Imaging & Spectroscopy

Reflected Spectroscopy Of Small Exoplanets III: Probing The UV Band To Measure Biosignature Gasses

By Keith Cowing
Status Report
August 16, 2023
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Reflected Spectroscopy Of Small Exoplanets III: Probing The UV Band To Measure Biosignature Gasses
The full posterior distributions (corner plots) of the Proterozoic Earth-like scenario with 1% of Modern Earth’s O2. The different cases explore a combination of different wavelength bands used for the retrieval process. The black lines in the corner plots refer to the true value used to simulate the data. — astro-ph.EP

Direct-imaging observations of terrestrial exoplanets will enable their atmospheric characterization and habitability assessment. Considering the Earth, the key atmospheric signatures for the biosphere is O2 and the photochemical product O3.

However, this O2-O3 biosignature is not detectable in the visible wavelengths for most of the time after the emergence of oxygenic photosynthesis life (i.e., the Proterozoic Earth). Here we demonstrate spectroscopic observations in the ultraviolet wavelengths for detecting and characterizing O2 and O3 in Proterozoic Earth-like planets, using ExoReLℜ. For an O2 mixing ratio 2 to 3 orders of magnitude less than the present-day Earth, and an O3 mixing ratio of 10−7−10−6, we find that O3 can be detected and its mixing ratio can be measured precisely (within 1 order of magnitude) in the ultraviolet (0.25−0.4 μm) in addition to visible-wavelength spectroscopy.

With modest spectral resolution (R=7) and S/N (∼10) in the ultraviolet, the O3 detection is robust against other potential gases absorbing in the ultraviolet (e.g., H2S and SO2), as well as the short-wavelength cutoff between 0.2 and 0.25 μm. While the O3 detection does not rely on the near-infrared spectra, extending the wavelength coverage to the near-infrared (1−1.8 μm) would provide essential information to interpret the O3 biosignature, including the mixing ratio of H2O, the cloud pressure, as well as the determination of the dominant gas of the atmosphere. The ultraviolet and near-infrared capabilities should thus be evaluated as critical components for future missions aiming at imaging and characterizing terrestrial exoplanets, such as the Habitable Worlds Observatory.

Mario Damiano, Renyu Hu, Bertrand Mennesson

Comments: 13 pages, 8 figures, 3 tables, accepted for publication in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2308.08490 [astro-ph.EP] (or arXiv:2308.08490v1 [astro-ph.EP] for this version)
Submission history
From: Mario Damiano
[v1] Wed, 16 Aug 2023 16:45:49 UTC (8,095 KB)


Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