Abstract
Context. Planets that form early enough to be embedded in the circumstellar gas disk accumulate thick atmospheres of nebular gas. Models of these atmospheres need to specify the surface luminosity (i.e. energy loss rate) of the planet. This luminosity is usually associated with a continuous inflow of solid bodies, where the gravitational energy released from these bodies is the source of energy. However, if these bodies release energy in the atmosphere instead of at the surface, this assumption might not be justified. Aims. Our aim is to explore the interactions of infalling planetesimals with primordial atmospheres at an embedded phase of evolution. We investigate effects of atmospheric interaction on the planetesimals (mass loss) and the atmosphere (heating/cooling). Methods. We used atmospheric parameters from a snapshot of time-dependent evolution simulations for embedded atmospheres and simulated purely radial, infall events of siliceous planetesimals in a 1D, explicit code. We implemented energy transfer between friction, radiation transfer by the atmosphere and the body, and thermal ablation; this gives us the possibility to examine the effects on the planetesimals and the atmosphere. Results. We find that a significant amount of gravitational energy is indeed dissipated into the atmosphere, especially for larger planetary cores, which consequently cannot contribute to the atmospheric planetary luminosity. Furthermore, we examine that planetesimal infall events for cores, MC > 2M⊕, which actually result in a local cooling of the atmosphere; this is totally in contradiction with the classical model.
Highlights
At early stages of planet formation, coagulation of dust and ice triggers solidification of bodies within the circumstellar gas disk that is present in the first few Myr
In order to carry out time-dependent simulations for such atmospheres, it is a practical approach to assume hydrostatic and thermal equilibrium (Stökl et al 2016)
Hydrostatic equilibrium is fulfilled during most phases of atmospheric evolution, but thermal equilibrium is much more difficult to maintain
Summary
At early stages of planet formation, coagulation of dust and ice triggers solidification of bodies within the circumstellar gas disk that is present in the first few Myr. Once a planetary core reaches a sufficient mass, its gravitational potential dominates the local enthalpy of the surrounding disk gas and the gravitational accumulation of gas into an atmosphere begins. In order to carry out time-dependent simulations for such atmospheres, it is a practical approach to assume hydrostatic and thermal equilibrium (Stökl et al 2016). The absence of energy sources and sinks corresponds to a radially constant energy flow, and a stationary atmospheric model requires a specification of the luminosity of a planet. The common approach in this instance is to associate the planetary luminosity with gravitational energy released by a flow of accreted planetesimals onto the surface of the protoplanet (Hayashi et al 1979). Despite the plausibility of such a luminosity source, this requires a quantification of the accretion rate and the distributions of planetesimal size and material strength
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