A 2D dust chemistry of the inner Solar Nebula

The chemical composition of the dust in the inner layers of protoplanetary discs is unknown since infrared observation only probe the chemistry of the thin surface layer of discs. Given that planets formation occurs in the midplane, direct important information from the bulk chemistry of the disc is missing, and modelling is required. We compute for the first time the 2D chemical distribution of condensates in the inner Solar Nebula using a thermodynamic equilibrium model, and derive timescales for vertical settling and radial migration of the dust to predict the chemical evolution of the dust. We find two enstatite-rich zones within 1 AU from the protosun: a band ∼0.1 AU thick in the upper layer of the disc interior to 0.8 AU, and in the disc midplane out to ∼0.4 AU. Our results are consistent with infrared observation of protoplanetary disc which show emission of enstatite-rich dust arising from the inner warmer surface of the disc. The inner midplane of the disc is a chemically diverse zone in which enstatite-rich dust coexists with sulfides and unprocessed material. Our finding of two enstatite-rich zones in the disc supports recent evidence that Mercury and enstatite chondrites shared a bulk material with similar composition. The derived timescales for vertical settling suggest that dust can be chemically sorted in the hotter, inner surface of the disc leading to fractionated Mg-Fe-poor gas which can produce enstatite-rich dust. We suggest that the migration of enstatite-rich grains toward the midplane and-or condensation after gas fractionation may account for the formation of the bulk material which then formed the EL (low-Fe) chondrites.