Researchers suggest that deep layers of molten rock within large super-Earths could power a magmatic dynamo, producing strong, persistent magnetic fields over billions of years, and improving the chances of life in the habitable zone.
Far below the surface of distant rocky exoplanets called super-Earths, vast layers of molten rock may play a surprising role. These hidden reservoirs could create magnetic fields strong enough to shield entire planets from cosmic rays and other high-energy particles.
On Earth, the magnetic field comes from the movement of an outer core made of liquid iron, a process called a dynamo, but larger rocky planets may work differently. Some super-Earths may have a core that is solid or entirely liquid, which limits their ability to generate a magnetic field through this familiar mechanism.
In a paper published in Nature Astronomy, a team of researchers describes a different source. They point to a deep layer of molten rock called a basaltic magma ocean. The idea could change scientists’ understanding of the interiors of planets and influence how we assess the ability of distant worlds to support life.
"A strong magnetic field is very important for life on a planet," says Miki Nakajima, one of the researchers, "but most terrestrial planets in the solar system, such as Venus and Mars, do not have one because their cores do not have the physical conditions to create a magnetic field. But super-Earths can create a dynamo in their core and/or magma, which increases their habitability."
What is a Super Earth?
Super-Earths are planets that are larger than Earth but smaller than ice giants like Neptune. They are thought to be mostly rocky, with a solid surface and not a thick gas envelope like the ones surrounding Jupiter or Saturn. Although they are the most common type of exoplanet discovered in our galaxy, none of them exist in our solar system. The term "super-Earth" refers only to their size and mass, not to how similar they are to Earth in other ways.
Because they are so common, super-Earths provide valuable insights into how planets form and change over time. Many orbit their star in the habitable zone, where liquid water could exist. By examining their structure, atmosphere, and magnetic field, scientists are gathering clues about how planetary systems evolve and where conditions that are friendly to life might emerge.
Super Earth simulation on Earth
Researchers think that early in its history, Earth may have had a basal magma ocean. This layer of molten or partially molten rock at the base of the mantle can influence a planet's magnetic field, internal heat flow, and chemical evolution. Super-Earths are larger and have much greater internal pressure, so they are more likely to maintain these molten layers for longer periods of time, so basal magma oceans play a key role in understanding their internal dynamics and potential for settlement.
To investigate these extreme conditions, Nakajima and her team conducted laser compression experiments. They combined these experiments with quantum mechanical simulations and planetary evolution models, focusing on the behavior of molten rock subjected to pressures similar to those in a basaltic magma ocean.
Their results show that at such high pressures, molten rock deep within a planet's mantle can become electrically conductive enough to sustain a magnetic field for billions of years. This finding suggests that super-Earths more than three to six times the size of Earth could create strong, persistent magnetic fields through a magneto-driven dynamo. These fields could be even stronger and more persistent than Earth's, increasing the likelihood that such planets could support life.
for the scientific article DOI: 10.1038 / s41550-025-02729-x
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One response
"Super-Earths that are three to six times the size of Earth" Even if they could support life. They would not be able to support human life. They would not be able to serve as a goal for life for us. Because it is assumed that the gravity on such stars would be many times greater than that of Earth, and anyone who got there would be paralyzed and their heart would stop within a few seconds.