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11/17/16: SO/NOAO Joint Colloquium Series: Evgenya Shkolnik, ASU

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Title: The High-Energy Radiation Environment of Planets around Low-Mass Stars with GALEX, HST, & SPARCS

Abstract:
A planet’s habitability, including atmospheric retention, is strongly dependent on the star’s ultraviolet (UV) emission, which chemically modifies, ionizes, and even erodes the atmosphere over time including the photodissociation of important diagnostic molecules, e.g. H2O, CH4, and CO2. The UV spectral slope of a low-mass star can enhance atmospheric lifetimes, and increase the detectability of biologically generated gases. But, a different slope may lead to the formation of abiotic oxygen and ozone producing a false-positive biosignature for oxygenic photosynthesis. Realistic constraints on the incident UV flux over a planet’s lifetime are necessary to explore the cumulative effects on the evolution, composition, and fate of a HZ planetary atmosphere. The GALEX mission provided a unique data set with which to study the broadband UV emission and variability of many hundreds of M dwarfs in the near-UV and far-UV. With these data these, we have characterize the UV emission and variability of M dwarfs over critical planet formation and evolution time scales to better understand the probable conditions in HZ planetary atmospheres. Upcoming HST UV spectra will allow for the study of individual emission lines and help guide new upper-atmosphere stellar models. In the not-too-distant future, dedicated CubeSats (miniaturized satellites for space research) to monitor M dwarf hosts of transiting exoplanets may provide the best opportunity to measure their UV variability, constrain the probabilities of detecting habitable (and inhabited) planets, and provide the correct context within which to interpret IR transmission and emission spectroscopy of transiting exoplanets.

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