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Summary: Mercurys surface studies are difficult from ground-based observations and from the limited number of missions that have explored the Hermean environment. Characterising further Mercurys properties from laboratory measurements is a great and timely opportunity given BepiColombos arrival in late 2025. Through spectral measurements of Mercury analogues, our goal is to explore the mineralogical properties of Mercurys surface and its dependency on orbital measurements and Mercurys environment. Through dedicated measurements, we have explored the variability of spectral properties as a function of observation conditions and irradiation level. Our analysis shows that the variability of spectral properties with varying illumination conditions can be correlated to specific compositions, particularly the magnesium content. We notice that spectral slopes increase with higher magnesium content and higher phase angle. Similarly, we noticed that the spectral slopes increase with irradiations of samples and reach a plateau. This puts important constraints on the capability of orbital measurements to observe spectral variabilities that are linked to recent geological phenomena and specific mineralogical and elemental compositions.High irradiation effects on reflectance spectroscopy: We used 20 keV He+ with fluences up to 5 x 1017 ions/cm2 to simulate ion irradiation reaching the surface. Terrestrial ultramafic lava already identified as good analogues for Mercury were used: a boninite, a basaltic komatiite and a komatiite. Spectra were acquired in the visible to mid-infrared (VMIR) wavelength range, between 0.4 and 16 m. Spectral alterations induced by irradiation are observed in the visible to near-infrared (VNIR) with an exponential darkening, a reddening and a flattening of spectra. Above a certain irradiation dose (1 x 1017 ions/cm2 in our conditions), the darkening reaches a plateau and the reddening as well. In the mid-infrared (MIR) we observe a shift of Reststrahlen bands towards longer wavelengths (
Besse et al. (Wed,) studied this question.