In the immense crucibles of planetary formation, young planets collide and coalesce in violent, cataclysmic impacts that sculpt their internal structures and surface compositions. These colossal impacts generate vast oceans of molten rock—magma oceans—that undergo complex physical and chemical transformations as they cool and crystallize. A particularly intriguing and enigmatic phase in this evolutionary narrative is the formation of an iron-enriched basal magma ocean (BMO) at the core-mantle boundary. In the latest breakthrough study, Nakajima and colleagues have illuminated the electrical behavior of this deep, iron-rich layer under extreme conditions, paving the way to understanding how such early planetary environments could generate their own magnetic dynamos, with profound implications for both Earth and super-Earth exoplanets.
Throughout the early stages of terrestrial planet formation, immense collisions trigger widespread melting, creating global magma oceans that blanket the planet’s interior. As these molten layers cool and begin to crystallize, differentiation processes driven by iron enrichment cause a dense Fe-rich melt to segregate and pool at the core-mantle boundary. The resulting basal magma ocean is thought to persist for millions to billions of years, playing a critical role in dictating a planet’s magnetic field history. The key to this magnetic puzzle lies in the electrical conductivity of the BMO, a property historically poorly constrained and assumed to be heavily dependent on iron concentration.
To demystify this, Nakajima et al. employed a multifaceted approach that pushes the boundaries of experimental and computational techniques. In a remarkable series of laser-driven shock compression experiments, the team recreated the extreme pressure conditions—up to an astounding 1,400 gigapascals (GPa)—found at the base of planetary mantles. Their samples focused on ferropericlase ((Mg,Fe)O) with variable iron content, directly simulating the compositional makeup of the suspected iron-rich BMO. These painstaking experiments allowed the researchers to probe how electrical conductivity behaves in these complex oxide melts at pressures and temperatures previously unreachable in laboratory settings.
Contrary to longstanding theoretical expectations that electrical conductivity would increase dramatically with iron content, the experimental results revealed a surprising outcome: the d.c. (direct current) electrical conductivities of MgO and iron-bearing (Mg,Fe)O converge under extreme compression, becoming indistinguishable in the pressure range of 467 GPa to 1,400 GPa. This finding overturns conventional wisdom, indicating that the iron enrichment in the BMO does not necessarily yield higher conductivity as once believed. This insight redefines our understanding of the electrical transport properties in planetary interiors and has significant ramifications for modeling planetary dynamos.
Complementing the experimental work, the team conducted density functional theory molecular dynamics (DFT-MD) simulations to theoretically investigate the microscopic transport mechanisms of these oxides under extreme conditions. This computational lens provided atomic-scale clarity on how electrons move through the crystal lattice and disordered molten states, confirming the experimental observations. Such synergy between experimental data and first-principles calculations reinforces the robustness of the conclusions and highlights the nuanced interplay between composition, pressure, and electronic behavior in deep planetary materials.
Beyond the laboratory and simulation frameworks, Nakajima et al. took the bold step of integrating their findings into long-term evolutionary models of super-Earths, exoplanets larger than Earth but smaller than Neptune. These models simulate the thermal and magnetic histories of these massive rocky worlds, incorporating the newly determined conductivity parameters of the basal magma ocean analogues. The results are transformative, suggesting that super-Earths exceeding roughly 3 to 6 times Earth’s mass could sustain basal magma ocean-driven dynamos with magnetic field strengths nearly an order of magnitude greater than those generated by their metallic iron cores alone.
This revelation has sweeping implications for our exoplanetary census and our understanding of planet habitability, atmospheric retention, and magnetic shielding. A long-lived, highly conductive BMO dynamo could produce robust magnetic fields during crucial early epochs, protecting planetary surfaces from atmospheric erosion by stellar winds and cosmic radiation. These findings herald a paradigm shift, underscoring that molten silicate mantles—traditionally considered poor electrical conductors—may play an outsized role in planetary magnetism under the most extreme pressures.
