Discovery and Characterization of Transiting SuperEarths Using an All-Sky Transit Survey and Follow-up by the James Webb Space Telescope

摘要

Doppler and transit surveys are finding extrasolar planets of ever smallermass and radius, and are now sampling the domain of superEarths (1-3 Earthradii). Recent results from the Doppler surveys suggest that discovery of atransiting superEarth in the habitable zone of a lower main sequence star maybe possible. We evaluate the prospects for an all-sky transit survey targetedto the brightest stars, that would find the most favorable cases forphotometric and spectroscopic characterization using the James Webb SpaceTelescope (JWST). We use the proposed Transiting Exoplanet Survey Satellite(TESS) as representative of an all-sky survey. We couple the simulated TESSyield to a sensitivity model for the MIRI and NIRSpec instruments on JWST. Wefocus on the TESS planets with radii between Earth and Neptune. Our simulationsconsider secondary eclipse filter photometry using JWST/MIRI, comparing the 11-and 15-micron bands to measure CO2 absorption in superEarths, as well asJWST/NIRSpec spectroscopy of water absorption from 1.7-3.0 microns, and CO2absorption at 4.3-microns. We project that TESS will discover about eightnearby habitable transiting superEarths. The principal sources of uncertaintyin the prospects for JWST characterization of habitable superEarths aresuperEarth frequency and the nature of superEarth atmospheres. Based on ourestimates of these uncertainties, we project that JWST will be able to measurethe temperature, and identify molecular absorptions (water, CO2) in one to fournearby habitable TESS superEarths.