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JWST COMPASS: The 3-5 Micron Transmission Spectrum of the Super-Earth L 98-59 c

By Keith Cowing
Status Report
astro-ph.EP
September 13, 2024
Filed under , , , , , , , , , ,
JWST COMPASS: The 3-5 Micron Transmission Spectrum of the Super-Earth L 98-59 c
The compatibility of the combined Eureka! spectrum with a wide range of atmospheric compositions and opaque pressure levels. Colored contours show the σ-confidence to which each model can be ruled out by the data. Model spectra permit an offset between the NRS1 and NRS2 detectors as to best fit the data. Panel (a) considers a grid of atmospheres with compositions between 1× and 1000× solar. Panel (b) explores H2-CO2 atmospheres, while panel (c) concerns H2-H2O atmospheres. For an opaque pressure level of 1 bar, the data confidently (> 3-σ) rules out atmospheres with mean molecular weights ≲ 10 g mol−1 in all cases. Smaller mean molecular weights are allowed by the data for lower opaque pressure levels (e.g., 10−4 bar). — astro-ph.EP

We present a JWST NIRSpec transmission spectrum of the super-Earth exoplanet L 98-59 c. This small (Rp=1.385±0.085R⊕, Mp=2.22±0.26R⊕), warm (Teq=553K) planet resides in a multi-planet system around a nearby, bright (J = 7.933) M3V star.

We find that the transmission spectrum of L 98-59 c is featureless at the precision of our data. We achieve precisions of 22ppm in NIRSpec G395H’s NRS1 detector and 36ppm in the NRS2 detector at a resolution R∼200 (30 pixel wide bins).

At this level of precision, we are able rule out primordial H2-He atmospheres across a range of cloud pressure levels up to at least ∼0.1mbar. By comparison to atmospheric forward models, we also rule out atmospheric metallicities below ∼300× solar at 3σ (or equivalently, atmospheric mean molecular weights below ∼10~g/mol).

We also rule out pure methane atmospheres. The remaining scenarios that are compatible with our data include a planet with no atmosphere at all, or higher mean-molecular weight atmospheres, such as CO2– or H2O-rich atmospheres.

This study adds to a growing body of evidence suggesting that planets ≲1.5R⊕ lack extended atmospheres.

Nicholas Scarsdale, Nicholas Wogan, Hannah R. Wakeford, Nicole L. Wallack, Natasha E. Batalha, Lili Alderson, Artyom Aguichine, Angie Wolfgang, Johanna Teske, Sarah E. Moran, Mercedes Lopez-Morales, James Kirk, Tyler Gordon, Peter Gao, Natalie M. Batalha, Munazza K. Alam, Jea Adams Redai

Comments: 21 Pages, 13 Figures; Accepted to AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2409.07552 [astro-ph.EP] (or arXiv:2409.07552v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2409.07552
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Submission history
From: Nicholas Scarsdale
[v1] Wed, 11 Sep 2024 18:16:06 UTC (7,152 KB)
https://arxiv.org/abs/2409.07552
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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