Infrared 8-13µ Spectroscopy of the Moon and Some Cold Silicate Powders

Citation

Goetz, Alexander Franklin Hermann (1967) Infrared 8-13µ Spectroscopy of the Moon and Some Cold Silicate Powders. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z362-5914. https://resolver.caltech.edu/CaltechTHESIS:04262017-152729036

Abstract

Laboratory investigations were made of the spectral emission properties of a limited number of silicate powders in vacuum and surface temperatures of 180-240°K. The effect on the emission spectrum of mineral composition, powder grain-size, surface contamination and thermal gradient was studied.

The low sample surface temperature enhanced the spectral contrast of quartz but had little effect on spectra of rock materials. In general, there was a decrease in spectral contrast with decreasing sample grain-size. However, this effect was more pronounced for individual mineral samples than for rock samples. When the particle size was reduced to less than 38μ individual rock types could not be identified. However, quartz bearing or generally acidic rocks could be differentiated from quartz free or generally basic rock types. A quartz sample which had been contaminated by iron oxide did not lose its spectral features in spite of being visibly colored. The effect of a thermal gradient in the sample on its emission spectrum was shown to be negligible.

Differential 8-13μ spectroscopy of 22 lunar points, spanning the major types of lunar features, was undertaken to determine if compositional differences or age are evidenced in the 8-13μ emission spectra of the features. A method was devised to remove precisely the atmospheric absorption and allow the integration of many spectra in order to reduce uncertainties caused by atmospheric absorption fluctuations and detector noise.

Twenty of the 22 points showed no spectral differences greater than 1%. Two points, Plato and Mare Humorum, showed definite, consistent spectral differences from the rest of the points measured, at the short wavelength end of the spectrum.

The interpretation made here of these results is that these two points have significantly fresher surfaces exposed which still show some spectral contrast or they are compositionally different from their surroundings. In the former case the anomalous areas must be partially covered with a non-silicate material in order to be consistent with the data obtained. If the points are compositionally different and the uniform areas show spectral contrast, the uniform areas must contain quartz and the anomalous areas are then more basic in composition than the uniform areas. The alternative to these two possibilities is that some process, perhaps an effect of the solar wind, is operating in such a way as to produce spectra which are unknown and hence can be falsely interpreted.

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