^1,2Mutsumi Komatsu et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14234]
¹Division of Liberal Arts and Sciences, Saitama Prefectural University, Koshigaya, Saitama, Japan
²Department of Earth Sciences, Waseda University, Shinjuku, Tokyo, Japan
Published by arrangement with John Wiley & Sons

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.

^1,2Thomas Kohout et al. (>10)
The Planetary Science Journal 5, 128 Open Access Link to Article [DOI 10.3847/PSJ/ad4266]
¹Department of Geosciences and Geography, University of Helsinki, Finland; tomas.kohout@helsinki.fi
²Institute of Geology of the Czech Academy of Sciences, Czech Republic

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¹Andy J. López-Oquendo,^1,2Mark J. Loeffler,¹David E. Trilling
Planetary Science Journal 5, 117 Open Access Link to Article [DOI 10.3847/PSJ/ad4028]
¹Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ 86011, USA; al2987@nau.edu
²Center for Material Interfaces in Research and Applications, Northern Arizona University, Flagstaff, AZ 86011, USA

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹K.Yumoto et al. (>10)
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.116204]
¹Department of Earth and Planetary Science, The University of Tokyo, Bunkyo, Tokyo, Japan
Copyright Elsevier

Various natural effects gradually alter the surfaces of asteroids exposed to the space environment. These processes are collectively known as space weathering. The influence of space weathering on the observed spectra of C-complex asteroids remains uncertain. This has long hindered our understanding of their composition and evolution through ground-based telescope observations. Proximity observations of (162173) Ryugu by the telescopic Optical Navigation Camera (ONC-T) onboard Hayabusa2 and that of (101955) Bennu by MapCam onboard Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) found opposite spectral trends of space weathering; Ryugu darkened and reddened while Bennu brightened and blued. How the space weathering trends on Ryugu and Bennu evolved relative to each other would place an important constraint for understanding their mutual relationship and differences in their origins and evolutions. In this study, we compared the space weathering trends on Ryugu and Bennu by applying the results of cross calibration between ONC-T and MapCam obtained in our companion paper. We show that the average Bennu surface is brighter by 18.0 ± 1.5% at v band (550 nm) and bluer by 0.18 ± 0.03 (μm−1; in the 480–850 nm spectral slope) than Ryugu. The spectral slopes of surface materials are more uniform on Bennu than on Ryugu at spatial scales larger than ~1 m, but Bennu is more heterogeneous at scales below ~1 m. This suggests that lateral mixing due to global-scale resurfacing processes may have been more efficient on Bennu. The reflectance−spectral slope distributions of craters on Ryugu and Bennu appeared to follow two parallel trend lines with an offset before cross calibration, but they converged to a single straight trend without a bend after cross calibration. We show that the spectra of the freshest craters on Ryugu and Bennu are indistinguishable within the uncertainty of cross calibration. These results suggest that Ryugu and Bennu initially had similar spectra before space weathering and that they evolved in completely opposite directions along the same trend line, subsequently evolving into asteroids with different disk-averaged spectra. These findings further suggest that space weathering likely expanded the spectral slope variation of C-complex asteroids, implying that they may have formed from materials with more uniform spectral slopes.

¹B.G. Rider-Stokes,^1,2A. Stephant,^1,3M. Anand,¹I.A. Franchi,¹X. Zhao,¹L.F. White⁴A. Yamaguchi,¹R.C. Greenwood,¹S.L. Jackson
Earth and Planetary Science Letters 642, 118860 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2024.118860]
¹School of Physical Sciences, The Open University, Milton Keynes MK7 6AA, UK
²Istituto di Astrofisica e Planetologia Spaziali – INAF 00111 Rome, Italy
³Department of Earth Sciences, The Natural History Museum, London SW7 5BD, UK
⁴National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
Copyright Elsevier

