Exoplanets & Exomoons

The Impending Opacity Challenge in Exoplanet Atmospheric Characterization

By Keith Cowing
Press Release
September 15, 2022
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The Impending Opacity Challenge in Exoplanet Atmospheric Characterization
Framework for sensitivity analysis of retrieved atmospheric properties to opacity model. The four building blocks of the transmission spectra are shown in green, analysis techniques are marked in blue, and the orange parallelogram highlights the remote sensing technique at the center of this perturbation/sensitivity analysis. The arrows are shown to indicate the direction of the information flow. We perform self- and cross-retrieval for two planetary cases (a super-Earth around M-dwarf and a Jupiter-sized planet around Kdwarf, see Supplementary Table 2) with nine distinct sets of cross-sections (see Supplementary Table 1) to access their impacts.

With a new generation of observatories coming online this decade, the process of characterizing exoplanet atmospheres will need to be reinvented.

Currently mostly on the instrumental side, characterization bottlenecks will soon stand by the models used to translate spectra into atmospheric properties. Limitations stemming from our stellar and atmospheric models have already been highlighted.

Here, we show that the current limitations of the opacity models used to decode exoplanet spectra propagate into an accuracy wall at ~0.5-1.0 dex (i.e., 3 to 10x) on the atmospheric properties, which is an order of magnitude above the precision targeted by JWST Cycle 1 programs and needed for, e.g., meaningful C/O-ratio constraints and biosignatures identification.

We perform a sensitivity analysis using nine different opacity models and find that most of the retrievals produce harmonious fits owing to compensations in the form of >5σ biases on the derived atmospheric parameters translating in the aforementioned accuracy wall. We suggest a two-tier approach to alleviate this problem involving a new retrieval procedure and guided improvements in opacity data, their standardization and optimal dissemination.

Prajwal Niraula, Julien de Wit, Iouli E. Gordon, Robert J. Hargreaves, Clara Sousa-Silva, Roman V. Kochanov

Comments: 16 Pages, 12 Figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2209.07464 [astro-ph.EP] (or arXiv:2209.07464v1 [astro-ph.EP] for this version)
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Journal reference: Nature Astronomy, Sept 15, 2022
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Submission history
From: Prajwal Niraula
[v1] Thu, 15 Sep 2022 17:06:26 UTC (12,020 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) 🖖🏻