Letters to the Editor

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

¹ Laboratoire de Minéralogie et de Cosmochimie du Muséum (LMCM), CNRS & Muséum National d’Histoire Naturelle, UMR 7202, 57 rue Cuvier, 75005 Paris, France
e-mail: ejacquet@mnhn.fr
² CEA, Irfu, SAp, Centre de Saclay, 91191 Gif-sur-Yvette, France
³ UMR AIM, CEA-CNRS-Univ. Paris VII, Centre de Saclay, 91191 Gif-sur-Yvette, France

Received: 10 November 2010
Accepted: 21 December 2010

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 10⁵ 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.