Suchergebnisse

The physical processes during planet formation span a large range of pressures and temperatures. Giant impacts, such as the one that formed the Moon, achieve peak pressures of 100s of GPa. The peak shock states generate sufficient entropy such that subsequent decompression to low pressures intersects the liquid-vapor phase boundary. The entire shock-and-release thermodynamic path must be calculated accurately in order to predict the post-impact structures of planetary bodies. Forsterite (Mg2SiO4) is a commonly used mineral to represent the mantles of differentiated bodies in hydrocode models of planetary collisions. Here, we performed shock experiments on the Sandia Z Machine to obtain the density and temperature of the liquid branch of the liquid-vapor phase boundary of forsterite. This work is combined with previous work constraining pressure, density, temperature, and entropy of the forsterite principal Hugoniot. We find that the vapor curves in previous forsterite equation of state models used in giant impacts vary substantially from our experimental results, and we compare our results to a recently updated equation of state. We have also found that due to under-predicted entropy production on the principal Hugoniot and elevated temperatures of the liquid vapor phase boundary of these past models, past impact studies may have underestimated vapor production. Furthermore, our results provide experimental support to the idea that giant impacts can transform much of the mantles of rocky planets into supercritical fluids. ; DOE-NNSA grant [DE-NA0003842, DE-NA0003904]; NASANational Aeronautics & Space Administration (NASA) [NNX15AH54G, NNX16AP35H]; UC Office of the President grant [LFR-17-449059]; U.S. Department of Energy's National Nuclear Security AdministrationNational Nuclear Security Administration [DE-NA0003525]; U.S. Department of EnergyUnited States Department of Energy (DOE) [DE-AC52-07NA27344] ; Published version ; This work was conducted under the Z Fundamental Science Program. The authors thank the support from DOE-NNSA grant DE-NA0003842 and DE-NA0003904, NASA grants NNX15AH54G and NNX16AP35H, and UC Office of the President grant LFR-17-449059. Sandia National Laboratories is a multimission laboratory managed and operated by 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 United States 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 authors would like to express thanks to the reviewers for their helpful comments.