Grid of upper atmosphere models for 1–40 M_⊕ planets: application to CoRoT-7 b and HD 219134 b,c

Abstract

There is growing observational and theoretical evidence suggesting that atmospheric escape is a key driver of planetary evolution. Commonly, planetary evolution models employ simple analytic formulae (e.g., energy limited escape) that are often inaccurate, and more detailed physical models of atmospheric loss usually only give snapshots of an atmosphere's structure and are difficult to use for evolutionary studies. To overcome this problem, we upgrade and employ an already existing upper atmosphere hydrodynamic code to produce a large grid of about 7000 models covering planets with masses 1 -39 M ⊕ with hydrogen-dominated atmospheres and orbiting late-type stars. The modelled planets have equilibrium temperatures ranging between 300 and 2000 K. For each considered stellar mass, we account for three different values of the high-energy stellar flux (i.e., low, moderate, and high activity). For each computed model, we derive the atmospheric temperature, number density, bulk velocity, X-ray and EUV (XUV) volume heating rates, and abundance of the considered species as a function of distance from the planetary center. From these quantities, we estimate the positions of the maximum dissociation and ionisation, the mass-loss rate, and the effective radius of the XUV absorption. We show that our results are in good agreement with previously published studies employing similar codes. We further present an interpolation routine capable to extract the modelling output parameters for any planet lying within the grid boundaries. We use the grid to identify the connection between the system parameters and the resulting atmospheric properties. We finally apply the grid and the interpolation routine to estimate atmospheric evolutionary tracks for the close-in, high-density planets CoRoT-7 b and HD219134 b,c. Assuming the planets ever accreted primary, hydrogen-dominated atmospheres, we find that the three planets must have lost them within a few Myr.

Testing exoplanet evaporation with multitransiting systems

“…However, the model can equally be applied to any mass-loss model, for example detailed numerical radiation-hydrodynamic simulations (e.g. Owen & Jackson 2012;Kubyshkina et al 2018). In-fact finding planetary systems that are inconsistent with our test may point, not to errors in the underlying photoevaporation scenario, but rather errors in the mass-loss efficiency.…”

Hydrodynamic Escape of Water Vapor Atmospheres near Very Active Stars

“…Thermal escape mechanisms include hydrodynamic escape, which takes place when the upper atmosphere is heated to such a temperature that the thermal pressure causes it to accelerate away from the planet at speeds exceeding the escape velocity. This can happen without any outside influences for very low-mass planets (Stökl et al 2015), in response to the star's bolometric radiation for planets on short period orbits (Owen & Wu 2016), or most notably in response to the star's X-ray and ultraviolet emission for planets orbiting active stars (Tian et al 2005;Erkaev et al 2016;Kubyshkina et al 2018). Heating can also take place due to other mechanisms, mostly in response to the star's wind (Cohen et al 2014;Lichtenegger et al 2016).…”

Close-in Sub-Neptunes Reveal the Past Rotation History of Their Host Stars: Atmospheric Evolution of Planets in the HD 3167 and K2-32 Planetary Systems

“…Here, we present a framework, based on mass-loss rates extracted from hydrodynamic simulations (Kubyshkina et al 2018b), enabling the modeling of the atmospheric evolution of super-Earths and sub-Neptunes that we apply to the HD3167 and K2-32 planetary systems. Section 2 summarises the algorithms and tools employed to compute the planetary atmospheric evolutionary tracks.…”