Deep Mantle Mineral Could Redefine the Interior Dynamics of Super‑Earths

New research shows that magnesium oxide, a dominant mineral in Earth’s lowermost mantle, may undergo a structural transformation under the extreme pressures found inside massive rocky exoplanets, known as super‑Earths. The study, reported by Phys.org, suggests that the way this mineral deforms – specifically the direction and magnitude of applied stress – could dramatically alter the physical behavior of a planet’s deep interior.

On Earth, magnesium oxide (MgO) exists as a simple cubic crystal that remains stable from the surface down to the core‑mantle boundary, roughly 2,900 kilometres deep. In super‑Earths, however, the pressure at comparable depths can be several times higher than on our planet. Laboratory simulations and high‑pressure calculations indicate that under such conditions MgO may convert into a denser, more complex crystal structure, potentially affecting how heat and material move through the planet.

The transformation matters because the mantle’s ability to conduct heat and to flow viscously controls a planet’s tectonic activity, magnetic field generation, and long‑term habitability. If MgO becomes less deformable in the super‑Earth mantle, convection could slow, leading to a hotter interior and a weaker magnetic shield. Conversely, a more pliable phase might enhance mantle mixing, fostering plate‑like motions even on worlds much larger than Earth.

Scientists arrived at these conclusions by subjecting MgO samples to pressures exceeding 200 gigapascals in diamond‑anvil cells, then using synchrotron X‑ray diffraction to observe changes in crystal symmetry. Complementary computational models confirmed that the new phase becomes energetically favorable only when the stress is applied in specific orientations, underscoring the “how you push matters” insight highlighted by the authors.

The findings open fresh avenues for exoplanet modeling. Current interior models often assume Earth‑like mineralogy across a wide range of planet sizes, but the MgO transition suggests that super‑Earths could host fundamentally different mantle dynamics. Future telescopic observations of exoplanetary atmospheres, combined with refined seismic analogues, may help test whether these deep‑mantle processes leave observable signatures on surface geology or magnetic activity.