A strange and long-standing mystery deep beneath Earth’s surface is becoming even more puzzling. The South Atlantic Anomaly (SAA) a massive weak spot in Earth’s magnetic field stretching between South America and southern Africa is expanding at a surprisingly rapid pace, according to a new scientific analysis.
This anomaly isn’t new. Scientists have known about the weakened region for more than a century. But new data collected over the last eleven years shows that it is Earth’s Magnetic Field Now Growing Rapidly, expanding by an area nearly half the size of continental Europe. These findings, published in Physics of the Earth and Planetary Interiors, raise important questions about what’s happening deep inside the planet.
A Weak Shield Over the South Atlantic
The Earth’s magnetic field acts like a planetary shield, protecting life from harmful solar radiation and cosmic particles. Where the field weakens as it does in the South Atlantic satellites and astronauts are exposed to higher radiation levels. Instruments glitch, electronic systems degrade, and spacecraft passing through the SAA must routinely shut down sensitive equipment.
The unusual weakening in this region has been documented since the early 20th century, but until recently, its growth appeared relatively slow. The new study, however, shows that the anomaly has expanded dramatically in just over a decade, suggesting that Earth’s magnetic field is shifting in ways not fully understood.
A Satellite View Deep into Earth
To uncover what’s driving this change, an international team examined high-resolution data from ESA’s Swarm satellite constellation. Launched in 2013, Swarm’s three identical satellites orbit Earth in precise formation, measuring magnetic signals from:
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Earth’s outer core
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The mantle and crust
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The ionosphere
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The oceans
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Solar and space weather activity
Because Earth’s magnetic field is generated in the molten outer core, studying these signals helps researchers understand the dynamic processes happening thousands of kilometers beneath the surface.
A Turbulent Core May Be to Blame But Not Alone
Scientists’ leading theory is that the SAA is linked to a huge, swirling mass of molten iron located about 1,800 miles (2,900 km) below Earth’s surface. This turbulent flow distorts the magnetic field above it. If this churning mass weakens the magnetic field in one region more than others, a localized magnetic “dent” forms — like the SAA.
But the new research suggests the story is more complicated. The anomaly isn’t weakening uniformly. Instead, different parts of it are behaving differently.
Not One Weak Spot But Several
Chris Finlay, lead author and geomagnetism expert at the Technical University of Denmark, explains that the SAA is actually a cluster of interacting weak regions, not a single smooth dip.
“The South Atlantic Anomaly is not just a single block,” Finlay said. “It’s changing differently toward Africa than it is near South America. There’s something special happening in this region that is causing the field to weaken in a more intense way.”
According to the Swarm data, the magnetic field lines in some parts of the anomaly behave in unexpected ways. Normally, magnetic lines flow outward from Earth’s core in the Southern Hemisphere. But within the SAA, researchers found areas where the magnetic field lines bend downward and plunge back into the core an unusual and poorly understood reversal.
Magnetic Changes Around the World
The South Atlantic isn’t the only region experiencing unusual magnetic changes. Swarm has also recorded two major trends:
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The magnetic field is strengthening over Siberia
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It is weakening significantly over Canada
These changes are likely connected to the north magnetic pole’s rapid drift toward Siberia — a phenomenon that has accelerated over the past two decades. This movement forces magnetic models to be updated more frequently to keep GPS, navigation, and communication systems accurate.
Why the Magnetic Field Matters
Earth’s magnetic field affects far more than compass readings. It shapes:
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Satellite stability and radiation exposure
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Aviation routes
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GPS accuracy
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Power grid resilience
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Deep-Earth geophysics
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Space weather prediction
If the SAA continues to expand, more satellites — especially those in low-Earth orbit — will pass through regions of intensified radiation. Understanding the anomaly isn’t just academic; it’s essential for protecting modern technology.
A Window into Earth’s Hidden Interior
Earth’s magnetic field is incredibly complex. Although it is often compared to a bar magnet, Finlay emphasizes that this analogy only captures a small part of the full structure.
“Earth’s magnetic field is not a simple dipole,” he said. “Only by using satellites like Swarm can we map its structure in detail and watch it evolve over time.”
As the SAA continues to grow and shift, scientists hope that long-term monitoring will help unravel the forces reshaping Earth’s core.
Looking Ahead: The Mission Continues
Given the anomaly’s rapid evolution, the European Space Agency plans to extend the Swarm mission through at least 2030, allowing scientists to track subtle changes in the magnetic field with unprecedented precision.