Shock compression of stishovite and melting of silica at planetary interior conditions

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Science  23 Jan 2015:
Vol. 347, Issue 6220, pp. 418-420
DOI: 10.1126/science.1261507

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Melting silica in massive planets

To simulate the extreme conditions inside large planets requires extreme experiments. Millot et al. used high-pressure shock waves almost twice that of the center of Earth to melt silica, one of the primary components of planetary interiors. This was possible only by shocking a very dense form of silica called stishovite. Determining the melting point of silica is vital for developing better computational models of the interior of planets several times the mass of Earth. The high-pressure liquid was electrically conductive, a property that may contribute to magnetic dynamos in very large terrestrial exoplanets.

Science, this issue p. 418


Deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials. In particular, how much heat solids can sustain before melting under pressure is key to determining a planet’s internal structure and evolution. We report laser-driven shock experiments on fused silica, α-quartz, and stishovite yielding equation-of-state and electronic conductivity data at unprecedented conditions and showing that the melting temperature of SiO2 rises to 8300 K at a pressure of 500 gigapascals, comparable to the core-mantle boundary conditions for a 5–Earth mass super-Earth. We show that mantle silicates and core metal have comparable melting temperatures above 500 to 700 gigapascals, which could favor long-lived magma oceans for large terrestrial planets with implications for planetary magnetic-field generation in silicate magma layers deep inside such planets.

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