In:
The Astrophysical Journal, American Astronomical Society, Vol. 937, No. 2 ( 2022-10-01), p. 109-
Abstract:
Nitrous oxide (N 2 O)—a product of microbial nitrogen metabolism—is a compelling exoplanet biosignature gas with distinctive spectral features in the near- and mid-infrared, and only minor abiotic sources on Earth. Previous investigations of N 2 O as a biosignature have examined scenarios using Earthlike N 2 O mixing ratios or surface fluxes, or those inferred from Earth’s geologic record. However, biological fluxes of N 2 O could be substantially higher, due to a lack of metal catalysts or if the last step of the denitrification metabolism that yields N 2 from N 2 O had never evolved. Here, we use a global biogeochemical model coupled with photochemical and spectral models to systematically quantify the limits of plausible N 2 O abundances and spectral detectability for Earth analogs orbiting main-sequence (FGKM) stars. We examine N 2 O buildup over a range of oxygen conditions (1%–100% present atmospheric level) and N 2 O fluxes (0.01–100 teramole per year; Tmol = 10 12 mole) that are compatible with Earth’s history. We find that N 2 O fluxes of 10 [100] Tmol yr −1 would lead to maximum N 2 O abundances of ∼5 [50] ppm for Earth–Sun analogs, 90 [1600] ppm for Earths around late K dwarfs, and 30 [300] ppm for an Earthlike TRAPPIST-1e. We simulate emission and transmission spectra for intermediate and maximum N 2 O concentrations that are relevant to current and future space-based telescopes. We calculate the detectability of N 2 O spectral features for high-flux scenarios for TRAPPIST-1e with JWST. We review potential false positives, including chemodenitrification and abiotic production via stellar activity, and identify key spectral and contextual discriminants to confirm or refute the biogenicity of the observed N 2 O.
Type of Medium:
Online Resource
ISSN:
0004-637X
,
1538-4357
DOI:
10.3847/1538-4357/ac8cfb
Language:
Unknown
Publisher:
American Astronomical Society
Publication Date:
2022
detail.hit.zdb_id:
2207648-7
detail.hit.zdb_id:
1473835-1
SSG:
16,12
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