Volume 612, April 2018
|Number of page(s)||10|
|Section||Planets and planetary systems|
|Published online||16 April 2018|
Young planets under extreme UV irradiation
I. Upper atmosphere modelling of the young exoplanet K2-33b
Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6,
2 Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
3 Institute of Computational Modelling, FRC “Krasnoyarsk Science Center” SB RAS, 660036 Krasnoyarsk, Russian Federation
4 Siberian Federal University, 660041 Krasnoyarsk, Russian Federation
5 University of Vienna, Department of Astrophysics, Türkenschanzstrasse 17, 1180 Vienna, Austria
Accepted: 5 December 2017
The K2-33 planetary system hosts one transiting ~5 R⊕ planet orbiting the young M-type host star. The planet’s mass is still unknown, with an estimated upper limit of 5.4 MJ. The extreme youth of the system (<20 Myr) gives the unprecedented opportunity to study the earliest phases of planetary evolution, at a stage when the planet is exposed to an extremely high level of high-energy radiation emitted by the host star. We perform a series of 1D hydrodynamic simulations of the planet’s upper atmosphere considering a range of possible planetary masses, from 2 to 40 M⊕, and equilibrium temperatures, from 850 to 1300 K, to account for internal heating as a result of contraction. We obtain temperature profiles mostly controlled by the planet’s mass, while the equilibrium temperature has a secondary effect. For planetary masses below 7–10 M⊕, the atmosphere is subject to extremely high escape rates, driven by the planet’s weak gravity and high thermal energy, which increase with decreasing mass and/or increasing temperature. For higher masses, the escape is instead driven by the absorption of the high-energy stellar radiation. A rough comparison of the timescales for complete atmospheric escape and age of the system indicates that the planet is more massive than 10 M⊕.
Key words: stars: low mass / stars: late type / planets and satellites: general
© ESO 2018
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