AIOLOS – A multipurpose 1D hydrodynamics code for planetary atmospheres

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