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Space Weather-driven Variations in Lyman alpha Absorption Signatures of Exoplanet Atmospheric Escape: MHD Simulations and the Case of AU Mic b

Presentation #102.280 in the session Poster Session.

Published onJun 20, 2022
Space Weather-driven Variations in Lyman alpha Absorption Signatures of Exoplanet Atmospheric Escape: MHD Simulations and the Case of AU Mic b

We simulate the space environment around the planet AU Microscopii b and the response of the escaping planetary atmospheric to space weather conditions of a time-varying ambient stellar wind and Coronal Mass Ejection (CME). We calculate the Lyman alpha line profile and its variations as a result of the space weather conditions. The synthetic Ly alpha line profile shows stronger absorption in the blue wing around velocities of -100 km/s, as seen from observations. However, our simulations show that: i) the line profile is highly variable and sensitive to the stellar wind conditions; ii) for extreme stellar wind conditions (i.e., CME conditions), the absorption completely disappears; iii) the velocity of the escaping atmosphere is less than -20 km/s in magnitude, suggesting that the higher blue-shift velocity in the Ly alpha profile may be attributed to the stellar wind via sweeping the escaping atmospheric material. We also find that the atmospheric escape, which is driven by a pressure gradient between the dense planetary atmospheric base and space, may be significantly suppressed in the case of close-in exoplanets, and extreme space weather conditions. This is due to the fact that the stellar wind conditions for close-in exoplanets hold a pressure (thermal, dynamic, and magnetic) that is not much smaller, and even greater than that of the top of the exoplanet atmosphere. Our findings show that interpretations of the Ly alpha line profile in the context of exoplanetary atmospheric escape must be supported by information of the varying stellar wind conditions near the planet. Our findings also show that it is imperative for models of exoplanetary hydrodynamic escape to include the stellar wind conditions as the upper boundary condition.

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