JWST COMPASS: The 3–5 μm Transmission Spectrum of the Super-Earth L 98-59 c
Nicholas Scarsdale, Nicholas F. Wogan, Hannah R. Wakeford, Nicole L. Wallack, Natasha E. Batalha, Lili Alderson, Artyom Aguichine, Angie Wolfgang, Johanna Teske, Sarah E. Moran, Mercedes López‐Morales, James Kirk, Tyler A. Gordon, Peter Gao, Natalie M. Batalha, Munazza K. Alam, Jéa Adams Redai
Abstract
Abstract We present a JWST Near-InfraRed Spectrograph (NIRSpec) transmission spectrum of the super-Earth exoplanet L 98-59 c. This small ( R p = 1.385 ± 0.085 R ⊕ , M p = 2.22 ± 0.26 R ⊕ ), warm ( T eq = 553 K) planet resides in a multiplanet 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 22 ppm in NIRSpec G395H’s NRS1 detector and 36 ppm in the NRS2 detector at a resolution R ∼ 200 (30 pixel wide bins). At this level of precision, we are able rule out primordial H 2 –He atmospheres across a range of cloud pressure levels up to at least ∼0.1 mbar. By comparison to atmospheric forward models, we also rule out atmospheric metallicities below ∼300× solar at 3 σ (or, equivalently, atmospheric mean molecular weights below ∼10 g mol −1 ). 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 CO 2 - or H 2 O-rich atmospheres. This study adds to a growing body of evidence suggesting that planets ≲1.5 R ⊕ lack extended atmospheres.