Among exoplanets, the way some super-earths, these giant rocky planets, produce their magnetic field is particularly noteworthy. While on Earth, this shield comes from the liquid outer core, these worlds might rely on vast reservoirs of molten rock.
Deep layers of molten rock in some super-earths could generate powerful magnetic fields, potentially stronger than Earth's, and protect these exoplanets from harmful radiation.
Credit: Illustration from the Laboratory for Laser Energetics at the University of Rochester / Michael Franchot
Super-earths are planets more massive than our own, but without the gaseous envelope of giants like Neptune. They represent the most common category of exoplanets in our galaxy, although absent from our Solar System. Their size and mass make them prime objects of study for understanding planetary diversity.
On our planet, the magnetic field is produced by convection motions in the liquid iron outer core, a phenomenon known as a dynamo. However, for super-earths, the situation could be very different. Their cores, depending on whether they are solid or liquid, do not always allow this mechanism, which raises the question of their magnetic protection.
In a study published in
Nature Astronomy, researchers from the University of Rochester propose an alternative. They highlight the role of a basal magma ocean, a layer of molten rock located at the base of the mantle. This idea opens new perspectives on the internal structure of planets and their ability to host life, by providing an unexpected source of magnetic field.
To verify this idea, the team conducted laser shock experiments, combined with simulations. Under the extreme pressures encountered in super-earths, molten rock becomes conductive enough to establish and maintain a lasting magnetic field. These fields could even be more powerful and persistent than Earth's, according to the developed models.
This discovery has major implications for habitability. A sufficiently powerful magnetic field protects a planet from cosmic radiation, which is essential for the development of life as we know it. Therefore, super-earths with magma oceans could offer stable and conducive environments, increasing the chances of finding favorable conditions elsewhere in the Universe.