Spectroscopic Identification of Carbonates in the Martian

Introduction: Carbonates play a significant role in determining the history of the Martian atmosphere, geology, and hydrology. Their presence and properties can give useful information about the specific environment in which they formed in the past. The work presented here demonstrates that the spectral character of Mars is consistent with and unique to the presence of small amounts of carbonates within a fine particulate dust. The systematics and accuracy of the TES data has allowed for the isolation of the thermal infrared emis-sivity spectra of the surface dust, providing a new measurement with unique mineralogical sensitivities [1]. Absorptions at ~800cm-1 and >1300cm-1 are due to fine particulate silicates that contain an unknown concentration of plagioclase or zeolites [1,2]. While the absorption present at >1300cm-1 is consistent with volume scattering effects in fine-particulate silicates [1,3], the spectral shape and depth requires the presence of a material that is highly absorbing at these wavenumbers to raise the emissivity to the level seen on Mars. Similar to the 4.5µm absorption [4-6], the spectral character near 7µm (~1500 cm-1) in the Martian spectrum appears to be sensitive and unique to small quantities of carbonates intimately mixed with silicates in fine particulate materials. The extent and variability of this spectral character is investigated with the TES and laboratory data to both confirm the compositional implications of the Martian spectral features as well as attempt to put constraints on the abundance present. Methods and Results: Twenty-one multiple emission angle sequences were selected from a variety of longitudes and latitudes between 30 S and 15 N and the surface emissivity was derived using an atmospheric correction method similar to [1]. The distribution of the selected observations is highly correlated with moderate to high albedo regions, which have a large dust contribution to the measured spectra. All surface spectra have the same spectral character. The standard deviation in the spectral shape of the surfaces is <0.01 from 250 cm-1 to 1610 cm-1 and climbs from 0.01 to 0.02 for the 1620-1650 cm