Exoplanets & Exomoons

A JWST Transmission Spectrum Of A Nearby Earth-sized Exoplanet

By Keith Cowing

Status Report

astro-ph.EP

January 11, 2023

Filed under astro-ph.EP, atmosphere, exoplanet, extrasolar, JWST, LHS 475b, M dwarf, transmission spectrum, Webb Space Telescope

A JWST Transmission Spectrum Of A Nearby Earth-sized Exoplanet — Final, binned spectrum (black points) compared to models (coloured lines). Top: Our data strongly (> 10σ) rule out hydrogen-dominated atmospheres with compositions from 1× – 100× solar metallicity, with reduced-χ 2 s reported in the legend for each model. The blue shaded bar highlights the region detailed in the bottom panel. Bottom: Our data also rule out, though to lower (2–5σ) significance, high mean molecular weight compositions of 1000× solar metallicity or a pure methane atmosphere. We weakly disfavor a pure water atmosphere or an Earth composition atmosphere. The data are consistent with a pure carbon dioxide atmosphere or that of an airless body. Each model is plotted relative to the mean transit depth. — astro-ph.EP

The critical first step in the search for life on exoplanets over the next decade is to determine whether rocky planets transiting small M-dwarf stars possess atmospheres and, if so, what processes sculpt them over time.

Because of its broad wavelength coverage and improved resolution compared to previous methods, spectroscopy with JWST offers a new capability to detect and characterize the atmospheres of Earth-sized, M-dwarf planets.

Here we use JWST to independently validate the discovery of LHS 475b, a warm (586 K), 0.99 Earth-radius exoplanet, interior to the habitable zone, and report a precise 2.9-5.3 um transmission spectrum.

With two transit observations, we rule out primordial hydrogen-dominated and cloudless pure methane atmospheres. Thus far, the featureless transmission spectrum remains consistent with a planet that has a high-altitude cloud deck (similar to Venus), a tenuous atmosphere (similar to Mars), or no appreciable atmosphere at all (akin to Mercury).

There are no signs of stellar contamination due to spots or faculae. Our observations demonstrate that JWST has the requisite sensitivity to constrain the secondary atmospheres of terrestrial exoplanets with absorption features <50 ppm, and that our current atmospheric constraints speak to the nature of the planet itself, rather than instrumental limits.

J. Lustig-Yaeger, G. Fu, E. M. May, K. N. Ortiz Ceballos, S. E. Moran, S. Peacock, K. B. Stevenson, M. López-Morales, R. J. MacDonald, L. C. Mayorga, D. K. Sing, K. S. Sotzen, J. A. Valenti, J. Adams, M. K. Alam, N. E. Batalha, K. A. Bennett, J. Gonzalez-Quiles, J. Kirk, E. Kruse, J. D. Lothringer, Z. Rustamkulov, H. R. Wakeford

Comments: A co-first author paper Lustig-Yaeger and Fu et al., Under review in Nature Astronomy, Comments welcome
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2301.04191 [astro-ph.EP] (or arXiv:2301.04191v1 [astro-ph.EP] for this version)
Submission history
From: Jacob Lustig-Yaeger
[v1] Tue, 10 Jan 2023 20:04:58 UTC (17,492 KB)
https://arxiv.org/abs/2301.04191
Astrobiology

Keith Cowing

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) 🖖🏻

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