Gap opening by planets in discs with magnetised winds

Abstract

Planets open deep gaps in protoplanetary discs when their mass exceeds a gap opening mass, $M_{\mathrm{gap}}$. We use one- and two-dimensional simulations to study planet gap opening in discs with angular momentum transport powered by MHD disc winds. We parameterise the efficiency of the MHD disc wind angular momentum transport through a dimensionless parameter ${\alpha }_{\mathrm{dw}}$, which is an analogue to the turbulent viscosity ${\alpha }_{\mathrm{v}}$. We find that magnetised winds are much less efficient in counteracting planet tidal torques than turbulence is. For discs with astrophysically realistic values of ${\alpha }_{\mathrm{dw}}$, $M_{\mathrm{gap}}$ 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 ${\alpha }_{\mathrm{v}}$ and ${\alpha }_{\mathrm{dw}}$ that may be useful for planet formation population synthesis. We show that in discs powered by magnetised winds, growing planets detach from the disc at planet masses below $\sim 0.1M_{\mathrm{Jup}}$ 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.

14 pages, 9 figures, accepted to MNRAS

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• Three-dimensional Global Simulations of Type-II Planet-disk Interaction with a Magnetized Disk Wind: I. Magnetic Flux Concentration and Gap Properties
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• Distinguishing Magnetized Disc Winds from Turbulent Viscosity through Substructure Morphology in Planet-forming Discs
• Magnetic disk winds in protoplanetary disks: Description of the model and impact on global disk evolution
• Using planet migration and dust drift to weigh protoplanetary discs
• The interplay between forming planets and photoevaporating discs II: Wind-driven gas redistribution
• exoALMA XXIII. Estimating Disk and Planet Properties from Dust Morphologies with DBNets2.0