HYDRATED SULFATES ON MARS: CHARACTERIZING VISIBLE TO NEAR-INFRARED SPECTRA AND IMPLICATIONS FOR ROVER-BASED MULTISPECTRAL IMAGERS

Hydrated sulfates have been detected across widespread regions of the Martian surface, and are critical to understanding ancient aqueous environments on Mars. Thus, it is important to investigate how different hydrated sulfates can be identified on Mars. The Mars Exploration Rover and Mars Science Laboratory missions are equipped with multispectral visible to near-infrared (VNIR) cameras, Pancam and Mastcam, that have some sensitivity to hydration in sulfate minerals (their longest-wavelength filters near 1010 nm can detect a weak absorption due to H₂O and/or OH near 950-1000 nm). Their low spectral resolution, however, has made characterizing these narrow hydration bands difficult. The upcoming Mars 2020 rover’s Mastcam-Z instrument will include a new filter position near 975nm to better constrain the band position and depth of these hydration features. To aid investigations of Mars’ surface with these cameras, we have analyzed VNIR reflectance spectra of Ca-sulfates (gypsum, bassanite, anhydrite) and Mg-sulfates (hexahydrate, epsomite, kieserite). Spectra were acquired for all sulfates at various grain sizes, including pure samples and multi-phase mixtures. The spectral effects of adding the Mars dust simulant JSC-Mars1 to sulfate mixtures were also examined. Spectra were convolved to Pancam, Mastcam, and Mastcam-Z bandpasses to constrain hydrated sulfate detection thresholds and to study the effects of hydration state, grain size, mineral mixing, and dust contamination. Results suggest that gypsum may be detectable by Pancam, Mastcam and Mastcam-Z at larger grain sizes, but the bassanite hydration band may be too weak to detect at any grain size. Results also show that hydration associated with hexahydrate and epsomite is likely detectable by Pancam, Mastcam and Mastcam-Z, including in mixtures and at very fine grain sizes. The kieserite hydration band may be too weak to detect at any grain size. Dust contamination obscures the hydration bands of all pure and mixed Ca-sulfates, but all pure and mixed polyhydrated Mg-sulfates may be detectable at larger grain sizes even with 5 wt.% dust contamination. Similar work will be conducted for a broader suite of Mars-relevant hydrated minerals and will serve to constrain Pancam, Mastcam, and Mastcam-Z’s capabilities for detecting hydrated minerals on Mars.