Collection of a database of spectroscopic measurements of Mercury analogs to support the interpretation of remotely sensed data from the ESA/JAXA BepiColombo mission to Mercury

Abstract

BepiColombo is a joint international mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) on the way to the least explored terrestrial planet Mercury. Among the payload of the BepiColombo Mercury Planetary Orbiter (MPO) is the MErcury Radiometer and Thermal infrared Imaging Spectrometer (MERTIS). To support the interpretation of remote sensing data from this mission, we have collected a database of spectroscopic measurements of possible Mercury surface analogs. Very little is known until now about the mineralogy of the closest planet to the Sun. The first part of this Master thesis project is the measurement of bidirectional reflectance, hemispherical reflectance, and emissivity spectra (at Mercury relevant surface temperatures from 250◦C to 450◦C) of five salts under vacuum in the MERTIS spectral range (7-14) µm. The salts used for this experiment are part of the sample collection of the Planetary Spectroscopy Laboratory (PSL) of the department of Planetary Laboratories (PLL) at the Institute of Space Research (WR), DLR, Berlin. Five salt samples (Apatite, Calcite, Dolomite, Halite, and Siderite) were prepared at the Sample Preparation Laboratory of PLL. The main goal of these measurements is to help in the interpretation of MERTIS spectral data. The second part of this Master thesis is based on the acquisition and study of the vvi bidirectional reflectance spectra of two endmembers Diopside (Pyroxene group) and Oligoclase (Plagioclase feldspar group) and their mixtures from UV to MIR along a wide range of grain size separates and analyze the grain size effect. The purpose of the second part of this project is to support the other spectrometers like Mercury Imaging X-ray Spectrometer (MIXS) and Spectrometers and Imagers for MPO BepiColombo Integrated Observatory System (SIMBIO-SYS) on BepiColombo. The result of the emissivity experiment shows that the emissivity maxima of salts such as Calcite, Dolomite, and Siderite lie in the wavelength range of (11-12) µm. In the case of emissivity spectra of salts Apatite and Halite, the emissivity maxima are observed in the wavelength range of (8-9) µm. The result of the bidirectional reflectance measurement in the second experiment shows that the reflectance of Oligoclase is higher than that of Diopside in the UV, VIS and VNIR spectral range. In contrast, the reflectance of Diopside is observed to be higher than that of Oligoclase in the MIR spectral range. The analysis of the grain size effect shows that the reflectance of a sample decreases as the grain size increases. This study will contribute to the interpretation of spectral data acquired from the BepiColombo mission. Keywords: Mercury, BepiColombo, MERTIS, reflectance and emissivity spectra, FTIR spectrometer.