Radial transport of refractory inclusions and their preservation in the dead zone

TL;DR

This paper proposes a model where CAIs are transported outward in the early solar protoplanetary disk via viscous expansion, then preserved in a dead zone, explaining their age range and distribution.

Contribution

It introduces a novel mechanism combining viscous disk expansion and dead zone trapping to explain CAI preservation in the early solar system.

Findings

Outward transport of CAIs occurs within 10^5 years due to disk expansion.

Dead zones trap CAIs, preventing inward drift and diffusion.

This mechanism explains the narrow age range of CAIs.

Abstract

Calcium-aluminum-rich inclusions (CAIs) are the oldest solar system solids known in primitive meteorites (chondrites). They predate the other components by 1-2 Myr, and likely condensed within a short time interval, close to the Sun in the gaseous protoplanetary disk. Their preservation must counterbalance both the sunward drift caused by gas drag and the general inward motion of the entraining gas. We propose that an efficient outward transport of CAIs can be achieved by advection as a result of the viscous expansion of the disk, provided it is initially less than 10 AU in size, which we argue is plausible from both observational and theoretical points of view. Gas drag would stop this outward motion within $10^5$ yr. However, by that time, a magnetically dead zone would have developed as gravitational instabilities fade away, which would trap CAIs for a significant fraction of the disk lifetime because of the reduced advection velocities. The dead zone would also prevent outward diffusion of subsequently condensed CAIs, contributing to their observed narrow age range. This preservation mechanism is independent of the outward transport scenario (before the dead zone formation) and a natural consequence of considering the source of turbulence in accretion disks.