Factors Affecting Exoplanet Habitability
Habitability is a measure of an environment’s potential to support life, and for exoplanets this is tied to the presence of surface liquid water. Whether or not an exoplanet is able to maintain liquid water on its surface is due to a complex interplay of planetary, stellar, and planetary system characteristics over the planet’s lifetime. Although a planet’s habitability depends critically on the effect of stellar type and planetary semimajor axis on climate balance, many additional factors can also impact habitability. Processes which can modify a habitable planet’s environment include photochemistry; stellar effects on climate balance; atmospheric loss; gravitational interactions with the star, moons, other planets and minor bodies; and galactic phenomena. Here we briefly review characteristics and processes that can impact exoplanet habitability. Ultimately, understanding these processes will enable identification of those exoplanets that are most likely to be habitable and will illuminate global characteristics of habitable planets that may be observable.
This chapter benefited from discussions with Matt Tilley, Eric Agol, Lucianne Walkowicz, Andrew Lincowski, and the attendees of the NASA Astrobiology Institute “Revisiting the Habitable Zone” workshop. This work was supported by the NASA Astrobiology Institute Virtual Planetary Laboratory Lead Team, funded through the NASA Astrobiology Institute under solicitation NNH12ZDA002C and Cooperative Agreement Number NNA13AA93A.
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