Gap opening by planets in discs with magnetized winds

Abstract

ABSTRACT Planets open deep gaps in protoplanetary discs when their mass exceeds a gap opening mass, Mgap. We use one- and two-dimensional simulations to study planet gap opening in discs with angular momentum transport powered by MHD disc winds. We parametrize the efficiency of the MHD disc wind angular momentum transport through a dimensionless parameter αdw, which is an analogue to the turbulent viscosity αv. We find that magnetized winds are much less efficient in counteracting planet tidal torques than turbulence is. For discs with astrophysically realistic values of αdw, Mgap is always determined by the residual disc turbulence, and is a factor of a few to ten smaller than usually obtained for viscous discs. We introduce a gap opening criterion applicable for any values of αv and αdw that may be useful for planet formation population synthesis. We show that in discs powered by magnetized winds growing planets detach from the disc at planet masses below $\sim 0.1{\, {\rm M}_{\rm J}}$ inside 10 au. This promotes formation of super-Earth planets rather than gas giants in this region, in particular precluding formation of hot jupiters in situ. On larger scales, ALMA gap opening planet candidates may be less massive than currently believed. Future high-resolution observations with instruments such as the extended ALMA, ngVLA, and SKA are likely to show abundant narrow annular features at R < 10 au due to ubiquitous super-Earth planets.