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2020-09-16 Abstract

Title: Rocky Exoplanets in 3D: Influence of Stellar X-ray and UV Flares
 
Speaker:  Howard Chen (Northwestern University)
 
Date: September 16 at 12:20
 
Location: R521, General Building II
 
Abstract: 
Planets orbiting low-mass stars are prime systems for atmospheric characterization due to their low star-to-planet brightness contrast, high transit frequency, and prolonged main sequence stellar lifetimes. However, small stars such as M-dwarfs are highly magnetically active stemming from strong interactions between the stellar photosphere and corona. As a result, the atmospheres of attendant rocky planets in these systems may suffer severe atmospheric escape and chemical modulations by strong X-ray and UV activity. Previous 1D models found that although a single large flare does not substantially impact the ozone layers, repeated secular flaring with the inclusion of highly energetic particles could rapidly destroy the ozone columns of planets with initially Earth-like atmospheres.
In this talk, I present preliminary results of studying the effects of repeated stellar flares on planets orbiting G-, K-, and M-stars using newly developed state-art-of-science 3D models. First, I will briefly present key conclusions from my previous work simulating the atmospheres of rocky planets (https://arxiv.org/abs/1810.12904, https://arxiv.org/abs/1907.10048). Second, I will describe our methodology of this study by coupling an M-dwarf flare model to the 3D atmosphere model. Specifically, I will discuss how we compute realistic flare intensities, frequencies, and durations with a flare toolkit with data drawn from Hubble Space Telescope observational campaigns. I will then present new results in that we find that recurring stellar flares drive planetary atmospheres around K- and M-dwarfs into new chemical equilibria that substantially deviate from their initial pre-flare regimes. This stems from increased M-dwarf proton fluences, changes in the latitudinal extensions of energetic particle deposition due to absence of planetary magnetic fields, and transport via large-scale circulation and wave breaking. Using a newly published radiative transfer model, I will show that chemical compounds such as nitrous oxide (N2O) and nitric acid (HNO3) can be prominently observed throughout the entirety of the planet's orbit in active stellar systems, making these "beacons of life" highly amenable to detection by the James Webb Space Telescope and next-generation instruments.
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