The lunar solid inner core and the mantle overturn

ABSTRACT 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. Access through your institution Buy or subscribe

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EARTH’S BASAL MANTLE ANOMALIES Article 01 November 2023 GEOPHYSICAL EVIDENCE FOR AN ENRICHED MOLTEN SILICATE LAYER ABOVE MARS’S CORE Article Open access 25 October 2023 EVIDENCE FOR A LIQUID

SILICATE LAYER ATOP THE MARTIAN CORE Article Open access 25 October 2023 DATA AVAILABILITY The dataset used in this study is provided at https://doi.org/10.5281/zenodo.7661158. CODE

AVAILABILITY The code ALMA3 is freely available at https://github.com/danielemelini/ALMA3. The code Perple_X is freely available at https://www.perplex.ethz.ch. REFERENCES * Nakamura, Y. et

al. in _Encyclopedia of Planetary Science. Encyclopedia of Earth Science_ Vol. 10, 2299–2309 (Springer, 1979). * Weber, R. C., Lin, P.-Y., Garnero, E. J., Williams, Q. & Lognonné, P.

Seismic detection of the lunar core. _Science_ 331, 309–312 (2011). Article  ADS  CAS  PubMed  Google Scholar  * Garcia, R. F. et al. Lunar seismology: an update on interior structure

models. _Space Sci. Rev._ 215, 50 (2019). Article  ADS  Google Scholar  * Snyder, G. A. et al. in _Workshop on Geology of the Apollo 17 Landing Site_ (eds Ryder, G., Schmitt, H. H. &

Spudis, P. D.) 53–55 (Lunar and Planetary Institute, 1992). * Elphic, R. C. et al. Lunar Fe and Ti abundances: comparison of Lunar Prospector and Clementine data. _Science_ 281, 1493–1496

(1998). Article  ADS  CAS  PubMed  Google Scholar  * Li, H. et al. Lunar cumulate mantle overturn: a model constrained by ilmenite rheology. _J. Geophys. Res. Planets_ 124, 1357–1378 (2019).

ADS  CAS  Google Scholar  * Wieczorek, M. A. in _Treatise on Geophysics: Planets and Moons_ Vol. 10 (ed. Schubert, G.) 165–206 (Elsevier, 2007). * Morbidelli, A. et al. The timeline of the

lunar bombardment: revisited. _Icarus_ 305, 262–276 (2018). Article  ADS  CAS  Google Scholar  * Hess, P. C. & Parmentier, E. A model for the thermal and chemical evolution of the Moon’s

interior: implications for the onset of mare volcanism. _Earth Planet. Sci. Lett._ 134, 501–514 (1995). Article  ADS  CAS  Google Scholar  * Zhong, S., Parmentier, E. & Zuber, M. T. A

dynamic origin for the global asymmetry of lunar mare basalts. _Earth Planet. Sci. Lett._ 177, 131–140 (2000). Article  ADS  CAS  Google Scholar  * Zhang, N., Dygert, N., Liang, Y. &

Parmentier, E. The effect of ilmenite viscosity on the dynamics and evolution of an overturned lunar cumulate mantle. _Geophys. Res. Lett._ 44, 6543–6552 (2017). Article  ADS  CAS  Google

Scholar  * Dygert, N., Hirth, G. & Liang, Y. A flow law for ilmenite in dislocation creep: implications for lunar cumulate mantle overturn. _Geophys. Res. Lett._ 43, 532–540 (2016).

Article  ADS  Google Scholar  * Tokle, L., Hirth, G., Liang, Y., Raterron, P. & Dygert, N. The effect of pressure and Mg-content on ilmenite rheology: implications for lunar cumulate

mantle overturn. _J. Geophys. Res. Planets_ 126, e2020JE006494 (2021). Article  ADS  CAS  Google Scholar  * Tan, Y. & Harada, Y. Tidal constraints on the low-viscosity zone of the Moon.

