Presence of clay minerals can obscure spectral evidence of Mg sulfates: implications for orbital observations of Mars

The martian crust is often viewed through the lens of its dominant secondary minerals, Noachian phyllosilicates and Hesperian sulfates, based on orbital spectral observations. However, effects surface exposure spectra these hydrous minerals are not fully understood. We use an environmental chamber to measure changes in near-infrared (NIR) absorptions related H2O smectite (montmorillonite) Mg-sulfate under different temperature, pressure, relative humidity conditions with relevance Mars. Observed differences attributed water content (hydration state), mineral phase, degree crystallinity. It observed that even minor hydration state phase (for Mg sulfate) cause perceptible NIR absorption features when measured a controlled laboratory setting dry Mars-like conditions. Based results known ability rehydrate increased RH, smectites exposed at Mars expected exchange atmosphere specific conditions, making them active participants present-day hydrological cycle Mars, theory hydration-dehydration processes should be detectable using reflectance spectroscopy. some associated subtle may or landed VNIR spectrometers. Furthermore, we find presence clay can spectrally mask sulfates range states if above ∼10 wt% abundance. Random noise was added data simulate orbital-quality data, it crystallinity likely difficult detect current such as CRISM OMEGA. This highlights importance future situ observations accurately determine extent which properly assess role budget.