Hi Marsbug.In the report they talk about...

Hi Marsbug.
In the report they talk about relative humidity which is the partial pressure of the water vapour divided by the saturation vapour pressure of water in the Martian atmosphere at the reading air temperature. But Relative Humidity is temperature dependent and would be expected to vary significantly as a function of the daily temperature swings at the Phoenix site. Zent was reported as saying that the variation in relative humidity ‘suggests there's a lot of moisture moving in and out of the soil’ so I guess we have to assume that the relative humidity change is greater than what would be expected for stable water content. It would have made more sense if they had used Absolute Humidity being the quantity of water in a unit volume of air.

From the article they seem to be expecting H2O molecules adhering to the surface of soil particles as is the case with permafrost on Earth. They are not there so perhaps the regolith really is hydrophobic. Or maybe only the grains right at the surface are affected.

Thanks for the guidance on the liquid film at the ice/vapour interface at depressed temperatures. I had thought that such would only exist when the kinetic energy of translation was effectively equal to the Van der Walls forces. Live and learn.