Magnesium Oxide Phase Shift Could Transform Super‑Earth Interior Dynamics

New research indicates that magnesium oxide, a prevalent mineral in Earth’s lowermost mantle, might experience a structural shift under the extreme pressures encountered within massive rocky exoplanets known as super‑Earths. The study, reported by Phys.org, proposes that the manner in which this mineral deforms—the direction and magnitude of the applied stress—could significantly modify the physical behavior of a planet’s deep interior.

On our planet, magnesium oxide (MgO) adopts a simple cubic crystal that stays stable from the surface down to the core‑mantle boundary, about 2,900 kilometres deep. In super‑Earths, however, comparable depths are subjected to pressures several times greater than Earth’s. Laboratory simulations and high‑pressure calculations suggest that under such conditions MgO could transform into a denser, more intricate crystal structure, potentially influencing the transport of heat and material through the planet.

This transformation is important because the mantle’s capacity to conduct heat and flow viscously governs a planet’s tectonic activity, magnetic field generation, and long‑term habitability. Should MgO become less deformable within a super‑Earth mantle, convection may decelerate, leading to a hotter interior and a weaker magnetic shield. Conversely, a more pliable phase could accelerate mantle mixing, encouraging plate‑like motions even on worlds far larger than Earth.

Researchers arrived at these conclusions by compressing MgO samples to pressures exceeding 200 gigapascals in diamond‑anvil cells, then employing synchrotron X‑ray diffraction to track changes in crystal symmetry. Complementary computational models verified that the new phase becomes energetically favorable only when stress is applied in particular orientations, highlighting the “how you push matters” insight emphasized by the authors.

The results open new pathways for exoplanet modeling. Existing interior models often presume Earth‑like mineralogy across a broad range of planet sizes, yet the MgO transition implies that super‑Earths might exhibit fundamentally different mantle dynamics. Upcoming telescopic observations of exoplanetary atmospheres, together with refined seismic analogues, could help determine whether these deep‑mantle processes leave detectable imprints on surface geology or magnetic activity.