_Icarus_ 365, 114361 (2021). Article  Google Scholar  * Melini, D., Saliby, C. & Spada, G. On computing viscoelastic Love numbers for general planetary models: the ALMA3 code. _Geophys.

J. Int._ 231, 1502–1517 (2022). Article  ADS  Google Scholar  * Briaud, A. et al. Constraints on the lunar core viscosity from tidal deformation. _Icarus_ 394, 115426 (2023). Article  Google

Scholar  * Wieczorek, M. A. et al. The crust of the Moon as seen by GRAIL. _Science_ 339, 671–675 (2013). Article  ADS  CAS  PubMed  Google Scholar  * Morard, G. et al. Liquid properties in

the Fe-FeS system under moderate pressure: tool box to model small planetary cores. _Am. Mineral._ 103, 1770–1779 (2018). Google Scholar  * Harada, Y. et al. The deep lunar interior with a

low-viscosity zone: revised constraints from recent geodetic parameters on the tidal response of the Moon. _Icarus_ 276, 96–101 (2016). Article  ADS  Google Scholar  * Viswanathan, V.,

Rambaux, N., Fienga, A., Laskar, J. & Gastineau, M. Observational constraint on the radius and oblateness of the lunar core-mantle boundary. _Geophys. Res. Lett._ 46, 7295–7303 (2019).

Article  ADS  Google Scholar  * Stähler, S. C. et al. Seismic detection of the martian core. _Science_ 373, 443–448 (2021). Article  ADS  PubMed  Google Scholar  * Murphy, C. A. in _Deep

Earth: Physics and Chemistry of the Lower Mantle and Core_ (eds Terasaki, H. & Fischer, R. A.) 253–264 (Wiley, 2016). * Matsumoto, K. et al. Internal structure of the Moon inferred from

Apollo seismic data and selenodetic data from GRAIL and LLR. _Geophys. Res. Lett._ 42, 7351–7358 (2015). Article  ADS  Google Scholar  * Mallik, A., Ejaz, T., Shcheka, S. & Garapic, G. A

petrologic study on the effect of mantle overturn: implications for evolution of the lunar interior. _Geochim. Cosmochim. Acta_ 250, 238–250 (2019). Article  ADS  CAS  Google Scholar  *

Karato, S.-I. & Wang, D. in _Physics and Chemistry of the Deep Earth_ (ed. Karato, S.-I.) 145–182 (Wiley, 2013). * Karato, S.-i Rheology of the deep upper mantle and its implications for

the preservation of the continental roots: a review. _Tectonophysics_ 481, 82–98 (2010). Article  ADS  Google Scholar  * Connolly, J. Multivariable phase diagrams; an algorithm based on

generalized thermodynamics. _Am. J. Sci._ 290, 666–718 (1990). Article  ADS  Google Scholar  * Gomes, R., Levison, H. F., Tsiganis, K. & Morbidelli, A. Origin of the cataclysmic Late

Heavy Bombardment period of the terrestrial planets. _Nature_ 435, 466–469 (2005). Article  ADS  CAS  PubMed  Google Scholar  * Landeau, M., Fournier, A., Nataf, H.-C., Cébron, D. &

Schaeffer, N. Sustaining Earth’s magnetic dynamo. _Nat. Rev. Earth Environ._ 3, 255–269 (2022). Article  ADS  Google Scholar  * Suavet, C. et al. Persistence and origin of the lunar core

dynamo. _Proc. Natl Acad. Sci. USA_ 110, 8453–8458 (2013). Article  ADS  CAS  PubMed  PubMed Central  Google Scholar  * Mazarico, E., Barker, M. K., Neumann, G. A., Zuber, M. T. & Smith,

D. E. Detection of the lunar body tide by the Lunar Orbiter Laser Altimeter. _Geophys. Res. Lett._ 41, 2282–2288 (2014). Article  ADS  PubMed  PubMed Central  Google Scholar  * Steinbrügge,

