Abstract DGP2026-131

Three-dimensional thermo-chemical evolution modeling has been established as a powerful tool for constraining the internal structure of terrestrial bodies in planetary science (e.g., Plesa et al., 2010, 2015; Laneuville et al., 2013, 2018). In particular, combining geodynamical models with crustal thickness models by patching a rigid crustal layer on top of a convecting mantle has significant advantages: it provides an orientation for the geodynamic model and it allows to capture subsurface temperature fluctuations induced by crustal thickness variations (Plesa et al., 2016; Fleury et al., 2024; Santangelo et al., 2025).

In the case of the Moon, the highly asymmetric volcanic history between the near and farside has been suggested to be caused by an anomaly in the distribution of radiogenic elements (i.e., Th, U, K) in the subsurface. Here, we use a novel 3D thermal evolution model setup to investigate the lateral distribution and concentration of heat sources within the lunar interior. We test various extents and enrichments of the putative radiogenic anomaly, which could have formed during or after LMO crystallization Moriarty et al. (2021). We then compare the modeled present-day surface heat flux with the values measured by Apollo 15 and Apollo 17 to identify best-fit models of lunar interior (Langseth et al., 1976).

This method indicates that an asymmetric concentration of radioactive isotopes in the lunar interior is necessary to reproduce the surface heat flux measurements from the Apollo 15 and 17 missions. This result is also qualitatively consistent with an independent observation based on tidal deformations (Park et al., 2025). In addition, we constrain the size of the anomaly to be between ~1200 and ~1600 km, and its Th enrichment to 20-50 ppm for a 1.6 km-thick layer. 

Using these constraints, we are able to provide predictions on the likely present-day thermal state of the lunar mantle, as well as plausible ranges for the upcoming heat flux measurements by Blue Ghost-1 and Apex 1 landers. Further implications of our results include the abundant presence of water within the first meter of regolith at the lunar south pole and further constraining of the bulk silicate Moon composition.

As a next step, we convert the thermal anomaly predicted by our best-fit models into a density anomaly to feed back into a crustal thickness inversion model (Broquet et al., 2024). Iterating this process, we can update the crustal thickness model and ensure its consistency with our thermal evolution setup for future investigations.