^1,2Noah Jäggi,²Antoine S. G. Roth,²Miriam Rüfenacht,²Maria Schönbächler,²André Galli
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14026]
¹Physikalisches Institut, University of Bern, Bern, Switzerland
²Institute für Geochemie und Petrologie, ETH Zürich, Zürich, Switzerland
Published by arrangement with John Wiley & Sons

Chondrules are microscopic, recrystallized melt droplets found in chondritic meteorites. High-resolution isotope analyses of minor elements require large enough element quantities which are obtained by dissolving entire chondrules. This work emphasizes the importance of X-ray computed tomography (XCT) to detect features that can significantly affect the bulk chondrule isotope composition. It thereby expands on other works by looking into chondrules from a wide range of chondrites including CR, CV, CB, CM, L, and EL samples before turning toward complex and time-consuming chemical processing. The features considered are metal and igneous rims, compound chondrules, matrix remnants, and metal contents. In addition to the identification of these features, computed tomography prevents the inclusion of non-chondrule samples (pure matrix or metal) as well as samples where two different chondrule fragments with potentially different isotope compositions are held together by matrix. Matrix surrounding chondrules is also easily detected and the affected chondrules can be omitted or reprocessed. The results strongly encourage to perform XCT before dissolution of chondrules for isotope analysis as a non-invasive method.

^1,2S. K. Bell,¹K. H. Joy,¹J. F. Pernet-Fisher,¹M. E. Hartley
Meteoritics & Planetary Science Open Access Link to Article [https://doi.org/10.1111/maps.14032]
¹Department of Earth and Environmental Sciences, University of Manchester, Manchester, UK
²Rocktype Ltd, Magdalen Centre, Oxford, UK
Published by arrangement with John Wiley & Sons

Mare basalts collected at the Apollo 15 landing site are classified as belonging to either the quartz-normative suite or the olivine-normative suite, based on differences in whole-rock major element chemistry. A wide range of textures are displayed within samples from both suites, which provide insight into eruption processes on the Moon. Here we use crystal size distribution (CSD) analysis and spatial distribution pattern (SDP) analysis of pyroxene, olivine, and plagioclase crystals in eight Apollo 15 mare basalt samples to investigate the crystallization and emplacement of the quartz-normative and olivine-normative suites. In general, our results show similarities between the CSDs and SDPs for both mare basalt suites. However, we also report two distinct groups of pyroxene CSD trends that likely represent samples with common cooling histories, originating from comparable depths within respective olivine-normative and quartz-normative lava flows. We use our results to determine the relative depths of samples within the lava flows at the Apollo 15 landing site.

¹A. Deanne Rogers,²Steven W. Ruff,³Michael D. Smith
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2023.115687]
¹Stony Brook University, Stony Brook, NY, USA
²Arizona State University, Tempe, AZ, USA
³NASA Goddard Space Flight Center, Greenbelt, MD, USA
Copyright Elsevier

It has been hypothesized that the dust component of the Martian surface is globally homogeneous, based on chemical similarity between landing sites and spectral similarity from select areas within bright regions. We tested that hypothesis by producing the first near-global data set of surface spectral emissivity (excluding polar regions) across the ~233–508 and 825–1650 cm−1 (~20–50 and 6–12 μm) spectral ranges from Mars Global Surveyor Thermal Emission Spectrometer data and using various data reduction techniques to search for any spectral heterogeneity in bright regions that might be present. We found no unequivocal evidence for spectral heterogeneity, supporting the hypothesis that dust is globally homogenized. The global emissivity product permits new spectral parameter maps and preliminary assessments of atmosphere-regolith interactions. We produced the first map of the Christiansen feature (CF) and show that, unlike on the Moon, where CF is a proxy for bulk silica content, CF position on Mars is primarily associated with dust cover. We produced an updated map of the 1630 cm−1 emissivity peak that arises from bound H2O in fine-particulate material and show that the peak is nearly ubiquitous across the Martian surface, including in dark regions with relatively low dust cover. This is attributed to minor amounts of dust disproportionally contributing to the spectral signal in the ~1630 cm−1 region. We show that regions within the equatorial dust deposits with higher annual modeled frequency of nighttime CO2 frosts are more likely to have lower emissivity in the ~1350-1400 cm−1 region, consistent with a higher fraction of unconsolidated dust. This provides the first spectral evidence for a previously hypothesized regolith gardening process via a diurnal CO2 cycle, representing an important surface-atmosphere interaction that may contribute to near-surface porosity and affect diffusive exchange of H2O between atmosphere and hydrated solids (ice, minerals) in the regolith.