Using laser-driven compression, a team of researchers have created an experiment that’s giving new insight into what it’s like in the cores of giant super-Earths and during the birth of earth-like planets.
The experiment subjects synthetic stishovite, a high density form of silica, to laser-induced shock compression. It then measures the short-lived reaction using extremely fast diagnostics.
What Lawrence Livermore National Laboratory (LLNL) physicist Marius Millot and colleagues from Bayreuth University (Germany), LLNL and the University of California, Berkeley found gave them a picture of the melting temperature of silica at around 500 GPa (gigapascal, a unit of pressure), roughly five million times the air pressure on Earth. This is comparable to the core-mantle boundary pressure of a planet about five times the mass of Earth or an Earth-like planet in the throes of the giant impacts involved in the final stage of its birth.
“Deep inside planets, extreme density, pressure and temperature strongly modify the properties of the constituent materials,” Millot said. “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.”
Scientists found that at these pressures silica and the metals in planetary cores have comparable melting temperatures. So it’s likely that rocky super-Earths have oceans of magma within, allowing them to form planetary magnetic fields in the way Earth does. A magnetic field is very important to supporting life, as it shields a planet from solar and cosmic radiation.
Millot said the research also indicates that the silica is “likely solid” in the cores of gaseous planets like Neptune, Uranus, Saturn and Jupiter.
The research wouldn’t have been possible if Natalia Dubrovinskaia and colleagues at Bayreuth University in Germany had not worked out a new method to synthesize stishovite. Stishovite is usually only found in trace amounts in meteor impact craters. It’s obviously an extremely rare thing to find on Earth’s surface, although scientist think it may be common deep underground. The unique properties of the substance were required to simulate the super earth conditions.
“Stishovite, being much denser than quartz or fused-silica, stays cooler under shock compression, and that allowed us to measure the melting temperature at a much higher pressure,” Millot said. “Dynamic compression of planetary-relevant materials is a very exciting field right now. Deep inside planets hydrogen is a metallic fluid, helium rains, fluid silica is a metal and water may be superionic.”
[Source: Lawrence Livermore]
Image by E. Kowaluk