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Hot Molecules in Exoplanets and Inner Disks

Final Report Summary - HOTMOL (Hot Molecules in Exoplanets and Inner Disks)

Understanding the nature and distribution of habitable environments in the Universe is one of the fundamental goals of modern astrophysics. For the life we know, liquid water on the planetary surface is a prerequisite. However, a direct detection of liquid water on exoplanets, and especially on a potentially habitable Earth-size planet, is not yet possible. The existence of water almost certainly implies the presence of atmospheric water vapour which must evaporate under stellar irradiation from a cloud deck or from the surface, together with other related molecules. Therefore, devising sensitive methods to detect hot molecules on exoplanets is of high importance.
This project has developed a variety of exploratory theoretical and observational tools based on precision spectropolarimetry for detecting water vapour and other hot molecules in exoplanets and in the inner part of protoplanetary disks. As a “double differential” technique, spectropolarimetry has enormous advantages for dynamic range problems, like detection of weak line signals against a large stellar background and exploration at scales beyond the angular resolution of telescopes, which are crucial for both exoplanets and inner disks. Direct detection of polarized spectral lines enables recovering precise orbits of exoplanets (including non-transiting systems) and evaluating their masses as well as potentially their magnetic fields.
We have created new theoretical tools which help improve our understanding which fraction of planets acquires water and how planet formation influences their habitability. These include simulations of molecular polarization from exoplanets and protoplanets, inversions of photometric and polarimetric observations of exoplanets, molecule and condensate formation in planetary atmospheres, multiple scattering in stellar and planetary atmospheres, stellar limb polarization during planetary transits, effect of starspots on transit photometry and polarization. These components combined represent the most advanced tool ever developed for studying exoplanetary atmospheres using polarization. First applied to hot Jupiters the developed tools will create a firm foundation for future exploration of Earth-like planets with larger telescopes. We have also obtained laboratory polarized spectra of biological and non-biological samples and have modeled spectra of Earth-like planets with different coverages by ocean, deserts, various organisms with photosynthetic molecules. The developed tools are made available to the community through the project webpage