Data from a trio of European satellites circling the globe reveals that a vast and growing weak spot in Earth’s magnetic field is expanding and becoming more complex. For more than a decade, the European Space Agency’s Swarm mission has precisely tracked our planet’s protective magnetic shield, providing the longest continuous record of it from space and offering unprecedented insight into the dynamic forces that shape it.
These new findings, based on 11 years of high-resolution measurements, show the continued evolution of the South Atlantic Anomaly, an area of reduced magnetic intensity that stretches from South America to Africa. The changes observed deep within the planet’s core carry significant implications for the satellites and spacecraft that pass through the region, as the weakened field offers less protection from harmful solar radiation. By untangling the signals from Earth’s deep interior, scientists are beginning to understand the intricate processes that govern our planet’s first line of defense against the harsh environment of space.
A Watchful Swarm in Orbit
The European Space Agency launched the Swarm mission on November 22, 2013, to provide a comprehensive survey of the geomagnetic field. The mission consists of a constellation of three identical spacecraft—named Alpha, Bravo, and Charlie—that orbit Earth in two different polar orbits. Two of the satellites fly side-by-side at a lower altitude of about 450 kilometers, while the third orbits higher at 530 kilometers. This unique configuration allows scientists to separate the magnetic signals originating from different parts of the planet, from the deep core to the crust, oceans, and atmosphere.
Each satellite is equipped with highly sensitive instruments, including vector and scalar magnetometers, which measure the direction and strength of the magnetic field with exceptional accuracy. Over their 11-year operational history, far exceeding their planned four-year lifespan, the Swarm satellites have generated the most detailed 3D map of the magnetic field and its evolution ever produced. This long-term dataset is critical for modeling how the field changes over time, offering a deeper understanding of planetary dynamics and providing essential data for practical applications like global navigation and space weather forecasting.
Mapping a Growing Anomaly
The most dramatic changes observed by Swarm are centered on the South Atlantic Anomaly (SAA), a feature first identified in the 19th century. This region is characterized by a significant dip in magnetic field strength compared to the global average. The latest models show that since 2014, this anomaly has steadily expanded, growing by an area roughly half the size of continental Europe. The minimum field intensity within the SAA has also continued to drop, falling by approximately 336 nanoteslas between 2014 and 2025. The anomaly now covers almost 1% of the planet’s surface.
This weakening is not a uniform process. Researchers have identified distinct centers of change, suggesting complex behaviors at the source of the field. According to Chris Finlay, a professor at the Technical University of Denmark, the field is evolving differently in the areas near South America compared to a region southwest of Africa. Data indicates that since 2020, the field weakening has accelerated in a concentrated area of the Atlantic off the southwestern coast of Africa. These localized, rapid changes point to dynamic and turbulent processes occurring thousands of kilometers below the surface.
Pockets of Rapid Change
While the South Atlantic Anomaly represents the most prominent area of weakening, the Swarm data reveals a global magnetic field in constant flux. In a contrasting development, the magnetic field has actually strengthened over Siberia. At the same time, a historically strong region over Canada has diminished in size. The growth of the Siberian high-intensity zone and the shrinking of the Canadian one illustrate the push-and-pull nature of our planet’s magnetic environment. These shifts are not isolated events but are interconnected through the deep geodynamic processes that sustain the field.
Probing the Planetary Engine
Earth’s magnetic field is generated by the geodynamo, a process driven by the movement of a vast ocean of molten iron in the planet’s outer core, approximately 3,000 kilometers beneath our feet. This swirling, electrically conducting liquid acts like a massive dynamo, creating electrical currents that produce our ever-changing magnetic shield. The precision of the Swarm constellation allows scientists to peer deep into this region and map the flows of this liquid metal.
The latest results suggest that the expansion of the South Atlantic Anomaly is linked to the behavior of “reversed flux patches” on the core-mantle boundary. These are areas where the magnetic field’s polarity is opposite to the dominant global field. The migration and interaction of these patches appear to drive the weakening seen at the surface. In 2016, scientists using Swarm data also discovered a jet-stream of liquid iron moving rapidly within the outer core, another element in the complex system that powers the geodynamo. These findings confirm that changes at the surface are direct expressions of the restless activity deep within the planet’s interior.
Consequences for a Wired World
While these magnetic fluctuations pose no direct danger to life on Earth’s surface, they have significant consequences for our technological infrastructure in space. The reduced magnetic field strength inside the South Atlantic Anomaly allows a higher dose of energetic particles from the sun and cosmic rays to penetrate closer to the planet. For satellites in low-Earth orbit, passing through this region is like flying through a radiation storm.
This increased radiation can disrupt sensitive electronic systems, corrupt data, damage critical hardware, and trigger temporary blackouts in satellite operations. Mission operators often power down non-essential components when a spacecraft’s trajectory takes it through the SAA to minimize potential damage. The Swarm mission itself has recorded hundreds of GPS signal blackouts linked to ionospheric thunderstorms, which are influenced by the magnetic field. As the anomaly expands and evolves, the risk to the thousands of satellites that provide global communication, navigation, and observation services increases, making accurate monitoring and forecasting of space weather more critical than ever.
An Evolving Planetary Shield
The continuous weakening of the magnetic field has led to speculation about whether Earth is heading toward a magnetic pole reversal, an event where the north and south magnetic poles swap places. While the current changes observed by Swarm are part of this long-term trend, they do not necessarily mean a reversal is imminent. The geological record shows that Earth’s field undergoes excursions and fluctuations as a normal part of its cycle.
By providing an unprecedentedly clear view of the field’s behavior, the Swarm mission is helping scientists distinguish between normal oscillations and the potential onset of a major planetary transition. The detailed models derived from Swarm data are essential for refining our understanding of the core’s hidden engine and improving our ability to forecast geomagnetic activity. These insights are vital not only for fundamental science but for safeguarding the space-based technologies that have become integral to modern life.