Determination of rock type on Mercury and the Moon through remote sensing in the thermal infrared

Abstract

Thermal infrared emission spectra of the Moon and Mercury have been obtained using the Si:As photoconductor and circular variable filter (CVF) at the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawaii. Lunar spectra from 7.2 µm to 12.2 µm for two different locations in the south polar highlands have Christiansen frequency peaks at 8.1 µm and 7.9 µm respectively. This indicates different compositions at the two locations; mafic in the first case, more felsic in the second. Emission spectra from Mercury are not as spatially localized; however the longitude of maximum contribution to the spectrum can be calculated from thermal models of the earth‐facing disk. Results for areas centered at two longitudes have been obtained so far. Two locations in the intercrater plains were observed. At 40° longitude (very near the crater Homer), a peak at 7.9 µm indicates mafic igneous rock type. One day later, spectra emanating from 46° longitude have peaks at 7.8 µm and indicate a region borderline between mafic and intermediate composition.