Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

DOI： 10.1016/j.orggeochem.2022.104514

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Publishing type：Research paper (scientific journal)   Publisher：Japan Academy  

DOI： 10.2183/pjab.98.015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press ({OUP})  

ABSTRACT

Comets and asteroids have traditionally been separated categories, but main belt comets skew this view, portraying a possible intermediate stage between these two endmembers. Investigating the relationship between these bodies can improve our understanding of the formation and evolution of the Solar System and help to identify potentially interesting parent bodies from within our solar system, for future sample return missions. Furthermore, elucidating the ice-organic-silicate ratios of potential meteorite parent bodies can help to explain the observed isotopic ratios and petrography of meteorite samples. While the ice-organic-silicate ratios of particular bodies have been estimated, there has been no study undertaken which compares different types of bodies in terms of their ice-organic-silicate ratios. Therefore, this study presents a geophysical-chemical mass balance model, to estimate the ice-organic-silicate ratios of comets, main belt comets and asteroids. The results drawn from the model form a diagonal trend upon an ice-organic-silicate ternary diagram, in which comets and main belt comets plot together at generally higher ice contents, with asteroids typically plotting at lower ice contents. However, an overlap between all three body types is observed and supports the scenario in which comets, main belt comets and asteroids are genetically linked.

DOI： 10.1093/mnras/stac1068

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Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

<jats:title>Abstract</jats:title>
<jats:p>Enstatite chondrites have been regarded as major building blocks of the Earth and other differentiated inner planetary bodies due to the similarity of Δ<jats:sup>17</jats:sup>O (deviation of the <jats:italic>δ</jats:italic>
<jats:sup>17</jats:sup>O value from the terrestrial silicate fractionation line) and nucleosynthetic isotope anomalies. However, this hypothesis has been rebutted by the fact that the Earth and enstatite chondrites show distinct Si isotopic compositions. It has been debated whether the origin of this Si isotope difference is the result of nebular or planetary processes. Here we show that the <jats:italic>δ</jats:italic>
<jats:sup>30</jats:sup>Si (deviation of <jats:sup>30</jats:sup>Si/<jats:sup>28</jats:sup>Si relative to NBS 28 standard) and the Δ<jats:sup>17</jats:sup>O values of chondrules in unequilibrated enstatite chondrites are between −0.20‰ and −0.54‰ and −0.36‰ and +0.26‰, respectively. Furthermore, the chondrules with higher Δ<jats:sup>17</jats:sup>O values tend to have lower <jats:italic>δ</jats:italic>
<jats:sup>30</jats:sup>Si. The data exhibit values consistent with most of the noncarbonaceous group differentiated planetary bodies. This consistency suggests that the Si and O isotopic compositions of enstatite chondrules record those of the major precursors that formed the differentiated planetary bodies in the inner solar system. Model calculations based on the results reveal that the Si and O isotope variations of the enstatite chondrite chondrules were generated by an interaction between the evaporation-driven SiO-rich gas and partially or fully melted forsterite-rich precursor chondrules. The Mg/Si of the evaporated dust-gas mixtures increased with increasing silicate/metal ratio in the evaporated dust, which may have increased the bulk Mg/Si and <jats:italic>δ</jats:italic>
<jats:sup>30</jats:sup>Si value of the inner planetary bodies.</jats:p>

DOI： 10.3847/PSJ/abf490

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.epsl.2021.117149

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

Sample return missions represent great opportunities to study terrestrially uncontaminated solar system materials. However, the size of returned samples will be limited, and thus, it is necessary to understand the most appropriate techniques to apply. Accordingly, the sensitivity of laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and secondary ion mass spectrometry (SIMS) was compared through the analyses of trace elements in reference materials and the Allende CV3 chondrite. While the SIMS method was found to be more sensitive than the laser method toward all elements of interest, the LA-ICPMS appears to be more suitable in terms of precision for certain elements. Using both analytical techniques, we measured chemical composition of an Allende chondrule and its igneous rim. These data were used to understand the nature of the reservoir that interacted with the host chondrule during formation of its igneous rim. We find that the igneous rim is enriched in silica, alkalis, and rare earth elements compared to the host chondrule. We suggest that the igneous rim could be explained by melting of a mixture of the chondrule-like and REE-enriched CAI-like precursors that accreted on the surface of the host chondrule followed by gas-melt interaction with a silica- and alkali-rich gas. Alternatively, these observations could be interpreted as a result of interaction between the chondrule and the melt resulting from partial melting of a pre-existing planetesimal in the early stages of its differentiation.

