Simulated<i>JWST</i>/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\n2-year wide-field survey mission, discovering over a thousand terrestrial,\nsuper-Earth and sub-Neptune-sized exoplanets potentially suitable for follow-up\nobservations using the James Webb Space Telescope (JWST). This work aims to\nunderstand the suitability of anticipated TESS planet discoveries for\natmospheric characterization by JWST's Near InfraRed Imager and Slitless\nSpectrograph (NIRISS) by employing a simulation tool to estimate the\nsignal-to-noise (S/N) achievable in transmission spectroscopy. We applied this\ntool to Monte Carlo predictions of the TESS expected planet yield and then\ncompared the S/N for anticipated TESS discoveries to our estimates of S/N for\n18 known exoplanets. We analyzed the sensitivity of our results to planetary\ncomposition, cloud cover, and presence of an observational noise floor. We\nfound that several hundred anticipated TESS discoveries with radii from 1.5 to\n2.5 times the Earth's radius will produce S/N higher than currently known\nexoplanets in this radius regime, such as K2-3b or K2-3c. In the terrestrial\nplanet regime, we found that only a few anticipated TESS discoveries will\nresult in higher S/N than currently known exoplanets, such as the TRAPPIST-1\nplanets, GJ1132b, and LHS1140b. However, we emphasize that this outcome is\nbased upon Kepler-derived occurrence rates, and that co-planar compact\nmulti-planet systems (e.g., TRAPPIST-1) may be under-represented in the\npredicted TESS planet yield. Finally, we apply our calculations to estimate the\nrequired magnitude of a JWST follow-up program devoted to mapping the\ntransition region between hydrogen-dominated and high molecular weight\natmospheres. We find that a modest observing program of between 60 to 100 hours\nof charged JWST time can define the nature of that transition (e.g., step\nfunction versus a power law).\n