Convective-region geometry as the cause of Uranus' and Neptune's unusual magnetic fields


The discovery of Uranus' and Neptune's non-dipolar, non-axisymmetric magnetic fields1,2,3,4 destroyed the picture—established by Earth, Jupiter and Saturn5,6—that planetary magnetic fields are dominated by axial dipoles. Although various explanations for these unusual fields have been proposed3,7,8,9,10, the cause of such field morphologies remains unexplained. Planetary magnetic fields are generated by complex fluid motions in electrically conducting regions of the planets (a process known as dynamo action), and so are intimately linked to the structure and evolution of planetary interiors. Determining why Uranus and Neptune have different field morphologies is not only critical for studying the interiors of these planets, but also essential for understanding the dynamics of magnetic-field generation in all planets. Here we present three-dimensional numerical dynamo simulations that model the dynamo source region as a convecting thin shell surrounding a stably stratified fluid interior. We show that this convective-region geometry produces magnetic fields similar in morphology to those of Uranus and Neptune. The fields are non-dipolar and non-axisymmetric, and result from a combination of the stable fluid's response to electromagnetic stress and the small length scales imposed by the thin shell.

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Figure 1: Dynamo model geometries.
Figure 2: Surface radial magnetic fields.
Figure 3: Surface magnetic power spectra.


  1. 1

    Ness, N. F. et al. Magnetic fields at Uranus. Science 233, 85–89 (1986)

    ADS  CAS  Article  Google Scholar 

  2. 2

    Ness, N. F. et al. Magnetic fields at Neptune. Science 246, 1473–1478 (1989)

    ADS  CAS  Article  Google Scholar 

  3. 3

    Connerney, J. E. P., Acuna, M. H. & Ness, N. F. The magnetic field of Uranus. J. Geophys. Res. 92, 15329–15336 (1987)

    ADS  Article  Google Scholar 

  4. 4

    Connerney, J. E. P., Acuna, M. H. & Ness, N. F. The magnetic field of Neptune. J. Geophys. Res. 96, 19023–19042 (1991)

    ADS  Article  Google Scholar 

  5. 5

    Connerney, J. E. P. Magnetic fields of the outer planets. J. Geophys. Res. 98, 18659–18679 (1993)

    ADS  Article  Google Scholar 

  6. 6

    Russell, C. T. Magnetic fields of the terrestrial planets. J. Geophys. Res. 98, 18681–18695 (1993)

    ADS  Article  Google Scholar 

  7. 7

    Ruzmaikin, A. A. & Starchenko, S. V. On the origin of Uranus and Neptune magnetic fields. Icarus 93, 82–87 (1991)

    ADS  Article  Google Scholar 

  8. 8

    Podolak, M., Hubbard, W. B. & Stevenson, D. J. in Uranus (eds Bergstralh, J. T., Miner, E. D. & Matthews, M. S.) 29–61 (Univ. Arizona Press, Tucson, 1991)

    Google Scholar 

  9. 9

    Hubbard, W. B., Podolak, M. & Stevenson, D. J. in Neptune and Triton (ed. Cruikshank, D. P.) 109–138 (Univ. Arizona Press, Tucson, 1995)

    Google Scholar 

  10. 10

    Holme, R. Three-dimensional kinematic dynamos with equatorial symmetry: application to the magnetic fields of Uranus and Neptune. Phys. Earth Planet. Inter. 102, 105–122 (1997)

    ADS  Article  Google Scholar 

  11. 11

    Hubbard, W. B. et al. Interior structure of Neptune—comparison with Uranus. Science 253, 648–651 (1991)

    ADS  CAS  Article  Google Scholar 

  12. 12

    Nellis, W. J. et al. The nature of the interior of Uranus based on studies of planetary ices at high dynamic pressure. Science 240, 779–781 (1988)

    ADS  CAS  Article  Google Scholar 

  13. 13

    Kuang, W. & Bloxham, J. An earth-like numerical dynamo model. Nature 389, 371–374 (1997)

