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Several lines of evidence suggest that fine silicate crystals observed inprimitive meteorite and interplanetary dust particles (IDPs) nucleated in asupersaturated silicate vapor followed by crystalline growth. We investigatedevaporation of $\mu$m-sized silicate particles heated by a bow shock producedby a planetesimal orbiting in the gas in the early solar nebula andcondensation of crystalline silicate from the vapor thus produced. Ournumerical simulation of shock-wave heating showed that these {\mu}m-sizedparticles evaporated almost completely when the bow shock is strong enough tocause melting of chondrule precursor dust particles. We found that the silicatevapor cools very rapidly with expansion into the ambient unshocked nebularregion; the cooling rate is estimated, for instance, to be as high as 2000 Ks$^{-1}$ for a vapor heated by a bow shock associated with a planetesimal ofradius 1 km. The rapid cooling of the vapor leads to nonequilibrium gas-phasecondensation of dust at temperatures much lower than those expected from theequilibrium condensation. It was found that the condensation temperatures arelower by a few hundred K or more than the equilibrium temperatures. Thisexplains the results of the recent experimental studies of condensation from asilicate vapor that condensation in such large supercooling reproducesmorphologies similar to those of silicate crystals found in meteorites. Ourresults suggest strongly that the planetesimal bow shock is one of theplausible sites for formation of not only chondrules but also other cosmiccrystals in the early solar system.

Formation of Cosmic Crystals in Highly-Supersaturated Silicate Vapor Produced by Planetesimal Bow Shocks