Photoevaporative flows from exoplanet atmospheres: a 3D radiative hydrodynamic parameter study

The photoionization-driven evaporation of planetary atmospheres has emerged as a potentially fundamental process for planets on short-period orbits. While 1D studies have proven the effectiveness of stellar fluxes at altering the atmospheric mass and composition for sub-Jupiter mass planets, there remains much that is uncertain with regard to the larger scale, multidimensional nature of such `planetary wind' flows. In this paper we use a new radiation-hydrodynamic platform to simulate atmospheric evaporative flows. Using the ASTROBEAR adaptive mesh refinement (AMR) multiphysics code in a co-rotating frame centred on the planet, we model the transfer of ionizing photons into the atmosphere, the subsequent launch of the wind and the wind's large-scale evolution subject to tidal and non-inertial forces. We run simulations for planets of 0.263 and 0.07 Jupiter masses and stellar fluxes of 2 × 10¹³ and 2 × 10¹⁴ photons cm^-2 s^-1. Our results reveal new, potentially observable planetary wind flow patterns, including the development, in some cases, of an extended neutral tail lagging behind the planet in its orbit.