Magnetodynamo Lifetimes for Rocky, Earth-Mass Exoplanets with Contrasting Mantle Convection Regimes

TL;DR

This study models the magnetic field evolution of Earth-mass exoplanets, revealing how mantle convection regimes, surface temperatures, and core properties influence dynamo longevity and strength, with implications for planetary habitability.

Contribution

It introduces a thermal evolution model linking mantle convection regimes to dynamo lifetime and intensity, highlighting the impact of tectonic style and core properties on magnetic field presence.

Findings

Plate tectonics promote long-lived (~8 Gyr) dynamos.

Stagnant lid planets can have dynamos lasting over 10 Gyr.

Dynamo activity is highly sensitive to initial core conditions.

Abstract

We used a thermal model of an iron core to calculate magnetodynamo evolution in Earth-mass rocky planets to determine the sensitivity of dynamo lifetime and intensity to planets with different mantle tectonic regimes, surface temperatures, and core properties. The heat flow at the core-mantle boundary (CMB) is derived from numerical models of mantle convection with a viscous/pseudo-plastic rheology that captures the phenomenology of plate-like tectonics. Our thermal evolution models predict a long-lived (~8 Gyr) field for Earth and similar dynamo evolution for Earth-mass exoplanets with plate tectonics. Both elevated surface temperature and pressure-dependent mantle viscosity reduce the CMB heat flow but produce only slightly longer-lived dynamos (~8-9.5 Gyr). Single-plate ("stagnant lid") planets with relatively low CMB heat flow produce long-lived (~10.5 Gyr) dynamos. These weaker dynamos can cease for several billions of years and subsequently reactivate due to the additional entropy production associated with inner core growth, a possible explanation for the absence of a magnetic field on present-day Venus. We also show that dynamo operation is sensitive to the initial temperature, size, and solidus of a planet's core. These dependencies would severely challenge any attempt to distinguish exoplanets with plate tectonics and stagnant lids based on the presence or absence of a magnetic field.