  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.

Earth and Planetary Astrophysics