X-rays improve understanding of boundary between Earth’s core and mantle and super-Earth’s magma oceans

Researchers at the Department of Energy’s SLAC National Accelerator Laboratory have revealed new details about Earth’s core-mantle boundary and similar regions found in exoplanets.

The team, led by Guillaume Morard, a scientist at the University of Grenoble and the University of Sorbonne in France, used SLAC’s Linac Coherent Light Source (LCLS) X-ray laser to study the behavior of the rock melting under extreme conditions. The results were published in Natural communications.

“This study marks a significant advance in our understanding of Earth’s deep interior,” said SLAC collaborator and principal scientist Arianna Gleason. “The results highlight the potential of advanced X-ray techniques to reveal the hidden secrets of our planet and beyond.”

About 1,800 miles below Earth’s surface lies a bubbling region of magma sandwiched between the solid silicate-based mantle and the molten iron-rich core: the core-mantle boundary. It is a remnant of ancient times, around 4.3 to 4.5 billion years ago, when the entire planet was in meltdown. Although the region’s extreme pressures and temperatures make it difficult to study, it contains clues to the history of Earth’s origin and insight into the planet’s internal processes.

To overcome this challenge, researchers used advanced X-ray techniques to recreate the conditions expected in the middle and lower mantle of exoplanets two to three times larger than Earth. Using hard X-rays with higher energy levels than previously possible, the researchers were able to see how the atoms in the molten rock were arranged. The team also used computer simulations to compare experimental data, providing a comprehensive view of the properties of silicate melts.

One surprising result concerned the role of iron in molten rock. Despite expectations, the variation in iron content did not significantly change the density of the rock. This discovery is particularly relevant to our understanding of the formation of the Earth, where the surface was once made of molten rock and the difference in density between crystalline and molten materials significantly influenced the development of the planet.

The study also suggests that this atomic response to compression can change the properties of melt at the pressures expected in the magma oceans of super-Earths, exoplanets with masses nearly three times that of Earth. This could potentially have a different impact on their early development compared to smaller rocky planets, such as Earth and Venus in our solar system.

The research highlights the importance of advanced experimental tools for studying high pressure and high temperature conditions. The team hopes that their findings will lead to the further development of these tools, opening new avenues of research in Earth and planetary sciences.

“Now that we know we can get this quality of data and achieve these conditions, we want to go deeper into exoplanet regimes,” Gleason said. “The ability to generate pressures equivalent to three times Earth’s mantle conditions is exciting. It expands our understanding of the properties of silicates under extreme conditions, which is crucial for studies of Earth and exoplanets.”