Water is thought to be a major constituent of celestial bodies formed far enough from their host star for H2O to condense. The transport properties of water at extreme pT-conditions govern the evolution of water-rich planets and moons, such as the ice giants (Uranus and Neptune), or satellites possessing rigid icy shells and interior water oceans, like Europa and Enceladus. New theoretical and data-analysis methods have been recently developed to estimate accurate transport coefficients of electronically-gapped materials from ab initio equilibrium molecular dynamics and the Green-Kubo theory of linear response [1-3].  In this talk, we report on recent results on the application of these methods to heat and charge transport in water at the extreme pT-conditions occurring in the interior of water-rich planets and moons, in all the different relevant phases (partially dissociated liquid, solid, and super-ionic) [4].

These results are finally employed to build a model of the thermal evolution of Uranus, which accounts for its hitherto poorly understood very low luminosity [5].

References:
[1] A. Marcolongo, P.Umari, and S. Baroni, Nature Physics 12, 80–84 (2016)
[2] F. Grasselli and S. Baroni, Nature Physics 15, 967–972 (2019)
[3] R. Bertossa, F. Grasselli, L. Ercole, and S. Baroni, Phys. Rev. Lett. 122, 255901 (2019)
[4] F. Grasselli, L. Stixrude, S. Baroni, arXiv:2003.12557 [cond-mat.mtrl-sci] (2020)
[5] L. Stixrude, S. Baroni, F. Grasselli, in preparation.