¹Sylvain Laforet,¹Hugues Leroux,¹Corentin Le Guillou,²Maya Marinova,¹Adrien Néri,¹Adrien Teurtrie,¹Francisco de la Peña,¹Damien Jacob,²Alexandre Fadel,³David Troadec
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14366]
¹Université de Lille, CNRS, INRAE, Centrale Lille, UMR 8207-UMET-Unité Matériaux et Transformations, Lille, France
²Université de Lille, CNRS, INRAE, Centrale Lille, Université Artois, FR 2638-IMEC-Institut Michel-Eugène Chevreul, Lille, France
³Université de Lille, CNRS, Centrale Lille, Junia, Univ. Polytechnique Hauts-de-France, UMR 8520 – IEMN – Institut d’Electronique de Microélectronique et de Nanotechnologie, Lille, France
Published by arrangement with John Wiley & Sons

The first few microns of the surface of airless bodies are subject to severe changes due to the harsh environment of space, known as space weathering. The Hayabusa2 sample return mission from the asteroid Ryugu provides the first opportunity to study these effects on a carbonaceous and hydrated body. Understanding the structural and chemical changes that occur in the space weathered layers of Ryugu is crucial to correctly interpreting the mechanisms involved in such processes. This study employs transmission electron microscopy to achieve the spatial resolution necessary to analyze the nanoscale heterogeneities in these modified layers. The chemical analyses indicate that features present are likely to represent the spattering of a Ryugu-like material, possibly from a different lithology of the asteroid. However, such material appears to be completely dehydroxylated and depleted in sulfur by approximately 20%. Furthermore, the nanoscale dispersion of vesicles and rounded nanosulfides found in these melt layers helps to estimate the temperatures (>1300°C) and the time scales (<10−8 s) involved in their formation. In addition, this study describes and discusses a unique spherical feature not previously observed in Ryugu samples. The 3 μm-sized object shows strong similarities to microchondrules observed in some carbonaceous (CM2) and ordinary chondrites, suggesting a divergent thermal history from that of the melt layers.

¹M. V. Goryunov et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14368]
¹Institute of Physics and Technology, Ural Federal University, Ekaterinburg, Russian Federation
Published by arrangement with John Wiley & Sons

The iron-bearing phases and crystals within (i) the bulk interior and the fusion crust from Tamdakht H5 and (ii) the bulk interior from Annama H5 ordinary chondrites were studied by optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray diffraction (XRD), magnetization measurements, and Mössbauer spectroscopy. The main iron-bearing phases/crystals such as olivine, orthopyroxene, clinopyroxene, troilite, chromite, and hercynite, as well as Fe-Ni-Co alloy with the α2-Fe(Ni, Co), α-Fe(Ni, Co) and γ-Fe(Ni, Co) phases were identified in both meteorites. XRD and Mössbauer spectroscopy showed high contents of Fe-Ni-Co alloy in the bulk interiors from Tamdakht H5 and Annama H5 ordinary chondrites. The fusion crust from Tamdakht H5 contains a new phase of magnesioferrite. A classification scheme for H, L, and LL ordinary chondrites using the relative areas of Mössbauer spectral components was applied to these meteorites’ classification. The ratios of the M1 and M2 site occupations by Fe2+ in olivine and orthopyroxene were determined using XRD and Mössbauer spectroscopy, showing consistent results. The equilibrium cation distribution temperatures for olivine and orthopyroxene in Tamdakht H5 and Annama H5 were determined using XRD and Mössbauer spectroscopy.