Protostars and Planets VI, Heidelberg, July 15-20, 2013
The Flow Pattern around Low-Mass Planets
Ormel, Chris (UC Berkeley)
Shi, Ji-Ming (UC Berkeley)
When protoplanets have grown to sizes ∼1000 km, their escape velocity starts to exceed the thermal motions of the nebula gas and an atmosphere forms. However, until the so called critical core mass has been reached (which may be several Earth masses or larger) this atmosphere is in pressure-equilibrium with the nebula gas, which means that it smoothly connects to the nebula flow.
The flow structure around small mass planets is important as it shapes the further evolution of the protoplanet in many ways; it will determine the thermodynamical evolution of the core, the co-orbital torque, circumplanetary disk formation, and the accretion behavior of small particles. Therefore, it
is important to solve for the flow pattern around bodies. As a first step, we have applied several simplifying assumptions (subsonic, 2D, inviscid flow, etc.) to solve for the flow pattern in steady-state. It is found that the boundary between the atmosphere and the nebula gas strongly depends on the value
of the disk headwind (deviation from Keplerian rotation). With increasing headwind the atmosphere decreases in size and also becomes more asymmetrical. Using the derived flow pattern for the gas, trajectories of small solid particles, which experience both gas drag and gravitational forces, are
integrated numerically. Accretion rates for small particles (dust) are found to be low, as they closely follow the gas streamlines, which curl away from the planet. However, pebble-size particles achieve much large accretion rates.
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