Comparison of Mid-IR Spectra of Various Silicates Under High Vacuum

Abstract

The analysis of spectral properties in the mid-IR range has become an important tool for the investigation of the surface mineralogy of Mercury [1]. The MERTIS-instrument (MErcury Radiometer and Thermal Infrared Spectrometer) collects emission spectra in the range of 7 μm to 14 μm (spectrometer channels) and 7 μm to 40 μm (radiometer channels) of surface-forming minerals [1]. The spectra can not only be used to investigate the surface evolution of Mercury, but provide also information about the evolutionary history of the early Solar System [1]. The minerals expected on Mercury include olivine and plagioclase, which is why we performed a detailed investigation of the spectral characteristics of these two minerals [2]. In particular, we used mixtures of the two minerals in different amounts, hence, producing relevant analog samples of Mercury in preparation of results of the MERTIS instrument. The samples were measured under conditions similar to the conditions on Mercury’s surface under high vacuum and in uncompressed state to serve as regolith analog. The measurements on the powders are particularly important, since the surface on Mercury is covered by loose regolith resulting from strong space weathering on this planet without atmosphere [1]. In addition, pellets were investigated to compare the results to [3,4], whether the spectra of the pressed pellets change compared to the loose sample. Thus, the results obtained for the loose powders are closer to reality than those for the tightly pressed samples. The aim of the study is to show whether the Christiansen feature (CF) in the mid-IR shows a linear dependence of the composition or not.