Liquid iron in Earth’s outer core can behave in surprising ways. Scientists discovered that a large flow of molten material deep beneath the Pacific Ocean changed direction for reasons that remain unclear. Data from ESA satellites helped researchers trace the shift and build a more detailed picture of what is happening near the center of the planet.
Earth’s molten outer core lies about 2200 km below the surface. As this electrically conducting liquid iron moves, it helps generate the planet’s geomagnetic field. For many years, scientists studying small variations in that field concluded that much of the outer core was flowing mainly westward.
A Sudden Reversal Beneath the Pacific
That pattern changed dramatically in 2010. Beneath the Pacific Ocean, a large region of molten material began moving strongly eastward instead of continuing its weaker westward flow. Scientists still do not know what caused the reversal.
Satellite observations, including measurements from ESA’s Swarm and CryoSat missions, have now allowed researchers to study the event in greater detail.
Published in the Journal of Studies of Earth’s Deep Interior, the study combines ground-based observations with satellite measurements collected from 1997 through 2025. The researchers used data from ESA’s Swarm and Cryosat missions, along with observations from Germany’s CHAMP mission and the Ørsted mission.
Their analysis showed that a broad area of iron-rich fluid below the equatorial Pacific shifted from a weak westward flow to a strong eastward flow in 2010.
Scientists had generally viewed large-scale circulation in the outer core as relatively stable. The sudden change beneath the Pacific suggests that the system can vary much more quickly than previously believed. The findings offer new clues about the turbulent motions responsible for producing Earth’s magnetic field. They may also point to connections between activity in the outer core and changes taking place even deeper inside the planet.
Lead author of the study, Frederik Dahl Madsen, of the University of Edinburgh — School of Geosciences, said, “The large-scale flow reversal beneath the Pacific raises new questions about the behavior of Earth’s deep interior. Scientists now want to understand whether the reversal represents a short-lived fluctuation, part of a repeating oscillation, or a new stable equilibrium for core circulation. Continued monitoring will be essential to determine how the flow evolves over the coming years.”
Possible Links to Earth’s Inner Core
Madsen also said the research model indicates that the strong eastward flow beneath the Pacific has weakened since 2020. He added, “The rise of the strong eastward flow in the Pacific is contemporary with a change in behavior in the inner core, as inferred from geodesy and seismology, and we hypothesize that these changes in the deep interior are associated with the changes in flow beneath the Pacific.”
Detecting Earth’s Molten Core From Space
Earth’s magnetic field is produced by movement within the liquid outer core. There, electrically conducting molten iron circulates around the solid inner core. This process, known as the geodynamo, changes continuously. Even so, many of its broad flow patterns have appeared relatively consistent over decades of observation.
ESA launched the three Swarm satellites in 2013. Each carries highly sensitive magnetometers that can measure Earth’s magnetic field with exceptional precision. Because the satellites travel in carefully coordinated orbits, they can separate magnetic signals coming from the core from signals produced by the crust, oceans, ionosphere and magnetosphere.
These measurements allowed scientists to reconstruct changing flow patterns near the core-mantle boundary. They also helped researchers identify the abrupt changes linked to the Pacific reversal and the 2017 geomagnetic jerk.
According to ESA’s Swarm Mission Manager, Anja Stromme, the mission’s long record of observations was essential to the research. She noted, “Although Swarm was launched after the dramatic reversal event of 2010, it has provided high-precision data that tell us about Earth’s inner core in the period that followed.
“Importantly, Swarm provides continuous global coverage over many years, allowing scientists to track how core dynamics evolve over time rather than relying only on ground-based magnetic observatories. Long-duration satellite magnetic measurements allow researchers to follow changes in the geodynamo in near-real-time and improve models of Earth’s magnetic field evolution. Future observations from missions such as Swarm will play a crucial role.”
Signs of a Possible Natural Cycle
The satellite measurements also revealed wave-like accelerations and rapidly shifting flow structures that could have been difficult to detect in noisier datasets.
The findings indicate that the eastward flow may now be weakening after reaching its strongest point several years ago. This raises the possibility that the reversal was temporary or that it forms part of a longer natural cycle within the outer core.
Why Earth’s Core Matters
These events occur far beneath the surface and do not pose a threat to people or the climate. However, they are central to understanding how Earth functions.
The movement of liquid iron in the outer core generates the magnetic field that protects the planet from charged particles released by the Sun. Without this protective field, Earth’s atmosphere and technological systems would face much greater exposure to harmful solar radiation.
Earth’s magnetic field is always changing. As the flow within the core evolves, the field gradually shifts as well. These changes can influence navigation systems, spacecraft operations and models used to study near-Earth space weather. Learning how and why the outer core changes is therefore important for both scientific research and practical applications.
According to Elisabetta Iorfida, ESA’s Swarm Mission Scientist, the Pacific reversal challenges the idea that stable westward circulation dominates the outer core. She noted, “This study shows that regional changes can emerge rapidly within just a decade. The findings may also help scientists investigate possible interactions between Earth’s outer core, inner core, lower mantle and, therefore, give more insights into core-mantle boundary, which is a critical region for the deep Earth dynamics.
“This research raises intriguing questions about how Earth’s deepest layers are dynamically connected. As the magnetic field continues to evolve, satellite missions are providing an increasingly detailed view of the dynamic processes unfolding deep inside our planet, revealing that Earth’s core may be far more variable and complex than once believed.”
