Chuck Bednar for redOrbit.com – Your Universe Online
Laser-driving compression experiments have allowed a team of scientists at the Lawrence Livermore National Laboratory (LLNL) and Bayreuth University in Germany to recreate the planetary-formation process.
The experiments, which are detailed in Friday’s edition of the journal Science, reproduced the conditions present deep inside exotic super-Earths and giant planet cores, as well as those found during the violent birth of Earth-like planets, the LLNL researchers explained.
The experiments also document the material properties that help determine planet formation and evolution processes by revealing the unusual properties of silica under the extreme temperatures and pressures relevant to planet formation.
LLNL physicist Marius Millot and his co-authors used laser-driven shock compression and ultra-fast diagnostics to measure the melting temperature of silica at five million atmospheres, or 500 GPa. That pressure is comparable to the core-mantle boundary pressure for a super-Earth planet (one equal to five Earth masses), as well as Uranus or Neptune, the researchers said.
“Deep inside planets, extreme density, pressure, and temperature strongly modify the properties of the constituent materials,” he explained. “How much heat solids can sustain before melting under pressure is key to determining a planet’s internal structure and evolution, and now we can measure it directly in the laboratory.”
The new data, when combined with prior measurements governing the melting of iron and other oxides, indicates that core metal and mantle silicates have comparable melting temperatures of more than 300-500 GPa. This conclusion would seem to indicate that large, rocky planets could have molten rock or long-lasting oceans of magma in their depths, and that the magnetic fields of a planet could be formed within this layer of liquid rock.
“In addition, our research suggests that silica is likely solid inside Neptune, Uranus, Saturn and Jupiter cores, which sets new constraints on future improved models for the structure and evolution of these planets,” said Millot.
How they did it
Natalia Dubrovinskaia and colleagues at Bayreuth University in Germany helped make these advances possible by synthesizing tiny transparent polycrystals and single crystals of stishovite, an extremely dense form of silica typically found in trace amounts near impact craters. These crystals made it possible for the LLNL researchers to conduct the first-ever laser-driven shock compression of stishovite using ultrafast optical pyrometry (determines temperature) and velocimetry (measurements of fluid velocity).
“Stishovite, being much denser than quartz or fused-silica, stays cooler under shock compression,” Millot said, “and that allowed us to measure the melting temperature at a much higher pressure. Dynamic compression of planetary-relevant materials is a very exciting field right now.”
“Using the ability to reproduce in the laboratory the extreme conditions deep inside giant planets, as well as during planet formation, Millot and colleagues plan to study the exotic behavior of the main planetary constituents using dynamic compression to contribute to a better understanding of the formation of the Earth and the origin of life,” the laboratory concluded.
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