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

TL;DR

This study models the atmospheres of nine nearby Earth-sized exoplanets to assess their detectability with JWST, highlighting promising targets for atmospheric characterization through emission and transmission spectroscopy.

Contribution

It provides detailed spectral models for these planets considering various atmospheric compositions and predicts JWST observation requirements, guiding future atmospheric studies.

Findings

GJ 1132b and TRAPPIST-1b are ideal for emission spectroscopy with fewer than 10 JWST/MIRI eclipses.

Seven planets are strong candidates for transmission spectroscopy, requiring fewer than 20 transits for detection.

Certain planets may have surface liquid water and are accessible with JWST photometry or spectroscopy.

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 5 sigma 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.