Two-dimensional distribution of volatiles in the lunar regolith from space weathering simulations

We present simulations of space weathering effects on ice deposits in regions of permanent shadow on the Moon. These Monte Carlo simulations follow the effects of space weathering processes on the distribution of the volatiles over time. The model output constrains the coherence of volatile deposits with depth, lateral separation, and time. The results suggest that ice sheets become broken and buried with time. As impacts begin to puncture an initially coherent surficial ice sheet, small areas with a deficit of ice compared to surrounding areas are formed first. As time progresses, holes become prevalent and the anomalous regions are local enhancements of ice concentration in a volume. The 3-D distribution is also heterogeneous because the ice is buried to varying depths in different locations. Analysis of the coherence of ice on 10 cm scales predicts that putative ice sheets in anomalous radar craters are <100 Myr old. Surface frost becomes homogenized within 20 Myr. The simulations show the data from the LCROSS impact and surrounding region are consistent with the ice deposit in Cabeus being >1000 Myr old. For future in situ analysis of cold trap volatiles, a horizontal range of 10 m is sufficient to acquire surface-based measurements of heterogeneously distributed ice. These results also support previous analyses that Mercury's cold traps are young. Citation: Hurley, D. M., D. J. Lawrence, D. B. J. Bussey, R. R. Vondrak, R. C. Elphic, and G. R. Gladstone (2012), Two-dimensional distribution of volatiles in the lunar regolith from space weathering simulations, Geophys. Res. Lett., 39, L09203, doi:10.1029/2012GL051105.