Direct Detection and Characterization of Exoplanetary Atmospheres: Haze, Molecules, and Biosignatures
Svetlana Berdyugina



Polarimetry is a powerful technique for detecting directly exoplanetary atmospheres and probing their geometry, chemistry, and thermodynamics. The light scattered in the planetary atmosphere is linearly polarized perpendicular to the scattering plane. In general, when the planet revolves around the parent star, the scattering angle changes and the Stokes parameters vary. Therefore, the observed polarization variability exhibits the orbital period of the planet and reveal the inclination, eccentricity, and orientation of the orbit as well as the nature of scattering particles in the planetary atmosphere. Recently, we have started a polarimetric survey of nearby planetary systems with hot Jupiters closely orbiting their host stars. We found some inflated and highly reflective hot Jupiters with albedo defined by Rayleigh scattering on, most probably, condensates in high altitude haze or clouds. The scattering results in the blue shine similar to Neptune. While improving the sensitivity of our astronomical polarimetric measurements, we go on identifying biological polarization effects, e.g., selective light absorption or scattering by biogenic molecules. This helps to enhance the reliability of other biomarkers for distant detection of life which can be contaminated by non-biological sources. We have started a laboratory study of reflected light polarization from various terrestrial plants and non-biological samples (rocks and sands). We use these measured reflection spectra to synthesize polarized spectra of Earth-like planets with various contributions from the land, photosynthetic organisms, ocean, atmosphere, and clouds. We estimate the required photometric and polarimetric sensitivity to detect such planets in habitable zones of nearby stars.