[27.02] Radial drift, evaporation, and diffusion: enhancement and redistribution of silicates, water, and other condensibles in the nebula

DPS 35th Meeting, 1-6 September 2003
Session 27. Planet and Satellite Origins II: Accretion, Terrestrial Planets
Oral, Chairs: F. Spahn and T. J. Ahrens, Thursday, September 4, 2003, 3:40-5:50pm, DeAnza I-II

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[27.02] Radial drift, evaporation, and diffusion: enhancement and redistribution of silicates, water, and other condensibles in the nebula

J. N. Cuzzi, S. S. Davis (Space Science Division, Ames Research Center), A. R. Dobrovolskis (University of California, Santa Cruz)

We have developed a simple model of global transport of solids in the protoplanetary nebula, including radial drift of large particles and diffusion of small ones. The model has been applied to the formation and redistribution of the Ca-Al rich refractory mineral inclusions (CAIs) found in primitive chondrites. These objects form at much higher temperatures, and appear to be 1-3 million years older than, the dominant (chondrule) components found in the same parent bodies. A widespread concern has been the retention of CAIs for this long against gas-drag-induced radial drift into the sun. We show that outward radial diffusion in a weakly turbulent nebula can overwhelm inward drift, and prevent significant numbers of CAI-size particles from being lost into the sun for times on the order of several Myr. An element of this model is rapid inward radial drift of boulder-sized primitive (carbon-rich) silicate material, more like Halley-dust than CI chondrites in the early days of the nebula. This process can enrich the abundance of silicate and carbon material in the inner nebula, and may provide possible explanations for both chemical and isotopic properties of CAIs. The predicted enhancement of CO relative to water might be of relevance to recent IR astronomical observations of CO in the inner disks of several actively accreting T Tauri stars.

This process has applications to the transport and redistribution of volatiles in general. Depending on the rubble particle size distribution, rapid radial drift of boulder-sized solids can bring more material inwards across a condensation front, to evaporate, than can subsequently be removed by nebula advection or diffusion, until a strong local enhancement is produced which allows diffusive loss to balance the drifting source. Application of this process to enhancement of the abundance of water near the ``ice line" will be discussed. Supported by the Origins of Solar Systems program.

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