Mid-IR Spectroscopy of Carbonate Decomposition Products with Application to Mars

To date, no outcrops of carbonate on Mars have been found using either mid-IR or VNIR data. One possible explanation for this is that previously existing carbonates have been destroyed by incident ultraviolet radiation. Therefore, a search for carbonate decomposition products in the Mars remote sensing data is warranted. We have acquired mid-infrared reflectance spectra of high quality samples of CaO, Ca(OH)₂, MgO, and Mg(OH)₂ that were synthesized at Stony Brook University. Reflectance spectra were converted to emissivity via Kirchhoff's Law (ε=1-R). We have retrieved and binned TES spectra from warm surfaces (>250 K) and periods of low dust and ice opacities at a resolution of 8 ppd. The Ca/Mg oxide/hydroxide spectra were added to a representative library of mineral, glass, and atmospheric spectra. The binned spectra were deconvolved with the spectral library between 220-1301 cm^-1 and the modeled abundances were grouped by mineral type. The Ca/Mg oxide/hydroxides are modeled at concentrations ranging from 0.0-0.20 and coincide with low-albedo regions. Within the low albedo regions, there are no areas where elevated concentrations of these phases are found in spatially contiguous patterns. Rather, there appears to be little geographic control on the distributions. Inclusion of these phases in end-member libraries does not reduce the modeled concentration of carbonates. A spectral index was also used to identify Ca oxide/hydroxide from the binned TES spectra. The index highlights numerous areas where these phases may be present. Spectra from two of these areas were selected for modeling with and without the Ca oxide/hydroxide end-members. Preliminary results indicate that derived surface emissivity spectra are significantly affected by the presence/absence of the new phases and that RMS errors are improved by 0.03% or more with inclusion of the new phases. Future work will include detailed mineralogical comparisons, factor analysis, and VIS/NIR analyses of promising regions.