Constraining Background N2 Inventories on Directly Imaged Terrestrial Exoplanets to Rule Out O2 False Positives
Direct imaging spectroscopy with future space-based telescopes will constrain terrestrial planet atmospheric composition and potentially detect biosignature gases. One promising indication of life is abundant atmospheric O _2 . However, various non-biological processes could also lead to O _2 accumu...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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IOP Publishing
2023-01-01
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| Series: | The Astronomical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-3881/ad03e9 |
| _version_ | 1797559348122091520 |
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| author | Sawyer Hall Joshua Krissansen-Totton Tyler Robinson Arnaud Salvador Jonathan J. Fortney |
| author_facet | Sawyer Hall Joshua Krissansen-Totton Tyler Robinson Arnaud Salvador Jonathan J. Fortney |
| author_sort | Sawyer Hall |
| collection | DOAJ |
| description | Direct imaging spectroscopy with future space-based telescopes will constrain terrestrial planet atmospheric composition and potentially detect biosignature gases. One promising indication of life is abundant atmospheric O _2 . However, various non-biological processes could also lead to O _2 accumulation in the atmospheres of potentially habitable planets around Sun-like stars. In particular, the absence of non-condensible background gases such as N _2 could result in appreciable H escape and abiotic O _2 buildup, so identifying background atmosphere composition is crucial for contextualizing any O _2 detections. Here, we perform retrievals on simulated directly imaged terrestrial planets using rfast , a new exoplanet atmospheric retrieval suite with direct imaging analysis capabilities. By simulating Earth-analog retrievals for varied atmospheric compositions, cloud properties, and surface pressures, we determine what wavelength range, spectral resolution, and signal-to-noise ratio (S/N) are necessary to constrain background gases’ identity and abundance. We find N _2 backgrounds can be uniquely identified with S/N ∼ 20 observations, provided that wavelength coverage extends beyond ∼1.6 μ m to rule out CO-dominated atmospheres. Additionally, there is a low probability of O _2 -dominated atmospheres due to an O _2 –N _2 degeneracy that is only totally ruled out at S/N ∼ 40. If wavelength coverage is limited to 0.2–1.1 μ m, then although all other cosmochemically plausible backgrounds can be readily excluded, N _2 and CO backgrounds cannot be distinguished. Overall, our simulated retrievals and associated integration time calculations suggest that near-infrared coverage to at least 1.6 μ m and apertures approaching 8 m are needed to confidently rule out O _2 biosignature false positives within feasible integration times. |
| first_indexed | 2024-03-10T17:44:00Z |
| format | Article |
| id | doaj.art-9d493d0b954343c09c2e50514e853889 |
| institution | Directory Open Access Journal |
| issn | 1538-3881 |
| language | English |
| last_indexed | 2024-03-10T17:44:00Z |
| publishDate | 2023-01-01 |
| publisher | IOP Publishing |
| record_format | Article |
| series | The Astronomical Journal |
| spelling | doaj.art-9d493d0b954343c09c2e50514e8538892023-11-20T09:35:23ZengIOP PublishingThe Astronomical Journal1538-38812023-01-01166625410.3847/1538-3881/ad03e9Constraining Background N2 Inventories on Directly Imaged Terrestrial Exoplanets to Rule Out O2 False PositivesSawyer Hall0https://orcid.org/0000-0003-2070-5334Joshua Krissansen-Totton1https://orcid.org/0000-0001-6878-4866Tyler Robinson2https://orcid.org/0000-0002-3196-414XArnaud Salvador3https://orcid.org/0000-0001-8106-6164Jonathan J. Fortney4https://orcid.org/0000-0002-9843-4354Department of Astronomy & Astrophysics, UC Santa Cruz , Santa Cruz, CA 95064, USA ; sajhall@ucsc.eduDepartment of Astronomy & Astrophysics, UC Santa Cruz , Santa Cruz, CA 95064, USA ; sajhall@ucsc.edu; Department of Earth and Space Sciences, University of Washington , Seattle, WA, USA; NASA Nexus