James Webb Space Telescope Feed Post

Arxiv: Promise and Peril: Stellar Contamination and Strict Limits on the Atmosphere Composition of TRAPPIST-1c from JWST NIRISS Transmission Spectra Published: 9/28/2024 3:34:10 PM Updated: 9/28/2024 3:34:10 PM

Paper abstract: Attempts to probe the atmospheres of rocky planets around M dwarfs presentboth promise and peril. While their favorable planet-to-star radius ratiosenable searches for even thin secondary atmospheres, their high activity levelsand high-energy outputs threaten atmosphere survival. Here, we present the0.6--2.85\mum transmission spectrum of the 1.1 Earth-radius, ~340K rockyplanet TRAPPIST-1c obtained over two JWST NIRISS/SOSS transit observations.Each of the two spectra displays 100--500 ppm signatures of stellarcontamination. Despite being separated by 367 days, the retrieved spot andfaculae properties are consistent between the two visits, resulting in nearlyidentical transmission spectra. Jointly retrieving for stellar contaminationand a planetary atmosphere rules out with high confidence (>3-\sigma) notonly clear hydrogen-dominated atmospheres, but even thin, 1-bar high-meanmolecular weight atmospheres rich in H_2O, NH_3, or CO (at the 2-\sigmalevel). We find that the only atmosphere scenarios which our spectrum cannotrule out are CH_4- or CO_2-rich atmospheres, which are both unlikely to beretained when considering the photodestruction of CH_4 and the susceptibilityof even a CO_2-rich atmosphere to escape given the cumulative high-energyirradiation experienced by the planet. Our results further stress theimportance of robustly accounting for stellar contamination when analyzing JWSTobservations of exo-Earths around M dwarfs, as well as the need forhigh-fidelity stellar models to search for the potential signals of thinsecondary atmospheres.