Carbonate-Silicate Cycle Predictions of Earth-like Planetary Climates and Testing the Habitable Zone Concept

Abstract

In the conventional habitable zone (HZ) concept, a CO${}_2$-H${}_2$O greenhouse maintains surface liquid water. Through the water-mediated carbonate-silicate weathering cycle, atmospheric CO${}_2$ partial pressure (pCO${}_2$) responds to changes in surface temperature, stabilizing the climate over geologic timescales. We show that this weathering feedback ought to produce a log-linear relationship between pCO${}_2$ and incident flux on Earth-like planets in the HZ. However, this trend has scatter because geophysical and physicochemical parameters can vary, such as land area for weathering and CO${}_2$ outgassing fluxes. Using a coupled climate and carbonate-silicate weathering model, we quantify the likely scatter in pCO${}_2$ with orbital distance throughout the HZ. From this dispersion, we predict a two-dimensional relationship between incident flux and pCO${}_2$ in the HZ and show that it could be detected from at least 83 ($2\sigma$) Earth-like exoplanet observations. If fewer Earth-like exoplanets are observed, testing the HZ hypothesis from this relationship could be difficult.

Published 12/1/2020 in Nature Communications. The supplemental data and code referenced in this work are available from the Nature Communications website (see DOI below) or by email from the authors

References in corpus (13)

• Was Venus the First Habitable World of our Solar System?
• Strong Dependence of the Inner Edge of the Habitable Zone on Planetary Rotation Rate
• Detecting the Glint of Starlight on the Oceans of Distant Planets
• Disequilibrium biosignatures over Earth history and implications for detecting exoplanet life
• Oxygen fugacities of extrasolar rocks: Evidence for an Earth-like geochemistry of exoplanets
• Constraints on Climate and Habitability for Earth-like Exoplanets Determined from a General Circulation Model
• Detecting Ocean Glint on Exoplanets Using Multiphase Mapping
• A Statistical Comparative Planetology Approach to the Hunt for Habitable Exoplanets and Life Beyond the Solar System
• A warm or a cold early Earth? New insights from a 3-D climate-carbon model
• Abundant atmospheric methane from volcanism on terrestrial planets is unlikely and strengthens the case for methane as a biosignature
• Thermodynamic and Energetic Limits on Continental Silicate Weathering Strongly Impact the Climate and Habitability of Wet, Rocky Worlds
• A Statistical Comparative Planetology Approach to Maximize the Scientific Return of Future Exoplanet Characterization Efforts
• Two examples of how to use observations of terrestrial planets orbiting in temperate orbits around low mass stars to test key concepts of planetary habitability

Cited by in corpus (5)

• Understanding planetary context to enable life detection on exoplanets and test the Copernican principle
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• Hierarchical Bayesian Atmospheric Retrieval Modeling for Population Studies of Exoplanet Atmospheres: A Case Study on the Habitable Zone
• CO${}_2$ ocean bistability on terrestrial exoplanets
• The Abundance of Belatedly Habitable Planets and Ambiguities in Definitions of the Continuously Habitable Zone