A mid-infrared study of synthetic glass and crystal mixtures analog to the geochemical terranes on mercury

The MERTIS (MErcury Radiometer and Thermal Infrared Spectrometer) onboard of the BepiColombo ESA/JAXA mission to Mercury will map the surface of Mercury in the wavelength range of 7-14 & mu;m and for the interpretation of these spectra a database of analog materials is needed. We analyzed bulk grain size fractions of a series of analog materials relevant to the distinct terranes of Mercury in diffuse reflectance in the mid-infrared (2.5 & mu;m to 18 & mu;m). Mineral mixtures cover a wide range of modal amounts of forsterite, enstatite, diopside and plagioclase, the resulting spectra can be divided into three distinct groups: (1) is dominated by a single glass feature, (2) by forsterite bands, and (3) by pyroxene bands. Despite often high contents, plagioclase features, are usually 'overprinted' by forsterite and pyroxene bands.Spectral parameter CF, an easy obtainable proxy for chemistry (SiO2) and polymerization (SCFM) places the hermean mixtures mostly in the intermediate and basaltic range. The correlation of parameters easily obtainable in remote sensing, Mg/Si ratio, and CF, allows differing materials from high-energy evaporation processes in impacts from such formed in igneous processes.Preliminary comparison with a spectrum covering most of the hermean surface shows some similarity with band positions of the Inter Crater Plain and Heavily Cratered Terrains (IcP-HCT) and High-Mg Northern Volcanic Plains (High-Mg NVP) mixtures, but none of our spectra is able to reproduce the remote sensing data entirely.

Automated summary

The MERTIS instrument on the BepiColombo mission will map the surface of Mercury and requires a database of analog materials for spectral interpretation. We analyzed analog materials relevant to Mercury's distinct terrains using mid-infrared reflectance spectroscopy. Different mineral mixtures showed distinct spectral features dominated by glass, forsterite, or pyroxene bands. The easily obtainable spectral parameter CF can be used to classify the analog mixtures. The spectra analyzed in this study showed some similarity to certain terrains on Mercury, but could not fully reproduce the remote sensing data.