James Webb Space Telescope Feed Post

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

Paper abstract: We present a JWST NIRSpec transmission spectrum of the super-Earth exoplanet L 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 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 H_2-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\times solar at 3\sigma (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 CO_2- or H_2O-rich atmospheres. This study adds to a growing body of evidence suggesting that planets <~1.5R_\oplus lack extended atmospheres.