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With hundreds of exoplanets detected, it is necessary to revisit giantplanets accretion models to explain their mass distribution. In particular,formation of sub-jovian planets remains unclear, given the short timescale forthe runaway accretion of massive atmospheres. However, gas needs to passthrough a circum-planetary disc. If the latter has a low viscosity (as expectedif planets form in "dead zones"), it might act as a bottleneck for gasaccretion. We investigate what the minimum accretion rate is for a planet underthe limit assumption that the circum-planetary disc is totally inviscid, andthe transport of angular momentum occurs solely because of the gravitationalperturbations from the star. To estimate the accretion rate, we present asteady-state model of an inviscid circum-planetary disc, with vertical gasinflow and external torque from the star. Hydrodynamical simulations of acircum-planetary disc were conducted in 2D, in a planetocentric frame, with thestar as an external perturber in order to measure the torque exerted by thestar on the disc. The disc shows a two-armed spiral wave caused by stellartides, propagating all the way in from the outer edge of the disc towards theplanet. The stellar torque is small and corresponds to a doubling time for aJupiter mass planet of the order of 5 Myrs. Given the limit assumptions, thisis clearly a lower bound of the real accretion rate. This result shows that gasaccretion onto a giant planet can be regulated by circum-planetary discs. Thissuggests that the diversity of masses of extra-solar planets may be the resultof different viscosities in these discs.

Circum-planetary discs as bottlenecks for gas accretion onto giant planets