G. et al. Viscoelastic tides of Mercury and the determination of its inner core size. _J. Geophys. Res. Planets_ 123, 2760–2772 (2018). Article  ADS  Google Scholar  * Bürgmann, R., Rosen,

P. A. & Fielding, E. J. Synthetic aperture radar interferometry to measure Earth’s surface topography and its deformation. _Annu. Rev. Earth Planet. Sci._ 28, 169–209 (2000). Article 

ADS  Google Scholar  * Williams, J. G. et al. Lunar interior properties from the GRAIL mission. _J. Geophys. Res. Planets_ 119, 1546–1578 (2014). Article  ADS  Google Scholar  * Williams, J.

G. & Boggs, D. H. Tides on the Moon: theory and determination of dissipation. _J. Geophys. Res. Planets_ 120, 689–724 (2015). Article  ADS  Google Scholar  * Khan, A., Connolly, J. A.,

Pommier, A. & Noir, J. Geophysical evidence for melt in the deep lunar interior and implications for lunar evolution. _J. Geophys. Res. Planets_ 119, 2197–2221 (2014). Article  ADS  CAS

  Google Scholar  * Harada, Y. et al. Strong tidal heating in an ultralow-viscosity zone at the core–mantle boundary of the Moon. _Nat. Geosci._ 7, 569–572 (2014). Article  ADS  CAS  Google

Scholar  * Khan, A., Mosegaard, K., Williams, J. & Lognonné, P. Does the Moon possess a molten core? Probing the deep lunar interior using results from LLR and Lunar Prospector. _J.

Geophys. Res. Planets_ 109, E09007 (2004). Article  ADS  Google Scholar  * Wieczorek, M. A. et al. The constitution and structure of the lunar interior. _Rev. Mineral. Geochem._ 60, 221–364

(2006). Article  CAS  Google Scholar  * Viswanathan, V., Fienga, A., Gastineau, M. & Laskar, J. INPOP17a planetary ephemerides. Notes Scientifiques et Techniques de l’Institut de

mécanique séleste, #108 (2017). * Thor, R. N. et al. Determination of the lunar body tide from global laser altimetry data. _J. Geod._ 95, 4 (2021). Article  ADS  Google Scholar  * Spada, G.

ALMA, a Fortran program for computing the viscoelastic Love numbers of a spherically symmetric planet. _Comput. Geosci._ 34, 667–687 (2008). Article  ADS  Google Scholar  * Karato, S.-I.

Geophysical constraints on the water content of the lunar mantle and its implications for the origin of the Moon. _Earth Planet. Sci. Lett._ 384, 144–153 (2013). Article  ADS  CAS  Google

Scholar  * Karato, S.-I. & Wu, P. Rheology of the upper mantle: a synthesis. _Science_ 260, 771–778 (1993). Article  ADS  CAS  PubMed  Google Scholar  * Delano, J. W. Pristine lunar

glasses: criteria, data, and implications. _J. Geophys. Res. Solid Earth_ 91, 201–213 (1986). Article  Google Scholar  * Zhao, Y., De Vries, J., van den Berg, A., Jacobs, M. & van

Westrenen, W. The participation of ilmenite-bearing cumulates in lunar mantle overturn. _Earth Planet. Sci. Lett._ 511, 1–11 (2019). Article  ADS  CAS  Google Scholar  * Wyatt, B. The

melting and crystallisation behaviour of a natural clinopyroxene-ilmenite intergrowth. _Contrib. Mineral. Petrol._ 61, 1–9 (1977). Article  ADS  CAS  Google Scholar  * van Kan Parker, M. et

al. Neutral buoyancy of titanium-rich melts in the deep lunar interior. _Nat. Geosci._ 5, 186–189 (2012). Article  ADS  Google Scholar  * Andersen, D. J. & Lindsley, D. H. in _Tenth

Lunar and Planetary Science Conference_ 493–507 (Pergamon, 1980). * Yu, S. et al. Overturn of ilmenite-bearing cumulates in a rheologically weak lunar mantle. _J. Geophys. Res. Planets_ 124,

