We have obtained spectra of the thermal emission from Mars in the 5.4--10.5 μm wavelength domain at a resolving power of about 60 from the Kuiper Airborne Observatory. Spectra were obtained for several large spots on Mars, whose ground temperatures and air masses through the Martian atmosphere differed significantly. These data were taken at two times during the flight. By taking the ratio of the spectral flux from one spot to that of a second spot, we obtained results that were independent of uncertainties in the instrument's sepctral response and the transmission of the Earth's atmosphere. These data, as well as spectral fluxes of single spots based using the star α Tau as a calibration standard, show a number of emission and absorption features. They are present in sets of spectra taken at two different times. Some of the absoption features are due to gaseous CO2 in the Martian atmosphere. The remainder of the absorption and emission features are due to minerals present in the airborne dust and on the surface. Comparison of the strength of features seen at similar times, but with three different air masses and ground temperatures, suggests that the emission features arise primarily from surface emissivity spectral variations and that the absorption features arise from components of the atmosphere. Based on comparisons of the observed features with laboratory data for a broad ensemble of minerals, spectra of other solar system bodies, and relevant compositional information about Mars, we have made the following tentative identifications of the observed features.

Emission features at 7.8 and 9.7 μm are attributed to surface silicates; an emission feature at 6.1 μm is attributed to a molecular water component of the surface material; an absorption band at 8.7 μm as well as possibly one at 9.8 μm is ascribed to sulfate or bisulfate anions, probably located in a distorted crystalline site; and an absorption band at 6.7 μm is attributed to carbonate or bicarbonate anions located in a distorted crystalline site, although we cannot totally rule out a nitrate orgin for this feature. We have simulated these spectra with radiative transfer programs for the atmosphere and surface. These simulations indicate that the sulfate- and carbonate-bearing minerals are contained in the same particles of the airborne dusts as the dominant silicate minerals, that the dust optical depth was about 0.6 at a reference wavelength of 0.3 μm over the area of the observed spots, and that sulfates and carbonates constitute about 10--15% and 1--3% by volume of the airborne dust, respectively. These results imply that minerals formed by weathering processes represent major reservoirs of volatile species on current Mars. ¿American Geophysical Union 1990