부산대학교 도서관

Proxima Centauri b provides an unprecedented opportunity to understand theevolution and nature of terrestrial planets orbiting M dwarfs. Although ProximaCen b orbits within its star's habitable zone, multiple plausible evolutionarypaths could have generated different environments that may or may not behabitable. Here we use 1D coupled climate-photochemical models to generateself-consistent atmospheres for evolutionary scenarios predicted in ourcompanion paper (Barnes et al., 2016). These include high-O2, high-CO2, andmore Earth-like atmospheres, with either oxidizing or reducing compositions. Weshow that these modeled environments can be habitable or uninhabitable atProxima Cen b's position in the habitable zone. We use radiative transfermodels to generate synthetic spectra and thermal phase curves for thesesimulated environments, and instrument models to explore our ability todiscriminate between possible planetary states. These results are applicablenot only to Proxima Cen b, but to other terrestrial planets orbiting M dwarfs.Thermal phase curves may provide the first constraint on the existence of anatmosphere, and JWST observations longward of 7 microns could characterizeatmospheric heat transport and molecular composition. Detection of ocean glintis unlikely with JWST, but may be within the reach of larger aperturetelescopes. Direct imaging spectra may detect O4, which is diagnostic ofmassive water loss and O2 retention, rather than a photosynthesis. Similarly,strong CO2 and CO bands at wavelengths shortward of 2.5 {\mu}m would indicate aCO2-dominated atmosphere. If the planet is habitable and volatile-rich, directimaging will be the best means of detecting habitability. Earth-like planetswith microbial biospheres may be identified by the presence of CH4 and eitherphotosynthetically produced O2 or a hydrocarbon haze layer.