Regolith-Atmosphere Water Exchange at Jezero Crater

Near-surface water vapour exchange is a small but important part of the Martian water cycle. As temperatures drop at night, water vapour is adsorbed into the regolith, and as the surface warms in the morning, water is released back into the atmosphere. Evidence for this process has been seen since Viking and it has been studied for decades (e.g., Fanale and Cannon, 1971, 1974; Zent et al., 1993; Jakosky et al., 1997; Rivera-Valentín et al., 2020), but we still do not fully know what controls the strength of this exchange, especially at the local scale. Recent studies have shown that present-day conditions at Jezero crater can permit salt hydration and occasional frost formation. Modeling efforts show that estimated diurnal atmosphere–surface water exchange can range from 0.5 to 10 g/m². At night, when temperatures drop below 190 K, surface water activity can exceed 0.5, the lower limit often discussed for cell reproduction, while during the day, when temperatures are above 245 K, water activity remains below 0.02 (Zorzano et al., 2024). One-dimensional models, such as the Single Column Model (SCM), have been used to study this exchange and compare it with lander and rover observations (e.g., Savijärvi et al., 2016, 2019, 2021, 2024a, 2024b; Polkko et al., 2025). However, a comprehensive sensitivity analysis of the SCM to identify the dominant factors governing regolith–atmosphere water vapour exchange remains unexplored.

Here, we use the SCM to carry out a sensitivity study of near-surface water vapour exchange at Jezero crater. Jezero is a useful case study because Perseverance is measuring the near-surface environment directly using the Mars Environmental Dynamics Analyzer (MEDA), which includes pressure, air temperature, relative humidity, thermal infrared radiation, radiation and dust, and wind measurements (Rodriguez-Manfredi et al., 2021). We vary key atmospheric, surface, and regolith parameters, including thermal inertia, porosity, initial soil temperature, surface pressure, and initial water content, and examine how these affect temperature, relative humidity, vapour mixing ratio, and regolith water content. We also compare the model results with MEDA observations as Perseverance drives over diverse terrains within the crater.

Our results show that some parameters affect water exchange mainly by changing the diurnal temperature cycle. However, matching the observed temperature cycle is not enough to fully constrain the exchange. Parameters such as thermal inertia, albedo, pressure, and dust mainly influence water exchange by changing the thermal and atmospheric environment, while regolith properties, such as porosity and initial water content, more directly control how much water can be stored and released, often without strongly affecting temperature. Overall, this work identifies the key controls on the daily water cycle at Jezero and shows what additional constraints are needed to better understand regolith–atmosphere exchange on Mars.

 

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