UV-visible-infrared spectral survey of Antarctic carbonaceous chondrite chips

Antarctic carbonaceous chondrite (CC) meteorite chip samples in the Japanese and US collections have been studied by an ultraviolet (UV), visible (Vis), and near-infrared (NIR) (UVVNIR) spectrometer and a Fourier-transform infrared (FTIR) spectrometer, targeting small areas of about 2–6 mm in diameter. UVVNIR and FTIR reflectance spectra of 169 spots on 148 CC chips were measured on their naturally broken surfaces with no sample preparation. Among them, 83 spectra were accepted as reasonably free of terrestrial weathering or surface texture effects. X-ray diffraction (XRD) and FTIR measurements of a weathered sample revealed that gypsum likely formed on its surface after recovery from Antarctica. Principal component analysis (PCA) of the UVVNIR-FTIR combined spectra allowed distinguishing powder and chip or surface texture and identifying their class and thermal metamorphism. Gaussian fitting of the 3 μm absorption band of hydrous CC samples allowed for removal of the spectral effects of adsorbed H2O and for the extraction of structural absorption bands which are characteristic of CC classes and degree of aqueous alteration. These results suggest that CC-like rocks on small asteroids without fine regolith can be identified through spectral reflectance measurements by spacecraft, landers, or rovers.