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The lunar solid inner core and the mantle overturn


Seismological models from Apollo missions provided the first records of the Moon inner structure with a decrease in seismic wave velocities at the core–mantle boundary1,2,3. The resolution of these records prevents a strict detection of a putative lunar solid inner core and the impact of the lunar mantle overturn in the lowest part of the Moon is still discussed4,5,6,7. Here we combine geophysical and geodesic constraints from Monte Carlo exploration and thermodynamical simulations for different Moon internal structures to show that only models with a low viscosity zone enriched in ilmenite and an inner core present densities deduced from thermodynamic constraints compatible with densities deduced from tidal deformations. We thus obtain strong indications in favour of the lunar mantle overturn scenario and, in this context, demonstrate the existence of the lunar inner core with a radius of 258 ± 40 km and density 7,822 ± 1,615 kg m−3. Our results question the evolution of the Moon magnetic field thanks to its demonstration of the existence of the inner core and support a global mantle overturn scenario that brings substantial insights on the timeline of the lunar bombardment in the first billion years of the Solar System8.

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Fig. 1: Moon temperature and density profiles.

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We thank A. Morbidelli and M. Wieczorek for their careful reading of the manuscript and H. Hussman, A. Stark, G. Spada, D. Melini, V. Viswanathan and D. Andrault for their fruitful discussions. We would like to thank K. Mosegaard and an anonymous reviewer for their constructive reviews that improved the paper. This project has been supported by the French ANR, project LDLR (Lunar tidal Deformation from earth-based and orbital Laser Ranging) number ANR-19-CE31-0026, and the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Advanced Grant AstroGeo-885250).

Author information

Authors and Affiliations



A.B. and A.F. conceived the preliminary idea and C.G., A.M. and N.R. participated in its development. A.B. performed the computations and made most of the plots. A.B. and C.G. set up the petrochemical assumptions and designed the thermodynamical simulations. A.B., C.G. and A.F. wrote the text. A.F. and C.G. contributed to the design of the figures. A.M. and N.R. contributed to the final version of the manuscript.

Corresponding authors

Correspondence to Arthur Briaud or Agnès Fienga.

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Nature thanks Klaus Mosegaard and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 Histograms of relative differences between observables and models.

Histograms of relative differences over their 3σ uncertainties between the values of the observational constraints given in Extended Data Table 2 and the values of the same parameters but extracted from our models for models without an inner core (top) and with an inner core (bottom).

Extended Data Fig. 2 Model without inner core distribution after filtering the geodetic parameters.

ad, Distribution of the core parameters. Distributions of the LVZ (eh) and the mantle (i,j). Black and dashed grey lines correspond to the median and the 25th and 75th percentiles, respectively.

Extended Data Fig. 3 Model with inner core distribution after filtering the geodetic parameters.

ac, Distribution of the inner core parameters. Distributions of the outer core (dg), the LVZ (hk) and the mantle (l,m). Black and dashed grey lines correspond to the median and the 25th and 75th percentiles, respectively.

Extended Data Fig. 4 Behaviour of the k2 and Q ratio over the tidal periods.

The Delaunay arguments F and ℓ′ correspond to periods defined in ref. 35 of 27.212 days and 365.260 days, respectively. Error bars refer to 1σ.

Extended Data Fig. 5 Temperature and density profiles for different mantle viscosities.

a,c, LVZ temperature (TLVZ) as a function of LVZ density (ρLVZ) deduced from the thermodynamic models at the LVZ pressure spanning from 4.2 to 4.6 GPa. b,d, LVZ temperature (TLVZ) as a function of the activation enthalpy (H*). For more details, see Fig. 1. Grey areas correspond to mantle viscosities (ηm) that are in agreement with the geophysical constraints.

Extended Data Fig. 6 Sensitivity analysis of geodetic parameters to the lunar interior characteristics.

Sensitivity of the mass, moment of inertia, tidal Love numbers and quality factors Qℓ′ and QF to the input parameters: radius, viscosity V, rigidity Ri and density D for each layer (crust C, mantle M, low-velocity zone L, outer core OC and inner core IC). Variations are about 10% around the model reference values.

Extended Data Table 1 Intervals of LVZ densities inferred by tidal deformation and thermodynamical models
Extended Data Table 2 Selenodetic observables used to constrain the modelled interior of the Moon
Extended Data Table 3 Selenodetic 1D profiles used as inputs for interior modellings of the Moon
Extended Data Table 4 LVZ characteristics

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Briaud, A., Ganino, C., Fienga, A. et al. The lunar solid inner core and the mantle overturn. Nature 617, 743–746 (2023).

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