Insights into Earth’s molten outer core from space

The molten core, which swirls about 2200 km beneath our feet, generates Earth’s geomagnetic field as it moves. By measuring small changes in the magnetic field, scientists have historically inferred the core flowing mainly westwards.

But in 2010, it unexpectedly changed direction deep beneath the Pacific Ocean and started moving strongly eastwards. The reasons for this unexplained reversal in the flow of molten material are still a mystery. But satellites, including ESA’s Swarm and CryoSat, provided data that have now been analysed and published.

The study, in the Journal of Studies of Earth’s Deep Interior, analyses both ground observations and satellite data between 1997 and 2025. Data from ESA’s Swarm and Cryosat missions were used in the study as well as data from the German CHAMP mission and the Ørsted mission. The research found that in 2010, a broad region of iron-rich fluid beneath the equatorial Pacific switched from moving weakly westwards to strongly eastwards.

The outer core system was previously thought to move in a comparatively stable way – this dramatic change of flow suggests this is not always the case. The study provides insights into the turbulent processes that generate Earth’s magnetic field and hint at possible links between outer core dynamics and changes occurring deeper within 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 behaviour 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.”

Frederik also explained that the model used in the research suggests that the Pacific eastward flow has weakened since 2020, adding, “The rise of the strong eastward flow in the Pacific is contemporary with a change in behaviour in the inner core, as inferred from geodesy and seismology, and we hypothesise that these changes in the deep interior are associated with the changes in flow beneath the Pacific.”

Earth’s molten core detected from space

Earth’s magnetic field is generated by motion in the liquid outer core, where electrically conducting molten iron circulates around the solid inner core. This geodynamo is constantly evolving, but many of its long-term flow patterns have appeared to be relatively persistent over decades of observation.

Launched in 2013, the three Swarm satellites carry highly sensitive magnetometers capable of mapping Earth’s magnetic field with exceptional precision. By flying in carefully coordinated orbits, the satellites can distinguish magnetic signals originating from the core from those produced by the crust, oceans, ionosphere and magnetosphere.

These observations enabled researchers to reconstruct evolving flow patterns at the core–mantle boundary and identify the sudden changes associated with the Pacific reversal and the 2017 geomagnetic jerk.

According to ESA’s Swarm Mission Manager, Anja Stromme, the long-term dataset provided by Swarm is important for this study. 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-realtime and improve models of Earth’s magnetic field evolution. Future observations from missions such as Swarm will play a crucial role.”

The satellite data also allowed researchers to detect wave-like accelerations and rapidly changing flow structures that may otherwise have remained hidden within noisier datasets. The study also suggests that the eastward flow may now be weakening again after reaching a peak several years ago, raising the possibility that the event represents a temporary oscillation or part of a longer natural cycle in core dynamics.

Understanding our Earth system

Although these processes occur far below Earth’s surface and pose no danger to people or climate, they are fundamental to understanding how our planet works. The movement of liquid iron in the outer core generates Earth’s magnetic field, which shields the planet from charged particles streaming from the Sun. Without it, Earth’s atmosphere and technological infrastructure would be far more exposed to harmful solar radiation.

The magnetic field is not fixed. It slowly changes over time as the core flow evolves, affecting everything from navigation systems to spacecraft operations and models of near-Earth space weather. Understanding how and why the core changes is therefore important both scientifically and practically.

According to Elisabetta Iorfida, ESA’s Swarm Mission Scientist, the Pacific reversal challenges assumptions that the outer core is dominated by stable westward circulation. 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.”