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

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 $C{O}_2$ pressure, and the ability of a long-term carbon cycle driven by plate tectonics to control the atmospheric $C{O}_2$ 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 $C{O}_2$ pressure with time, up to an order of magnitude over 10 Gyr. Higher abundances of radioactive isotopes result in higher $C{O}_2$ pressures. We find a decreasing Rayleigh number and plate speed toward planets with larger core mass fractions $f_c$, which leads to lower atmospheric $C{O}_2$ pressure. More massive planets may favor the development of more $C{O}_2$ 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 $C{O}_2$ 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.

20 pages, 16 figures, to appear in Astronomy & Astrophysics

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• Orbital Dynamics and the Evolution of Planetary Habitability in the AU Mic System
• A rocky exoplanet classification method and its application to calculating surface pressure and surface temperature
• Exploring the habitability and interior composition of exoplanets lying within the extended habitable zone
• Bioverse: Potentially Observable Exoplanet Biosignature Patterns Under the UV Threshold Hypothesis for the Origin of Life
• The effect of a biosphere on the habitable timespan of stagnant-lid planets and implications for the atmospheric spectrum
• Mantle Degassing Lifetimes through Galactic Time and the Maximum Age Stagnant-lid Rocky Exoplanets can Support Temperate Climates
• Planetary interior and habitability of exoplanets: Recent developments