Interior convection regime, host star luminosity, and predicted atmospheric CO2 abundance in terrestrial exoplanets

TL;DR

This study models atmospheric evolution in terrestrial exoplanets to predict how interior convection regimes influence atmospheric CO2 levels, aiding future observational strategies for habitability assessment.

Contribution

It introduces coupled models of planetary interior convection, atmospheric chemistry, and climate to predict observable atmospheric CO2 signatures distinguishing convection regimes.

Findings

Similar likelihood of surface liquid water in both regimes

Detection of CO2 >0.1 bar can infer interior regime with high confidence

Guides future mission design for habitability assessment

Abstract

Terrestrial planets in the Habitable Zone of Sun-like stars are priority targets for detection and observation by the next generation of space telescopes. Earth's long-term habitability may have been tied to the geological carbon cycle, a process critically facilitated by plate tectonics. In the modern Earth, plate motion corresponds to a mantle convection regime called mobile-lid. The alternate, stagnant-lid regime is found on Mars and Venus, which may have lacked strong enough weathering feedbacks to sustain surface liquid water over geological timescales if initially present. Constraining observational strategies able to infer the most common regime in terrestrial exoplanets requires quantitative predictions of the atmospheric composition of planets in either regime. We use endmember models of volcanic outgassing and crust weathering for the stagnant- and mobile-lid convection regimes, that we couple to models of atmospheric chemistry and climate, and ocean chemistry to simulate the atmospheric evolution of these worlds in the Habitable Zone. In our simulations under the two alternate regimes, we find that the fraction of planets possessing climates consistent with surface liquid water is virtually the same. Despite this unexpected similarity, we predict that a mission capable of detecting atmospheric CO2 abundance above 0.1 bar in 25 terrestrial exoplanets is extremely likely (>95% of samples) to infer the dominant interior convection regime in that sample with strong evidence (10:1 odds). This offers guidance for the specifications of the Habitable Worlds Observatory NASA concept mission and other future missions capable of probing samples of habitable exoplanets.