Prompt planetesimal formation beyond the snow line

TL;DR

This paper presents a simple model predicting where planetesimals form beyond the snow line, emphasizing the role of dust drift, metallicity, and disk properties, and suggests formation favors regions outside the snow line for giant planet cores.

Contribution

It introduces an analytic model linking dust growth, drift, and streaming instability to predict planetesimal formation zones beyond the snow line, incorporating turbulence and vapor effects.

Findings

Prompt planetesimal formation requires high particle accretion rates.

Formation results in a broad, massive belt with a sharp outer edge.

Solid enhancement near the snow line is minimal for planetesimal formation.

Abstract

We develop a simple model to predict the radial distribution of planetesimal formation. The model is based on the observed growth of dust to mm-sized particles, which drift radially, pile-up, and form planetesimals where the stopping time and dust-to-gas ratio intersect the allowed region for streaming instability-induced gravitational collapse. Using an approximate analytic treatment, we first show that drifting particles define a track in metallicity--stopping time space whose only substantial dependence is on the disk's angular momentum transport efficiency. Prompt planetesimal formation is feasible for high particle accretion rates (relative to the gas, $\dot{M}_p / \dot{M} > 3 \times 10^{-2}$ for $\alpha = 10^{-2}$), that could only be sustained for a limited period of time. If it is possible, it would lead to the deposition of a broad and massive belt of planetesimals with a sharp outer edge. Including turbulent diffusion and vapor condensation processes numerically, we find that a modest enhancement of solids near the snow line occurs for cm-sized particles, but that this is largely immaterial for planetesimal formation. We note that radial drift couples planetesimal formation across radii in the disk, and suggest that considerations of planetesimal formation favor a model in which the initial deposition of material for giant planet cores occurs well beyond the snow line.