Hayabusa2 was launched on December 3, 2014, to collect and return samples from a C-type asteroid, 162173 Ryugu (provisional designation, 1999 JU₃). It is expected that the samples collected contain organic matter and water-bearing minerals and have key information to elucidate the origin and history of the Solar System and the evolution of bio-related organics prior to delivery to the early Earth. In order to obtain samples with volatile species without terrestrial contamination, based on lessons learned from the Hayabusa mission, the sample catcher and container of Hayabusa2 were refined from those used in Hayabusa. The improvements include (1) a mirror finish of the inner wall surface of the sample catcher and the container, (2) adoption of an aluminum metal sealing system, and (3) addition of a gas-sampling interface for gas collection and evacuation. The former two improvements were made to limit contamination of the samples by terrestrial atmosphere below 1 Pa after the container is sealed. The gas-sampling interface will be used to promptly collect volatile species released from the samples in the sample container after sealing of the container. These improvements maintain the value of the returned samples.

DOI： 10.1007/s11214-016-0289-5

Language：English   Publishing type：Research paper (scientific journal)  

Micrometeorites (MMs) recovered from surface snow near the Dome Fuji Station, Antarctica are almost free from terrestrial weathering and contain very primitive materials, and are suitable for investigation of the evolution and interaction of inorganic and organic materials in the early solar system. We carried out a comprehensive study on seven porous and fluffy MMs [four Chondritic porous (CP) MMs and three fluffy fine-grained (Fluffy Fg) MMs] and one fine-grained type 1 (Fg C1) MM for comparison with scanning electron microscope, transmission electron microscope, X-ray absorption near-edge structure analysis, and secondary ion mass spectrometer. They show a variety of early aqueous activities. Four out of the seven CP MMs contain glass with embedded metal and sulfide (GEMS) and enstatite whiskers/platelets and do not have hydrated minerals. Despite the same mineralogy, organic chemistry of the CP MMs shows diversity. Two of them contain considerable amounts of organic materials with high carboxyl functionality, and one of them contains nitrile (CN) and/or nitrogen heterocyclic groups with D and ¹⁵N enrichments, suggesting formation in the molecular cloud or a very low temperature region of the outer solar system. Another two CP MMs are poorer in organic materials than the above-mentioned MMs. Organic material in one of them is richer in aromatic C than the CP MMs mentioned above, being indistinguishable from those of hydrated carbonaceous chondrites. In addition, bulk chemical compositions of GEMS in the latter organic poor CP MMs are more homogeneous and have higher Fe/(Si + Mg + Fe) ratios than those of GEMS in the former organic-rich CP MMs. Functional group of the organic materials and amorphous silicate in GEMS in the organic-poor CP MMs may have transformed in the earliest stage of aqueous alteration, which did not form hydrated minerals. Three Fluffy Fg MMs contain abundant phyllosilicates, showing a clear evidence of aqueous alteration. Phyllosilicates in thee MMs are richer in Fe than those in hydrated IDPs, typical fine-grained hydrated (Fg C1) MMs, and hydrated carbonaceous chondrites. One of the Fluffy Fg MMs contains amorphous silicate, which is richer in Fe than GEMS and contains little or no nanophase Fe metal but contains Fe sulfide. Because the chemical compositions of the amorphous silicate are within the compositional field of GEMS in CP IDPs, the amorphous silicate may be alteration products of GEMS. The entire compositional field of GEMS in the CP MMs and the amorphous silicate in the Fluffy Fg MM matches that of the previously reported total compositional range of GEMS in IDPs. One Fluffy Fg MM contains Mg-rich phyllosilicate along with Fe-rich phyllosilicate and Mg-Fe carbonate. Mg-rich phyllosilicate and Mg-Fe carbonate may have been formed through the reaction of Fe-rich phyllosilicate, Mg-rich olivine and pyroxene, and water with C-bearing chemical species. These data indicate that CP MMs and Fluffy Fg MMs recovered from Antarctic surface snow contain materials that throw a light on the earliest stages of aqueous alteration on very primitive solar system bodies. Because mineralogy and isotopic and structural features of organic materials in D10IB009 are comparable with isotopically primitive IDPs, its parent body could be comets or icy asteroids showing mass ejection (active asteroids). By contrast, organic-poor CP MMs may have experienced the earliest stage of aqueous alteration and Fluffy Fg MMs experienced weak aqueous alteration. The precursor materials of the parent bodies of Fluffy Fg MMs probably contained abundant GEMS or GEMS-like materials like CP IDPs, which is common to fine-grained matrices of very primitive carbonaceous chondrites such as CR3s. However, highly porous nature of organic-poor CP MMs and Fluffy Fg MMs suggests that parent bodies of these MMs must have been much more porous than the parent bodies of primitive carbonaceous chondrites. Given no phyllosilicate among the returned samples of 81P/Wild 2 comet, the MMs may have been derived from porous icy asteroids such as active asteroids as well as P- and D-type asteroids rather than comets.

