Exoplanetology: Exoplanets & Exomoons

Evidence For A Volcanic Atmosphere On The Sub-Earth L98-59b

By Keith Cowing
Status Report
astro-ph.EP
February 5, 2025
Filed under , , , , , , , , , ,
Evidence For A Volcanic Atmosphere On The Sub-Earth L98-59b
The average Eureka! transmission spectrum of L 98-59 b from the four JWST NIRSpec/G395H transits compared against the 98% SO2 model predicted in Seligman et al. (2024) and a self-consistent photochemical model assuming an SO2 -dominated atmosphere. We also show the best-fit flat line and atmosphere models retrieved with Aurora on the ∆λ = 0.01 µm data and the corresponding 2σ uncertainty bands. All models include an offset between the two detectors. — astro-ph.EP

Assessing the prevalence of atmospheres on rocky planets around M-dwarf stars is a top priority of exoplanet science. High-energy activity from M-dwarfs can destroy the atmospheres of these planets, which could explain the lack of atmosphere detections to date.

Volcanic outgassing has been proposed as a mechanism to replenish the atmospheres of tidally-heated rocky planets. L 98-59 b, a sub-Earth transiting a nearby M dwarf, was recently identified as the most promising exoplanet to detect a volcanic atmosphere. We present the transmission spectrum of L 98-59 b from four transits observed with JWST NIRSpec G395H.

Although the airless model provides an adequate fit to the data based on its χ2, an SO2 atmosphere is preferred by 3.6σ over a flat line in terms of the Bayesian evidence. Such an atmosphere would likely be in a steady state where volcanism balances escape. If so, L 98-59 b must experience at least eight times as much volcanism and tidal heating per unit mass as Io.

If volcanism is driven by runaway melting of the mantle, we predict the existence of a subsurface magma ocean in L 98-59 b extending up to Rp∼60−90%. An SO2-rich volcanic atmosphere on L 98-59 b would be indicative of an oxidized mantle with an oxygen fugacity of fO2>IW+2.7, and it would imply that L 98-59 b must have retained some of its volatile endowment despite its proximity to its star.

Our findings suggest that volcanism may revive secondary atmospheres on tidally heated rocky planets around M-dwarfs.

Aaron Bello-Arufe, Mario Damiano, Katherine A. Bennett, Renyu Hu, Luis Welbanks, Ryan J. MacDonald, Darryl Z. Seligman, David K. Sing, Armen Tokadjian, Apurva Oza, Jeehyun Yang

Comments: Accepted for publication in ApJL, 22 pages, 13 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2501.18680 [astro-ph.EP] (or arXiv:2501.18680v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2501.18680
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Submission history
From: Aaron Bello-Arufe
[v1] Thu, 30 Jan 2025 19:00:00 UTC (8,869 KB)
https://arxiv.org/abs/2501.18680
Astrobiology,

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) 🖖🏻