Two-Dimensional Transport of Solids in Viscous Protoplanetary Disks

TL;DR

This study models the two-dimensional transport of solids in viscous protoplanetary disks, revealing how particle size and disk evolution stage influence inward and outward material movement, affecting disk composition and mineral crystallinity.

Contribution

It provides a detailed analysis of solid transport mechanisms in 2D viscous disks, highlighting the impact of disk evolution on material distribution and mineral processing.

Findings

Outward flows can transport solids up to CAI size, increasing silicate crystallinity to 40%.

Inward flows along the surface rapidly move small dust from outer to inner disk.

Large-scale flows prevent complete mixing, allowing compositional gradients to persist for a million years.

Abstract

Large-scale radial transport of solids appears to be a fundamental consequence of protoplanetary disk evolution based on the presence of high temperature minerals in comets and the outer regions of protoplanetary disks around other stars. Further, inward transport of solids from the outer regions of the solar nebula has been postulated to be the manner in which short-lived radionuclides were introduced to the terrestrial planet region and the cause of the variations in oxygen isotope ratios seen in primitive materials. Here, both outward and inward transport of solids are investigated in the context of a two-dimensional, viscously evolving protoplanetary disk. The dynamics of solids are investigated to determine how they depend on particle size and the particular stage of protoplanetary disk evolution, corresponding to different rates of mass transport. It is found that the outward flows that arise around the disk midplane of a protoplanetary disk aid in the outward transport of solids up to the size of CAIs and can increase the crystallinity fraction of silicate dust at 10 AU around a solar mass star to as much as $\sim$40% in the case of rapidly evolving disks, decreasing as the accretion rate onto the star slows. High velocity, inward flows along the disk surface aid in the rapid transport of solids from the outer disk to the inner disk, particularly for small dust. Despite the diffusion that occurs throughout the disk, the large-scale, meridonal flows associated with mass transport prevent complete homogenization of the disk, allowing compositional gradients to develop that vary in intensity for a timescale of one million years.