Far below the surface of distant super-Earth exoplanets, vast oceans of molten rock could be generating powerful magnetic fields capable of protecting the planets from hazardous cosmic radiation and other high-energy particles.
Earth’s magnetic field arises from movements in its liquid iron outer core, a process called a dynamo. However, larger rocky planets like super-Earths may have cores that are entirely solid or fully liquid, making them unable to generate magnetic fields in the same way.
In a study published in Nature Astronomy, researchers at the University of Rochester, including Associate Professor Miki Nakajima from the Department of Earth and Environmental Sciences, propose an alternative source: a deep layer of molten rock known as a basal magma ocean (BMO). Their findings could change our understanding of planetary interiors and influence assessments of exoplanet habitability.
“A strong magnetic field is crucial for supporting life on a planet,” Nakajima explains. “Most terrestrial planets in our solar system, like Venus and Mars, lack them because their cores don’t have the conditions needed to generate a magnetic field. Super-Earths, however, can create dynamos in their cores or magma, which could enhance their potential for habitability.”
What Defines a Super-Earth?
Super-Earths are planets larger than Earth but smaller than ice giants like Neptune. They are thought to be mostly rocky, with solid surfaces rather than thick gaseous layers like Jupiter or Saturn. While they are the most commonly detected type of exoplanet in our galaxy, none exist in our solar system. The term “super-Earth” refers only to a planet’s size and mass, not its similarity to Earth in other characteristics.
Their prevalence makes super-Earths important for understanding planetary formation and evolution. Many orbit within their stars’ habitable zones, where liquid water might exist. By examining their makeup, atmospheres, and magnetic fields, scientists can gain insights into how planetary systems develop and explore potential conditions for life beyond Earth.
Recreating Super-Earth Conditions on Earth
Scientists think that Earth probably had a basal magma ocean (BMO) shortly after its formation. This layer of partially or fully molten rock at the base of the mantle can influence a planet’s magnetic field, heat flow, and chemical development. Because super-Earths are larger and experience much higher internal pressures than Earth, they are more likely to maintain long-lived BMOs, making these layers crucial for understanding super-Earth interiors, magnetic fields, and potential habitability.
To replicate the extreme pressures inside super-Earths, Nakajima and her team carried out laser shock experiments at the University of Rochester’s Laboratory for Laser Energetics, supplementing them with quantum mechanical simulations and planetary evolution models. Their research focused on the behavior of molten rock under conditions expected in a BMO.
The team found that under the immense pressures of a super-Earth’s deep mantle, molten rock becomes electrically conductive enough to generate a strong magnetic field lasting billions of years. This indicates that on super-Earths more than three to six times Earth’s size, BMO-driven dynamos—powered by the movement of molten rock—could produce stronger and longer-lived magnetic fields than Earth’s core, potentially supporting habitable conditions on planets across the galaxy.
“This project was both exciting and challenging, especially since my background is mainly computational and this was my first hands-on experimental work,” Nakajima said. “I’m very grateful for the support from collaborators across different fields that made this interdisciplinary research possible. I look forward to future observations of exoplanet magnetic fields to test our predictions.”
Read the original article on: Phys.Org
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