Impact scaling for lunar impact basins: Contributions from GRAIL and hydrocode modeling

Abstract:

Impact events forming large craters (or, impact 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 basin formation process. High-resolution crustal thickness maps derived from the Gravity Recovery And Interior Laboratory (GRAIL) and Lunar Orbiter Laser Altimeter (LOLA) data afford an unambiguous measure of the lateral extent of crustal thinning in lunar basins (protobasins, peak-ring and multi-ring basins). This region of crustal thinning can be used as a measure of basin size. In this work, we used the iSALE-2D numerical shock physics hydrocode to model the formation of lunar basins. We tested our simulations against crater structures observed by GRAIL. As a result, a new scaling law for impact basins on the Moon is derived. We show relationships between the transient crater size (including the impactor properties) as calculated by the hydrocode and the final crustal thinning diameter of an impact basin as well as an approximate relationship to the location of the basin rings, as mapped by LOLA and GRAIL. These scaling laws include lateral variations in the target properties, namely between the Procellarum KREEP Terrane on the nearside and the lunar highlands on the farside hemisphere. This work provides additional constraints on the extent of the Late Heavy Bombardment epoch.