ATMOSPHERE EXPANSION AND MASS LOSS OF CLOSE-ORBIT GIANT EXOPLANETS HEATED BY STELLAR XUV. I. MODELING OF HYDRODYNAMIC ESCAPE OF UPPER ATMOSPHERIC MATERIAL

Abstract

In the present series of papers we propose a consistent description of the\nmass loss process. To study the effects of intrinsic magnetic field of a\nclose-orbit giant exoplanet (so-called Hot Jupiter) on the atmospheric material\nescape and formation of planetary inner magnetosphere in a comprehensive way,\nwe start with a hydrodynamic model of an upper atmosphere expansion presented\nin this paper. While considering a simple hydrogen atmosphere model, we focus\non selfconsistent inclusion of the effects of radiative heating and ionization\nof the atmospheric gas with its consequent expansion in the outer space.\nPrimary attention is paid to investigation of the role of specific conditions\nat the inner and outer boundaries of the simulation domain, under which\ndifferent regimes of material escape (free- and restricted- flow) are formed.\nComparative study of different processes, such as XUV heating, material\nionization and recombination, H3+ cooling, adiabatic and Lyman-alpha cooling,\nLyman-alpha reabsorption is performed. We confirm basic consistence of the\noutcomes of our modeling with the results of other hydrodynamic models of\nexpanding planetary atmospheres. In particular, we obtain that under the\ntypical conditions of an orbital distance 0.05 AU around a Sun-type star a Hot\nJupiter plasma envelope may reach maximum temperatures up to ~9000K with a\nhydrodynamic escape speed ~9 km/s resulting in the mass loss rates ~(4-7)*10^10\ng*s . In the range of considered stellar-planetary parameters and XUV fluxes\nthat is close to mass loss in the energy limited case. The inclusion of\nplanetary intrinsic magnetic fields in the model is a subject of the following\nup paper (Paper II).\n