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

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, H 2 O, CH 4 , NH 3 and an outer hydrogen–helium layer of solar composition 1 . 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 liquids 2–5 , as well as theoretical studies 5–7 , imply that the H 2 O and NH 3 in the ice layer are almost totally ionized and the CH 4 has been pyrolysed to carbon, possibly in the metallic or diamond form 8,9 .