JWST/NIRSpec Transmission Spectroscopy of the Habitable-Zone Exo-Earth TRAPPIST-1g

The James Webb Space Telescope offers the first opportunity to characterize the transmission spectrum of rocky habitable-zone exoplanets with sufficient precision to identify the molecular constituents within their secondary atmospheres. The rocky exo-Earth TRAPPIST-1g is particularly well-suited for this kind of first study because the low stellar insolation can allow for habitable conditions on its surface, while the small host star strongly amplifies the observable spectroscopic transit signature compared to planets orbiting Sun-like stars. Here, we present the first high-precision JWST transmission spectrum of a habitable-zone exo-Earth, the planet TRAPPIST-1g, covering the full range between 0.6-5.3µm, obtained through two JWST transits observations using the NIRSpec PRISM BOTS mode. The sensitivity of these observations is sufficient to detect secondary terrestrial atmospheres of a wide variety of compositions, with molecular bands of CO2, H2O, CH4, NH3, and SO2. The coverage over the entire NIR up to 5.3µm furthermore allows for detecting molecular absorbers even in the presence of high-altitude Titan-like hazes that become more significant less opaque towards long wavelengths. In this talk, we present the results and discuss the prospects of in-depth follow-up studies of TRAPPIST-1g’s atmosphere in future JWST Cycles.