Zimmerman, Michael - Simulations of the thermal and plasma environment within lunar pits and lava tubes: could cryogenic regions trap ions from the solar wind?

Observed lunar holes and hypothesized lava tubes have been identified as possible targets for human exploration because they provide at least partial shelter from solar wind, radiation, and extreme heat variations.  In this work we begin to characterize the full thermal cycle and plasma particle flow within an idealized lunar pit including a subsurface lava tube.  Finite-difference heat transport simulations show development of a quasi-steady lunar heating cycle over thousands of lunar days, and plasma treecode simulations are used to model daily surface charging, photoemission, and ion flow into the pit.   Interestingly, preliminary simulations of a 50 m-wide and 50 m-deep pit show that ions flow directly onto the hot, illuminated regions of the pit at times around local noon when the solar wind flow and solar radiation are close to vertical.  The solar wind could thus provide a daily source of hydrogen and other ions that is quickly sublimated, with some fraction hopping laterally into adjacent lava tubes where it could remain cryogenically trapped.