Photoevaporation from Exoplanet Atmospheres: Understanding the Role of Stellar Winds and Considering Water-rich Atmospheres

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• Laura Harbach (Imperial)
• Tuesday 06 February 2024, 13:00-14:00
• Hoyle Committee Room + ONLINE - Details to be sent by email.

If you have a question about this talk, please contact Dr Emily Sandford.

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The atmospheres of close-in exoplanets are extremely vulnerable to the effects of stellar UV to X-ray radiation. Photoevaporation can significantly alter planetary atmospheres or even strip them entirely, potentially rendering a planet uninhabitable. Understanding how these atmospheres evolve, persist, or fade away remains a fundamental challenge. In this talk, I will discuss two distinct but interconnected areas of photoevaporative research.

Firstly, I will discuss the interaction between the stellar wind and photoevaporating atmospheres. I will present 3D magnetohydrodynamic simulations of the interaction between the stellar wind and the photoevaporating outflow of a planet orbiting an M dwarf. This analysis reveals a diverse range of magnetosphere morphologies and plasma distributions due to the wind-outflow interaction. I consider how these changing morphologies might impact observable hydrogen Lyman-alpha signatures during planetary transits.

In the second part, I will delve into our current understanding of photoevaporation from water-rich atmospheres. Conventional analytic approaches often oversimplify the process, assuming two scenarios: the escape of only lighter hydrogen, or the dragging of oxygen along with escaping hydrogen. These two scenarios lead to two end cases: a planet that has retained its water-rich atmosphere or a planet which has lost its atmosphere, becoming dry and desiccated. I will challenge these oversimplifications by presenting results from a novel 1D multifluid hydrodynamic model of photoevaporation from a water-rich atmosphere, which shows oxygen escape should no longer be described by a simple on/off switch but instead requires careful modelling.

This talk is part of the Exoplanet Seminars series.

This talk is included in these lists:

• Combined External Astrophysics Talks DAMTP
• Cosmology, Astrophysics and General Relativity
• Exoplanet Seminars
• Hoyle Committee Room + ONLINE - Details to be sent by email
• Institute of Astronomy Talk Lists
• LCLU Departmental Talks

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