for Exoplanet System Science Virtual Planetary Laboratory, University of Washington , Box 351580, Seattle, WA 98195, USANASA Nexus for Exoplanet System Science Virtual Planetary Laboratory, University of Washington , Box 351580, Seattle, WA 98195, USA; Lunar & Planetary Laboratory, University of Arizona , Tucson, AZ 85721, USA; Department of Astronomy and Planetary Science, Northern Arizona University , Flagstaff, AZ 86011, USA; Habitability, Atmospheres, and Biosignatures Laboratory, University of Arizona , Tucson, AZ 85721, USALunar & Planetary Laboratory, University of Arizona , Tucson, AZ 85721, USA; Department of Astronomy and Planetary Science, Northern Arizona University , Flagstaff, AZ 86011, USA; Habitability, Atmospheres, and Biosignatures Laboratory, University of Arizona , Tucson, AZ 85721, USADepartment of Astronomy & Astrophysics, UC Santa Cruz , Santa Cruz, CA 95064, USA ; sajhall@ucsc.eduDirect imaging spectroscopy with future space-based telescopes will constrain terrestrial planet atmospheric composition and potentially detect biosignature gases. One promising indication of life is abundant atmospheric O _2 . However, various non-biological processes could also lead to O _2 accumulation in the atmospheres of potentially habitable planets around Sun-like stars. In particular, the absence of non-condensible background gases such as N _2 could result in appreciable H escape and abiotic O _2 buildup, so identifying background atmosphere composition is crucial for contextualizing any O _2 detections. Here, we perform retrievals on simulated directly imaged terrestrial planets using rfast , a new exoplanet atmospheric retrieval suite with direct imaging analysis capabilities. By simulating Earth-analog retrievals for varied atmospheric compositions, cloud properties, and surface pressures, we determine what wavelength range, spectral resolution, and signal-to-noise ratio (S/N) are necessary to constrain background gases’ identity and abundance. We find N _2 backgrounds can be uniquely identified with S/N ∼ 20 observations, provided that wavelength coverage extends beyond ∼1.6 μ m to rule out CO-dominated atmospheres. Additionally, there is a low probability of O _2 -dominated atmospheres due to an O _2 –N _2 degeneracy that is only totally ruled out at S/N ∼ 40. If wavelength coverage is limited to 0.2–1.1 μ m, then although all other cosmochemically plausible backgrounds can be readily excluded, N _2 and CO backgrounds cannot be distinguished. Overall, our simulated retrievals and associated integration time calculations suggest that near-infrared coverage to at least 1.6 μ m and apertures approaching 8 m are needed to confidently rule out O _2 biosignature false positives within feasible integration times.https://doi.org/10.3847/1538-3881/ad03e9Exoplanet atmospheresSpectroscopyTelescopesAstrobiology |
| spellingShingle | Sawyer Hall Joshua Krissansen-Totton Tyler Robinson Arnaud Salvador Jonathan J. Fortney Constraining Background N2 Inventories on Directly Imaged Terrestrial Exoplanets to Rule Out O2 False Positives The Astronomical Journal Exoplanet atmospheres Spectroscopy Telescopes Astrobiology |
| title | Constraining Background N2 Inventories on Directly Imaged Terrestrial Exoplanets to Rule Out O2 False Positives |
| title_full | Constraining Background N2 Inventories on Directly Imaged Terrestrial Exoplanets to Rule Out O2 False Positives |
| title_fullStr | Constraining Background N2 Inventories on Directly Imaged Terrestrial Exoplanets to Rule Out O2 False Positives |
| title_full_unstemmed | Constraining Background N2 Inventories on Directly Imaged Terrestrial Exoplanets to Rule Out O2 False Positives |
| title_short | Constraining Background N2 Inventories on Directly Imaged Terrestrial Exoplanets to Rule Out O2 False Positives |
| title_sort | constraining background n2 inventories on directly imaged terrestrial exoplanets to rule out o2 false positives |
| topic | Exoplanet atmospheres Spectroscopy Telescopes Astrobiology |
| url | https://doi.org/10.3847/1538-3881/ad03e9 |
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