Unveiling the Extent of Lunar Subsurface KREEP Layer from Geodynamic Modeling

Kurzfassung

Introduction: An asymmetric distribution of subsurface heat producing elements (HPE, i.e. Th, U, and K) has been suggested to explain the different thermochemical evolutions of the lunar nearside and farside [1]. However, lunar differentiation models predict a globally uniform KREEP layer (Potassium, Rare-Earth Elements, Phosphorus + Th and U) [2]. The timeline and nature of a potential redistribution of HPE, during or after the lunar magma ocean (LMO) solidification, remains highly debated [2]. Surface heat flux measurements are key indicators of a planet’s subsurface thermal state, serving as primary constraints for thermal evolution models. In-situ heat flux measurements by Apollo 15 and Apollo 17 crews provided values higher than the Moon’s proposed surface average [3]. Conversely, remote sensing estimates close to the south pole retrieved much lower heat fluxes [4]. Here, we use the most recent global crustal thickness map derived from gravity and topography data [5] and new constraints on the abundance of HPE from LMO crystallization studies [6] to model lunar evolution. We investigate the lateral distribution and concentration of HPE, testing various extents and enrichments of a putative KREEP-rich anomaly formed during or after LMO crystallization [2]. Predicted present-day surface heat flux is then compared to observations.