2023ApJ...942L...4R

Terrestrial exoplanets such as TRAPPIST-1e will be observed in a new capacity with the JWST/Near Infrared Spectrograph (NIRSpec), which is expected to be able to detect CO₂, CH₄, and O₂ signals, if present, with multiple coadded transit observations. The CO₂-CH₄ pair in particular is theorized to be a potential biosignature when inferred to be in chemical disequilibrium. Here, we simulate TRAPPIST-1e's atmosphere using the ExoCAM general circulation model, assuming an optimistic haze-free, tidally locked planet with an aquaplanet surface, with varying atmospheric compositions from 10^–4 bar to 1 bar of partial CO₂ pressure with 1 bar of background N₂. We investigate cases both with and without a modern Earth-like CH₄ mixing ratio to examine the effect of CO₂ and CH₄ on the transmission spectrum and climate state of the planet. We demonstrate that in the optimistic haze-free cloudy case, H₂O, CO₂, and CH₄ could all be detectable in less than 50 transits within an atmosphere of 1 bar N₂ and 10 mbar CO₂ during JWST's lifespan with NIRSpec as long as the noise floor is ≲10 ppm. We find that in these optimistic cases, JWST may be able to detect potential biosignature pairs such as CO₂-CH₄ in TRAPPIST-1e's atmosphere across a variety of atmospheric CO₂ content, and that temporal climate variability does not significantly affect spectral feature variability for NIRSpec PRISM.