The quenched (rapidly-cooled) angrite meteorites, which formed in the inner Solar System, record large-scale planetary mixing in the first few Ma of Solar System history, and therefore, provide a unique opportunity to investigate the role of impacts in terms of water addition to the growing planetesimals. Here we investigate the H isotopic composition and H2O abundance of relict olivine grains that survived impact melting within Asuka (A) 12,209 and compare them with impact melt-produced groundmass fractions using in-situ nanoscale secondary ion mass spectrometry (NanoSIMS). These analyses test if the angrite parent body (APB) acquired a CC-like H isotopic composition before early large-scale impact mixing and/or acquired volatiles by subsequent impact(s). Furthermore, we analyse the H isotopic composition and H2O abundance of later-forming plutonic (NWA 4801), intermediate (NWA 10,463) and dunitic (NWA 8535) angrite meteorites to assess the role of impacts, in terms of volatile delivery, during the first 50 Ma of the inner Solar System history. The H isotopic composition of most quenched angrites appears to be affected by degassing. Consequently, we opt to use the weighted average δD of pyroxenes and olivines in the plutonic angrite, NWA 4801, to estimate the original composition of the APB (-235 ± 113 ‰ 1σ, n = 18), in agreement with recent studies on the hydrogen isotopic signatures of mineral-hosted melt inclusions in D’Orbigny and Sahara 99,555. Additionally, we use the H2O abundances of NWA 4801 pyroxene (7.9 ± 1 µg/g 2σ) and olivine (6.1 ± 0.6 µg/g 2σ) to estimate the lower (85 to 110 µg/g) and upper (519 to 1089 µg/g) limits of the primitive APB mantle H2O content, implying that the APB was one of the most hydrated bodies in the early inner Solar System. The similarity of δD/H2O systematics in the relict olivine grains and groundmass olivine within A 12,209 argues against water delivery through impacts in the early inner Solar System. Overall, the non-carbonaceous reservoir in the inner Solar System appears to retain a single source of water, which isotopically resembles either water ice in carbonaceous chondrite parent bodies or fractionated nebula water.

^1,2Camilla Cioria,^1,2Giuseppe Mitri,³James Alexander Denis Connolly,⁴Jean-Philippe Perrillat,⁵Fabrizio Saracino
Journal of Geophysical Research (Planets) Link to Article [https://doi.org/10.1029/2023JE008234]
¹International Research School of Planetary Sciences, Università d’Annunzio, Pescara, Italy
²Dipartimento di Ingegneria e Geologia, Università d’Annunzio, Pescara, Italy
³Department of Earth Sciences, Institute for Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland
⁴Laboratoire de Géologie de Lyon, CNRS, Université de Lyon, Université Lyon 1, Ens de Lyon, Villeurbanne, France
⁵Department of Geology, University of Liège, Liège, Belgium
Published by arrangement with John Wiley & Sons

The mineralogy of planetary mantles formed under reducing conditions, as documented in the inner regions of the solar system, is not well constrained. We present thermodynamic models of mineral assemblages that would constitute the mantles of exo-Mercuries. We investigated reduced materials such as enstatite chondrites, CH, and CB chondrites, and aubrites, as precursor bulk compositions in phase equilibrium modeling. The resulting isochemical phase diagram sections indicate that dominant phases in these reduced mantles would be pyroxenes rather than olivine, contrasting with the olivine-rich mantles found within Earth, Mars, and Venus. The pyroxene abundances in the modeled mantles assemblages depend on the silica content shown by precursor materials. The silica abundance in the mantle is closely related to Si abundance in the core, particularly in reduced environments. In addition, we propose that pyroxene-rich mantles exhibit more vigorous convective and tectonic activity than olivine-rich mantles, given that pyroxene-rich mantles would have lower viscosity and a lower solidus temperature (Ts).

^1,2Chen Li,^1,3Yang Li,²Kuixian Wei,^1,4huang Guo,⁴Rui Li,^1,3Xiongyao Li,^1,3Jianzhong Liu²Wenhui Ma
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.06.038]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
²Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
³Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei 230026, China
⁴Institute of Remote Sensing and Geographical Information System, School of Earth and Space Sciences, Peking University, Beijing 100871, China
Copyright Elsevier

Lunar soil undergoes space weathering and accumulates optically active opaque particles (OAOpq) of different sizes, resulting in a darkening or red shift of the reflectance spectrum. The surfaces of weakly weathered objects exhibit spectral characteristics of strong weathering; these mechanisms are still unclear. The causes of OAOpq in lunar soil are complex, especially for submicrometer particles, which account for the largest mass proportion. We found ubiquitous impact-dispersed Fe–Fe1-xS core–shell particles in Chang’e-5 lunar soil impact glass and splatter. The crystal structure, particle size distribution, and chemical composition of OAOpq in the impact glass indicate that these OAOpq consist of sulfides or metals from multiple sources. Thermodynamic evidence, diffusion behavior, and particle dispersion characteristics indicate that impact dispersion is the most likely formation mechanism of these OAOpq. The proposed impact dispersion provides a reason for the large number of OAOpq and the limited products for in situ reactions. This process explains why lunar soil with a low degree of weathering exhibits substantial spectral modification properties. The results provide insights into space weathering of the lunar surface and also imply that impact-dispersed OAOpq may be the primary modification type on asteroid surfaces. The unique chemical properties of Fe–Fe1-xS OAOpq also indicate that the lunar regolith has the potential for resource utilization.