Nature 292, 435 - 436 (30 July 1981); doi:10.1038/292435a0

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

Marvin Ross

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

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 form^8,9.

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