Hi All

I was reading some recent modelling of mini-Jovian planets, which typically have 10 kilobar atmospheres, then shallowish oceans overlaying huge depths of ice. I wondered at this assumption of so much ice, so I read up on ice phases here...

C:\Documents and Settings\Adam\My Documents\Phase diagram of water and ice.htm

...weirdest thing is Ice VII being able to exist way, way past the critical point temperature (647.5 K) for liquid water. Given 140 kilobars at that temperature Ice VII is solid, at a density of 1.7 times water. As the pressure rises it apparently turns into the even denser (~2.51) Ice X, though things get pretty hazy above a megabar - at which Ice VII melts at 964 K!!!

Back in the 60s Isaac Asimov was one of the first to speculate on water oceans instead of ice-layers within Jupiter, warmed by the greenhouse effect. He wrote of a hydrosphere thousands of miles deep. But it really would become ice not too far in. We now know that all the Jovians are too hot for liquid water oceans - though Ben Bova felt free to imagine such in his recent "Jupiter" - but mini-Neptunes might exist that allow them, overlying Ice VII and X.

Ice VII forms at pressures above 2210 MPa from either Ice VI or liquid water. Its triple point with the three is at 81.6 degrees C. Freaky...

I once read an idea for terraforming Jovians which involves fusing H/He into O/N. Eventually, I'd hazard that the Ice VII/X that formed might "float" in the liquid H/He until a shell forms? Then a deepish ocean above a thick shell of ice. Depends on what ultra-pressure H/He mixtures are like...

But that's another phase diagram.

Adam