DOI： 10.1016/j.gca.2017.03.034

Language：English   Publishing type：Research paper (scientific journal)  

Japan Aerospace Exploration Agency (JAXA) launched the asteroid exploration probe “Hayabusa2” in December 3rd, 2014, following the 1st Hayabusa mission. With technological and scientific improvements from the Hayabusa probe, we plan to visit the C-type asteroid 162137 Ryugu (1999 JU3), and to sample surface materials of the C-type asteroid that is likely to be different from the S-type asteroid Itokawa and contain more pristine materials, including organic matter and/or hydrated minerals, than S-type asteroids. We developed the Hayabusa2 sampler to collect a minimum of 100 mg of surface samples including several mm-sized particles at three surface locations without any severe terrestrial contamination. The basic configuration of the sampler design is mainly as same as the 1st Hayabusa (Yano et al. in Science, 312(5778):1350–1353, 2006), with several minor but important modifications based on lessons learned from the Hayabusa to fulfill the scientific requirements and to raise the scientific value of the returned samples. In this paper, we will report the details of the sampling system of Hayabusa2 with results of performance tests during the development and the current status of the sampling system.

DOI： 10.1007/s11214-017-0338-8

Language：English   Publishing type：Research paper (scientific journal)  

The Sutter's Mill (SM) CM chondrite fell in California in 2012. The CM chondrite group is one of the most primitive, consisting of unequilibrated minerals, but some of them have experienced complex processes occurring on their parent body, such as aqueous alteration, thermal metamorphism, brecciation, and solar wind implantation. We have determined noble gas concentrations and isotopic compositions for SM samples using a stepped heating gas extraction method, in addition to mineralogical observation of the specimens. The primordial noble gas abundances, especially the P3 component trapped in presolar diamonds, confirm the classification of SM as a CM chondrite. The mineralogical features of SM indicate that it experienced mild thermal alteration after aqueous alteration. The heating temperature is estimated to be <350 °C based on the release profile of primordial ³⁶Ar. The presence of a Ni-rich Fe-Ni metal suggests that a minor part of SM has experienced heating at >500 °C. The variation in the heating temperature of thermal alteration is consistent with the texture as a breccia. The heterogeneous distribution of solar wind noble gases is also consistent with it. The cosmic-ray exposure (CRE) age for SM is calculated to be 0.059 ± 0.023 Myr based on cosmogenic ²¹Ne by considering trapped noble gases as solar wind, the terrestrial atmosphere, P1 (or Q), P3, A2, and G components. The CRE age lies at the shorter end of the CRE age distribution of the CM chondrite group.