The confirmation that (Mg,Fe)O’s electrical conductivity converges with pure MgO under high compression also demands revisions of geophysical models that interpret magnetic signatures and thermal evolution. Previously, the assumption of iron content enhancing conductivity has influenced predictions of heat flow, mantle convection vigor, and core cooling rates. Incorporating the newly discovered conductivity plateau alters these thermal and magnetic evolution trajectories, offering fresh perspectives on early Earth’s magnetic field generation and its sustaining mechanisms.
Intriguingly, this study bridges observations of early Earth with the magnetic phenomena inferred in distant exoplanets, suggesting a universal mechanism that governs planetary magnetic activity in the magma ocean phase. Understanding the longevity and strength of BMO dynamos refines the timeline for when protective magnetic fields emerge on terrestrial planets, directly influencing their capacity to harbor life. It also evaluates the role of magma oceans in stripping or preserving primordial atmospheres, factors critical to assessing exoplanetary habitability.
The authors’ employment of cutting-edge laser shock compression experiments provides a new platform for investigating extreme mineral physics. By simulating pressures many times those at the Earth’s core-mantle boundary, these experiments open uncharted territory for exploring electronic and structural transitions in mantle materials. Their method offers a powerful tool to test theoretical predictions about planetary interiors, potentially transforming how we anticipate magnetic field generation in varied planetary contexts across the galaxy.
In parallel, the DFT-MD simulations shed light on the atomic-scale origins of electrical transport, capturing the complex interplay between iron atoms, oxygen sublattices, and magnesium ions. This computational insight reveals that while iron contributes localized electronic states, its effect on overall conductivity diminishes under the crushing immense pressures found deep within planets. Such understanding clarifies the fundamental physics of oxide melts and highlights the necessity of integrating experiments with simulations.
By weaving together experimental, theoretical, and modeling techniques, Nakajima et al. present a compelling narrative of planetary magnetic evolution, grounded in rigorous data and sophisticated interpretations. Their work challenges established dogma and forwards a refined framework that planetary scientists and astrophysicists will integrate into future explorations of planetary magnetism and interior dynamics.
This research not only resolves long-standing ambiguities about the electrical properties of ferropericlase but also redefines the potential for basal magma oceans as engines of planetary magnetism. The presence of powerful BMO dynamos in super-Earths invokes exciting possibilities for detecting magnetic fields on exoplanets, a goal that informs next-generation space telescopes and observational missions. By better understanding the internal magnetic processes of rocky planets, scientists edge closer to unlocking the secrets of planetary habitability and magnetic shielding across the cosmos.
Overall, the study offers a transformative leap forward in understanding the deep interiors of Earth-like planets and their magnetic environments. As planetary missions and astronomical observations probe exoplanets in unprecedented detail, integrating such rigorous mineral physics and dynamo models will be essential to interpreting their magnetic signatures—and, by extension, their potential to support life. This work truly expands the frontier of planetary sciences, revealing the subtle but critical role of molten silicate chemistry and conductivity under cosmic pressures.
For planetary scientists, geophysicists, and astronomers alike, the discovery that super-Earths can host extraordinarily strong, long-lived basal magma ocean dynamos revises foundational concepts about planetary magnetic field origins. It opens promising new pathways to explore the universality of dynamo generation, the variability of magnetic fields in rocky planets, and the magnetic fingerprints that may one day guide our search for habitats beyond our solar system.
In the grand tapestry of planetary formation and evolution, the basal magma ocean emerges as a vital, dynamic player—a molten molten heartbeat that drums beneath planetary surfaces, powering magnetic fields that protect atmospheres and potentially life itself. Nakajima and their collaborators have crafted a landmark study that will undoubtedly resonate through planetary science for years to come, advancing the quest to understand worlds far beyond our own.
Subject of Research: Electrical conductivities of magnesium-iron oxides under extreme pressures and implications for planetary mantle dynamics and magnetic field generation.
Article Title: Electrical conductivities of (Mg,Fe)O at extreme pressures and implications for planetary magma oceans
Article References:
Nakajima, M., Harter, S.K., Jasko, A.V. et al. Electrical conductivities of (Mg,Fe)O at extreme pressures and implications for planetary magma oceans. Nat Astron (2026). https://doi.org/10.1038/s41550-025-02729-x
Image Credits: AI Generated
