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Using Lyman-⍺ transits to constrain models of atmospheric escape

Presentation #627.16 in the session Planetary Atmospheres - Theory.

Published onApr 03, 2024
Using Lyman-⍺ transits to constrain models of atmospheric escape

Atmospheric escape plays a significant role in the evolution of close-in small exoplanets. These planets experience a large amount of UV irradiation which heats their upper atmosphere and drives mass loss in the form of a hydrodynamic wind. Lyman-⍺ transits provide an opportunity to directly test escape models, however translating observations into constraints on the mass loss rate of the planet is challenging as the outflow and its interaction with the circumstellar environment must be modelled in 3D. We present a semi-analytic model of the outflow, tested against 3D hydrodynamics simulations, which we use to perform synthetic Lyman-⍺ transits as a function of planetary and system properties. We use this model to perform retrievals of outflow properties on Lyman-⍺ transit observations of a system with two sub-Neptunes. The retrieved mass loss rates and outflow velocities are consistent with both planets consisting of a rocky core with an extended hydrogen/helium envelope rather than a water rich interior.

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