Could hidden magma oceans be the secret weapon to protect rocky exoplanets from harmful radiation? A groundbreaking study by University of Rochester researchers suggests that deep beneath the surface of distant exoplanets known as super-earths, oceans of molten rock may be doing something extraordinary: powering magnetic fields strong enough to shield entire planets from dangerous cosmic radiation and other harmful high-energy particles.
The study, published in Nature Astronomy, reveals an alternative source for magnetic fields in super-earths. Instead of relying on the movement of liquid iron in their cores, like Earth does, these larger rocky worlds might have solid or fully liquid cores that cannot produce magnetic fields in the same way. Researchers propose a deep layer of molten rock called a basal magma ocean (BMO) as the solution. This discovery could significantly impact our understanding of planetary interiors and the habitability of planets beyond our solar system.
"A strong magnetic field is crucial for life on a planet," says Miki Nakajima, an associate professor in the Department of Earth and Environmental Sciences. "However, most terrestrial planets in our solar system, such as Venus and Mars, lack magnetic fields due to their cores' physical conditions. But super-earths can generate dynamos in their core and/or magma, enhancing their planetary habitability."
Super-earths, larger than Earth but smaller than ice giants like Neptune, are primarily rocky with solid surfaces. They are the most common exoplanets in our galaxy, yet they are notably absent from our solar system. The term 'super-earth' refers solely to size and mass, not to their resemblance to Earth. Super-earths offer a crucial window into planetary formation and evolution, with many orbiting within their stars' habitable zones, where liquid water could exist. Studying their compositions, atmospheres, and magnetic fields provides insights into the origins of planetary systems and signs of conditions conducive to life elsewhere.
The study suggests that super-earths, due to their larger size and higher internal pressures, are more likely to have long-lasting BMOs. This could make BMOs a key factor in understanding the interiors, magnetic fields, and habitability of super-earths. To recreate the extreme pressures inside super-earths, Nakajima and her colleagues conducted laser shock experiments at URochester's Laboratory for Laser Energetics, combined with quantum mechanical simulations and planetary evolution models. They focused on studying molten rock under conditions similar to those expected in a BMO.
The researchers discovered that under crushing pressures, deep-mantle molten rock becomes electrically conductive, capable of sustaining a powerful magnetic field for billions of years. This suggests that on super-earths more than three to six times the size of Earth, BMO dynamos could generate stronger, longer-lasting magnetic fields than those produced by Earth's core. This could potentially create habitable conditions for life across the galaxy.
"This work was exciting and challenging, given that my background is primarily computational and this was my first experimental work," Nakajima says. "I'm very grateful for the support from my collaborators from various research fields to conduct this interdisciplinary work. I cannot wait for future magnetic field observations of exoplanets to test our hypothesis."
The study opens up new avenues for research, inviting further exploration of the potential for life on super-earths and the role of BMOs in shaping their habitability. It also highlights the importance of understanding the interiors of exoplanets and the potential for hidden processes to have a significant impact on their characteristics and potential for life.
