Exoearth study with TMT

摘要

Ground-based optical and infrared telescopes with diameters of 30-meters or greater have theoretical potential to study objects at the contrast levels predicted for reflecting terrestrial planets in orbits within the habitable zone of nearby stars. Despite the corrupting effect of the Earth's turbulent atmosphere, the theoretical limits can be approached through the use of an adaptive optics (AO) system optimized for high contrast operating at near-infrared wavelength. With proper flow-down of functional requirements and contrast-optimized choice of site, the highly segmented Thirty Meter Telescope (TMT) could study scores of nearby star systems, to apparent magnitude 5, for resident terrestrial planets at spectral resolution R = 5 in either visible or near-infrared band, and a few systems, to magnitude 3, at R = 20 in the infrared. Even at low spectral resolution, a wealth of information could be obtained by direct imaging of exoearths, including determination of the presence of an atmosphere, clouds, equilibrium temperature, tidal locking, and the presence of non-Earth-like atmospheric chemistry such as steam lines. Our own atmosphere, however, limits the study of exoearth biological markers, unless these planets have environmental conditions and chemical composition significantly different from our own.