Some 2,200 kilometers beneath our feet lies the outer core, a molten layer of rock that moves constantly. This rotation creates the planet’s natural magnetic field. For decades, scientists had observed the core rotating primarily westward. But in 2010, something bizarre happened: the flow beneath the Pacific Ocean suddenly reversed direction and began surging east. The reason for this rebound is still unclear.
Thanks to satellites like ESA’s Swarm and CryoSat, researchers gathered detailed measurements of small changes in the strength of Earth’s magnetic field.
The team analyzed almost 30 years (1997–2025) of data collected by ground stations and satellite missions, including ESA’s Swarm and CryoSat, Germany’s CHAMP, and Denmark’s Ørsted. The results call into question long-held assumptions about the outer core being stable.
This reversal indicates that explosive things are happening deep within the Earth, allowing us to glimpse new clues about how such magnetic fields come into being. It also provides an indication of potential new, previously unrecognized connections between what is happening in the outer core and changes occurring deeper in the Earth.
Scientists reveal Earth’s crust was moving far earlier
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.”
The geodynamo is driven by the circulation of molten iron in the outer core around the solid inner core, and it is this circulation that maintains Earth’s magnetic field. Despite the highly dynamic nature of this circulation, most of its main flow patterns remained stable over several decades.
In 2013, ESA launched the trio of Swarm satellites, each carrying ultra‑sensitive magnetometers. These satellites, flying in precisely coordinated orbits, can separate magnetic signals originating in the core from those originating in the crust, oceans, atmosphere, and space.
This accuracy has allowed scientists to piece together the evolution of flows at the core–mantle boundary over time. There were unexpected things associated with these reconstructions, for example, the Pacific reversal in 2010 or the sharp ‘geomagnetic jerk’ of 2017, which showed that Earth’s deep interior is capable of undergoing rapid and unpredictable changes.
New insight into Earth’s crust, mantle and outer core interactions
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 tells us about Earth’s inner core in the period that followed.
The broader data set also revealed the more nuanced, wave-like accelerations and rapid flow changes buried within less precise records. That research indicates the eastward flow beneath the Pacific may be waning, signaling a possible deceleration of a much larger oscillation, or longer cycle, in Earth’s deep interior.
At its core lies the swirling molten iron of the outer layer, from which much of Earth’s magnetic field originates, protecting us from particles emitted by the Sun. The atmosphere and our technological systems would be much more exposed to debilitating radiation coming from the Sun without that shielding field.
However, the magnetic field is not fixed. Over time, it slowly changes as the flow patterns in the core evolve, making navigation systems less accurate and spacecraft communications useless, along with models of near-Earth space weather. There are thus both scientific and technical (as well as societal) reasons to understand the mechanisms that control core motion. Keeping tabs on these small shifts helps keep technology safe and adds to our knowledge of Earth’s internal workings.
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 the 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.”
Journal Reference:
Frederik Dahl Madsen, Isobel Howard, William Brown., Kathryn Whaler. Principal component analysis of the 2010 reversal of core-surface flow beneath the Pacific Ocean. Journal of Studies of Earth’s Deep Interior. DOI: 10.46298/jsedi.17268