Hot interiors of ice giant planets inferred from electrical conductivity of dense H2O fluid

TL;DR

This study measures the electrical conductivity of dense H2O to better understand the magnetic fields of ice giant planets, revealing that hotter interiors are needed to explain observed magnetic phenomena.

Contribution

First static compression measurements of ionic H2O's electrical conductivity up to 45 GPa and 2750 K, challenging previous shock experiment data.

Findings

Electrical conductivity of molten H2O is lower than shock data suggested.

Conventional thermal structures cannot generate observed magnetic fields.

Hotter interior models are required for Uranus and Neptune.

Abstract

Uranus and Neptune have intrinsic magnetic fields generated via convection in a molten H2O layer, where the field strength is determined by its electrical conductivity (EC) along with convection size and velocity. Previous shock experiments reported that the EC of molten H2O is high enough to generate magnetic fields of these ice giant planets with adiabatic thermal structures. Here we measured the EC of ionic H2O fluid for the first time by static compression experiments up to 45 GPa and 2,750 K. The EC determined is lower by a few orders of magnitude than earlier data by shock compression measurements and not capable of generating a magnetic field with the conventional interior thermal structures. Our results necessitate recently-suggested fewfold hotter interiors of Uranus and Neptune to explain their magnetic fields.