¹R.M. Marshal,¹M. Patzek,¹O. Rüsch
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2024.115984]
¹Institut für Planetologie, Universität Münster, 48149 Münster, Germany
Copyright Elsevier

This study investigates the key role of boulders, particularly their surface texture, which are primary surface features on small airless planetary bodies, that serve as indicators to better understand the geological history and evolutionary processes undergone by the small bodies and their respective parent bodies. In particular, this study focuses on characterizing the unpolished surface of meteorite samples, which can be likened to the surfaces of boulders on small bodies. We use surface roughness metrics such as the mean (bidirectional) slope and a Hapke mean slope angle in order to characterize the surface texture of the samples. Furthermore, considering a fractal roughness of the surface we estimate the Hurst exponent and the associated scaling factor at an arbitrary scale of ~60 μm. We find that on the ~4 μm scale, the mean bidirectional slope and the mean Hapke slope are in the range of 20–40° and 15–35° respectively, with carbonaceous chondrites collectively exhibiting the lowest average value for both. Furthermore, we provide surface roughness measurements for a subsample of the Ryugu sample A0008, which is broadly in agreement with the measurements derived from MASCam data. This study also investigated intra-sample heterogeneities, specifically surface roughness variations between matrix and non-matrix components such as impact melt, shock veins, and chondrules. The results suggest that surface roughness variations exist between these components and the matrix, however, the amplitude of the variation is strongly influenced by the petrological homogeneity of the chosen region of interest.

¹A.-M. Seydoux-Guillaume,²T. de Resseguier,³G. Montagnac,⁴S. Reynaud,⁵H. Leroux,³B. Reynard,⁶A.J. Cavosie
Earth and Planetary Science Letters 628, 118587 Link to Article [https://doi.org/10.1016/j.epsl.2024.118587]

¹UJM-Saint-Etienne, LGL-TPE UMR5276 CNRS, 42023 Saint Etienne, France
²PPRIME, CNRS-ENSMA-Université de Poitiers, 1 avenue Clément Ader, Futuroscope, 86961, France
³ENSL, UCBL, UJM, CNRS, LGL-TPE, Univ Lyon, Lyon F-69007, France
⁴UJM-Saint-Etienne, CNRS, Institut d’Optique Graduate School, Laboratoire Hubert Curien UMR 5516, Université de Lyon, Saint-Etienne F-42023, France
⁵CNRS, INRAE, Centrale Lille, UMR 8207 – UMET – Unité Matériaux et Transformations, Univ. Lille, Lille F-59000, France
⁶The Space Science and Technology Centre (SSTC) and the Institute for Geoscience Research (TIGeR), School of Earth and Planetary Science, Curtin University, Perth, WA 6102, Australia
Copyright Elsevier

Impact-related damage in minerals and rocks provides key evidence to identify impact structures, and deformation of U-Th-minerals in target rocks, such as monazite, makes possible precise dating and determination of pressure-temperature conditions for impact events. Here a laser-driven shock experiment using a high-energy laser pulse of ns-order duration was carried out on a natural monazite crystal to compare experimentally produced shock-deformation microstructures with those observed in naturally shocked monazite. Deformation microstructures from regions that may have experienced up to ∼50 GPa and 1000 °C were characterized using Raman spectroscopy and transmission electron microscopy. Experimental results were compared with nanoscale observations of deformation microstructures found in naturally shocked monazite from the Vredefort impact structure (South Africa). Raman-band broadening observed between unshocked and shocked monazite, responsible for a variation of ∼3 cm−1 in the FWHM, is interpreted to result from the competition between shock-induced distortion of the lattice, and post-shock annealing. At nanoscale, two main plastic deformation structures were found in experimentally shocked monazite: mosaïcism, and deformation bands. In contrast, the naturally shocked monazite sample, contained only deformation twins with elemental enrichment along host-twin boundaries. Both mosaicism and deformation bands, expressed in SAED patterns as streaking of spots, and the presence of extra spots (more or less pronounced), are proposed as nano-scale signatures of shock metamorphism in monazite. Experimentally calibrated deformation features, such as those documented here at TEM-scale, provide new tools for identifying evidence of shock deformation in natural samples.