Planetary Atmospheric Escape in Their Stellar Environments

Hydrodynamic atmospheric escape plays a key role in the final stages of planetary evolution and has already been observed over a range of planets. For planets undergoing escape, their mass, radius and chemical composition may be significantly altered from their initial formation. Moreover, the stellar environment in certain cases can feedback into the escape rate itself, and almost always will play an important role in determining the large scale wind structure and, in turn, the observations. Currently, simulations of self-consistently launched 3D atmospheric winds in stellar environments are needed to further aid in understanding observations. To this end, we use ATHENA to perform 3D radiative-hydrodynamic simulations of tidally-locked Hydrogen atmospheres bathed in large amounts of ionizing XUV flux in various stellar environments for the low magnetic field case. We provide a step-by-step framework for how each piece of physics precisely affects the overall structure and find three structurally distinct stellar wind regimes: weak, intermediate and strong. Our findings include stellar wind confinement in the form of a bowshock, a prolonged enhanced neutral tail in the shadow of the planet, a wick-shaped shock outside the sonic surface and periodic burping from stellar wind interactions. Furthermore, from resolving the structure of the winds we can perform wavelength dependent synthetic observations, finding various unique transit curves such as extended, double and skewed transits. By understanding the general outflow properties, structural features and transit curves, we hope to guide future observations and demographic surveys.

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