Recycling of Planetary Proto-Atmospheres

Protoplanets formed by core accretion can become massive enough to accrete gas from the disk they are born in. If the
planetary proto-atmosphere exceeds a critical mass, runaway gas accretion starts and the planetary atmosphere collapses into a gas
giant. In recent years, many close-in super-Earths have been observed which raises the question on how they avoided becoming hot
Jupiters. We investigate the recycling hypothesis as a possible mechanism to avoid the collapse of the atmosphere.
We use three-dimensional radiation-hydrodynamics to simulate the formation of proto-atmosphere in the local frame around
the planet. In post-processing we use tracer particles to calculate the shape of the atmosphere and determine the non-uniform recycling
timescale in a quantitative manner. Our simulations converge to a quasi-steady state where the velocity field of the gas does not change anymore. For the
parameter space explored, a = 0.1 au, m_c ∈ [1, 2, 5, 10] M_Earth, we find that recycling of the atmosphere counteracts the collapse by
preventing the gas from cooling efficiently.