418–436 (2019). Article  ADS  Google Scholar  * Holland, T. & Powell, R. An improved and extended internally consistent thermodynamic dataset for phases of petrological interest,

involving a new equation of state for solids. _J. Metamorph. Geol._ 29, 333–383 (2011). Article  ADS  CAS  Google Scholar  * Holland, T. & Powell, R. An internally consistent

thermodynamic data set for phases of petrological interest. _J. Metamorph. Geol._ 16, 309–343 (1998). Article  ADS  CAS  Google Scholar  * Xu, W., Lithgow-Bertelloni, C., Stixrude, L. &

Ritsema, J. The effect of bulk composition and temperature on mantle seismic structure. _Earth Planet. Sci. Lett._ 275, 70–79 (2008). Article  ADS  CAS  Google Scholar  * Andersen, D. J.

& Lindsley, D. H. Internally consistent solution models for Fe-Mg-Mn-Ti oxides; Fe-Ti oxides. _Am. Mineral._ 73, 714–726 (1988). CAS  Google Scholar  * Holland, T. J., Green, E. C. &

Powell, R. Melting of peridotites through to granites: a simple thermodynamic model in the system KNCFMASHTOCr. _J. Petrol._ 59, 881–900 (2018). Article  ADS  CAS  Google Scholar  Download

references ACKNOWLEDGEMENTS 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 * Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS,

Géoazur, Valbonne, France Arthur Briaud, Clément Ganino, Agnès Fienga & Anthony Mémin * IMCCE, Observatoire de Paris, Sorbonne Université, PSL University, CNRS, Paris, France Agnès

Fienga & Nicolas Rambaux Authors * Arthur Briaud View author publications You can also search for this author inPubMed Google Scholar * Clément Ganino View author publications You can

also search for this author inPubMed Google Scholar * Agnès Fienga View author publications You can also search for this author inPubMed Google Scholar * Anthony Mémin View author

publications You can also search for this author inPubMed Google Scholar * Nicolas Rambaux View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS

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. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing

interests. PEER REVIEW PEER REVIEW INFORMATION _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. ADDITIONAL INFORMATION PUBLISHER’S NOTE Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. EXTENDED

DATA FIGURES AND TABLES EXTENDED DATA FIG. 1 HISTOGRAMS OF RELATIVE DIFFERENCES BETWEEN OBSERVABLES AND MODELS. Histograms of relative differences over their 3_σ_ 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. A–D, Distribution of the core parameters. Distributions of the LVZ

(E–H) 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. A–C, Distribution of the inner core parameters. Distributions of the outer core (D–G), the LVZ (H–K) 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 _K_2 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 1_σ_. EXTENDED DATA FIG. 5 TEMPERATURE AND DENSITY PROFILES FOR DIFFERENT

MANTLE VISCOSITIES. A,C, LVZ temperature (_T_LVZ) as a function of LVZ density (_ρ_LVZ) deduced from the thermodynamic models at the LVZ pressure spanning from 4.2 to 4.6 GPa. B,D, LVZ

temperature (_T_LVZ) as a function of the activation enthalpy (_H_*). For more details, see Fig. 1. Grey areas correspond to mantle viscosities (_η_m) 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 _Q_ℓ′ and _Q_F 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. SUPPLEMENTARY INFORMATION PEER REVIEW FILE RIGHTS AND PERMISSIONS Springer Nature or its licensor (e.g. a society

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A. _et al._ The lunar solid inner core and the mantle overturn. _Nature_ 617, 743–746 (2023). https://doi.org/10.1038/s41586-023-05935-7 Download citation * Received: 19 May 2022 * Accepted:

08 March 2023 * Published: 03 May 2023 * Issue Date: 25 May 2023 * DOI: https://doi.org/10.1038/s41586-023-05935-7 SHARE THIS ARTICLE Anyone you share the following link with will be able

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