Electrical conductivity of silicate liquids at extreme conditions and planetary dynamos*

We find that Earth’s earliest magnetic field may have been produced in a deep magma ocean, and that silicate dynamos may exist in super-Earth exoplanets as well. Our conclusions are based on ab initio molecular dynamics simulations and Kubo-Greenwood computations of the electrical conductivity. These show that silicate liquids are semi-metallic at the extreme pressure and temperature conditions characteristic of planetary interiors with conductivity exceeding 10,000 S/m. In silica, the electrical conductivity shows a remarkable non-monotonic dependence on pressure that reveals connections to the underlying atomic structure, and highlights broken charge ordering as a novel compression mechanism. We compare the behavior of silica liquid with that of (Mg,Fe)O liquid and a multi-component composition (MgO-FeO-CaO-Al₂O₃-Na₂O-SiO₂) representative of the bulk silicate Earth.