General Circulation Model Constraints on the Detectability of the CO<sub>2</sub>-CH<sub>4</sub> Biosignature Pair on TRAPPIST-1e with JWST
Yoav Rotman, Thaddeus D. Komacek, Gerónimo Villanueva, Thomas J. Fauchez, Erin May
Abstract
Abstract 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 CO 2 , CH 4 , and O 2 signals, if present, with multiple coadded transit observations. The CO 2 -CH 4 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 CO 2 pressure with 1 bar of background N 2 . We investigate cases both with and without a modern Earth-like CH 4 mixing ratio to examine the effect of CO 2 and CH 4 on the transmission spectrum and climate state of the planet. We demonstrate that in the optimistic haze-free cloudy case, H 2 O, CO 2 , and CH 4 could all be detectable in less than 50 transits within an atmosphere of 1 bar N 2 and 10 mbar CO 2 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 CO 2 -CH 4 in TRAPPIST-1e’s atmosphere across a variety of atmospheric CO 2 content, and that temporal climate variability does not significantly affect spectral feature variability for NIRSpec PRISM.