Imaging and Characterizing nearby habitable Exoplanets: Will it happen before you retire ?
Olivier Guyon



Directly imaging rocky planets in the habitable zones of nearby stars is key to characterizing their atmospheres and surfaces. Spectra may contain biomarkers - molecular species that reveal biological activity. Obtaining such measurements is however extremely challenging, due to the large contrast and small angular separation between potentially habitable planets and their host stars. Current high contrast imaging systems can detect strong thermal emission from young giant planets, but their performance is still far from catching reflected light from a habitable planet. Major technological breakthrough are required in coronagraphy (optical cancellation of starlight), wavefront control and image processing. Two complementary approaches are emerging: (1) space telescopes, free of the constraints imposed by atmospheric turbulence, can reach the contrast required to image Earth-like planets around Sun-like stars, and (2) 30m-class ground-based telescopes operating in near-IR, offer the angular resolution required to image habitable planets around M-type stars. I will describe recent major technology advances that bring us closer to imaging habitable planets from ground and space, and future projects that will make use of these technologies. While ground and space project aimed at imaging a significant number of habitable exoplanets remain two to three decades away, technology precursor missions/projects and short-term opportunities to image "low-hanging fruits" exist. From space, the NASA-led 2.4m Wide-Field Infrared Survey Telescope (WFIRST) will include a coronagraph instrument that validates key technologies for future more ambitious missions. A small to moderate size space telescope optimized for high contrast imaging could also image Earth-like planets around the few nearest Sun-like stars. From the ground, a high contrast imaging instrument could be deployed on 30-m class telescopes to image habitable planets around nearby M-type stars. The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument, currently in operation on a 8-m telescope, is evolving to become capable of imaging and characterizing habitable planets around the nearest M-type stars on the Thirty Meter Telescope (TMT).