Laboratory investigations were made of the spectralemission properties of a limited number of silicate powders invacuum and surface temperatures of 180-240°K. The effect onthe emission spectrum of mineral composition, powder grain-size,surface contamination and thermal gradient was studied.
The low sample surface temperature enhanced the spectralcontrast of quartz but had little effect on spectra of rock materials.In general, there was a decrease in spectral contrast with decreasingsample grain-size. However, this effect was more pronounced forindividual mineral samples than for rock samples. When the particlesize was reduced to less than 38μ individual rock types could not beidentified. However, quartz bearing or generally acidic rocks couldbe differentiated from quartz free or generally basic rock types. Aquartz sample which had been contaminated by iron oxide did notlose its spectral features in spite of being visibly colored. The effectof a thermal gradient in the sample on its emission spectrum wasshown to be negligible.
Differential 8-13μ spectroscopy of 22 lunar points, spanningthe major types of lunar features, was undertaken to determine ifcompositional differences or age are evidenced in the 8-13μ emissionspectra of the features. A method was devised to remove preciselythe atmospheric absorption and allow the integration of many spectrain order to reduce uncertainties caused by atmospheric absorptionfluctuations and detector noise.
Twenty of the 22 points showed no spectral differencesgreater than 1%. Two points, Plato and Mare Humorum, showeddefinite, consistent spectral differences from the rest of the pointsmeasured, at the short wavelength end of the spectrum.
The interpretation made here of these results is that thesetwo points have significantly fresher surfaces exposed which stillshow some spectral contrast or they are compositionally differentfrom their surroundings. In the former case the anomalous areasmust be partially covered with a non-silicate material in order tobe consistent with the data obtained. If the points are compositionallydifferent and the uniform areas show spectral contrast, the uniformareas must contain quartz and the anomalous areas are then morebasic in composition than the uniform areas. The alternative to thesetwo possibilities is that some process, perhaps an effect of the solarwind, is operating in such a way as to produce spectra which areunknown and hence can be falsely interpreted.
