Thermal asymmetry in the Moon's mantle inferred from monthly tidal response
Abstract
The Moon undergoes periodic tidal forcing due to its eccentric and oblique orbit around the Earth. The response to this tidal interaction drives temporal changes in the lunar gravity field and is sensitive to the satellite's internal structure. We use data from the NASA GRAIL spacecraft to recover the time-varying lunar gravity field, including a degree-3 gravitational tidal Love number, k₃. Here, we report our estimated value of k₃ = 0.0163 ± 0.0007, which is about 72% higher than that expected for a spherically symmetric moon. Such a large k₃ can be explained if the elastic shear modulus of the mantle varies by about 2–3% between the nearside and farside, 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 and could influence the spatial distribution of deep moonquakes.
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Acknowledgement
A portion of this research was carried out at the JPL, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (NASA) (grant no. 80NM0018D0004). R.S.P. and A.S.K. were partially supported by the NASA Advanced Multi-Mission Operations System program. A.B. and M.S. were partially supported by the Future Investigators in NASA Earth and Space Science and Technology (FINESST) Program (grant no. 80NSSC22K1318). M.R.-N. and I.M. were partially supported by the NASA Solar System Workings program (grant no. 80NSSC20K0570). We gratefully acknowledge the use of the Ames Pleiades Supercomputer that was used to generate the GL1800F gravity solutions of this paper.
Data Availability
The GRAIL data used to generate the results of this paper are available at the NASA Planetary Data System Geosciences Node (http://pds-geosciences.wustl.edu). The GL1800F gravity field tied to the principal axis frame and the mean-Earth frame can be downloaded from the GRAIL gravity archival directory (https://pds-geosciences.wustl.edu/grail/grail-l-lgrs-5-rdr-v1/grail_1001/shadr/).
Code Availability
The gravity recovery results presented in this study can be reproduced using the MONTE software available at NASA (https://montepy.jpl.nasa.gov). The LOV3D software is also available at GitHub (https://github.com/mroviranavarro/LOV3D_multi).
Supplemental Material
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Additional details
- PMCID
- PMC12119328
- PMID
- 40369068
- National Aeronautics and Space Administration
- 80NM0018D0004
- National Aeronautics and Space Administration
- 80NSSC22K1318
- National Aeronautics and Space Administration
- 80NSSC20K0570
- Accepted
-
2025-03-27
- Available
-
2025-05-14Published
- Caltech groups
- Division of Geological and Planetary Sciences (GPS), Seismological Laboratory
- Publication Status
- Published