Shock-Wave Heating Model for Chondrule Formation: Prevention of Isotopic Fractionation

Abstract

Chondrules are considered to have much information on dust particles and processes in the solar nebula. It is naturally expected that protoplanetary disks observed in present star forming regions have similar dust particles and processes, so study of chondrule formation may provide us great information on the formation of the planetary systems. Evaporation during chondrule melting may have resulted in depletion of volatile elements in chondrules. However, no evidence for a large degree of heavy-isotope enrichment has been reported in chondrules. In order to meet this observed constraint, the rapid heating rate at temperatures below the silicate solidus is required to suppress the isotopic fractionation. We have developed a new shock-wave heating model taking into account the radiative transfer of the dust thermal continuum emission and the line emission of gas molecules and calculated the thermal history of chondrules. We have found that optically-thin shock waves for the thermal continuum emission from dust particles can meet the rapid heating constraint, because the dust thermal emission does not keep the dust particles high temperature for a long time in the pre-shock region and dust particles are abruptly heated by the gas drag heating in the post-shock region. We have also derived the upper limit of optical depth of the pre-shock region using the radiative diffusion approximation, above which the rapid heating constraint is not satisfied. It is about 1 - 10.

58 pages, including 5 tables and 15 figures, accepted for publication in The Astrophysical Journal

References in corpus (1)

• Chondrule-Forming Shock Fronts in the Solar Nebula: A Possible Unified Scenario for Planet and Chondrite Formation

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• Thermal Histories of Chondrules in Solar Nebula Shocks
• Formation of Cosmic Crystals in Highly-Supersaturated Silicate Vapor Produced by Planetesimal Bow Shocks
• Shock-Wave Heating Model for Chondrule Formation: Hydrodynamic Simulation of Molten Droplets exposed to Gas Flows
• Revisiting Jovian-Resonance Induced Chondrule Formation
• Fragment-collision model for compound chondrule formation: Estimation of collision probability
• Cooling of Dense Gas by H2O Line Emission and an Assessment of its Effects in Chondrule-Forming Shocks
• Reexamination of Induction Heating of Primitive Bodies in Protoplanetary Disks
• Formation of chondrules in radiative shock waves I. First results, spherical dust particles, stationary shocks