Mapping of ice storage processes on the moon with time-dependent temperatures

Abstract

Lunar cold traps are defined by extremely low time-integrated sublimation loss, so that water ice is expected to accumulate in them. Due to the strong dependence of the sublimation rate on temperature, they have heretofore been delineated by the peak rather than the time-averaged sublimation rate. Here, time-averaged sublimation rates are calculated for the south polar region of the Moon based on 11 yr of Diviner surface temperature measurements. Data for each spatial pixel are binned according to subsolar (diurnal) and ecliptic (seasonal) longitude. Frequency-domain filtering of temperature time series is applied to interpolate and smooth the data set. The cold trap area is 17,000 km2 from 80°S to the south pole, about 24% larger than defined by peak temperature. In addition, subsurface ice stability is mapped based on solutions of the heat equation with Diviner surface temperatures as the upper boundary condition. Even a thin layer of dust reduces the sublimation loss dramatically. A third potential mechanism for ice storage, vapor pumping by temperature cycles, is also mapped, based on a model for the time-variable population of adsorbed water molecules on the lunar surface. The area of significant pumping is estimated to be 96,000 km2 poleward of 80°S. In summary, a new processing technique has been developed that exploits information about the time variability of lunar surface temperatures measured by Diviner, and it results in new maps for the geographic distribution of potential water-ice deposits in the south polar region of the Moon.