Can Ground-based Telescopes Detect The Oxygen 1.27 Micron Absorption Feature as a Biomarker in Exoplanets ?

摘要

The oxygen absorption line imprinted in the scattered light from theEarth-like planets has been considered the most promising metabolic biomarkerof the exo-life. We examine the feasibility of the detection of the 1.27 micronoxygen band from habitable exoplanets, in particular, around late- type starsobserved with a future instrument on a 30 m class ground-based telescope. Weanalyzed the night airglow around 1.27 micron with IRCS/echelle spectrometer onSubaru and found that the strong telluric emission from atmospheric oxygenmolecules declines by an order of magnitude by midnight. By compiling nearbystar catalogs combined with the sky background model, we estimate thedetectability of the oxygen absorption band from an Earth twin, if it exists,around nearby stars. We find that the most dominant source of photon noise forthe oxygen 1.27 micron band detection comes from the night airglow if thecontribution of the stellar PSF halo is suppressed enough to detect the planet.We conclude that the future detectors for which the detection contrast islimited by photon noise can detect the oxygen 1.27 micron absorption band ofthe Earth twins for ~50 candidates of the late type star. This paperdemonstrates the importance of deploying small inner working angle efficientcoronagraph and extreme adaptive optics on extremely large telescopes, andclearly shows that doing so will enable study of potentially habitable planets.