DOI： 10.1111/maps.12819

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Age is essential information for interpreting the geologic record on planetary surfaces. Although crater counting has been widely used to estimate the planetary surface ages, crater chronology in the inner solar system is largely built on radiometric age data from limited sites on the Moon. This has resulted in major uncertainty in planetary chronology. Because opportunities for sample-return missions are limited, in-situ geochronology measurements from one-way lander/rover missions are extremely valuable. Here we developed an in-situ isochron-based dating method using the K-Ar system, with K and Ar in a single rock sample extracted locally by laser ablation and measured using laser-induced breakdown spectroscopy (LIBS) and a quadrupole mass spectrometer (QMS), respectively. We built an experimental system combining flight-equivalent instruments and measured K-Ar ages for mineral samples with known ages (~1.8 Ga) and K contents (1-8 wt%); we achieved precision of 20% except for a mineral with low mechanical strength. Furthermore, validation measurements with two natural rocks (gneiss slabs) obtained K-Ar isochron ages and initial ⁴⁰Ar consistent with known values for both cases. This result supports that our LIBS-MS approach can derive both isochron ages and contributions of non-in situ radiogenic ⁴⁰Ar from natural rocks. Error assessments suggest that the absolute ages of key geologic events including the Noachian/Hesperian- and the Hesperian/Amazonian-transition can be dated with 10-20% errors for a rock containing ~1 wt% K₂O, greatly reducing the uncertainty of current crater chronology models on Mars.

DOI： 10.1016/j.pss.2016.05.004

Language：English   Publishing type：Research paper (scientific journal)  

We have investigated seven micrometeorites (MMs) from Antarctic snow collected in 2003 and 2010 by means of electron microscopy, X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy (TEM) observation, and noble-gas isotope analysis. Isotopic ratios of He and Ne indicate that the noble gases in these MMs are mostly of solar wind (SW). Based on the release patterns of SW ⁴He, which should reflect the degree of heating during atmospheric entry, the seven MMs were classified into three types including two least heated, three moderately heated, and two severely heated MMs. The heating degrees are well correlated to their mineralogical features determined by TEM observation. One of the least heated MMs is composed of phyllosilicates, whereas the other consists of anhydrous minerals within which solar flare tracks were observed. The two severely heated MMs show clear evidence of atmospheric heating such as partial melt of the uppermost surface layer in one and abundant patches of dendritic magnetite and Si-rich glass within an olivine grain in the other. It is noteworthy that a moderately heated MM composed of a single crystal of olivine has a ³He/⁴He ratio of 8.44∈×∈10^-4, which is higher than the SW value of 4.64∈×∈10^-4, but does not show a cosmogenic ²¹Ne signature such as ²⁰Ne/²¹Ne/²²Ne∈=∈12.83/0.0284/1. The isotopic compositions of He and Ne in this sample cannot be explained by mixing of a galactic cosmic ray (GCR)-produced component and SW gases. The high ³He/⁴He ratio without cosmogenic ²¹Ne signature likely indicates the presence of a ³He-enriched component derived from solar energetic particles.

DOI： 10.1186/s40623-015-0261-8

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English  

Language：Japanese  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Event date： 2019.7

Language：English  

Country：Japan  

Event date： 2013.9

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2013.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：茨城   Country：Japan  

Event date： 2013.3

Language：English  

Venue：Houston   Country：United States  

Event date： 2013.3

Language：English  

Venue：Houston   Country：United States  

Event date： 2011.4

Presentation type：Oral presentation (general)  

Country：United States  

Event date： 2011.4

Country：United States  

Event date： 2009.9

Presentation type：Oral presentation (general)  

Venue：広島大学   Country：Japan  

Venue：Matsue   Country：Japan  

Mineralogy and isotope compositions of coarse-grained Antarctic micrometeorites.

Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Venue：Tokyo   Country：Japan  

Noble-gas and oxygen isotopes and REE abundances in Antarctic micrometeorites.

