Title: Simulated JWST/NIRISS Transit Spectroscopy of Anticipated TESS Planets Compared to Select Discoveries from Space-Based and Ground-Based Surveys,
Abstract: The Transiting Exoplanet Survey Satellite (TESS) will embark in 2018 on a
2-year wide-field survey mission, discovering over a thousand terrestrial,
super-Earth and sub-Neptune-sized exoplanets potentially suitable for follow-up
observations using the James Webb Space Telescope (JWST). This work aims to
understand the suitability of anticipated TESS planet discoveries for
atmospheric characterization by JWST's Near InfraRed Imager and Slitless
Spectrograph (NIRISS) by employing a simulation tool to estimate the
signal-to-noise (S/N) achievable in transmission spectroscopy. We applied this
tool to Monte Carlo predictions of the TESS expected planet yield and then
compared the S/N for anticipated TESS discoveries to our estimates of S/N for
18 known exoplanets. We analyzed the sensitivity of our results to planetary
composition, cloud cover, and presence of an observational noise floor. We
found that several hundred anticipated TESS discoveries with radii from 1.5 to
2.5 times the Earth's radius will produce S/N higher than currently known
exoplanets in this radius regime, such as K2-3b or K2-3c. In the terrestrial
planet regime, we found that only a few anticipated TESS discoveries will
result in higher S/N than currently known exoplanets, such as the TRAPPIST-1
planets, GJ1132b, and LHS1140b. However, we emphasize that this outcome is
based upon Kepler-derived occurrence rates, and that co-planar compact
multi-planet systems (e.g., TRAPPIST-1) may be under-represented in the
predicted TESS planet yield. Finally, we apply our calculations to estimate the
required magnitude of a JWST follow-up program devoted to mapping the
transition region between hydrogen-dominated and high molecular weight
atmospheres. We find that a modest observing program of between 60 to 100 hours
of charged JWST time can define the nature of that transition (e.g., step
function versus a power law).