    ADS  CAS  Article  Google Scholar 

  14. 14

    Kuang, W. J. & Bloxham, J. Numerical modelling of magnetohydrodynamic convection in a rapidly rotating spherical shell: weak and strong field dynamo action. J. Comput. Phys. 153, 51–81 (1999)

    ADS  MathSciNet  Article  Google Scholar 

  15. 15

    Glatzmaier, G. A. & Roberts, P. H. A 3-dimensional convective dynamo solution with rotating and finitely conducting inner core and mantle. Phys. Earth Planet. Inter. 91, 63–75 (1995)

    ADS  Article  Google Scholar 

  16. 16

    Glatzmaier, G. A. & Roberts, P. H. A 3-dimensional self-consistent computer simulation of a geomagnetic field reversal. Nature 377, 203–209 (1995)

    ADS  CAS  Article  Google Scholar 

  17. 17

    Dormy, E., Valet, J. P. & Courtillot, V. Numerical models of the geodynamo and observational constraints. Geochem. Geophys. Geosyst. 1, 2000GC000062 (2000)

  18. 18

    Grote, E., Busse, F. H. & Tilgner, A. Regular and chaotic spherical dynamos. Phys. Earth Planet. Inter. 117, 259–272 (2000)

    ADS  Article  Google Scholar 

  19. 19

    Grote, E. & Busse, F. H. Hemispherical dynamos generated by convection in rotating spherical shells. Phys. Rev. E 62, 4457–4460 (2000)

    ADS  CAS  Article  Google Scholar 

  20. 20

    Kutzner, C. & Christensen, U. R. From stable dipolar towards reversing numerical dynamos. Phys. Earth Planet. Inter. 131, 29–45 (2002)

    ADS  Article  Google Scholar 

  21. 21

    Ishihara, N. & Kida, S. Equatorial magnetic dipole field intensification by convection vortices in a rotating spherical shell. Fluid Dyn. Res. 31, 253–274 (2002)

    ADS  MathSciNet  Article  Google Scholar 

  22. 22

    Aubert, J. & Wicht, J. Axial versus equatorial dipolar dynamo models with implications for planetary magnetic fields. Earth Planet. Sci. Lett. (in the press)

  23. 23

    Roberts, P. H. & Glatzmaier, G. A. The geodynamo, past, present and future. Geophys. Astrophys. Fluid Dynam. 94, 47–84 (2001)

    ADS  Article  Google Scholar 

  24. 24

    Hollerbach, R. & Jones, C. A. Influence of the Earth's inner core on geomagnetic fluctuations and reversals. Nature 365, 541–543 (1993)

    ADS  Article  Google Scholar 

  25. 25

    Wicht, J. Inner core conductivity in numerical dynamo simulations. Phys. Earth Planet. Inter. 132, 281–302 (2002)

    ADS  Article  Google Scholar 

  26. 26

    Marley, M., Gomez, P. & Podolak, M. Monte Carlo interior models for Uranus and Neptune. J. Geophys. Res. 100, 23349–23353 (1995)

    ADS  Article  Google Scholar 

  27. 27

    Zhang, K. K. & Schubert, G. Teleconvection: remotely driven thermal convection in rotating stratified spherical layers. Science 290, 1944–1947 (2000)

    ADS  CAS  Article  Google Scholar 

  28. 28

    Jones, C. A., Longbottom, A. W. & Hollerbach, R. A self-consistent convection driven geodynamo model, using a mean field approximation. Phys. Earth Planet. Inter. 92, 119–141 (1995)

    ADS  Article  Google Scholar 

  29. 29

    Merrill, R. T., McElhinny, M. W. & McFadden, P. L. The Magnetic Field of the Earth 31 (Academic, San Diego, 1996)

    Google Scholar 

  30. 30

    Holme, R. & Bloxham, J. The magnetic fields of Uranus and Neptune: methods and models. J. Geophys. Res. 101, 2177–2200 (1996)

    ADS  Article  Google Scholar 

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We thank D. Stevenson for comments on the manuscript. This work was supported by NSERC and NSF.

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Correspondence to Sabine Stanley.

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Stanley, S., Bloxham, J. Convective-region geometry as the cause of Uranus' and Neptune's unusual magnetic fields. Nature 428, 151–153 (2004).

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