Comparison of Numerically Modelled Lunar Impact Basins with GRAIL-derived Gravity Maps

Impact events forming basins several hundreds of kilometers in diameter have profoundly affected the evolution of the terrestrial planets. Previously acquired gravity and topography data of the Moon have shown evidence of crustal thinning in the central regions of these basins, which is a consequence of the excavation of vast quantities of crustal materials during the impact forming process. Recently acquired high resolution gravity and topography from NASA's GRAIL and LRO missions are now providing us with vastly improved information about the subsurface structure of lunar impact basins, allowing for a detailed comparison with numerical impact models. In this study, we model the formation of the largest impact basins on the Moon using the iSALE hydro-code and compare the output crustal structure with new gravity and crustal thickness maps. Both numerical impact modelling and GRAIL-derived crustal profiles show thinning of the crust in the center of the basin and a surrounding annulus of thickened crust. In addition to differences in impact conditions, we show that target properties have a strong influence on the final basin morphology. Differences in ambient crustal thickness exist between the near and far-side hemispheres of the Moon, with the farside crust being thicker by several 10s of km. Furthermore, the temperature of the crust is thought to be highly elevated within the Procellarum KREEP terrain on the nearside of the Moon. These two factors impart hemispheric differences in size and structure between impact basins located on the near and far sides of the Moon that are shown to be consistent with observations.