Abstract
The origin of lunar magnetic anomalies1,2,3,4,5 remains unresolved after their discovery more than four decades ago. A commonly invoked hypothesis is that the Moon might once have possessed a thermally driven core dynamo3, but this theory is problematical given the small size of the core and the required surface magnetic field strengths6. An alternative hypothesis is that impact events might have amplified ambient fields near the antipodes of the largest basins7, but many magnetic anomalies exist that are not associated with basin antipodes. Here we propose a new model for magnetic field generation, in which dynamo action comes from impact-induced changes in the Moon’s rotation rate. Basin-forming impact events are energetic enough to have unlocked the Moon from synchronous rotation8, and we demonstrate that the subsequent large-scale fluid flows in the core, excited by the tidal distortion of the core–mantle boundary9, could have powered a lunar dynamo. Predicted surface magnetic field strengths are on the order of several microteslas, consistent with palaeomagnetic measurements5, and the duration of these fields is sufficient to explain the central magnetic anomalies associated with several large impact basins.
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References
Purucker, M. E. & Nicholas, J. B. Global spherical harmonic models of the internal magnetic field strength of the Moon based on sequential and coestimation approaches. J. Geophys. Res. 115, E12007 (2010)
Fuller, M. & Cisowski, S. M. in Geomagnetism (ed. Jacobs, J. A. ) 307–455 (Academic, 1987)
Stegman, D. R., Jellinek, A. M., Zatman, S. A., Baumgardner, J. R. & Richards, M. A. An early lunar core dynamo driven by thermochemical mantle convection. Nature 421, 143–146 (2003)
Lawrence, K., Johnson, C., Tauxe, L. & Gee, J. Lunar paleointensity measurements: implications for lunar magnetic evolution. Phys. Earth Planet. Inter. 168, 71–87 (2008)
Garrick-Bethell, I., Weiss, B. P., Shuster, D. L. & Buz, J. Early lunar magnetism. Science 323, 356–359 (2009)
Wieczorek, M. A. et al. The constitution and structure of the lunar interior. Rev. Mineral. Geochem. 60, 221–364 (2006)
Hood, L. L. & Artemieva, N. A. Antipodal effects of lunar basin-forming impacts: initial 3D simulations and comparisons with observations. Icarus 193, 485–502 (2008)
Wieczorek, M. A. & Le Feuvre, M. Did a large impact reorient the Moon? Icarus 200, 358–366 (2009)
Le Bars, M., Lacaze, L., Le Dizès, S., Le Gal, P. & Rieutord, M. Tidal instability in stellar and planetary binary systems. Phys. Earth Planet. Inter. 178, 48–55 (2010)
Halekas, J. S., Lin, R. P. & Mitchell, D. L. Magnetic fields of lunar multi-ring impact basins. Meteorit. Planet. Sci. 38, 565–578 (2003)
Hood, L. L. Central magnetic anomalies of Nectarian-aged lunar impact basins: Probable evidence for an early core dynamo. Icarus 211, 1109–1128 (2011)
Cintala, M. J. & Grieve, R. A. F. Scaling impact melting and crater dimensions: implications for the lunar cratering record. Meteorit. Planet. Sci. 33, 889–912 (1998)
Williams, J. G., Boggs, D. H., Yoder, C. F., Ratcliff, J. T. & Dickey, J. O. Lunar rotational dissipation in solid body and molten core. J. Geophys. Res. 106, 27933–27968 (2001)
Malkus, W. V. R. Precession of the Earth as the cause of geomagnetism. Science 160, 259–264 (1968)
Kerswell, R. R. Upper bounds on the energy dissipation in turbulent precession. J. Fluid Mech. 321, 335–370 (1996)
Kerswell, R. R. & Malkus, W. V. R. Tidal instability as the source for Io’s magnetic signature. Geophys. Res. Lett. 25, 603–606 (1998)
Rochester, M. G., Jacobs, J. A., Smylie, D. E. & Chong, K. F. Can precession power the geomagnetic dynamo? Geophys. J. R. Astron. Soc. 43, 661–678 (1975)
