Adsorption driven regolith-atmospheric water vapor transfer on Mars: An analysis of Phoenix TECP data

We analyze Phoenix Thermal and Electric Conductivity Probe (TECP) instrument data and previous experimental data to present constraints on the parameters for regolith-driven adsorption at the Phoenix landing site. Modeling Brunauer-Emmett-Teller (BET) adsorption of the data across Mars-relevant materials yielded fairly constant surface coverage and enthalpy values, θ = 0.336, corresponding to 2.96 × 10−7 kg of H2O/m2 and ΔH = 52.783 +/−1.206 kJ/mol, respectively. With our modeled BET adsorption coefficient, C = 89.4, and ideal specific surface area, SSA = 1.7 × 104 m2/kg, we conclude that the regolith at the Phoenix landing site is most likely a mixture, which we bracket with a range of possible adsorption conditions. Ultimately, we explain adsorbed water content in the regolith at the Phoenix landing site and thus, adsorption being driven by localized, diurnal variations in the relative humidity.