Detectability of biosignatures on LHS 1140 b

Abstract

Context. Terrestrial extrasolar planets around low-mass stars are prime targets when searching for atmospheric biosignatures with current and near-future telescopes. The habitable-zone super-Earth LHS 1140 b could hold a hydrogen-dominated atmosphere, and is an excellent candidate for detecting atmospheric features. Aims. In this study we investigate how the instellation and planetary parameters influence the atmospheric climate, chemistry, and spectral appearance of LHS 1140 b. We study the detectability of selected molecules, in particular potential biosignatures, with the upcoming James Webb Space Telescope (JWST) and Extremely Large Telescope (ELT). Methods. In the first step we used the coupled climate–chemistry model 1D-TERRA to simulate a range of assumed atmospheric chemical compositions dominated by molecular hydrogen (H2) and carbon dioxide (CO2). In addition, we varied the concentrations of methane (CH4) by several orders of magnitude. In the second step we calculated transmission spectra of the simulated atmospheres and compared them to recent transit observations. Finally, we determined the observation time required to detect spectral bands with low-resolution spectroscopy using JWST, and the cross-correlation technique using ELT. Results. In H2-dominated and CH4-rich atmospheres oxygen (O2) has strong chemical sinks, leading to low concentrations of O2 and ozone (O3). The potential biosignatures ammonia (NH3), phosphine (PH3), chloromethane (CH3Cl), and nitrous oxide (N2O) are less sensitive to the concentration of H2, CO2, and CH4 in the atmosphere. In the simulated H2-dominated atmosphere the detection of these gases might be feasible within 20 to 100 observation hours with ELT or JWST when assuming weak extinction by hazes. Conclusions. If further observations of LHS 1140 b suggest a thin, clear, hydrogen-dominated atmosphere, the planet would be one of the best known targets to detect biosignature gases in the atmosphere of a habitable-zone rocky exoplanet with upcoming telescopes.

Detecting Biosignatures in the Atmospheres of Gas Dwarf Planets with the James Webb Space Telescope

“…Hazes can impact spectra and produce flatter transmission spectra similar to clouds (Marley et al 2013;Wunderlich et al 2021). Our gray cloud treatment results in the same behavior as hazes in the near-infrared.…”

“…is the uncertainty. Following Wunderlich et al (2021) and Chouqar et al (2020) we note ammonia features in the near and mid-infrared have other spectral features that overlap and can obscure these feature (Figure 5). For example, the 2.0 μm NH 3 feature overlaps with H 2 0 and H 2 -H 2 features.…”

“…For example, the 2.0 μm NH 3 feature overlaps with H 2 0 and H 2 -H 2 features. In the mid-infrared the 10.3-10.8 μm NH 3 feature overlaps with H 2 -H 2 (Wunderlich et al 2021).…”

“…Differing from petitRADTRANS, which is based on a radiative transfer model, the atmosphere of LHS 1140 b from Wunderlich et al (2021) is built using the radiative-convective photochemistry-climate coupled model, 1D-TERRA. The 1D-TERRA model has inputs the following: P-T profiles, initial compositions, stellar spectrum, and ion-pair production rates.…”

Early Habitability and Crustal Decarbonation of a Stagnant‐Lid Venus

“…absorption may be one of the few observable spectral signatures for favorable rocky exoplanetary targets with current and near-future platforms (e.g., Fauchez et al, 2019;Wunderlich et al, 2021). For this reason, the interpretation of the 2 CO E abundances following a bimodal distribution could be critical to assess exoplanet habitability since other variables relevant for habitability such as the possible presence of additional greenhouse gases are generally more challenging to determine (Fauchez et al, 2019).…”