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.