The role of planetary interior in the long-term evolution of atmospheric CO2 on Earth-like exoplanets

TL;DR

This study models how planetary interior properties like mantle heating, core size, and mass influence the long-term atmospheric CO2 evolution on Earth-like exoplanets, highlighting the role of plate tectonics and radioactive elements in climate regulation.

Contribution

It introduces a coupled box-model linking mantle convection, radioactive heating, and carbon cycling to assess long-term atmospheric CO2 evolution on exoplanets.

Findings

Atmospheric CO2 pressure decreases over 10 Gyr by up to an order of magnitude.

Higher radioactive isotope abundances lead to higher CO2 pressures.

Larger core mass fractions result in lower atmospheric CO2 due to reduced plate tectonics activity.

Abstract

Context: The long-term carbonate-silicate cycle plays an important role in the evolution of Earth's climate and, therefore, may also be an important mechanism in the evolution of the climates of Earth-like exoplanets. Aims: We investigate the effects of radiogenic mantle heating, core size, and planetary mass on the evolution of the atmospheric partial $CO_2$ pressure, and the ability of a long-term carbon cycle driven by plate tectonics to control the atmospheric $CO_2$ pressure. Methods: We developed a box-model which connects carbon cycling to parametrized mantle convection. The carbon cycle was coupled to the thermal evolution via the plate speed, which depends on the global Rayleigh number. Results: We find decreasing atmospheric $CO_2$ pressure with time, up to an order of magnitude over 10 Gyr. Higher abundances of radioactive isotopes result in higher $CO_2$ pressures. We find a decreasing Rayleigh number and plate speed toward planets with larger core mass fractions $f_c$, which leads to lower atmospheric $CO_2$ pressure. More massive planets may favor the development of more $CO_2$ rich atmospheres due to hotter interiors. Conclusions: The dependence of plate tectonics on mantle cooling has a significant effect on the long-term evolution of the atmospheric $CO_2$ pressure. Carbon cycling mediated by plate tectonics is efficient in regulating planetary climates for a wide range of mantle radioactive isotope abundances, planet masses and core sizes. More efficient carbon cycling on planets with a high mantle abundance of thorium or uranium highlights the importance of mapping the abundances of these elements in host stars of potentially habitable exoplanets. Inefficient carbon recycling on planets with a large core mass fraction ($f_c\gtrsim 0.8$) emphasizes the importance of precise mass-radius measurements of Earth-sized exoplanets.