Letter | Published:

The ice layer in Uranus and Neptune—diamonds in the sky?

Naturevolume 292pages435436 (1981) | Download Citation



Many of the current models of Uranus and Neptune postulate a three-layer structure, consisting of an inner rocky core, a middle ‘ice’ layer of fluid, H2O, CH4, NH3 and an outer hydrogen–helium layer of solar composition1. The estimated pressures and temperatures of the ice layer ranges from about 6Mbar and 7,000 K at the inner core-ice boundary, to 0.2 Mbar and 2,200 K at the outer ice/hydrogen–helium boundary. I point out here that shockwave experiments on these liquids2–5, as well as theoretical studies5–7, imply that the H2O and NH3 in the ice layer are almost totally ionized and the CH4 has been pyrolysed to carbon, possibly in the metallic or diamond form8,9.

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  1. 1

    Hubbard, W. B. & McFarland, J. J. J. geophys. Res. 85, 225 (1980).

  2. 2

    Mitchell, A. C. & Nellis, W. J. in High Pressure Science and Technology Vol. 1 (eds Timmerhans, K. D. & Barber, M. S.) 428 (Plenum, New York, 1980).

  3. 3

    Mitchell, A. C., Kovel, M. I., Nellis, W. J. & Keeler, R. N. in High Pressure Science and Technology Vol. 2 (eds Vodar, B. & Marteau, P.) 1048 (Pergamon, Oxford, 1980).

  4. 4

    Nellis, W. J., Mitchell, A. C., Ross, M. & van Thiel, M. in High Pressure Science and Technology Vol. 2 (eds Vodar, B. & Marteau, P.) 1043 (Pergamon, Oxford, 1980).

  5. 5

    Nellis, W. J., Ree, F. H., van Thiel, M. & Mitchell, A. C. J. chem. Phys. (submitted).

  6. 6

    Ross, M. & Ree, F. H. J. chem. Phys. 73, 6146 (1980).

  7. 7

    Ree, F. H. J. chem. Phys. 70, 974 (1979).

  8. 8

    Grover, R. J. chem. Phys. 71, 3824 (1979).

  9. 9

    Van Vechten, J. A. Phys. Rev. B 7, 1479 (1973).

  10. 10

    Brown, W. L. Astrophys. J. Lett. 207, L209 (1976).

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  1. Lawrence Livermore National Laboratory, University of California, Livermore, California, 94550, USA

    • Marvin Ross


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