Aiolos- A multi-purpose 1-D hydrodynamics code for planetary atmospheres

We present a new 1-D multi-physics simulation code with use cases intended for, but not limited to, hydrodynamic escapeproblems of planetary atmospheres and planetary accretion models. Our formulation treats an arbitrary number of species asseparated hydrodynamic fields, couples them via friction laws, allows for a multi-band flux-limited radiation transport, and tracksionization fronts in high-energy irradiation bands. Besides coupling various known numerical solution techniques together, weimprove on the numerical stability of deep hydrostatic atmospheres by using a well-balanced scheme, hence preventing unphysicaldriving of atmospheric in- or outflow. We demonstrate the correct physical behaviour of the individual code modules and presenta few simple, new applications, such as a proof-of-concept simulations of combined core-powered mass-loss and UV-drivenatmospheric escape, along with a fully time-dependent core-collapse giant planet simulation. The multi-species nature of thecode opens up the area of exploring simulations that are agnostic towards the dominant atmospheric species and can lead toimplementations of advanced planetary evolution schemes.