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Photochemical Oxygen in Non-1-bar CO_2 Atmospheres of Terrestrial Exoplanets

James, Tre’Shunda and Hu, Renyu (2018) Photochemical Oxygen in Non-1-bar CO_2 Atmospheres of Terrestrial Exoplanets. Astrophysical Journal, 867 (1). Art. No. 17. ISSN 1538-4357.

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Atmospheric chemistry models have shown that molecular oxygen can build up in CO_2-dominated atmospheres on potentially habitable exoplanets without input of life. Existing models typically assume a surface pressure of 1 bar. Here we present model scenarios of CO_2-dominated atmospheres with the surface pressure ranging from 0.1 to 10 bars, while keeping the surface temperature at 288 K. We use a one-dimensional photochemistry model to calculate the abundance of O_2 and other key species, for outgassing rates ranging from a Venus-like volcanic activity up to 20 times Earth-like activity. The model maintains the redox balance of the atmosphere and the ocean, and includes the pressure dependency of outgassing on the surface pressure. Our calculations show that the surface pressure is a controlling parameter in the photochemical stability and oxygen buildup of CO_2-dominated atmospheres. The mixing ratio of O_2 monotonically decreases as the surface pressure increases at very high outgassing rates, whereas it increases as the surface pressure increases at lower-than-Earth outgassing rates. Abiotic O_2 can only build up to the detectable level, defined as 10^(−3) in volume mixing ratio, in 10-bar atmospheres with the Venus-like volcanic activity rate and the reduced outgassing rate of H_2 due to the high surface pressure. Our results support the search for biological activities and habitability via atmospheric O_2 on terrestrial planets in the habitable zone of Sun-like stars.

Item Type:Article
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URLURL TypeDescription Paper
Alternate Title:Photochemical Oxygen in Non-1-bar CO2 Atmospheres of Terrestrial Exoplanets
Additional Information:© 2018 The American Astronomical Society. Received 2018 July 1; revised 2018 September 11; accepted 2018 September 12; published 2018 October 25. The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. T.J. thanks the support of the US National Science Foundation's (NSF) Division Of Undergraduate Education (DUE), under grant No.1457943.
Funding AgencyGrant Number
NSF Predoctoral FellowshipDUE-1457943
Subject Keywords:astrobiology – planets and satellites: atmospheres – planets and satellites: terrestrial planets
Record Number:CaltechAUTHORS:20181025-111313786
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Official Citation:Tre'Shunda James and Renyu Hu 2018 ApJ 867 17
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:90416
Deposited By: Tony Diaz
Deposited On:25 Oct 2018 18:22
Last Modified:25 Oct 2018 18:22

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