Seasons of Ice: Water Ice Migration and Seasonal Transient Shadow at the Lunar Poles

Abstract

AbstractLunar water ice can be broadly categorized as belonging to one of two populations: deep, ancient, stable deposits, and shallow, transient, recent deposits. However, a third state for lunar ice is also possible. Temporary sequestration occurs when ice is deposited into a transiently shadowed region at the lunar poles. These temporarily sequestered ice deposits are unstable over geologic time scales, but in the short term, are capable of a wide range of migration, sublimation, and retention patterns due to their thermally dependent sublimation and migration rates. We developed a model to characterize the range of possible migration and retention behaviors for temporarily sequestered ice deposits within locations with dynamic illumination conditions. We found that water ice migration, sublimation, and retention varies across the lunar polar environment, with neighboring locations experiencing different illumination and thermal conditions. We found that the residence times of temporarily sequestered ice deposits in some high latitude, non‐shadowed regions can be similar to or greater than the length of time spent above the long term stability temperature of ice during lunar winter months, leading to incomplete removal of surface or near surface ice during the day. We also found that shallowly buried, unstable ice deposits take longer to sublimate than surface deposits, leading to a temporal lag in escaping ice. This work suggests that temporary sequestration can lead to complex ice migration and retention patterns at high latitudes, with ice sublimation efficiency varying across the lunar polar environment due to local, small scale differences in illumination conditions.