Growing planet envelopes in spite of recycling flows

Abstract The hydrodynamic exchange of a protoplanet’s envelope material with the background protoplanetary disk has been proposed as one mechanism to account for the diversity of observed planet envelopes which range in mass fractions of 1~{\%} for super-Earths to 90~{\%} for giants. Here we present 3D radiation-hydrodynamics models of protoplanet envelopes applicable to gas-giant cores at intermediate distances and a subset of close-in super-Earths in hot or low-density disks. We analyze how hydrodynamic mass and energy exchange impact the formation process. Our protoplanet envelope simulations show an exchange of material bringing the outer ≳ 0. 4Rb envelope to steady-state. This exchange provides a continuous source of energy, which acts to increase the observed luminosity beyond that inferred from the binding energy liberated from Kelvin-Helmholtz contraction alone – a finding important for potential protoplanet observations. The inner envelope at ≲ 0. 4Rb remains insulated however – growing in accordance with 1D quasi-static theory. We incorporate these 3D hydrodynamic effects into an extensible 1D framework with a physically motivated three-layer recycling parameterization. Specializing to the case of Jupiter, recycling produces minimal changes to the growth rate with the planet still entering runaway accretion and becoming a gas giant in ∼1 Myr. Even in the inner disk (0. 1 AU), our 1D models suggest that recycling is not so robust and ubiquitous as to stop all cores from becoming giants. At the same time however, this recycling can delay a runaway phase by an order-of-magnitude depending on the inner disk conditions and core mass.