Exoplanets & Exomoons

Earth As A Transiting Exoplanet: A Validation Of Transmission Spectroscopy And Atmospheric Retrieval Methodologies For Terrestrial Exoplanets

By Keith Cowing
Status Report
August 29, 2023
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Earth As A Transiting Exoplanet: A Validation Of Transmission Spectroscopy And Atmospheric Retrieval Methodologies For Terrestrial Exoplanets
Earth’s observed cloud-free transit transmission spectrum from Macdonald & Cowan (2019) binned to a resolution of ∆λ = 0.02 µm and fit using smarter. The data are shown in black, the best-fitting model (Model 1) spectrum is shown in white and blue, and various colors are used to indicate each molecule’s contribution to the model spectrum. The most prominent features are due to CO2 and O3, but a rich diversity of habitability indicators, biosignatures, and technosignatures are present. — astro-ph.EP

The James Webb Space Telescope (JWST) will enable the search for and characterization of terrestrial exoplanet atmospheres in the habitable zone via transmission spectroscopy.

However, relatively little work has been done to use solar system data, where ground truth is known, to validate spectroscopic retrieval codes intended for exoplanet studies, particularly in the limit of high resolution and high signal-to-noise (S/N). In this work, we perform such a validation by analyzing a high S/N empirical transmission spectrum of Earth using a new terrestrial exoplanet atmospheric retrieval model with heritage in Solar System remote sensing and gaseous exoplanet retrievals.

We fit the Earth’s 2-14 um transmission spectrum in low resolution (R=250 at 5 um) and high resolution (R=100,000 at 5 um) under a variety of assumptions about the 1D vertical atmospheric structure. In the limit of noiseless transmission spectra, we find excellent agreement between model and data (deviations < 10%) that enable the robust detection of H2O, CO2, O3, CH4, N2, N2O, NO2, HNO3, CFC-11, and CFC-12 thereby providing compelling support for the detection of habitability, biosignature, and technosignature gases in the atmosphere of the planet using an exoplanet-analog transmission spectrum.

Our retrievals at high spectral resolution show a marked sensitivity to the thermal structure of the atmosphere, trace gas abundances, density-dependent effects, such as collision-induced absorption and refraction, and even hint at 3D spatial effects. However, we used synthetic observations of TRAPPIST-1e to verify that the use of simple 1D vertically homogeneous atmospheric models will likely suffice for JWST observations of terrestrial exoplanets transiting M dwarfs.

Jacob Lustig-Yaeger, Victoria S. Meadows, David Crisp, Michael R. Line, Tyler D. Robinson

Comments: 37 pages, 14 figures, 9 tables. Accepted for publication in PSJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2308.14804 [astro-ph.EP] (or arXiv:2308.14804v1 [astro-ph.EP] for this version)
Submission history
From: Jacob Lustig-Yaeger
[v1] Mon, 28 Aug 2023 18:00:14 UTC (21,760 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) 🖖🏻