Super-Earths May Generate Magnetic Fields Differently Than The Modern Earth

On the modern day Earth the magnetic field is thought to generated by electric currents in the liquid outer core, which is composed of highly conductive molten iron. But new research has found that when magnesium oxide is under extreme pressure and temperature it can behave similarly to molten iron, and could also generate a magnetic field. The researchers think that the early Earth may have generated a magnetic field like this, and that super-Earths could continue to generate one in this way for vast amounts of time.


Magnesium and oxygen are both present in large amounts in the mantle of the Earth and in other rocky planets. And because of its simplicity, the mineral magnesium oxide is a good way to gain insight into the nature of planetary interiors.

And now new research from a team led by Carnegie’s Stewart McWilliams has found evidence that is altering modern theory on planetary evolution, and has important implications for the Earth’s early history, and specifically for the evolution of life then.

“Magnesium oxide is particularly resistant to changes when under intense pressures and temperatures. Theoretical predictions claim that it has just three unique states with different structures and properties present under planetary conditions: solid under ambient conditions (such as on Earth’s surface), liquid at high temperatures, and another structure of the solid at high pressure. The latter structure has never been observed in nature or in experiments.”

“McWilliams and his team observed magnesium oxide between pressures of about 3 million times normal atmospheric pressure (0.3 terapascals) to 14 million times atmospheric pressure (1.4 terapascals) and at temperatures reaching as high as 90,000 degrees Fahrenheit (50,000 Kelvin), conditions that range from those at the center of our Earth to those of large exo-planet super-Earths. Their observations indicate substantial changes in molecular bonding as the magnesium oxide responds to these various conditions, including a transformation to a new high-pressure solid phase.”

There are clear signs that magnesium oxide changes from an electrically insulating material, where electrons don’t flow easily, to a metal that conducts electrons very easily, like iron.

Bringing all of their observations together, the researchers concluded that while magnesium oxide as we know it is solid and non-conductive, the magnesium oxide in the magma ocean of the early Earth could very possibly have been able to create a magnetic field. And in a similar way, “the metallic, liquid phase of magnesium oxide can exist today in the deep mantles of super-Earth planets, as can the newly observed solid phase.” Leading to magnetic fields potentially being generated on some super-Earths differently than the Earth’s is.

“Our findings blur the line between traditional definitions of mantle and core material and provide a path for understanding how young or hot planets can generate and sustain magnetic fields,” McWilliams said.

“This pioneering study takes advantage of new laser techniques to explore the nature of the materials that comprise the wide array of planets being discovered outside of our Solar System,” said Russell Hemley, director of Carnegie’s Geophysical Laboratory. “These methods allow investigations of the behavior of these materials at pressures and temperatures never before explored experimentally.”

The research was published November 22nd in the journal Science Express.

Source: Carnegie Institution

Image Credits: Eugene Kowaluk, Laboratory for Laser Energetics, University of Rochester

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