The Potential Habitability of Rocky Planets around Red Dwarfs: Stellar Drivers for Atmospheric Chemistry and Stability

High-energy photons and particles from stars regulate the atmospheric temperature structure and photochemistry on orbiting planets, influencing the long-term stability of planetary atmospheres and the production of potential “biomarker” gases.  Rocky planets orbiting low-mass stars (M dwarfs) will likely be the first exoplanets directly probed for signs of life, however, relatively few observational and theoretical constraints exist on the high-energy irradiance from typical (i.e., weakly active) M dwarf exoplanet host stars.  In this talk, I will describe results from an ongoing panchromatic survey (Chandra/XMM/Hubble/ground) of M and K dwarf exoplanet hosts. The MUSCLES* Treasury Survey combines UV, X-ray, and optical observations, reconstructed Lyman-alpha and EUV (10-90 nm) radiation, and next-generation stellar atmosphere models to provide realistic inputs for modeling the stability and climate on potentially habitable planets around red dwarfs. I will present an overview of the project and focus on three main results – 1) the evolution of the high-energy spectral energy distribution as a star’s habitable zone moves inward from 1 to 0.1 AU, including implications for the possible abiotic production of the suggested biomarkers O2 and O3, 2) new estimates of the high-energy particle fluxes (from CMEs/SEPs) from these stars based on solar UV flare/particle flux measurements, and 3) characterization of the high-energy variability on active and inactive M dwarfs, with an emphasis on the potential for these impulsive events to drive large-scale atmospheric mass loss.  I will conclude by presenting a short summary of our prospects to complete the stellar census at EUV wavelengths and spectroscopically characterize the atmospheres of potentially inhabited planets around M dwarfs in the next ~20 years.      * Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems 

Kevin France
University of Colorado
KIAA-PKU Auditorium
Gregory Herczeg
Thursday, June 13, 2019 - 4:00pm to 5:00pm