Thermal Emission Spectrometer hyperspectral analyses of proposed paleolake basins on Mars: No evidence for in-place carbonates

Several studies have described photogeologic evidence for paleolacustrine basins on Mars, mostly within impact craters. If these basins contained persistent standing water in the past, they could still contain deposits of evaporite minerals,(e.g., carbonates, sulfates). Many such deposits, if exposed at the surface to a sufficient extent, would be detectable in thermal infrared spectra taken from orbit. Using data from the Mars Global Surveyor Thermal Emission Spectrometer (TES), we have conducted a hyperspectral investigation of 43 putative paleolake basins to search for the spectral signatures of evaporite minerals exposed at a scale comparable to the spatial resolution of a single TES pixel(∼3 × 5 km). Seven basins displaying sufficient surface-related spectral variation were identified using a principal component analysis on the TES spectral image cube covering the basin and its surroundings and spectral regions of interest (ROls) were defined. Averaged spectra from ROls were evaluated using previously developed dust cover index. Those spectra determined to be "dust-free" were analyzed for composition using linear spectral deconvolution. The same spectra were also analyzed using a spectral ratio and a set of carbonate indices developed in the present work. Most TES spectra in this study were well-modeled using only previously defined TES spectral end-members. In addition, the spectral ratios and the carbonate index analyses of these basins indicated that carbonates are not present in abundances greater than the detection limits of these methods. Therefore this study did not find any spectral evidence for evaporite deposits in the basins studied.