ABIOTIC OZONE AND OXYGEN IN ATMOSPHERES SIMILAR TO PREBIOTIC EARTH

By S. Domagal‐Goldman, A. Segura, M. Claire, T. Robinson, V. Meadows. 2014

147 citations recorded by the source corpus.

The search for life on planets outside our solar system will use spectroscopic identification of atmospheric biosignatures. The most robust remotely detectable potential biosignature is considered to be the detection of oxygen (O2) or ozone (O3) simultaneous to methane (CH4) at levels indicating fluxes from the planetary surface in excess of those that could be produced abiotically. Here we use an altitude-dependent photochemical model with the enhanced lower boundary conditions necessary to carefully explore abiotic O2 and O3 production on lifeless planets with a wide variety of volcanic gas fluxes and stellar energy distributions. On some of these worlds, we predict limited O2 and O3 buildup, caused by fast chemical production of these gases. This results in detectable abiotic O3 and CH4 features in the UV-visible, but no detectable abiotic O2 features. Thus, simultaneous detection of O3 and CH4 by a UV-visible mission is not a strong biosignature without proper contextual information. Discrimination between biological and abiotic sources of O2 and O3 is possible through analysis of the stellar and atmospheric context—particularly redox state and O atom inventory—of the planet in question. Specifically, understanding the spectral characteristics of the star and obtaining a broad wavelength range for planetary spectra should allow more robust identification of false positives for life. This highlights the importance of wide spectral coverage for future exoplanet characterization missions. Specifically, discrimination between true and false positives may require spectral observations that extend into infrared wavelengths and provide contextual information on the planet's atmospheric chemistry.

Subfields: Astronomy and Astrophysics, Atmospheric Science

View Paper: https://www.semanticscholar.org/paper/5cde205c98da7b137aefb24af322d498dea12467

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Citations in the corpus

Pale Orange Dots: The Impact of Organic Haze on the Habitability and Detectability of Earthlike Exoplanets (2016, background): “As discussed in Domagal-Goldman et al. (2014), it is difficult to accumulate abiotic oxygen at detectable levels in atmospheres rich in organics because reactions with reduced gases are major oxygen sinks.”
THE MUSCLES TREASURY SURVEY. I. MOTIVATION AND OVERVIEW (2016, background): “…atmospheric heating and chemistry on Earth-like planets, is critical to the defini- tion and interpretation of biosignature gases (e.g., Seager et al. 2013), and may even produce false-positives in our search for biologic activity (Hu et al. 2012; Tian et al. 2014; Domagal-Goldman et al. 2014).”
ABIOTIC O2 LEVELS ON PLANETS AROUND F, G, K, AND M STARS: POSSIBLE FALSE POSITIVES FOR LIFE? (2015, methodology): “This type of planet has been modeled by Tian et al. (2014) and Domagal-Goldman et al. (2014), with conflicting results.”
How to Characterize Habitable Worlds and Signs of Life (2017, methodology): “As an example, under certain conditions, the UV O3 30 feature could be detected in prebiotic Earth models (Domagal-Goldman et al. 2014), whereas the same models did not produce detectable abiotic visible O2 or IR O3 features.”
Exoplanet Biosignatures: A Review of Remotely Detectable Signs of Life (2017, background): “At the CO2 levels suggested for the Archean Earth (atmospheric fractions of roughly 10-3–10-2) (Driese et al., 2011), a ratio of CH4/CO2 of about 0.2 is required to initiate the formation of a thick organic haze (e.g., Trainer et al., 2006).”
The Habitability of Planets Orbiting M-dwarf Stars (2016, background): “…2015; Tian, 2015; Schaefer et al., 2016; Barnes et al., 2016), and to also understand how to discriminate abiotic from biological sources using spectroscopic observations (Domagal-Goldman et al., 2014; Gao et al., 2015; Harman et al., 2015; Schwieterman et al., 2015, 2016b,a; Meadows et al., 2016).”