Loper, D. E. Torque balance and energy budget for the precessionally driven dynamo. Phys. Earth Planet. Inter. 11, 43–60 (1975)
Tilgner, A. Precession driven dynamo. Phys. Fluids 17, 034104 (2005)
Wu, C.-C. & Roberts, P. H. On a dynamo driven by topographic precession. Geophys. Astrophys. Fluid Dyn. 103, 467–501 (2009)
Kerswell, R. R. Elliptical instability. Annu. Rev. Fluid Mech. 34, 83–113 (2002)
Cébron, D., Le Bars, M., Leontini, J., Maubert, P. & Le Gal, P. A systematic numerical study of the tidal instability in a rotating triaxial ellipsoid. Phys. Earth Planet. Inter. 182, 119–128 (2010)
Christensen, U. R. & Tilgner, A. Power requirement of the geodynamo from ohmic losses in numerical and laboratory dynamos. Nature 429, 169–171 (2004)
Christensen, U. R. & Aubert, J. Scaling properties of convection-driven dynamos in rotating spherical shells and application to planetary magnetic fields. Geophys. J. Int. 166, 97–114 (2006)
Christensen, U. R., Holzwarth, V. & Reiners, A. Energy flux determines magnetic field strength of planets and stars. Nature 457, 167–169 (2009)
Yoder, F. & Hutchison, R. The free librations of a dissipative Moon. Phil. Trans. R. Soc. Lond. A 303, 327–338 (1981)
Meyer, J. & Wisdom, J. Precession of the lunar core. Icarus 211, 921–924 (2011)
Gattacceca, J. et al. Unraveling the simultaneous shock magnetization and demagnetization of rocks. Earth Planet. Sci. Lett. 299, 42–53 (2010)
Arkani-Hamed, J. Did tidal deformation power the core dynamo of Mars? Icarus 201, 31–43 (2009)
Smith, D. E. et al. Initial observations from the Lunar Orbiter Laser Altimeter (LOLA). Geophys. Res. Lett. 37, L18204 (2010)
Lavorel, G. & Le Bars, M. Experimental study of the interaction between convective and elliptical instabilities. Phys. Fluids 22, 114101 (2010)
Cébron, D., Maubert, P. & Le Bars, M. Tidal instability in a rotating and differentially heated ellipsoidal shell. Geophys. J. Int. 182, 1311–1318 (2010)
Greenspan, H. P. The Theory of Rotating Fluids (Cambridge Univ. Press, 1968)
Cébron, D., Le Bars, M. & Meunier, P. Tilt-over mode in a precessing triaxial ellipsoid. Phys. Fluids 22, 116601 (2010)
Peale, S. J. in Planetary Satellites (ed. Burns, J. A. ) 87–112 (Univ. Arizona Press, 1977)
Lacaze, L., Le Gal, P. & Le Dizès, S. Elliptical instability in a rotating spheroid. J. Fluid Mech. 505, 1–22 (2004)
Correia, A. C. M. & Laskar, J. Mercury’s capture into the 3/2 spin–orbit resonance including the effect of core–mantle friction. Icarus 201, 1–11 (2009)
Acknowledgements
M.L.B. and D.C. acknowledge discussions with P. Le Gal and S. Le Dizès. Ö.K. acknowledges the support of the Belgian PRODEX programme.
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M.L.B. and D.C. performed the fluid mechanics analysis, M.A.W. contributed to the analysis of the basin magnetic anomalies and post-impact rotation rates, Ö.K. contributed to analysis of the post-impact rotational evolution of the Moon and M.L. performed the impact melt thermal evolution analysis. All authors contributed to the conclusions presented in the manuscript.
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This file contains Supplementary Text and Data, Supplementary Figures 1-10 with legends, Supplementary Tables 1-2 and additional references. (PDF 3320 kb)
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Le Bars, M., Wieczorek, M., Karatekin, Ö. et al. An impact-driven dynamo for the early Moon. Nature 479, 215–218 (2011). https://doi.org/10.1038/nature10565
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DOI: https://doi.org/10.1038/nature10565
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