Mantle Convection, Plate Tectonics, and Volcanism on Hot Exo-Earths

TL;DR

This study uses numerical simulations to explore how extreme temperature contrasts on tidally locked, hot exo-Earths influence mantle convection patterns, tectonic regimes, and volcanic activity, revealing hemispheric dichotomies and the impact of atmospheres.

Contribution

It demonstrates how high surface temperature contrasts can lead to asymmetric mantle convection and distinct tectonic regimes on hot exo-Earths, advancing understanding of their geodynamics.

Findings

Asymmetric degree 1 mantle convection pattern with cold subduction zones on the night side.

Hemispheric dichotomy: plate tectonics on the night side and mobile lid volcanism on the day side.

Atmospheric heat redistribution leads to more uniform surface deformation and volcanism.

Abstract

Recently discovered exoplanets on close-in orbits should have surface temperatures of 100's to 1000's of K. They are likely tidally locked and synchronously rotating around their parent stars and, if an atmosphere is absent, have surface temperature contrasts of many 100's to 1000's K between permanent day and night sides. We investigated the effect of elevated surface temperature and strong surface temperature contrasts for Earth-mass planets on the (i) pattern of mantle convection, (ii) tectonic regime, and (iii) rate and distribution of partial melting, using numerical simulations of mantle convection with a composite viscous/pseudo-plastic rheology. Our simulations indicate that, if a close-in rocky exoplanet lacks an atmosphere to redistribute heat, a >~ 400 K surface temperature contrast can maintain an asymmetric degree 1 pattern of mantle convection in which the surface of the planet moves preferentially toward subduction zones on the cold night side. The planetary surface features a hemispheric dichotomy, with plate-like tectonics on the night side and a continuously evolving mobile lid day side with diffuse surface deformation and vigorous volcanism. If volcanic outgassing establishes an atmosphere and redistributes heat, plate tectonics is globally replaced by diffuse surface deformation and volcanism accelerates and becomes distributed more uniformly across the planetary surface.