Event date： 2025.3

Language：English   Presentation type：Oral presentation (invited, special)  

Event date： 2024.11

Event date： 2023.3

Language：English  

Country：United States  

Event date： 2022.12

Language：English  

Country：United States  

Event date： 2022.12

Language：English  

Country：United States  

Event date： 2022.8

Language：English  

Country：United Kingdom  

Event date： 2022.8

Language：English  

Country：United Kingdom  

Event date： 2022.8

Language：English  

Country：United Kingdom  

Event date： 2022.8

Language：English  

Country：United Kingdom  

Event date： 2021.5

Language：Japanese  

Venue：オンライン   Country：Japan  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

微小量の地球外物質の年代測定にための開発を行った。

Event date： 2019.5

Language：Japanese  

Country：Japan  

Event date： 2018.9

Language：Japanese  

Venue：琉球大学   Country：Japan  

Event date： 2018.9

Language：Japanese  

Venue：琉球大学   Country：Japan  

レーザーを用いた局所分析はICP-MSなど以外に希ガス分析でも利用されており、局所加熱で抽出される希ガス同位体を用いた特定の鉱物や包有物などの年代測定が可能となってきた。例えば、中性子照射した試料を用いて局所Ar-Ar年代測定が行われている。Ar-ArやI-Xe年代法のように親核種(KおよびI)を放射化により娘核種と同時に（同一の測定装置で）分析する場合以外は、親核種や標的元素の定量が必要である。しかし、レーザーアブレーションにより希ガスが抽出された領域そのものの元素分析は不可能であり、これまでは試料切片の表面観察・分析による情報で代用されてきた。本研究では、レーザーアブレーションの際に生じるプラズマ発光分光(Laser-Induced Breakdown Spectrometry, LIBS)による元素分析と希ガス同位体分析を組み合わせた分析システムの開発を行い、岩石試料の局所年代分析に適用した。
システムはNd:YAGパルスレーザー(1064 nm, pulse width ~8 nsec, beam diameter ~ 20 µm)、可視光分光器、希ガス質量分析計からなる。厚さ約100ミクロンのマダガスカル・Itlongay産orthoclaseおよび隕石試料に対して直径約20 µmの領域に0.1 uJのレーザーを10 Hzで1~2分間x10箇所（~0.5µg）に照射し、LIBS分析および希ガス質量分析を行った。希ガス抽出効率はorthoclaseのEPMAによるK濃度、K-Ar年代（435-461 Ma; Arnaud & Kelley, 1997; Wartho et al. 1999; Nägler &Villa, 2000）をもとに補正した。希ガス質量分析計の感度補正は既知量の地球大気により行った。LIBSのK感度はorthoclase (K2O=15.226 wt%)、albite (K2O=0.255 wt%)、wollastonite (K2O=0.466 wt%)のK (767 nm)と酸素(777.7nm)の輝線面積比をもとに線形近似により校正した。
これまでに普通コンドライト中のコンドリュールおよびマトリックスを分析し、K2O値が0.1wt%を超えるものについては約4.5GaのK-Ar年代を得ることができた。K濃度の低いものは輝線面積計算の不確かさが100%を超える。今後はLIBS検出器測定条件の見直し、バックグランド補正・関数フィッティングの精度向上により定量限界を改善していく。LIBSおよび希ガス質量分析計の検出限界を考慮すると、~100Maの年代を持つ地球岩石試料のhornblend, biotite, feldsparなどに対して、厚さ100µm、200x200 µmの領域での局所分析が可能である。これら複数鉱物年代を得ることができればアイソクロンK-Ar年代も可能になる。現在は更にK定量に加えて他の元素 (Mg, Si, Fe, Ca, Na)の定量を行い、隕石の宇宙線照射年代の精密測定（化学組成補正）を目指している。

Event date： 2017.1

Language：Japanese  

Venue：京都大学原子炉実験所事務棟大会議室   Country：Japan  

Event date： 2016.7

Language：English  

Country：Japan  

Event date： 2016.5 - 2015.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2016.2

Language：English  

Country：Japan  

Event date： 2015.6

Language：Japanese  

Country：Japan  

Event date： 2015.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2015.5

Language：Japanese  

Country：Japan  

Event date： 2015.1

Language：Japanese  

Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：茨城県つくば市   Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：京都大学原子炉実験所   Country：Japan  

