Dynamics Of Subsurface Migration Of Water On The Moon

We investigate the dynamics of a water pumping mechanism driven by temperature variations in the lunar subsurface. The thermal environment at three polar sites and three sites in the Clavius region was simulated, taking into account local terrain and scattered radiation. A separate heat and mass transfer model was used to simulate depth-dependent, temperature-dependent, and pressure-dependent properties of the lunar subsurface. The results suggest that diurnally varying heat fluxes create suitable conditions for water migration at many sites across the lunar surface. Enabled by a constant supply to the lunar surface, water molecules typically migrate a few centimeters deep via the formation of distinct concentration peaks, and a downward flux driven by the repeated desorption and resorption. With a constant supply rate of 10(-15) kg/(m(2) s), the quantity of adsorbed water stored at Ga timescales reaches values on the order of 10(-10) to 10(-7) mol/m(2) at the investigated sites. Based on our results, we present a new relation for the water migration depth that takes into account the ratios of surface temperatures. The results of a sensitivity analysis show that the desorption activation energy is a dominant factor for the quantity and depth of water migration. In addition to long-term accumulation of subsurface adsorbate, the model shows that temporarily captured water at shallower depths can be released during the lunar day at quantities of up to several mu g m(-2). This, as well as exposure of shallow water disturbed by impacts, may be a relevant source for surface water in illuminated areas.