惑星探査における鉱物分光学の重要性

Abstract

Planetary geology provides information on processes on the surface and interiorl of terrestria planets, satellites, and asteroids in the solar system. Surface composition and mineralogy is one of clues to understand planetary geology and, in particular, it is essential to determine the composition of planetary surface in order to discuss the origin and geologic/geochemical evolution. The mineralogical information is investigated using spectroscopy in the visible and near-infrared regions of the electromagnetic spectrum, because most of rock-forming minerals exhibit characteristic absorption features at these wavelengths. Especially, silicate minerals such as olivines and pyroxenes show diagnostic absorption bands due to the presence of Fe2+. The compositional interpretation of reflectance spectra using the remote sensing techniques is based on the principle of the crystal field theory. Recently, with the advances in computer and detector technology, the new field of imaging spectroscopy is developing in remote sensing. Imaging spectroscopy is an instrument of combination of imaging, technique to obtain planetary images, and spectroscopic technique. While the instrument is in use in the laboratory, in an aircraft, and in Earth-based telescope, only a few spaceborne instruments for planetary observation were applied because of difficulty in technical development. This instrument can obtain a three-dimensional cube data with two spatial and third spectral dimensions and may provide the determination of composition and mapping of compositions across the planetary surface at high resolution. To develop more general views on planetary geology, it will be required to develop the imaging spectroscopy for spacecrafts.