Establishing Dust Rings and Forming Planets Within Them

Abstract

Radio images of protoplanetary disks demonstrate that dust grains tend to organize themselves into rings. These rings may be a consequence of dust trapping within gas pressure maxima wherein the local high dust-to-gas ratio is expected to trigger the formation of planetesimals and eventually planets. We revisit the behavior of dust near gas pressure perturbations enforced by a prescribed Gaussian forcing and by a planet in two-dimensional, shearing box simulations. We show analytically and numerically that when traveling through Gaussian-like gas perturbations, dust grains are expected to clump not at the formal center of the gas pressure bump but at least 1--2 gas scale heights away, so that with the non-zero relative velocities between gas and grains, drag-induced instabilities can remain active. Over time, the dust feedback complicates the gas pressure profile, creating multiple local maxima. These dust rings are long-lived except when forced by a planet whereby particles with Stokes parameter τₛ ≲ 0.05 are advected out of the ring within a few drift timescales. Scaled to the properties of ALMA disks, we find that if a dust clump massive enough to trigger pebble accretion is nucleated in our simulated dust rings, then such a clump would ingest the entire dust ring well within ∼1 Myr. To ensure the survival of the dust rings, we favor a non-planetary origin and typical grain size τₛ < 0.05. Planet-driven rings may still be possible but if so we would expect the orbital distance of the dust rings to be larger for older systems.

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