Lunar Polar Dichotomy: Insights from Crater Morphometry

The lunar poles exhibit a puzzling dichotomy in crater depth-to-diameter ( d / D ) ratios. At the south pole, crater depths decrease toward the pole, and previous studies have mainly attributed this trend to water-ice infilling. However, a similar trend is not observed at the north pole despite evidence of ice. This study critically evaluates the d / D ratio of lunar impact craters to understand the observed north–south asymmetry and its relationship to water ice and other geological processes. Based on the updated crater catalog used, our results reveal that the previously reported significant decrease in d / D trend toward higher latitudes of the south pole is subdued, while the north polar craters shows an increasing mean d / D trend toward higher latitudes. Our systematic comparison of d / D of craters hosting permanently shadowed regions, cold traps, and craters suggested to be water ice rich reveals no distinct d / D trends related to water ice compared to the broader crater population. We infer that lunar polar ice deposits are not sufficiently thick to significantly alter crater morphology. We further investigated the factors contributing to the lunar polar dichotomy and found that d / D ratios in the lunar polar regions are primarily controlled by large-scale geological processes rather than solely by water ice. Therefore, using crater morphometry as a proxy for identifying ice-rich reservoirs should be contextualized by integrating information relevant to water-ice deposits from various sources.