Exoplanets & Exomoons

Exploring And Validating Exoplanet Atmospheric Retrievals With Solar System Analog Observations

By Keith Cowing
April 11, 2022
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Exploring And Validating Exoplanet Atmospheric Retrievals With Solar System Analog Observations
Simulated spectrum of an exo-Earth orbiting a solar twin at characteristic HabEx/LUVOIR spectral coverage and resolving power (ultraviolet [0.2–0.4 µm], visible [0.4–1.0 µm], and near-infrared [1.0–1.8 µm] at resolving power of 7, 140, and 70, respectively). Gas spectral impacts are indicated by showing sensitivity to mixing ratio changes for key species. For the sensitivity test, and relative to fiducial values, the water mixing ratio was halved, the ozone and molecular oxygen mixing ratios were doubled, and the carbon dioxide and methane mixing ratios were increased by a factor of 5.

Solar System observations that serve as analogs for exoplanet remote sensing data can provide important opportunities to validate ideas and models related to exoplanet environments.

Critically, and unlike true exoplanet observations, Solar System analog data benefit from available high-quality ground- or orbiter-derived “truth” constraints that enable strong validations of exoplanet data interpretation tools. In this work, we first present a versatile atmospheric retrieval suite, capable of application to reflected light, thermal emission, and transmission observations. The tool — dubbed rfast — is designed, in part, to enable exoplanet mission concept feasibility studies.

Following model validation, the retrieval tool is applied to a range of Solar System analog observations for exoplanet environments. Retrieval studies using Earth reflected light observations from NASA’s EPOXI mission provide a key proof-of-concept for under-development exo-Earth direct imaging concept missions. Inverse modeling applied to an infrared spectrum of Earth from the Mars Global Surveyor Thermal Emission Spectrometer achieves good constraints on atmospheric gases, including many biosignature gases.

Finally, retrieval analysis applied to a transit spectrum of Titan derived from the Cassini Visual and Infrared Mapping Spectrometer provides a proof-of-concept for interpreting more feature-rich transiting exoplanet observations from NASA’s James Webb Space Telescope (JWST). In the future, Solar System analog observations for exoplanets could be used to verify exoplanet models and parameterizations, and future exoplanet analog observations of any Solar System worlds from planetary science missions should be encouraged.

Tyler D. Robinson, Arnaud Salvador

Comments: submitted to PSJ; community comments and feedback welcome!
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2204.04231 [astro-ph.EP] (or arXiv:2204.04231v1 [astro-ph.EP] for this version)
Submission history
From: Tyler Robinson
[v1] Fri, 8 Apr 2022 18:00:03 UTC (29,000 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) 🖖🏻