Mercury Y – A Blind Sample to Cross-Validate and Determine Synergies of BepiColombo Instruments

Kurzfassung

BepiColombo will provide the first orbital measurements of Mercury’s surface mineralogy using instruments operating from X-rays to thermal infrared. To support the interpretation of these data, we developed a Mercury simulant, Mercury Y. The simulant consists of a fine-grained mixture of plagioclase, Mg-rich pyroxene, olivine, glass, and graphite. The composition was kept confidential and the simulant was analyzed independently by several laboratories using measurement methods representative of three BepiColombo surface instruments: X-ray fluorescence spectroscopy for MIXS (Mercury Imaging X-ray Spectrometer), visible to near-infrared reflectance spectroscopy for SIMBIO-SYS (Spectrometers and Imagers for MPO BepiColombo Integrated Observatory), and mid-infrared reflectance and emission spectroscopy for MERTIS (Mercury Radiometer and Thermal Imaging Spectrometer). Blind analyses enabled a successful determination of the composition of Mercury Y. MIXS measurements reproduced the bulk elemental composition and confirmed the low-iron nature of the sample. SIMBIO-SYS spectra exhibited weak absorptions near 1 μm, consistent with Mg-rich mafic phases and glass, providing only qualitative mineralogical information. MERTIS spectra displayed diagnostic features, enabling quantitative identification of a plagioclase-rich assemblage containing Mg-rich pyroxene, olivine, and glass. Although graphite was not directly detected, its presence was inferred from its effect on the reflectance and emissivity. This joint effort shows that no single technique can constrain both the mineral chemistry and modal mineralogy, however, the combined use of the three instruments significantly improves the interpretation of the composition and reduces the uncertainties inherent in individual datasets. The study therefore provides the first coordinated laboratory benchmark for evaluating the synergies of the BepiColombo instruments.