Water Ice Cloud Variability & Multi-Epoch Transmission Spectra of TRAPPIST-1e

TL;DR

This study investigates how patchy ice cloud variability in the atmospheres of TRAPPIST-1e could impact the accuracy of atmospheric composition measurements with JWST, finding that such variability does not significantly bias retrievals.

Contribution

It demonstrates that limb cloud variability in TRAPPIST-1e's atmosphere does not substantially affect multi-epoch spectral retrievals of atmospheric abundances.

Findings

Variable cloud cover does not bias abundance retrievals.

Simulated JWST observations can reliably characterize atmospheres.

Multi-epoch observations mitigate cloud variability effects.

Abstract

The precise characterization of terrestrial atmospheres with the James Webb Space Telescope (JWST) is one of the utmost goals of exoplanet astronomy in the next decade. With JWST's impending launch, it is crucial we are well prepared to understand the subtleties of terrestrial atmospheres - particularly ones we may have not needed to consider before due to instrumentation limitations. In this work we show that patchy ice cloud variability is present in the upper atmospheres of M-dwarf terrestrial planets, particularly along the limbs. Here we test whether these variable clouds will introduce unexpected biases in the multi-epoch observations necessary to constrain atmospheric abundances. Using 3D ExoCAM general circulation models (GCMs) of TRAPPIST-1e, we simulate five different climates with varying pCO$_2$ to explore the strength of this variability. These models are post-processed using NASA Goddard's Planetary Spectrum Generator (PSG) and PandExo to generate simulated observations with JWST's NIRSpec PRISM mode at 365 different temporal outputs from each climate. Assuming the need for 10 transits of TRAPPIST-1e to detect molecular features at great confidence, we then use CHIMERA to retrieve on several randomly selected weighted averages of our simulated observations to explore the effect of multi-epoch observations with variable cloud cover along the limb on retrieved abundances. We find that the variable spectra do not affect retrieved abundances at detectable levels for our sample of TRAPPIST-1e models.