So the soil is hydrophobic which probably means it is charged to repel those little H2O molecules as they pass through from the ice to the atmosphere. Now who would suspect that for surface soils sitting exposed in a radiation field? Unlike earth where soils are hydrophilic from all that organic matter. IMHO that radiation filed (UV, gamma, etc) plays a large role in the surface chemistry.Witness the amount of oxidation which is seen despite an awfully low pO2 in the atmosphere.
And on low pressures, in the article it states ""The relative humidity transitions from near zero to near 100 percent with every day-night cycle, which suggests there's a lot of moisture moving in and out of the soil," Zent said." Now are not the night pressures not very low so that 100% humidity could be 3/4ths of 5/9ths of sweet nothing and there may be little water actually moving?