Collisions that induce melting and vaporization can have a substantial effect on the thermal and geochemical evolution of planets. However, the thermodynamics of major minerals are not well known at the extreme conditions attained during planet formation. We obtained new data at the Sandia Z Machine and use published thermodynamic data for the major mineral forsterite (Mg2SiO4) to calculate the specific entropy in the liquid region of the principal Hugoniot. We use our calculated specific entropy of shocked forsterite, and revised entropies for shocked silica, to determine the critical impact velocities for melting or vaporization upon decompression from the shocked state to 1 bar and the triple points, which are near the pressures of the solar nebula. We also demonstrate the importance of the initial temperature on the criteria for vaporization. Applying these results to N-body simulations of terrestrial planet formation, we find that up to 20% to 40% of the total system mass is processed through collisions with velocities that exceed the criteria for incipient vaporization at the triple point. Vaporizing collisions between small bodies are an important component of terrestrial planet formation.
Bibliographical noteFunding Information:
This work was conducted under the Z Fundamental Science Program. The authors thank the support from DOE-NNSA Grant DE-NA0002937, NASA Grants NNX15AH54G and NNX16AP35H, UC Office of the President Grant LFR-17-449059, and DOE-NNSA Grant DE-NA0003842. Sandia National Laboratories is a multimission laboratory managed and operated by the National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the U.S. Government. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. The revised ANEOS parameter set for forsterite, modifications to the ANEOS code, and SESAME and GADGET format EOS tables are available online (https://github.com/isale-code/code/M-ANEOS and https://github.com/ststewart/aneos-forsterite-2019; https://doi.org/10.5281/zenodo.3478631).All scripts used for calculations in this work are available online (https://github.com/edavi006/Forsterite_entropy_2019; https://doi.org/10.5281/zenodo.3610687.)
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- shock wave physics