¹Audrey C. Martin,²Joshua P. Emery,^2,3Mark Loeffler,¹Kerri L. Donaldson Hanna
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008331]
¹Department of Physics, University of Central Florida, Orlando, FL, USA
²Department of Astronomy and Planetary Science, Northern Arizona University, Flagstaff, AZ, USA
³Center for Material Interfaces in Research and Applications, Northern Arizona University, Flagstaff, AZ, USA
Published by arrangement with John Wiley & Sons

Mid-infrared (MIR; 5–35 μm) spectroscopy is often used for mineralogical identification on planetary surfaces. Laboratory spectra aiding remote sensing observations are typically performed in reflection geometries, while MIR spectra of planetary surfaces are typically obtained via emission. Here we explore the validity of Kirchhoff’s Law in converting reflectance to emissivity spectra, focusing on the high-porosity regoliths found on airless bodies such as the Moon and asteroids. Specifically, we compared ambient reflectance, ambient emissivity, and simulated asteroid environment (SAE) spectra of fine-particulate olivine and pyroxene with varying regolith porosities, focusing on how spectral features, including the Christiansen feature (CF), reststrahlen bands (RBs), and transparency features (TF), changed under these different conditions. Our results indicate that Kirchhoff’s Law can be effectively employed to interpret 19 MIR reflectance spectra of high-porosity samples, provided environmental spectral effects (i.e., spectral changes due to different pressure and temperature conditions) are considered.

¹E. Dobrică, ²V. Megevand, ¹A.N. Krot, ³A.J. Brearley
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.05.020]
¹Hawai‘i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, HI, USA
²Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, Paris, France
³Department of Earth and Planetary Sciences, University of New Mexico, NM, USA
Copyright Elsevier

Studies of shock metamorphic effects in apatite and merrillite in nine ordinary chondrites (OCs) of petrologic types 3.5–6 and shock metamorphic stages S1–S5 using transmission electron microscopy (TEM) reveal a correlation between the extent of brittle deformation in phosphates and the shock metamorphic stage of six host meteorites. No correlation is observed in thermally annealed and partially melted phosphates in Kyushu (L6), Paragould (L5), and Hamlet (LL3.5 − 3.9). Apatites in several shocked equilibrated (petrologic type 6) OCs show micro- and nano-scale heterogeneities in volatile elements, suggesting they were locally mobilized during shock metamorphism rather than during thermal metamorphism. In Alfianello (L6, S5) and Kyushu (L6, S5), maskelynite associated with apatite shows clear evidence for melting. We suggest that maskelynite formed during melting processes rather than solid-state deformation, which has significant implications for geochronology and reflects the time of impact rather than the crystallization age of phosphates. Our study demonstrates the inadequacy of optical microscopy methods currently applied to determine shock metamorphic stages of chondrites; incorporation of micro and nanostructural observations will improve the accuracy of these determinations. We suggest that integration of detailed observations of shock and thermal metamorphism and fluid alteration is required for a comprehensive understanding of the secondary processes that modified most small Solar System bodies.