Event date： 2014.11

Language：Japanese  

Country：Japan  

Event date： 2013.3

Language：English  

Venue：Houston   Country：United States  

Event date： 2012.8

Language：English  

Country：Australia  

Event date： 2012.8

Language：English  

Venue：Cairns   Country：Australia  

Event date： 2012.3

Country：United States  

Event date： 2012.3

Country：United States  

Event date： 2012.3

Country：United States  

Event date： 2012.3

Country：United States  

Event date： 2012.3

Language：English  

Venue：Houston   Country：United States  

Event date： 2012.3

Language：English  

Venue：Houston   Country：United States  

Event date： 2011.11

Country：Korea, Republic of  

Event date： 2011.8

Country：United Kingdom  

Event date： 2011.8

Country：United Kingdom  

Event date： 2011.8

Country：United Kingdom  

Event date： 2011.8

Country：United Kingdom  

Event date： 2011.8

Country：United Kingdom  

Event date： 2011.8

Country：United Kingdom  

Event date： 2011.8

Country：United Kingdom  

Event date： 2011.8

Country：United Kingdom  

Event date： 2011.4

Country：United States  

Event date： 2011.4

Country：Japan  

Event date： 2011.4

Country：Japan  

Event date： 2011.4

Country：Japan  

Event date： 2011.4

Country：Japan  

Event date： 2011.4

Country：Japan  

Event date： 2011.4

Country：Japan  

Event date： 2011.4

Country：Japan  

Event date： 2011.4

Country：Japan  

Event date： 2011.4

Country：United States  

Event date： 2011.4

Country：United States  

Event date： 2011.4

Country：United States  

Event date： 2011.4

Country：United States  

Event date： 2011.4

Country：United States  

Event date： 2011.4

Country：United States  

Event date： 2011.4

Country：United States  

Event date： 2011.3

Presentation type：Oral presentation (general)  

Venue：Texas   Country：United States  

Event date： 2011.3

Country：United States  

Event date： 2008.12

Venue：San Francisco   Country：United States  

Event date： 2008.11

Venue：九州大学   Country：Japan  

Event date： 2008.9

Venue：秋田大学   Country：Japan  

Event date： 2008.9

Venue：東京大学   Country：Japan  

Event date： 2008.5

Venue：千葉   Country：Japan  

Event date： 2008.5

Venue：千葉   Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：Japanese  

Country：Japan  

Language：English  

Country：Canada  

Country：Japan  

Mineralogical and stable isotope signatures of El-Quss Abu Said CM2 carbonaceous chondrite: pristine material from outer asteroid belt.

Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Rio de Janeiro   Country：Brazil  

Presentation type：Oral presentation (general)  

Venue：北海道   Country：Japan  

Presentation type：Symposium, workshop panel (public)  

Venue：Texas   Country：United States  

Presentation type：Oral presentation (general)  

Venue：Texas   Country：United States  

Presentation type：Oral presentation (general)  

Venue：千葉   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Tennessee   Country：United States  

Presentation type：Oral presentation (general)  

Venue：福島   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：沖縄   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：沖縄   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：愛媛   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Texas   Country：United States  

Presentation type：Oral presentation (general)  

Venue：Texas   Country：United States  

Presentation type：Oral presentation (general)  

Venue：Texas   Country：United States  

Presentation type：Oral presentation (general)  

Venue：茨城   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：千葉   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Casablanca   Country：Morocco  

Presentation type：Oral presentation (general)  

Venue：Zuerich   Country：Switzerland  

Venue：Melbourne   Country：Australia  

Geochemical study on Temagami iron-formations, Canada.

Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Venue：Texas   Country：United States  

Chemical composition and formation process of silica-rich chondrule rims in the Sahara 00182 CR/CV chondrite.

Venue：Matsushima   Country：Japan  

Si and O diffusivity in ringwoodite.

Language：English  

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：1

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：2

Type：Competition, symposium, etc. 

Type：Academic society, research group, etc. 

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Other

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Seminar, workshop

Audience：General,　Scientific,　Company,　Civic organization,　Governmental agency

Type：Lecture