Experimental Investigation of Soil Adsorption Effects on Water Migration in Simulated Lunar Conditions

Adsorption is a key mechanism governing water vapor diffusion in lunar regolith. To investigate this process, we conducted experiments under simulated lunar conditions—Knudsen diffusion conditions—using three soil types with varying water vapor adsorption heats and specific surface areas. Results show that soils with higher adsorption heat and larger surface area captured more water vapor. Lower temperatures enhanced water retention across all soil types. In samples with underlying ice, upward migration of water vapor was hindered by adsorption onto soil particles, reducing water loss. Montmorillonite, with its superior adsorption properties, retained the most water under all test conditions. These findings suggest that cold lunar regoliths with high adsorption capacity may act as a favorable reservoir for water accumulation.