Bulletin of the American Physical Society
19th Biennial Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 60, Number 8
Sunday–Friday, June 14–19, 2015; Tampa, Florida
Session P3: Geophysics and Planetary Science II: Giant Planets and Planetary Ices |
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Chair: Dylan Spaulding, Harvard University, Arianna Gleason, Stanford University Room: Grand G |
Wednesday, June 17, 2015 11:15AM - 11:45AM |
P3.00001: Inside Neptune with laser shock compression: melting of silica and properties of metallic and superionic water Invited Speaker: Marius Millot Dynamic compression experiments now allow us to recreate planetary interior conditions in the laboratory, providing valuable data on material properties at unprecedented conditions. These data are of paramount importance to build confidence in numerical simulation methods and establish new planetary structure and evolution models. We will present new results on the optical properties and equation of state (pressure, density, temperature) of warm dense water and silica at extreme conditions of pressure and temperature directly relevant to the deep interiors of Uranus, Neptune and giant exoplanets. Laser shock compression of water starting from ice VII ($\rho_0$=1.6 g/cc) obtained by coupling static and dynamic compression reached 3.6g/cc at 3 Mbar. We obtained evidence for the transition to the superionic phase near 1 Mbar and to the dense metallic liquid at 2 Mbar . The optical properties of water were determined in the whole pressure range under investigation. The EOS data in the conducting liquid state provide a stringent test on recent ab-initio simulations. As superionic ices could dominate the deep interior or giant icy planets and exoplanets, the new conductivity and equation of state experimental benchmark provide basis for improved modeling of the internal structure and magnetic field generation. In addition, the new data on warm dense silica along the Hugoniot of fused silica, quartz and stishovite document the melting line to 5 Mbar and show that silica is likely solid in the core of Uranus and Neptune but could contribute to magnetic field generation in large rocky super-Earth [1]. Prepared by LLNL under Contract DE-AC52-07NA27344. \\[4pt] [1] Millot et al., Shock compression of stishovite and melting of silica at planetary interior conditions, Science, 347, 418-420 (2015). DOI:10.1126/science.1261507 [Preview Abstract] |
Wednesday, June 17, 2015 11:45AM - 12:00PM |
P3.00002: First-principles calculations of the high-pressure melt line of SiO2 and strength of H2O: planetary science implications Amit Samanta, Sebastien Hamel, Tingting Qi We report the results from high-pressure high-temperature quantum molecular dynamics simulations of two materials of importance to planetary science. First, the high-pressure melt line of SiO2 using constrained free energy calculations under condition relevant to the Outer Planets. Second, we explore the stability of the H2O super-ionic phase by calculating the elastic constants at finite temperature and provides insight into the generation of magnetic fields of Uranus and Neptune. [Preview Abstract] |
Wednesday, June 17, 2015 12:00PM - 12:15PM |
P3.00003: Unusual Magnetic Fields of Uranus and Neptune W.J. Nellis Voyager 2 discovered the unusual non-dipolar and non-axisymmetric magnetic fields of the Ice Giants Uranus and Neptune (U/N) in the 1980's. The cause of those unique fields has been a major scientific question ever since. The answer lies in physical properties of fluids that generate planetary magnetic fields by dynamo action: convecting, electrically conducting fluids at high pressures P and temperatures T. Properties of fluids at planetary P/Ts are measured under adiabatic shock compression and quasi-isentropic multiple-shock compression up to a few 100 GPa and several 1000 K. Dynamic-compression and Voyager 2 data measured over three decades indicate (i) There is little ``Ice'' in the Ice Giants. (ii) Magnetic fields of U/N are made by metallic fluid H close to outer planetary radii. (iii) Thus, it is reasonable to observe non-dipolar non-axisymmetric fields. (iv) Those fields are probably caused by decoupling of rotational motion of U/N from convective motions in their dynamos, unlike Earth with strong coupling between those motions and a dipolar field [1]. The full paper on this work is published [2]. \\[4pt] [1] R. Hide et al, \textit{Geophysical Monograph} 76, IUGG Vol. 16;\\[0pt] [2] \textit{Mod. Phys. Lett. B} \textbf{29}, 1430018 (2014). [Preview Abstract] |
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