Title: 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 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.