Infrared emissivity of lunar surface features: 2. Interpretation

Abstract

Thermal emission spectra of six different areas on the lunar surface are discussed in the light of laboratory studies of the spectral emissivity of rocks and minerals. It is shown that the emission maxima characteristics of lunar spectra are similar to emission maxima found in the spectra of particulate rock samples. Such emission maxima are shown to be diagnostic of general rock type, within limits that are defined. Differences in emission maxima of their respective spectra indicate a significant difference in bulk composition between the material ejected by the craters Copernicus and Theophilus and the surface material of the two circular maria, Imbrium and Serenitatis. Barring some unknown measurement error in the spectra, or some unanticipated effect of the lunar environment on surface spectral behavior, we can conclude that the crater materials display an emissivity maximum characteristic of silica-poor basic rocks, while the circular maria display a maximum characteristic of silica-rich ultrabasic rocks. If this preliminary result is confirmed by future research, it has profound implications for the origin and evolution of the lunar crust.