PHOTOCHEMISTRY IN TERRESTRIAL EXOPLANET ATMOSPHERES. I. PHOTOCHEMISTRY MODEL AND BENCHMARK CASES

By R. Hu, Sara Seager, William Bains. 2012

184 citations recorded by the source corpus.

We present a comprehensive photochemistry model for exploration of the chemical composition of terrestrial exoplanet atmospheres. The photochemistry model is designed from the ground up to have the capacity to treat all types of terrestrial planet atmospheres, ranging from oxidizing through reducing, which makes the code suitable for applications for the wide range of anticipated terrestrial exoplanet compositions. The one-dimensional chemical transport model treats up to 800 chemical reactions, photochemical processes, dry and wet deposition, surface emission, and thermal escape of O, H, C, N, and S bearing species, as well as formation and deposition of elemental sulfur and sulfuric acid aerosols. We validate the model by computing the atmospheric composition of current Earth and Mars and find agreement with observations of major trace gases in Earth's and Mars’ atmospheres. We simulate several plausible atmospheric scenarios of terrestrial exoplanets and choose three benchmark cases for atmospheres from reducing to oxidizing. The most interesting finding is that atomic hydrogen is always a more abundant reactive radical than the hydroxyl radical in anoxic atmospheres. Whether atomic hydrogen is the most important removal path for a molecule of interest also depends on the relevant reaction rates. We also find that volcanic carbon compounds (i.e., CH4 and CO2) are chemically long-lived and tend to be well mixed in both reducing and oxidizing atmospheres, and their dry deposition velocities to the surface control the atmospheric oxidation states. Furthermore, we revisit whether photochemically produced oxygen can cause false positives for detecting oxygenic photosynthesis, and find that in 1 bar CO2-rich atmospheres oxygen and ozone may build up to levels that have conventionally been accepted as signatures of life, if there is no surface emission of reducing gases. The atmospheric scenarios presented in this paper can serve as the benchmark atmospheres for quickly assessing the lifetime of trace gases in reducing, weakly oxidizing, and highly oxidizing atmospheres on terrestrial exoplanets for the exploration of possible biosignature gases.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/3bb0e9d9765928825cbe9c3214f860682484aa1a

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Atmospheric Science

Citations in the corpus

ABIOTIC O2 LEVELS ON PLANETS AROUND F, G, K, AND M STARS: POSSIBLE FALSE POSITIVES FOR LIFE? (2015, background): “Hu et al. (2012) simulated such a planet with three different H2 outgassing rates: 3×1010, 3×109, and 0 cm−2 s−1.”
Wide-Field InfrarRed Survey Telescope-Astrophysics Focused Telescope Assets WFIRST-AFTA 2015 Report (2015, background): “The atmospheres of these planets could span a huge range from gas-giant hydrogen to water vapor to CO2 to oxygen or hydrocarbons (Hu et al. 2012), with or without clouds.”
ABIOTIC OXYGEN-DOMINATED ATMOSPHERES ON TERRESTRIAL HABITABLE ZONE PLANETS (2014, background): “Various authors have investigated the idea that abiotic oxygen production could lead to ‘false positives’ for life (Selsis et al. 2002; Segura et al. 2007; Léger et al. 2011; Hu et al. 2012; Tian et al. 2014).”
ABIOTIC OZONE AND OXYGEN IN ATMOSPHERES SIMILAR TO PREBIOTIC EARTH (2014, methodology): “When we adopt the boundary conditions of Hu et al. (2012), we replicate their results.”
Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life (2017, methodology): “ra et al., 2003, 2007, 2010; Rauer et al., 2011; Arney et al., 2016), the Caltech/JPL model (e.g., Allen et al., 1981; Nair et al., 1994; Yung et al., 1988; Gao et al., 2015), and the Hu group model (Hu et al., 2012, 2013; Hu and Seager, 2014) all share the same general approach to simulating photoc”
HAZMAT. I. THE EVOLUTION OF FAR-UV AND NEAR-UV EMISSION FROM EARLY M STARS (2014, background): “…calculated for the atmospheres of all exoplanets, from Earths to Jupiters (e.g., Segura et al. 2010; Line et al. 2010; Kaltenegger et al. 2011; Hu et al. 2012; Kopparapu et al. 2012; Moses et al. 2013), require realistic input stellar fluxes, and are at the moment limited to using solar data…”
THE MUSCLES TREASURY SURVEY. I. MOTIVATION AND OVERVIEW (2016, background): “Therefore, on planets orbiting stars with strong FUV and weak NUV flux, a substantial O3 atmosphere may arise via photochemical processes alone (Segura et al. 2010; Hu et al. 2012; Gao et al. 2015; Harman et al. 2015).”