The researchers demonstrated, through high-energy laser experiments, that magnesium oxide is probably the first mineral to solidify in the formation of the super-Earth, crucially impacting the geophysical evolution of these planets.
A new study reveals that magnesium oxide, a key mineral in planetary formation, may be the first to solidify in the development of “super-Earth” exoplanets, with its behavior under extreme conditions significantly influencing planetary development.
Scientists have observed for the first time how magnesium oxide atoms transform and melt under ultra-harsh conditions, providing new insights into this key mineral in Earth’s mantle, which is known to influence planet formation.
High-energy laser experiments – which subjected small crystals of the mineral to the kind of heat and pressure found deep in a rocky planet’s mantle – suggest that the compound could be the first mineral to solidify in magma oceans, forming “super” exoplanets. -Lands”. .
“Magnesium oxide may be the most important solid controlling the thermodynamics of young super-Earths,” said June Wicks, an assistant professor of Earth and Planetary Sciences at Johns Hopkins University who led the research. “If it has this very high melting temperature, it would be the first solid to crystallize when a hot, rocky planet starts to cool and its interior separates into a core and mantle.”
Implications for young planets
The findings were recently published in 
View of experiments conducted by shock-compressed magnesium oxide (MgO) laser inside the Laser Energetics Laboratory chamber. High-power laser beams are used to compress MgO samples to pressures beyond those found at the center of the Earth. A secondary X-ray source is used to probe the crystal structure of MgO. Brighter regions are bright plasma emissions on nanosecond timescales. Credit: June Wicks/Johns Hopkins University
Bigger than Earth, but smaller than giants like
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” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>exoplanet research because they are commonly found among other solar systems in the galaxy. While the composition of these planets can range from gas to ice or water, rocky super-Earths are expected to contain significant amounts of magnesium oxide that could influence the planet’s magnetic field, volcanism, and other important geophysics, as they do on Earth. , said Wicks. .
To mimic the extreme conditions this mineral could endure during planet formation, Wick’s team subjected small samples to ultrahigh pressures using the Omega-EP laser facility at the University of Rochester’s Laser Energetics Laboratory. Scientists also fired X-rays and recorded how these light rays bounced off the crystals to track how their atoms reorganized in response to the increasing pressures, specifically noting at what point they transformed from solid to liquid.
When squeezed with extreme force, atoms in materials like magnesium oxide change their arrangement to sustain the crushing pressures. This is why the mineral transitions from a rock salt “phase,” similar to table salt, to a different configuration, like another salt called cesium chloride, as pressure increases. This causes a transformation that can affect a mineral’s viscosity and impact on the planet as it comes of age, Wicks said.
Stability of Magnesium Oxide at High Pressures
The team’s results show that magnesium oxide can exist in both of its phases, at pressures ranging from 430 to 500 gigapascals and temperatures of around 9,700 Kelvin, almost twice as hot as the surface of the Sun. The experiments also show that the highest pressures that the mineral can withstand before completely melting are greater than 600 gigapascals, about 600 times the pressure that would be felt in the deepest ocean trenches.
“Magnesium oxide melts at a much higher temperature than any other material or mineral. Diamonds may be the hardest materials, but they are what will melt last,” Wicks said. “When it comes to extreme materials on young planets, magnesium oxide will likely be solid, while everything else hanging in the mantle will turn to liquid.”
The study shows the stability and simplicity of magnesium oxide under extreme pressures and could help scientists develop more accurate theoretical models to investigate key questions about the behavior of this and other minerals on rocky worlds like Earth, Wicks said.
“The study is a love letter to magnesium oxide, because it is incredible that it has the highest melting point we know of – at pressures beyond the center of the Earth – and yet behaves like a normal salt,” Wicks said. “It’s just a beautiful, simple salt, even at these record pressures and temperatures.”
Reference: “B1-B2 transition in shock-compressed MgO” by June K. Wicks, Saransh Singh, Marius Millot, Dayne E. Fratanduono, Federica Coppari, Martin G. Gorman, Zixuan Ye, J. Ryan Rygg, Anirudh Hari, Jon H. Eggert, Thomas S. Duffy, and Raymond F. Smith, June 7, 2024, Science Advances.
DOI: 10.1126/sciadv.adk0306
Other authors are Saransh Singh, Marius Millot, Dayne E. Fratanduono, Federica Coppari, Martin G. Gorman, Jon H. Eggert, and Raymond F. Smith of Lawrence Livermore National Laboratory; Zixuan Ye and Anirudh Hari of Johns Hopkins University; J. Ryan Rygg of the University of Rochester; and Thomas S. Duffy of
” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]” tabindex=”0″ role=”link”>Princeton University.
This research was supported by NNSA through the National Laser User Facilities Program under contracts Nos. DE-NA0002154 and DE-NA0002720 and the Laboratory Directed Research and Development Program at LLNL (project No. 15-ERD-012). This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract No. DE-AC52-07NA27344. The research was supported by the National Nuclear Security Administration through the National Laser User Facilities Program (contracts Nos. DE-NA0002154 and DE-NA0002720) and the Laboratory Directed Research and Development Program at LLNL (projects Nos. 15-ERD -014, 17 -ERD-014 and 20-ERD-044).
