MERTIS - Mercury Radiometer and Thermal Infrared Spectrometer for the Bepi Colombo mission

Telescopic Measurements have shown that the surface composition of Mercury can be derived only indirectly from VIS/NIR-spectra: The spectral slopes and the absence of any feature in the range von 0.5 to 1 µm suggest anorthite as main component. From albedo value, it was concluded that at most 3 wt% FeO and less than 1 wt% TiO2 could be present in the hermean regolith. Feldspars are expected to belong to the main constituents of Mercury. In the NIR-range, however, pure feldspars have no specific spectral signature. The reliable detection of any feldspar and even their detailed classification are highly questionable. In the TIR-range, however, feldspars can be detected - and specified - by means of their diagnostic spectral signatures: Christiansen frequency, reststrahlen band, and transparency feature. In addition, pyroxenes and most other minerals can be detected and specified in this spectral range. MERTIS operating in the range between 7 and 14 µm will provide valuable mineral identification of feldspars and low-iron species that are expected to be prevailing on the surface of Mercury. In addition we will be able to measure surface thermophysical properties of the surface, characteristics of the polar volatiles, and the interior heat flux.