¹M. Barthez, ¹J. Flahaut, ²M. Guitreau, ¹R. Pik, ¹G. Ito, ³C. Delangle, ³J.-P. Gremilliet, ¹B. Luais, ¹F. Faure
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2026.117027]
¹Université de Lorraine, CNRS, CRPG, Nancy F-54000, France
²Laboratoire Magmas et Volcans, Université Clermont Auvergne, OPGC, CNRS UMR-6524, IRD UMR-163, F-63173 Clermont-Ferrand, France
³Centre Terrae Genesis, F-88120 Le Syndicat, France
Copyright Elsevier

Visible Near-InfraRed (VNIR) spectroscopy is a powerful tool to assess the mineralogical composition of planetary surfaces remotely. Despite decades of investigation with the Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instruments, new detections are still being made on Mars. Plagioclase signatures were reported on the surface of Mars with CRISM, and it could be indicative of uncommon lithologies, as plagioclase is known to be difficult to detect with VNIR spectroscopy, except for plagioclase-pure rocks (i.e., anorthosite).
The present study investigates the VNIR spectra of 67 plagioclase-bearing terrestrial igneous rocks of various nature (e.g., granite, anorthosite, gabbro, tonalite, syenite and their volcanic equivalents) that were kept uncrushed as Mars candidate analog rocks. Total rock spectra were measured with a point spectrometer, while the spectra of their plagioclase constituents are extracted from hyperspectral camera analyses. In parallel, the petrology of rocks and the chemical compositions of feldspar minerals are evaluated with optical microscopy and electron probe microanalyzer (EPMA) respectively.
Most plagioclase crystals in our sample collection exhibit diagnostic absorption features centered between 1.15 μm and 1.40 μm at the mineral level, unless the mineral is altered and/or weathered. Both physical and spectral evidence for alteration products, such as muscovite and prehnite, are observed. Still, plagioclase signatures are often masked on the total rock spectra (44 out of 67 samples). We found that the main factors that control the spectral signature of plagioclase in the total rock spectra are its chemical composition and grain size, as well as the associated minerals and the rock albedo. Plagioclase spectral signatures are observed in total rock spectra of samples containing as little as 18% plagioclase, challenging previously published estimates and interpretations based on studies of powders and grain mixtures. Diagnostic plagioclase signatures are visible in the spectra of rocks of various natures and textures, including plagioclase-phyric basalt, anorthosite, granite and granodiorite, opening up a range of possibilities for the nature of the lithologies involved in Mars detections.

¹Carine Sadaka et al. (>10)
Meteoritics & Planetary Science (in Press) Free Access Link to Article [https://doi.org/10.1111/maps.70125]
¹Aix-Marseille Université, CNRS, IRD, INRAE, CEREGE, Aix-en-Provence, France
Published by arrangement with John Wiley & Sons

The Atacama Desert in Chile is characterized by its high meteorite density and old meteorite terrestrial ages. In this work, we present new terrestrial ages derived from measurements of the concentration of cosmogenic 36Cl in the metal fraction of 51 ordinary chondrites collected over a 6.8 km2 area located in the Catalina Dense Collection Area (Atacama Desert). Cosmic-ray exposure ages were also measured on a subset of the oldest meteorites to confirm that all but one had reached 36Cl saturation before atmospheric entry. These meteorites have exceptionally old terrestrial ages, with an average of 937 ka (median 701 ka), making this collection the oldest known meteorite collection among hot deserts. This confirms that the Atacama Desert can preserve meteorites for long periods due to the prevailing stable hyper-arid climatic conditions. By combining terrestrial ages with pairing-corrected meteorite density estimates, we estimate the long-term meteorite flux to Earth over the past 2 Myr to be 74 ± 9 meteorites >20 g per km2 per Myr. This is consistent with estimates of (i) the modern flux, (ii) the integrated flux over the last ~100 kyr determined from Antarctic meteorites, and (iii) the average flux during the last ~50 kyr inferred from other hot desert collections. This suggests that the bulk meteorite flux to Earth has remained roughly stable over the past 2 Myr. We also investigate the compositional evolution of the flux by normalizing the H chondrite abundance to the total abundance of ordinary chondrites. Our results show a higher H chondrite abundance between 1200 and 400 ka, followed by a decline to present-day values. This temporal variation is not captured by the current dynamical models for meteoroid transfer to Earth, suggesting that short-term changes in the meteorite flux may be influenced by additional processes operating at a scale not considered by these models.