Abstract
Abstract Exoplanets orbiting M dwarfs within habitable zones are exposed to stellar environments more extreme than that terrestrial planets experience in our solar system, which can significantly impact the atmospheres of the exoplanets and affect their habitability and sustainability. This study provides the first prediction of hot oxygen corona structure and the associated photochemical loss from a 1 bar CO2-dominated atmosphere of a Venus-like rocky exoplanet, where dissociative recombination of O2 + ions is assumed to be the major source reaction for the escape of neutral O atoms and formation of the hot O corona (or exospheres) as on Mars and Venus. We employ a 3D Monte Carlo code to simulate the exosphere of Proxima Centauri b (PCb) based on the ionosphere simulated by a 3D magnetohydrodynamic model. Our simulation results show that variability of the stellar wind dynamic pressure over one orbital period of PCb does not affect the overall spatial structure of the hot O corona but contributes to the change in the global hot O escape rate that varies by an order of magnitude. The escape increases dramatically when the planet possesses its intrinsic magnetic fields as the ionosphere becomes more extended with the presence of a global magnetic field. The extended hot O corona may lead to a more extended H exosphere through collisions between thermal H and hot O, which exemplifies the importance of considering nonthermal populations in exospheres to interpret future observations.
Highlights
Introduction and MotivationThe processes by which the current status of planetary atmospheres evolved from their earlier conditions are complex
We examined the loss of neutral oxygen atoms from Proxima Centauri b (PCb) via photochemical escape and formation processes of resulting exoplanetary hot atomic coronae or exospheres
For all four conditions considered in this study, the overall structure of the hot O corona shows that the dayside envelope is radially inflated and decreases with increasing distance from the planet
Summary
Introduction and MotivationThe processes by which the current status of planetary atmospheres evolved from their earlier conditions are complex. Loss of atmosphere is one of the ways how a planet balances the energy from its host star absorbed by its atmosphere [Catling and Zahnle, 2009; Lammer et al, 2009]. For an escape to occur, an atmospheric particle must pass through the background atmospheric gases and overcome the planet's gravitational force. Escape processes primarily depend on the composition of an atmosphere, the size and mass of a planet (escape velocity), and the interaction between the host star and the planet. Depending on these characteristics, the dominant escaping gases and the escape processes vary for different planets
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