Summary and final comments

Abstract

Now that exoplanets are being discovered almost daily through transit, radial velocity, and other techniques, the direction of exoplanet research is changing from discovery to characterization of exoplanet properties. Of particular importance is the existence and composition of exoplanet atmospheres and whether these atmospheres are supportive of life forms on the surfaces of rocky planets. It is now recognized that the emissions of host stars, both their radiation and wind properties, determine whether their exoplanets retain their initial atmospheres and any secondary atmospheres that may later emerge. While there is only one present example of an inhabited planet, there are now more than a handful of possibly habitable rocky exoplanets and the number of such planets will surely increase rapidly in the near future. Although the presence of surface water was the original criterion for the term habitable zone, or more precisely “liquid water habitable zone” (LWHZ), there are additional factors that also determine habitability and many of these factors involve the present and past properties of the host star.