Turbulent radial mixing in the solar nebula as the source of crystalline silicates in comets

There is much debate about the origin of crystalline silicates in comets. Silicates in the protosolar cloud were likely amorphous, however the temperature of the outer solar nebula was too cold to allow their formation in this region by thermal annealing or direct condensation. This paper investigates the formation of crystalline silicates in the inner hot regions of the solar nebula, and their diffusive transport out to the comet formation zone, using a turbulent evolutionary model of the solar nebula. The model uses time-dependent temperature and surface density profiles generated from the 2-D alpha-disk model of Hersant et al. (2001). It is shown that turbulent diffusion is an efficient process to carry crystalline silicates from inner to outer disk regions within timescales of a few 10(4) yr. The warmest solar nebula models which reproduce the D/H ratios measured in meteorites, comets, Uranus and Neptune (Hersant et al. 2001) provide a mass fraction of crystalline silicates in the Jupiter-Neptune region in agreement with that measured in comet Hale-Bopp.