Deep Magma Oceans Could Make Super-Earths Habitable: A New Study Reveals
The Earth's habitability is a delicate balance between the Sun's solar wind and cosmic radiation. The Sun's solar wind would strip away the planet's atmosphere, but Earth's magnetosphere acts as a protective shield. Similarly, cosmic rays, which are high-energy particles that can damage living tissue, are deflected by the magnetosphere. Scientists are now exploring whether magma oceans could create similar protective shields on exoplanets, particularly super-Earths.
Super-Earths are the most common type of exoplanet, and a new study in Nature Astronomy suggests that magma oceans could boost their habitability. The research, titled 'Electrical conductivities of (Mg,Fe)O at extreme pressures and implications for planetary magma oceans', is led by Miki Nakajima, an associate professor in the Department of Earth and Environmental Sciences at the University of Rochester.
During planet formation, impacts can generate magma oceans. When these oceans crystallize, iron-rich basal magma oceans (BMOs) form at the core-mantle boundary. These BMOs could provide the same magnetic protection as Earth, but only if their iron content is high enough. The researchers explain that the BMO could generate a dynamo in early Earth and super-Earths if the electrical conductivity of the BMO is sufficiently high.
The study also addresses the question of what created Earth's early magnetic shield. Existing models have their problems, and the researchers point out that dynamo generation in a basal magma ocean (BMO) is an alternative focus. A BMO is a deep layer of molten rock under a solid crust.
The lead author, Nakajima, emphasizes the importance of a strong magnetic field for life on a planet. However, most terrestrial planets in the solar system, such as Venus and Mars, lack magnetic fields due to their core conditions. Super-Earths, on the other hand, can produce dynamos in their core and/or magma, increasing their planetary habitability.
To test their hypothesis, the research team conducted laser-driven shock experiments on ferropericlase and ran simulations to calculate the long-term evolution of super-Earths. The results show that the intense pressures inside super-Earths force molten rock in their deep mantles to become electrically conductive, which can last a long time and be much stronger than Earth's, boosting the potential habitability of these planets.
The study also explains Earth's ancient magnetosphere and suggests that dynamos created by basal magma oceans are likely stronger than those created by core-driven dynamos for super-Earths with masses greater than about 3 to 5 Earth masses. The BMO-driven dynamo can last for a few billion years, which may be detectable with future observations of super-Earths.
The detection of exoplanet magnetospheres is a critical and challenging issue in exoplanet science. Powerful radio-telescopes, such as those on the Moon or new ground-based observatories, could be the solution to studying distant magnetic fields. Only better future observations can shed more light on this fascinating topic.
The study's findings are exciting and challenging, given the interdisciplinary nature of the work. The author expresses gratitude for the support from collaborators across various research fields and looks forward to future magnetic field observations of exoplanets to test their hypothesis.
