¹Mireia Leon-Dasi, ²Sebastien Besse, ³Camille Cartier, ⁴Océane Barraud, ⁴Alessandro Maturilli, ¹Alain Doressoundiram, ⁵Johannes Benkhoff, ^3,6Laurie Llado
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116582]
¹LESIA, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, Meudon, 92195, France
²European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, Villanueva de la Canada, 28692, Spain
³Centre de Recherches Pétrographiques et Géochimiques, Université de Lorraine, 15 Rue Notre Dame des Pauvres, Vandœuvre-lès-Nancy, 54501, France
⁴German Aerospace Center DLR, Institute of Planetary Research, Rutherfordstr. 2, Berlin, 12489, Germany
⁵European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, Noordwijk, 2200 AG, The Netherlands
⁶Department of Geology, University of Liège, 4000 Sart Tilman, Belgium
Copyright Elsevier

The temperature of Mercury varies greatly across different latitudes due to the planet’s spin/orbit resonance, leading to modifications in the surface spectral properties. The upcoming BepiColombo mission will map the surface of the planet in the UV-TIR range, providing a more comprehensive understanding of the surface alteration. However, comparing the spectral measurements between BepiColombo and the past MESSENGER mission could be challenging due to the large differences in observation geometry. Laboratory experiments with close surface analogs in viewing conditions similar to the space-based observations are necessary to understand the effect of the space environment and interpret the orbital spectral measurements. This study presents the UV-NIR spectroscopy of a Mercury simulant to understand the impact of observation geometry and temperature on the spectral properties of the planet’s surface. The simulant (a mixture of aubrites, albite, and synthetic sulfides) and its endmembers are measured under six geometries that sample the viewing conditions of both missions. The samples are measured fresh and after heating to 450 °C during three cycles. This study finds that the observation geometry modifies the reflectance spectrum of the samples differently depending on the wavelength and composition. The analog presents a darkening, reddening, and flattening with increasing phase angle in the UV-NIR domain. The heated samples present a brightening and reddening, with a deepening of absorption bands. The spectral changes associated with observation geometry and heating are stronger with increasing Mg abundance.

^1,2Laura Noel García,³Frederic Danoix,⁴Martina Ávalos,⁵Pouyan Shen,¹María Eugenia Varela
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14352]
¹Instituto de Ciencias Astronómicas, de la Tierra y del Espacio, Universidad Nacional de San Juan, CONICET, San Juan, Argentina
²Instituto de Mecánica Aplicada, Universidad Nacional de San Juan, San Juan, Argentina
³Groupe de Physique des Matériaux, UMR CNRS 6634, Saint Etienne du Rouvray, France
⁴Instituto de Física Rosario, Universidad Nacional de Rosario, CONICET, Rosario, Argentina
⁵Department of Materials and Optoelectronic Science, National Sun Yat-sen University, Kaohsiung, Taiwan, ROC
Published by arrangement with John Wiley & Sons

The presence of spheroidized plessite (SP) in mesosiderites was recently reported in the literature. This finding coupled with the poor understanding of this plessite variant, motivated us to investigate its formation process and evaluate its implications in assessing the previous proposals concerning mesosiderites’ genesis and cooling history. SP consists of spherulitic taenite particles irregularly distributed, usually surrounded by carbides, and embedded in a kamacite matrix. It has been reported in iron meteorites containing graphite, carbides, and pearlitic plessite (PP), especially in the IAB main group and the sLL and sLH subgroups. From the combination of X-ray tomography, electron backscatter diffraction, energy-dispersive spectrometry, and atom probe tomography in three samples of Vaca Muerta mesosiderite (A1, low to moderate metamorphism) from the ICATE (Argentina) collection of meteorites, we were able to identify a common crystallographic orientation between spheroids and retained taenite, the absence of PP and the carbon depletion in the metallic portion contiguous to the spheroids, and the high volumetric connectivity of the metallic portion. Based on these findings: (i) SP likely grew at the expense of pearlite lamellae, with their absence resulting from complete consumption after an extraordinarily slow cooling rate, probably succeeding a deep burial in a breccia of rock fragments. (ii) Carbon introduction would have followed plessite formation in mesosiderites at a temperature low enough to prevent carbon solid-state diffusion. (iii) Metal would have been poured in silicates, which favors the collision model between a differentiated asteroid and a molten core for mesosiderite genesis.