Protonic thermoelectric effect of Superionic H2O and magnetic field generation in Uranus and Neptune

TL;DR

This paper proposes that the protonic thermoelectric effect in superionic H2O within Uranus and Neptune's icy mantles can explain their unique magnetic fields, driven by temperature gradients causing proton convection.

Contribution

It introduces a novel mechanism where superionic H2O's thermoelectric properties generate magnetic fields, explaining differences between Uranus and Neptune.

Findings

Superionic H2O exhibits a high Seebeck coefficient up to 620 uV/K.

Temperature gradients induce proton convection driving magnetic field generation.

Predicted magnetic field strengths align with observed data.

Abstract

Uranus and Neptune are characterized by anomalously tilted and multi-dipole magnetic fields, which poses substantial challenges for elucidating the internal mechanisms generating magnetic fields. Recent investigations confirmed that superionic H2O is thermodynamically stable and constitutes the dominant H2O phase within their icy mantles. In this study, we demonstrate that the superionic H2O ice exhibits a pronounced protonic thermoelectric effect, in which the maximum Seebeck coefficient within the interior of Uranus can reach approximately 620 uV/K, whereas that of Neptune is lower, within the range of 570-585 uV/K. Consequently, temperature gradients in the icy mantles can induce proton convection, which in turn drives magnetic field generation. Based on this novel mechanism, the disparities in magnetic field strength between Uranus and Neptune can be accounted for exclusively by their differing internal temperature gradients, and the predicted values are in agreement with observations.