Imagine the possibility of hidden magma oceans beneath the surfaces of distant exoplanets, acting as protective shields against harmful radiation. This captivating idea suggests that these molten rock layers might be crucial for sustaining life on planets beyond our own.
According to recent research from the University of Rochester, conducted by a team led by Miki Nakajima, an associate professor in the Department of Earth and Environmental Sciences, these oceans of molten rock, referred to as basal magma oceans (BMOs), could power magnetic fields robust enough to protect entire exoplanets from perilous cosmic radiation and other hazardous particles. This could dramatically change our understanding of planetary interiors and their potential for habitability.
On Earth, our own magnetic field is generated through the movement of liquid iron in the outer core, a process scientists call a dynamo. However, for larger rocky worlds, known as super-earths, the situation may differ. These planets might possess solid or fully liquid cores that do not produce magnetic fields in the same way as Earth does.
In their paper published in Nature Astronomy, the researchers highlight a game-changing alternative: the existence of BMOs. Nakajima emphasizes the importance of a strong magnetic field for supporting life on a planet. She points out that many terrestrial planets in our solar system, such as Venus and Mars, lack sufficient magnetic fields because their cores do not meet the necessary physical conditions. On the other hand, super-earths might generate dynamos in their molten rock layers, thereby enhancing their capacity to support life.
Super-earths are intriguing celestial bodies that are larger than Earth but smaller than the ice giants like Neptune. Most scientists believe that they are predominantly rocky, featuring solid surfaces rather than the gaseous layers seen in planets such as Jupiter or Saturn. Despite being the most commonly detected class of exoplanets in our galaxy, super-earths are notably absent from our solar system. It’s important to note that the term "super-earth" refers to size and mass alone, not necessarily to how closely these planets resemble our own.
Given their abundance, super-earths provide valuable insights into the processes of planetary formation and evolution. Many reside within their stars' habitable zones, where conditions could allow for the presence of liquid water. By examining their compositions, atmospheres, and magnetic fields, scientists are piecing together clues about the origins of planetary systems and the potential for extraterrestrial life.
Researchers believe that shortly after the formation of Earth, it too likely possessed a BMO. This layer of partially or entirely molten rock located at the base of a planet's mantle has significant impacts on the planet's magnetic field, heat distribution, and chemical development. Because super-earths are larger than Earth and experience much greater internal pressures, they are more prone to maintaining long-lasting BMOs. Hence, understanding BMOs is essential for deciphering the interiors, magnetic fields, and habitability prospects of super-earths.
To simulate the extreme pressures found inside super-earths, Nakajima and her team carried out laser shock experiments at the University of Rochester's Laboratory for Laser Energetics, alongside quantum mechanical simulations and planetary evolution models. Their focus was on investigating molten rock under the intense conditions characteristic of a BMO.
Their findings revealed that under these immense pressures, the deep-mantle molten rock can become electrically conductive enough to support a robust magnetic field for billions of years. This discovery implies that on super-earths that are three to six times the size of Earth, BMOs—driven by the movement of molten rock—could generate stronger and more enduring magnetic fields compared to those produced by Earth's core. Such conditions could potentially foster the development of life throughout the galaxy.
Nakajima expressed her excitement about the project, noting the challenges she faced since her background is primarily in computational studies, making this her first experimental endeavor. She acknowledged the invaluable contributions of her collaborators from various research domains, which made this interdisciplinary study possible. Looking ahead, she eagerly anticipates future observations of magnetic fields on exoplanets to validate their hypotheses.
