Exploration of Degree-1 Heterogeneities in the Lunar Mantle Using CitcomSVE

Recent reprocessing of NASA's GRAIL mission gravimetric data in the work of Park et al. (2025) allowed for the estimation of the third-degree lunar tidal Love number, k₃, at a monthly tidal period of 27.3288 days. The obtained value, k₃ = 0.0163 ± 0.0007, is significantly higher than predictions based on spherically symmetric models of the lunar interior. This same study suggests that this high k₃ value could be explained by the presence of a degree-1, order-1 anomaly in the lunar mantle shear modulus, with an amplitude of approximately 3%.

In this work, we investigate the tidal response of laterally heterogeneous lunar interiors using 3-D viscoelastic modeling and considering not only elastic framework but also viscoelastic rheology. Using CitcomSVE – a finite-element code initially developed for modeling glacial isostatic adjustment deformations – we model the lunar interior as suggested in the results of Park et al. (2025), i.e., for degree-1, order-1 mantle anomaly in shear modulus. We further quantify tidal dissipation at both monthly and yearly (365.260 days) forcing periods to assess whether the dissipation predicted by this model is consistent with current observational constraints on lunar tidal dissipation.