Ito, Y;
Ikoma, M;
(2020)
Hydrodynamic Escape of Mineral Atmosphere from Hot Rocky Exoplanet. I. Model Description.
Monthly Notices of the Royal Astronomical Society
10.1093/mnras/staa3962.
(In press).
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Abstract
Recent exoplanet statistics indicate that photo-evaporation has a great impact on the mass and bulk composition of close-in low-mass planets. While there are many studies addressing photo-evaporation of hydrogen-rich or water-rich atmospheres, no detailed investigation regarding rocky vapor atmospheres (or mineral atmospheres) has been conducted. Here, we develop a new 1-D hydrodynamic model of the UV-irradiated mineral atmosphere composed of Na, Mg, O, Si, their ions and electrons, includin molecular diffusion, thermal conduction, photo-/thermo-chemistry, X–ray and UV heating, and radiative line cooling (i.e., the effects of the optical thickness and non-LTE). The focus of this paper is on describing our methodology but presents some new findings. Our hydrodynamic simulations demonstrate that almost all of the incident X-ray and UV energy from the host-star is converted into and lost by the radiative emission of the coolant gas species such as Na, Mg, Mg+, Si2 +, Na3 + and Si3 +. For an Earth-size planet orbiting 0.02 AU around a young solar-type star, we find that the X-ray and UV heating efficiency is as small as 1 × 10−3, which corresponds to 0.3 M⊕/Gyr of the mass loss rate simply integrated over all the directions. Because of such efficient cooling, the photo-evaporation of the mineral atmosphere on hot rocky exoplanets with massesof 1M⊕ is not massive enough to exert a great influence on the planetary mass and bulk composition. This suggests that close-in high-density exoplanets with sizes larger than the Earth radius survive in the high-UV environments.
| Type: | Article |
|---|---|
| Title: | Hydrodynamic Escape of Mineral Atmosphere from Hot Rocky Exoplanet. I. Model Description |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.1093/mnras/staa3962 |
| Publisher version: | https://doi.org/10.1093/mnras/staa3962 |
| Language: | English |
| Additional information: | This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions. |
| Keywords: | planets and satellites: atmospheres, planets and satellites: physical evolution, planets and satellites: terrestrial planets |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10118493 |
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