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Impacts of Climate Variability on the Transmission Spectrum of TRAPPIST-1e

Presentation #102.14 in the session Poster Session.

Published onJun 20, 2022
Impacts of Climate Variability on the Transmission Spectrum of TRAPPIST-1e

With the recent launch of the James Webb Space Telescope (JWST), terrestrial exoplanets will be at the forefront of exoplanetary research. Among those, habitable zone terrestrial exoplanets, particularly planets about M dwarfs such as TRAPPIST-1e, will be observed in a new capacity, as JWST’s NIRSpec instrument will be able to perform high-precision infrared spectroscopic measurements of their atmospheres. TRAPPIST-1e has been previously well-studied as a potential habitable zone “ocean world,” and is commonly used in atmospheric studies of habitable zone M dwarf exoplanets. Throughout its expected twenty year lifetime, JWST is expected to be able to detect strong CO2, CH4, and molecular oxygen signals during transit observations. The CO2-CH4 pair in particular is expected to be a potential biosignature when seen at disequilibrium, which implies a potential biotic reaction. The characteristics of these spectra are dependent upon the atmospheric properties of the planet; cloud cover at higher altitudes can mask transmission signals from lower in the atmosphere and flatten the spectrum, while hotter temperatures and lower mean molecular weight increase the atmospheric scale height, which expands spectral features. Using the ExoCAM GCM and the Planetary Spectrum Generator (PSG), we run simulations for TRAPPIST-1e’s known planetary parameters assuming an optimistic haze-free, tidally locked planet with an aquaplanet surface. We vary atmospheric compositions from 10-4 bar to 1 bar of CO2 in a 1 bar N2 atmosphere, with modern Earth-like CH4 mixing ratios. We investigate the relationship between NIRSpec detection significance of CO2 and H2O and the climatology of TRAPPIST-1e’s atmosphere, namely temperature and cloud top height. We demonstrate that in the optimistic haze-free case, H2O, CO2, and CH4 would be detectable in a 10-1 bar CO2 atmosphere during JWST’s lifespan, using transit spectra observations with NIRSpec/PRISM between 0.5 and 5 microns. We also explore the previously noted temporal variability in spectral feature strength, and its relationship with climatological variability in temperature and cloud cover. This broadly agrees with previous work, which found that H2O clouds would diminish, but not extinguish spectral features in the atmosphere of TRAPPIST-1e. Even in the pessimistic cloudy cases with hazes, JWST may still be able to constrain abundances of potential biosignature pairs such as CO2-CH4 within its lifespan.

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