Dr. Rory Barnes (U. Washington)

University of Florida Astronomy Colloquium - Feb. 25th, 2015

Habitability of Planets Orbiting M Dwarfs

Current and future exoplanet surveys favor the discovery of potentially habitable planets around M dwarfs, which can then be spectroscopically characterized by JWST. This observation is so challenging that only ~1 planet is likely to be measured during the mission lifetime. Thus, prioritizing M dwarf planets for follow-up is a crucial step toward the discovery of an inhabited exoplanet. Identifying habitable planets begins with locating the planet's orbit relative to its star's "habitable zone." However, the habitable zone is only a zeroeth order approximation for planetary habitability, i.e rocky worlds with liquid surface water. Many phenomena impact the stability and longevity of surface water, including processes that are negligible on Earth. M dwarfs can cool significantly during their first gigayear, which can strip giant planet atmospheres to reveal a rocky core, or can permanently desiccate terrestrial exoplanets. Tidal torques can circularize orbits, damp obliquities, and lock rotation periods at relatively large values. Tidal heating can be significant, even driving a runaway greenhouse independent of stellar radiation. In more modest cases, tidal heating can significantly alter the thermal cooling of the interior and suppress magnetic field generation, especially in multiplanet systems. Careful modeling of these phenomena can determine the best candidate(s) for transit transmission spectroscopy.