James Webb Space Telescope Feed Post

Arxiv: JWST COMPASS: The 3-5 Micron Transmission Spectrum of the Super-Earth L 98-59 c Published: 9/11/2024 9:16:06 PM Updated: 9/11/2024 9:16:06 PM

Paper abstract: We present a JWST NIRSpec transmission spectrum of the super-Earth exoplanetL 98-59 c. This small (R_p=1.385\pm0.085R_\oplus,M_p=2.22\pm0.26R_\oplus), warm (T_\textrm{eq}=553K) planet resides in amulti-planet system around a nearby, bright (J = 7.933) M3V star. We find thatthe transmission spectrum of L 98-59 c is featureless at the precision of ourdata. We achieve precisions of 22ppm in NIRSpec G395H's NRS1 detector and 36ppmin the NRS2 detector at a resolution R~200 (30 pixel wide bins). At thislevel of precision, we are able rule out primordial H_2-He atmospheres acrossa range of cloud pressure levels up to at least ~0.1mbar. By comparison toatmospheric forward models, we also rule out atmospheric metallicities below~300\times solar at 3\sigma (or equivalently, atmospheric meanmolecular weights below ~10~g/mol). We also rule out pure methaneatmospheres. The remaining scenarios that are compatible with our data includea planet with no atmosphere at all, or higher mean-molecular weightatmospheres, such as CO_2- or H_2O-rich atmospheres. This study adds to agrowing body of evidence suggesting that planets <~1.5R_\oplus lackextended atmospheres.