STABILITY OF CO{sub 2} ATMOSPHERES ON DESICCATED M DWARF EXOPLANETS

Journal Article · Sat Jun 20 04:00:00 EDT 2015 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/806/2/249· OSTI ID:22522256

Gao, Peter; Hu, Renyu; Li, Cheng; Yung, Yuk L. ^[1]

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1. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States)

We investigate the chemical stability of CO{sub 2}-dominated atmospheres of desiccated M dwarf terrestrial exoplanets using a one-dimensional photochemical model. Around Sun-like stars, CO{sub 2} photolysis by Far-UV (FUV) radiation is balanced by recombination reactions that depend on water abundance. Planets orbiting M dwarf stars experience more FUV radiation, and could be depleted in water due to M dwarfs’ prolonged, high-luminosity pre-main sequences. We show that, for water-depleted M dwarf terrestrial planets, a catalytic cycle relying on H{sub 2}O{sub 2} photolysis can maintain a CO{sub 2} atmosphere. However, this cycle breaks down for atmospheric hydrogen mixing ratios <1 ppm, resulting in ∼40% of the atmospheric CO{sub 2} being converted to CO and O{sub 2} on a timescale of 1 Myr. The increased O{sub 2} abundance leads to high O{sub 3} concentrations, the photolysis of which forms another CO{sub 2}-regenerating catalytic cycle. For atmospheres with <0.1 ppm hydrogen, CO{sub 2} is produced directly from the recombination of CO and O. These catalytic cycles place an upper limit of ∼50% on the amount of CO{sub 2} that can be destroyed via photolysis, which is enough to generate Earth-like abundances of (abiotic) O{sub 2} and O{sub 3}. The conditions that lead to such high oxygen levels could be widespread on planets in the habitable zones of M dwarfs. Discrimination between biological and abiotic O{sub 2} and O{sub 3} in this case can perhaps be accomplished by noting the lack of water features in the reflectance and emission spectra of these planets, which necessitates observations at wavelengths longer than 0.95 μm.

• OSTI ID: 22522256
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 806; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CARBON DIOXIDE
CARBON MONOXIDE
CONCENTRATION RATIO
DWARF STARS
EMISSION SPECTRA
HYDROGEN
HYDROGEN PEROXIDE
LUMINOSITY
OXYGEN
OZONE
PHOTOCHEMISTRY
PHOTOLYSIS
PLANETS
RECOMBINATION
SATELLITE ATMOSPHERES
SATELLITES
SUN
WATER