Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST

Abstract

Nine transiting Earth-sized planets have recently been discovered around nearby late M dwarfs, including the TRAPPIST-1 planets and two planets discovered by the MEarth survey, GJ 1132b and LHS 1140b. These planets are the smallest known planets that may have atmospheres amenable to detection with JWST. We present model thermal emission and transmission spectra for each planet, varying composition and surface pressure of the atmosphere. We base elemental compositions on those of Earth, Titan, and Venus and calculate the molecular compositions assuming chemical equilibrium, which can strongly depend on temperature. Both thermal emission and transmission spectra are sensitive to the atmospheric composition; thermal emission spectra are sensitive to surface pressure and temperature. We predict the observability of each planet's atmosphere with JWST. GJ 1132b and TRAPPIST-1b are excellent targets for emission spectroscopy with JWST/MIRI, requiring fewer than 10 eclipse observations. Emission photometry for TRAPPIST-1c requires 5-15 eclipses; LHS 1140b and TRAPPIST-1d, TRAPPIST-1e, and TRAPPIST-1f, which could possibly have surface liquid water, may be accessible with photometry. Seven of the nine planets are strong candidates for transmission spectroscopy measurements with JWST, though the number of transits required depends strongly on the planets' actual masses. Using the measured masses, fewer than 20 transits are required for a 5σ detection of spectral features for GJ 1132b and six of the TRAPPIST-1 planets. Dedicated campaigns to measure the atmospheres of these nine planets will allow us, for the first time, to probe formation and evolution processes of terrestrial planetary atmospheres beyond our solar system.

TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI): motivations and protocol version 1.0

“…-Habitable case 1 (Hab1): In this case, constituted of a modern Earth-like atmosphere of 1 bar of N 2 and 400 ppm of CO 2 , the dynamical core, the clouds and atmospheric processes are tested together. It is also the most widespread benchmark for habitable planets in the literature (Barstow and Irwin, 2016;Morley et al, 2017;Lincowski et al, 2018).…”

“…OLR and ASR correspond to outgoing longwave radiation (at TOA) and absorbed shortwave radiation (at TOA), respectively, SW and LW correspond to shortwave and longwave, respectively, CF corresponds to cloud fraction and MMR at mass mixing ratio. The main objective of THAI is to highlight how differences in atmospheric profiles produced by each GCM are going to impact the predictions of atmosphere detectability and observational constraints for habitable planet targets such as TRAPPIST-1e (Morley et al, 2017;Fauchez et al, 2019). Therefore, in addition to the parameters of Table 3, we will emphasize the differences between the models in term of the planet's climate and habitability with a particular attention on the cloud coverage.…”

Stratosphere circulation on tidally locked ExoEarths

“…However, infrared spectroscopy mainly probes high atmospheric layers, which would correspond to the stratosphere and mesosphere on Earth (p 0.1 bar or altitudes greater than 20 km, see e.g. Barstow & Irwin (2016); ⋆ E-mail: carone@mpia.de (LC) Kreidberg & Loeb (2016); Morley et al (2017)). To discuss habitability, we have to reliably infer the properties of the underlying troposphere and potentially habitable surface from upper atmosphere composition derived from infrared spectra.…”

Atmospheric compositions and observability of nitrogen-dominated ultra-short-period super-Earths

“…These authors have shown that 1.4 bars of photospheric pressure is needed to explain the derived heat redistribution efficiency value. The profiles are constructed analytically, following a dryadiabatic profile from the surface of 1.4 bars to 0.1 bars and continuing in isothermal fashion until 10 −7 bar (Morley et al 2017;Miguel 2019). This is done using 120 equally spaced log atmospheric layers.…”