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Arxiv: Reading Between the Lines: Investigating the Ability of JWST to Identify Discerning Features in exoEarth and exoVenus Transmission Spectra Published: 10/2/2023 9:15:29 PM Updated: 10/2/2023 9:15:29 PM

Paper abstract: The success of the Transiting Exoplanet Survey Satellite (TESS) mission hasled to the discovery of an abundance of Venus Zone (VZ) terrestrial planetsthat orbit relatively bright host stars. Atmospheric observations of theseplanets play a crucial role in understanding the evolutionary history ofterrestrial planets, past habitable states, and the divergence of Venus andEarth climates. The transmission spectrum of a Venus-like exoplanet can bedifficult to distinguish from that of an Earth-like exoplanet however, whichcould severely limit what can be learned from studying exoVenuses. In this workwe further investigate differences in transmission between hypotheticalexoEarths and exoVenuses, both with varying amounts of atmospheric carbondioxide (CO_2). The exoEarths and exoVenuses were modelled assuming theyorbit TRAPPIST-1 on the runaway greenhouse boundary. We simulated James WebbSpace Telescope (JWST) Near-Infrared Spectrograph (NIRSpec) PRISM transitobservations of both sets of planets between 0.6-5.2 \mum, and quantified thedetectability of major absorption features in their transmission spectra. TheexoEarth spectra include several large methane (CH_4) features that can bedetected in as few as 6 transits. The CH_4 feature at 3.4 \mum is theoptimal for feature for discerning an exoEarth from an exoVenus since it iseasily detectable and does not overlap with CO_2 features. The sulfur dioxide(SO_2) feature at 4.0 \mum is the best indicator of an exoVenus, but it isdetectable in atmospheres with reduced CO_2 abundance.