A new study shows that huge magma "oceans" may be hidden deep in some rocky exoplanets "super-Earths" that are far more massive than Earth, generating powerful planetary magnetic fields in an unexpected way, thus providing key protection for potential alien life. This study led by the University of Rochester in the United States believes that these hidden magma layers are expected to act like planetary "generators" like the Earth's outer core, resisting high-energy radiation and charged particles from stars and space.
Inside the Earth, the convective motion of the liquid iron outer core drives a process called a "magnetohydrodynamic dynamo" (dynamo), which generates and maintains the Earth's magnetic field. However, for rocky planets with larger volumes and higher internal pressures, their iron cores may be partially or completely solidified, or in an unusual physical state, making it difficult for the traditional metal core power generation mechanism to operate stably. This means that without the intervention of other mechanisms, many super-Earths will lack a strong magnetic field barrier, making it difficult to maintain a surface environment suitable for the long-term survival of life.
Miki Nakajima, associate professor in the Department of Earth and Environmental Sciences at the University of Rochester, and his team proposed in a paper published in Nature Astronomy that a high-pressure molten layer deep in the planet called a "basal magma ocean" (BMO) may be able to independently maintain the planet's magnetic field. This magma ocean is located at the bottom of the planet's mantle in an extremely high-pressure and high-temperature environment. Research shows that under such conditions, the electrical conductivity of molten rock, which was originally considered an insulator or weak conductor, increases significantly enough to support a planetary-scale magnetic field that could last billions of years.
"Strong magnetic fields are essential for the existence of planetary life." Nakajima pointed out, but most terrestrial planets in the solar system - such as Mars and Venus - have either lost their global magnetic fields or never formed a stable magnetic field, largely because their cores lack sufficient convection and energy conditions. She said that in comparison, due to their greater mass and higher internal pressure, many super-Earths not only have the opportunity to maintain a metallic generator in the core, but may also attach a set of "magma generators" in the deep magma ocean. The dual mechanisms jointly increase the probability of the planet becoming habitable.
According to current exoplanet observations, super-Earths are the most common type of planet in the Milky Way: they are usually several times the size of the Earth, but smaller than ice giants such as Neptune. They are generally believed to be mainly composed of rocks and metals, with relatively "solid" surfaces rather than thick gas shells. Although such planets do not exist in the solar system, super-Earths have been found in the habitable zones of many stars. Liquid water can theoretically exist on their surfaces, so they have long been regarded as an important goal in the search for extraterrestrial life. The research team pointed out that to judge whether these planets are truly "habitable", magnetic field strength is a key indicator as important as atmosphere maintenance and radiation shielding capabilities.
In order to reproduce the extreme environment deep in the super-Earth in the laboratory, Nakajima's team carried out laser shock experiments at the University of Rochester's Laser Energy Laboratory, supplemented by quantum mechanical calculations and numerical models of planetary evolution. The researchers selected representative mantle materials such as magnesium- and iron-rich oxides ((Mg, Fe)O), and used high-power lasers to instantly pressurize and heat the samples, making them withstand pressure and temperatures comparable to those in the deep mantle of super-Earths, and then measured their conductivity changes in the molten state. Experimental results show that under extreme pressures of millions of atmospheres, molten rock can exhibit high enough electrical conductivity, and when combined with the internal convection motion of the planet, it can maintain a magnetic field similar to or even stronger than the Earth's magnetic field for billions of years.
Model projections show that a super-Earth with a volume about three to six times that of the Earth is most likely to maintain such a basement magma ocean for a long time and generate a strong and long-lasting magnetic field. The study also pointed out that compared with the core generator, the magma generator may be less sensitive to changes in alloy composition, last longer, and provide more stable protection for the atmosphere and surface life during the cooling and evolution of the planet. This provides astronomers with a new internal structure criterion when assessing whether an exoplanet is "habitable": Even if the planet's iron core conditions are not ideal, as long as the deep magma ocean is thick enough and the convection is strong enough, it may still have a magnetic field to protect the atmosphere and life.
"This work is both exciting and challenging for me, because my research background is mainly in theory and calculation, and this is the first time I have personally participated in high-pressure experiments." Nakajima said that she was grateful to the collaborators from multiple research directions for completing this interdisciplinary research, and looked forward to testing this hypothesis through exoplanet magnetic field observations in the future. With the advancement of astronomical observation technology, inferring the strength of the super-Earth's magnetic field through stellar occultation, radio radiation or stellar wind interaction signals in the future will provide key evidence to verify the "magma ocean magnetic field" mechanism.
The paper "Conductivity of (Mg, Fe)O under extreme pressure and its implications for planetary magma oceans" was published in "Nature Astronomy" on January 15, 2026, which further completes humankind's understanding of how the internal structure of planets shapes magnetic fields and habitability. The research team believes that as more information about the interior and magnetic field of exoplanets is obtained, we may find that the "dark ocean" of magma hidden deep in the planet is quietly providing an invisible but crucial protective umbrella for potential life worlds in the universe.