Sensitivity Analysis of Regolith-Atmosphere Water Exchange on Mars

Understanding the Martian water cycle is crucial for reconstructing the planet’s climatic evolution, evaluating its potential habitability, and informing future exploration strategies. A key, yet still poorly constrained, component of this cycle is the near-surface exchange of water vapour between the regolith and atmosphere. During the cold nighttime hours, water vapour from the atmosphere adsorbs onto or into the regolith, while solar-driven warming during the day triggers desorption, returning moisture to the atmosphere. This diurnal exchange mechanism has long been explored through both observations and modeling frameworks (Fanale & Cannon, 1971, 1974; Jakosky, 1983; Zent et al., 1993; Jakosky et al., 1997). More recent studies have demonstrated that current Martian conditions allow for transient processes such as salt hydration, frost deposition, and deliquescence (Martínez & Renno, 2013; Rivera-Valentín et al., 2020; Zorzano et al., 2024).

At Jezero Crater, these processes contribute to daily surface-atmosphere water exchanges estimated at 0.5–10 g/m². Notably, nighttime water activity levels can transiently exceed the threshold for microbial replication (water activity > 0.5), while daytime values remain well below limits necessary for life (≤0.02) (Zorzano et al., 2024).

Previous investigations using one-dimensional models such as the Single Column Model (SCM) have advanced our understanding of near-surface water vapour dynamics. However, key uncertainties remain regarding how specific regolith and atmospheric parameters modulate this exchange. In this study, we conduct a structured sensitivity analysis using the SCM to systematically assess the influence of thermal inertia, surface albedo, soil porosity, soil temperature, and water vapour content on near-surface water vapour behavior.

We benchmark the model against in situ observations from the Mars Environmental Dynamics Analyzer (MEDA) onboard the Perseverance rover, which provides hourly measurements of ground and air temperature, atmospheric pressure, relative humidity, and water vapour mixing ratios at Jezero Crater (Rodriguez-Manfredi et al., 2021). By aligning SCM output with MEDA observations, we iteratively refine model parameters to isolate the most influential controls on vapour fluxes and regolith-atmosphere interactions. Our findings provide insights into the role of regolith properties in shaping the Martian water cycle and have broader implications for climate modeling, transient hydration, and near-surface habitability.

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