The Effect of Lower Mantle Metallization on Magnetic Field Generation in Rocky Exoplanets

TL;DR

This study investigates how metallization of the lower mantle in rocky exoplanets affects their magnetic field generation, showing that conductive mantles strengthen core magnetic fields but weaken surface signals, complicating detection.

Contribution

It provides the first numerical analysis of how a metallized mantle influences planetary dynamo behavior and magnetic field characteristics in terrestrial exoplanets.

Findings

Conductive mantles strengthen core magnetic fields.

Metallization destabilizes the dynamo, reducing dipolar surface fields.

Surface magnetic signals are weaker due to mantle screening.

Abstract

Recent theoretical and experimental evidence indicates that many of the materials that are thought to exist in the mantles of terrestrial exoplanets will metallize and become good conductors of electricity at mantle pressures. This allows for strong electromagnetic coupling of the core and the mantle in these planets. We use a numerical dynamo model to study the effect of a metallized lower mantle on the dynamos of terrestrial exoplanets using several inner core sizes and mantle conductivities. We find that the addition of an electrically conducting mantle results in stronger core-mantle boundary fields because of the increase in magnetic field stretching. We also find that a metallized mantle destabilizes the dynamo resulting in less dipolar, less axisymmetric poloidal magnetic fields at the core-mantle boundary. The conducting mantle efficiently screens these fields to produce weaker surface fields. We conclude that a conducting mantle will make the detection of extrasolar terrestrial magnetic fields more difficult, while making the magnetic fields in the dynamo region stronger.