Are Super-Earths Solid Deep Inside Their Mantles?

Post-Post-Spinel Stability in Massive Rocky Exoplanets

Deep inside rocky planets possessing masses between one and ten times that of Earth, high pressure forces common minerals into unfamiliar crystal structures, according to findings reported in AGU Advances and highlighted by Scharping. Magnesium orthosilicate, or Mg2SiO4, serves as a primary building block for these worlds. As pressure mounts in planetary interiors, atoms within the mineral rearrange. While the spinel phase appears in Earth’s upper mantle and breaks down into bridgmanite and ferropericlase at greater depths, researchers predict an entirely different phase emerges under the extreme conditions of super-Earths.

According to the published research, this ultrahigh-pressure phase, termed post-post-spinel, becomes chemically stable again under the massive gravitational pressures of super-Earths. Because this phase dominates the deep mantles of such exoplanets, mapping its melting behavior provides critical insight into how massive rocky worlds form and evolve over cosmic timescales.

Simulating Melting Curves Up to 1,300 Gigapascals

Re-creating temperatures and pressures matching the interiors of massive rocky planets remains experimentally difficult in traditional laboratories. To overcome this hurdle, research led by Zheng and colleagues adopted a computational approach, utilizing thermodynamic integration to chart the melting curve of post-post-spinel Mg2SiO4 at pressures reaching 1,300 gigapascals, as detailed in AGU Advances.

Implications for Planetary Mantle Convection and Magnetic Fields

A solid deep mantle alters how heat transfers from a planet’s core toward its surface.

Furthermore, these internal dynamics influence planetary magnetic fields.

Frequently Asked Questions

What is a super-Earth?

Why are super-Earth mantles difficult to study?

Re-creating the extreme temperatures and pressures found deep inside massive rocky planets exceeds the physical limits of most traditional laboratory equipment, requiring researchers to use advanced computational techniques like thermodynamic integration.

What is post-post-spinel?

Post-post-spinel is an ultrahigh-pressure crystal structure of magnesium orthosilicate (Mg2SiO4) that scientists predict becomes stable in the deep mantles of massive super-Earths.

How do solid deep mantles affect exoplanet magnetic fields?

According to research highlighted by Nathaniel Scharping, the solid state of deep mantles influences interior convection and heat transfer, which in turn affects how molten metals flow and generate magnetic fields in planetary cores.