The Temporal and Geographic Extent of Seasonal Cold Trapping on the Moon

Abstract

AbstractWe assess the geographic distribution and temporal variability of seasonal shadow at the lunar polar regions and explore its influence on surface water migration and deposition within known permanently shadowed regions (PSRs) in the modern era. At its largest expanse near the winter solstice, seasonally shadowed area more than doubles the permanently shadowed area at both poles. The growth and decay of polar shadow throughout the year enforce distinct seasonal patterns in the poleward migration of water as well as a cyclical variation in the polar surface hydration throughout the year if a continual source of water is assumed. The polar surface water abundance peaks near the hemispheric vernal equinox—significantly offset from the solstice where the seasonal trapping area is most expansive—due to the retention of seasonally trapped water. Owing to their low areal density, lower‐latitude PSRs do not significantly hamper the poleward migration of water, enabling water to reach the high polar latitudes where cold trapping area is densest. We find that northern hemisphere PSRs accumulate more water per unit area than southern hemisphere PSRs and that this disparity is especially prominent beyond 85°. The north/south asymmetry is attributed to differences in the hemispheric PSR size‐frequency distributions; such differences enable unique north/south migration diffusivities, which favor more water reaching the high northern latitudes.