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Physics of the atmospheric escape driven by EUV photoionization heating: Classification of the hydrodynamic escape in close-in planets

Published online by Cambridge University Press:  16 August 2023

Hiroto Mitani Open the ORCID record for Hiroto Mitani [Opens in a new window] ,
Riouhei Nakatani  and
Naoki Yoshida
Hiroto Mitani
Affiliation:
Department of Physics, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 email: hiroto.mitani@phys.s.u-tokyo.ac.jp
Riouhei Nakatani
Affiliation:
RIKEN Cluster for Pioneering Research, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
Naoki Yoshida
Affiliation:
Department of Physics, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033 email: hiroto.mitani@phys.s.u-tokyo.ac.jp Kavli Institute for the Physics and Mathematics of the Universe (WPI), UT Institutes for Advanced Study, The University of Tokyo, Kashiwa, Chiba 277-8583, Japan Research Center for the Early Universe, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033
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Abstract

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The intense extreme ultraviolet radiation heats the upper atmosphere of close-in exoplanets and drives the atmospheric escape. The escaping process determines the planetary evolution of close-in planets. The mass loss rate depends on the UV flux at the planet. We introduce the relevant physical quantities which describe the dominant physics in the atmosphere. We find that the equilibrium temperature and the characteristic temperature determine whether the system becomes energy-limited or recombination-limited. We classify the observed close-in planets using the physical conditions. We also find that many of the Lyman-α absorptions detected planets receive intenser flux than the critical flux which can be determined from physical conditions. Our classification method can quantitatively reveal whether the EUV is not strong enough to drive the outflow or the Lyman- α absorption is not detected for some reason (e.g. stellar wind confinement). We also discuss the thermo-chemical structure of hydrodynamic simulations with the relevant physics.

Keywords

hydrodynamicsmethods: numericalplanets and satellites: atmospheresplanets and satellites: physical evolution
Type
Contributed Paper
Information
Proceedings of the International Astronomical Union , Volume 17 , Symposium S370: Winds of Stars and Exoplanets , August 2021 , pp. 155 - 160
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Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
© The Author(s), 2023. Published by Cambridge University Press on behalf of International Astronomical Union

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