ACCRETION OF JUPITER-MASS PLANETS IN THE LIMIT OF VANISHING VISCOSITY

Abstract

In the core-accretion model the nominal runaway gas-accretion phase brings\nmost planets to multiple Jupiter masses. However, known giant planets are\npredominantly Jupiter-mass bodies. Obtaining longer timescales for gas\naccretion may require using realistic equations of states, or accounting for\nthe dynamics of the circumplanetary disk (CPD) in low-viscosity regime, or\nboth. Here we explore the second way using global, three-dimensional isothermal\nhydrodynamical simulations with 8 levels of nested grids around the planet. In\nour simulations the vertical inflow from the circumstellar disk (CSD) to the\nCPD determines the shape of the CPD and its accretion rate. Even without\nprescribed viscosity Jupiter's mass-doubling time is $\\sim 10^4$ years,\nassuming the planet at 5.2 AU and a Minimum Mass Solar Nebula. However, we show\nthat this high accretion rate is due to resolution-dependent numerical\nviscosity. Furthermore, we consider the scenario of a layered CSD, viscous only\nin its surface layer, and an inviscid CPD. We identify two planet-accretion\nmechanisms that are independent of the viscosity in the CPD: (i) the polar\ninflow -- defined as a part of the vertical inflow with a centrifugal radius\nsmaller than 2 Jupiter-radii and (ii) the torque exerted by the star on the\nCPD. In the limit of zero effective viscosity, these two mechanisms would\nproduce an accretion rate 40 times smaller than in the simulation.\n