¹Léna Jossé,¹Zélia Dionnet,¹Alice Aléon-Toppani,¹Rosario Brunetto,²Andrew King,³Emmanuel Gardés,⁴Eva Heripré,^1,5Damien Loizeau,¹Sasha Cryan,⁶Kentaro Hatakeda
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70056]
¹Université Paris-Saclay, CNRS, Institut d’Astrophysique Spatiale (IAS), Orsay, France
²SOLEIL Synchrotron, Gif-sur-Yvette, France
³Laboratoire Magmas et Volcans (LMV), Université Clermont Auvergne, CNRS, IRD, Clermont-Ferrand, France
⁴Procédés et Ingénierie en Mécanique et Matériaux (PIMM), Arts et Métiers Sciences et Technologies, CNRS, CNAM, Paris, France
⁵Qualisat, Bièvres, France
⁶Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan
Published by arrangement with John Wiley & Sons

Extraterrestrial breccia samples are formed through impact-related processes that combine the fragments of distinct lithologies. As such, they are valuable indicators of the complex formation and evolution history of planetesimals in our solar system. Samples from asteroid (162173) Ryugu, returned to the Earth by the Hayabusa2 mission in December 2020, were characterized as breccias. The boundaries of mineralogical assemblages are typically drawn manually based on interpreted results from specific techniques, mostly performed on artificially produced 2D surfaces. This process inherently introduces subjectivity. Here, we present a semi-automated analytical method using synchrotron radiation micro X-ray computed tomography (SR-μXCT) data, called the Local Histogram method. It enables an unsupervised detection and 3D visualization of a few tens to hundreds of micrometer-sized lithologies showing sub-micrometer heterogeneities. We developed the method on a millimeter-sized Ryugu sample (A0159) in combination with a more traditional global grayscale threshold segmentation. In A0159, we report five distinct lithologies. They were confirmed and further characterized by an additional scanning electron microscopy (SEM) analysis on Xenon plasma-focused ion beam (Xe-pFIB) produced sections. Some lithologies show specific relationships with large fractures, while one is particularly enriched in sub-micrometer sulfides. A0159 is rich in carbonates and hosts the largest millimeter-scale dolomite vein seen on Ryugu.

¹B. Marty,¹L. Zimmermann,¹E. Füri,¹D. V. Bekaert,²J. J. Barnes,³A. N. Nguyen,^3,4,5H. C. Connolly,²D. S. Lauretta

Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70058]
¹CNRS, CRPG, UMR 7358, Université de Lorraine, Nancy, France
²Lunar and Planetary Laboratory, The University of Arizona, Tucson, Arizona, USA
³ARES (Astromaterials Research and Exploration Science), NASA Johnson Space Center, Houston, Texas, USA
⁴Department of Geology, Rowan University, Glassboro, New Jersey, USA
⁵Department of Earth and Planetary Science, American Museum of Natural History, New York, New York, USA
Published by arrangement with John Wiley & Sons

We report the elemental and isotopic abundances of all stable noble gases (helium, neon, argon, krypton, and xenon) in eight particles from asteroid Bennu returned by NASA’s OSIRIS-REx mission. We also report nitrogen abundances and isotopic ratios that were analyzed alongside neon and argon in four additional Bennu particles. These analyses confirm the similarities of Bennu material with Ivuna-type carbonaceous (CI) chondrites. The nitrogen isotopic compositions show intra- and inter-particle variations, pointing to the heterogeneous distribution of various N-bearing phases, while the abundances of nitrogen are within the range of those measured in CIs. Noble gas data indicate mixing between Q-like noble gases (a ubiquitous noble gas component found in most classes of primitive meteorites, presumably formed by noble gas incorporation into organic materials within the ionized regions of the parent cloud or in the protoplanetary disk) and various presolar components originally hosted by refractory grains that survived the high enthalpy birth of the solar system. The noble gases also include secondary contributions of three types: (i) noble gas isotopes produced by radioactivity, (ii) solar wind implantation, mostly identified in the light noble gas (He and Ne) isotopic compositions, and (iii) cosmogenic noble gases produced by interaction with high-energy cosmic rays, permitting us to estimate how long fresh surfaces were irradiated. We find that cosmic ray exposure (CRE) durations of Bennu material vary mostly between 1 and 3 Ma. These CRE ages are consistent with (i) radionuclide studies suggesting surface exposure for 2–7 Ma, (ii) small crater retention ages of 1.6–2.2 Ma, and (iii) the 1.75 ± 0.75 million years that Bennu is estimated to have been dynamically decoupled from the asteroid belt. In contrast to CRE ages, we find a maximum duration of solar wind irradiation of ≤100,000 a, in agreement with exposure duration of <85,000 a from solar energetic particle tracks and microcrater densities. The noble gas abundances in Bennu and Ryugu samples are higher by a factor ≥2 compared to CI meteorites, whereas their isotopic compositions are similar. This difference between material sampled directly from asteroids and their meteoritic equivalent suggests degradation of the latter through contact with the terrestrial environment. Neon–argon variations point to a potential genetic relationship between Bennu, Ryugu, CI materials on the one hand, and the terrestrial atmosphere on the other.