Thermal asymmetry in the Moon’s mantle inferred from monthly tidal response
- R. S. Park
- A. Berne
- A. S. Konopliv
- J. T. Keane
- I. Matsuyama
- F. Nimmo
- M. Rovira-Navarro
- M. P. Panning
- M. Simons
- D. J. Stevenson
- R. C. Weber
2025-05-14
The Moon undergoes periodic tidal forcing due to its eccentric and oblique orbit around the Earth 1 . The response to this tidal interaction drives temporal changes in the lunar gravity field and is sensitive to the satellite’s internal structure 2–4 . We use data from the NASA GRAIL spacecraft 5–9 to recover the time-varying lunar gravity field, including a degree-3 gravitational tidal Love number, k 3 . Here, we report our estimated value of k 3 = 0.0163 ± 0.0007, which is about 72% higher than that expected for a spherically symmetric moon 10 . Such a large k 3 can be explained if the elastic shear modulus of the mantle varies by about 2–3% between the nearside and farside 4 , providing an observational demonstration of lateral heterogeneities in the deep lunar interior. This asymmetric structure suggests preservation of a predominantly thermal anomaly of roughly 100–200 K in the nearside mantle that formed surface mare regions 3–4 billion years ago 11 and could influence the spatial distribution of deep moonquakes 12 .