DOI： 10.1111/maps.13665

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：MARY ANN LIEBERT, INC  

The Hayabusa2 mission successfully collected samples from the asteroid Ryugu last year and will return these to Earth in December 2020. It is anticipated that the samples will enable the analysis of terrestrially uncontaminated organic matter and minerals. Such analyses are in turn expected to elucidate the evolution of organic matter through Solar System history, including the origination and processing of biogenically important molecules, which could have been utilized by the first organisms on Earth. In anticipation, studies have made predictions concerning the properties of Ryugu, including its composition. The spectral characteristics of Ryugu, such as albedo, have been employed to relate the asteroid to members of the carbonaceous chondrite group that have been identified on Earth. However, the recent Hayabusa2 touchdown highlights a disparity between the color of surfaces of displaced platy fragments, indicating a brightening trend for the surface exposed to space compared to that facing into the body. Here we present a mass balance calculation with reference to data from the literature, which indicates that Ryugu may contain a significantly higher abundance of organic matter (likely >50%) than the currently most accepted meteorite analogues. A high organic content may result in high levels of extractable organic matter for the second touchdown site, where the spacecraft sampled freshly exposed material. However, high abundances of insoluble aromatic/graphitic rich organic matter may be present in the first touchdown site, which sampled the surface of Ryugu that had been exposed to space. Moreover, we suggest that the potentially high organic abundance and the rubble-pile nature of Ryugu may originate from the capture of rocky debris by a comet nucleus and subsequent water-organic-mineral interactions and sublimation of water ice.

DOI： 10.1089/ast.2019.2198

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：EUROPEAN ASSOC GEOCHEMISTRY  

Carbonaceous chondrites contain many abiotic organic compounds, some of which are found in life on Earth. Both the mineral and organic mat ter phases, of these meteorites, have been affected by aqueous alteration processes. Whilst organic matter is known to be associated with phyllosilicate phases, no such relationship has yet been identified for specific organic compound classes. Furthermore, ongoing sample return missions, Hyabusa 2 and OSIRIS-Rex, are set to return potentially organic rich C-type asteroid samples to the Earth. Consequently, strategies to investigate organic-mineral relationships are required. Here we report spatial data for free/soluble organic matter (FOM/SOM) components (akylimidazole and alkylpyridine homologues) and mineral phases. Low and intermediate molecular weight alkylimidazole homologues are more widely distributed than higher molecular weight members, likely due to their affinity for the aqueous phase. On aqueous alteration of anhydrous mineral phases, transported FOM is adsorbed onto the surface or into the interlayers of the resulting phyllosilicates and thus concentrated and protected from oxidising fluids. Therefore, aiding the delivery of biologically relevant molecules to earth, shortly preceding the origin of life.

DOI： 10.7185/geochemlet.2010

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Extraterrestrial organic matter has been widely studied; however, its response to pressure has not. Primitive organic matter bearing meteorites, such as CI and CM carbonaceous chondrites, have experienced variable pressures, up to 10 GPa. To appreciate the effects of these pressures on the organic content of these bodies, the model compounds isophthalic acid, vanillin, and vanillic acid were subjected to pressures of up to 11.5 GPa and subsequently decompressed. High-resolution synchrotron source Fourier transform infrared spectroscopy was used to determine the effects of different benzene substituents at high pressure on both the vibrational assignments of the benzene core of the molecules and the ability of the aromatic compounds to form intermolecular hydrogen bonds. The presence of additional peaks at high pressure was found to coincide with molecules that contain carboxyl groups; these features are interpreted as C-H center dot center dot center dot O intermolecular hydrogen bonds. The formation of these hydrogen bonds has implications for the origination of macromolecular organic matter (MOM), owing to the importance of such attractive forces during episodes of cross-linking, such as esterification. Pressure-induced hydrogen-bond formation is a process by which aromatic MOM precursors could have cross-linked to generate the organic polymers found within extraterrestrial bodies today.

DOI： 10.1021/acsearthspacechem.7b00053

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Lycopodium sporopollenin, a natural copolymer, shows exceptional stability under high hydrostatic pressures (10 GPa) as determined by in situ high pressure synchrotron source Fourier transform infrared spectroscopy. This stability is evaluated in terms of the component compounds of the sporopollenin: p-coumaric acid, phloretic acid, ferulic acid, and palmitic and sebacic acids, which represent the additional n-acid and n-diacid components. This high stability is attributed to interactions between these components, rather than the exceptional stability of any one molecular component. This study proposes a biomimetic solution for the creation of polymer materials that can withstand high pressures for a multitude of uses in aeronautics, vascular autografts, ballistics, and light-weight protective materials.

DOI： 10.1002/macp.201600142

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Event date： 2018.12.12 - 2018.12.19

Presentation type：Symposium, workshop panel (nominated)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Language：English   Presentation type：Oral presentation (general)  

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Author：Other 

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Author：Other 

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