INVESTIGATING THE DISTRIBUTION OF MARTIAN SALTS

The presence of salts on Mars is important for understanding the geological and chemical history of the planet, as their presence can help us infer the chemistry and evaporation history of surface lakes and playas. Furthermore, the spectral similarity between perchlorates and sulfates raises the possibility that previous sulfate detections may actually be perchlorates. This has major implications for habitability, as perchlorates indicate much lower water activity brines, which are less favorable for habitability than sulfates. This is because chloride, perchlorate, and chlorate salts can all suppress the freezing temperature of water significantly, in some cases with a eutectic temperature down to 204 K. They also slow down the evaporation rate, extending the lifetime of the liquid water solution.

We have developed routines specifically for identification and mapping of variations in the wavelength locations of absorption band minima in CRISM spectra. We have begun to apply these routines in order to identify chlorine salts in our specified CRISM images. We compare variability in our identified spectral units to our extensive database to constrain the salt assemblage present. Spectral variation within these units may include variations in band minima, spectral parameters, band depth, band width, overall slope, and shape of the bands. By using our new techniques, we are able to more accurately map variations and assess the minerals that may cause them.

Results in Columbus Crater indicate that Al- and Fe-sulfates are the predominant salts present, while Mg-bearing chlorine salts are also prevalent. This assemblage is consistent with upwelling of acidic groundwater or upwelling and oxidation of neutral Fe-bearing groundwater. In either case, the groundwater could have been enriched in K, SO₄²⁻, Al, Mg and Fe and later concentrated in a playa environment by evaporation, as previously hypothesized. This hypothesis is supported by observations of bedding within the sulfates and phyllosilicates, filled fractures potentially produced through the upwelling of groundwater, and polygonal patterns consistent with evaporites.