Chart showing that results from a family of simulations that track changing pressures of three gases
On “desert worlds” (planets with a low initial volatile inventory), a typical outcome of simulations of different amounts of volcanic outgassing, crustal weathering, and atmospheric escape is that atmospheric O2 is a dominant gas in the atmosphere for long periods in the planet’s history. The lines with shaded areas show results from a family of simulations that track changing pressures of three gases. Initial O2 production from a steam atmosphere above a magma ocean, coupled with efficient escape and inefficient crustal weathering, lead to high oxygen levels. Credit: Krissansen-Totton et al. [2021], Figure 7c
Source: AGU Advances

On Earth, oxygen came to comprise a substantial part of our atmosphere as a direct result of photosynthetic life, thus begging the question: Is oxygen a diagnostic signature for life for terrestrial planets around sun-like stars? Only sometimes, according to Krissansen-Totton et al. [2021] who model long-term evolution of planets, including a magma ocean phase, volcanism, weathering, and atmospheric escape. While they show that the most Earth-like worlds may generate significant oxygen only by biology, “waterworlds” and “desert worlds” can have significant oxygen buildup even without life because other geologic processes that destroy oxygen are suppressed while atmospheric escape generates oxygen over long time. The work has implications for telescope design and the types of observations that would need to be made to distinguish biotic versus abiotic oxygen on habitable exoplanets around sun-like stars.

Citation: Krissansen‐Totton, J., Fortney, J. J., Nimmo, F., & Wogan, N. [2021]. Oxygen false positives on habitable zone planets around sun‐like stars. AGU Advances, 2, e2020AV000294.

—Bethany Ehlmann, Editor, AGU Advances

Text © 2021. The authors. CC BY-NC-ND 3.0
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