The South Atlantic Anomaly: A Mysterious Weak Spot in Earth's Magnetic Field

The South Atlantic Anomaly: A Mysterious Weak Spot in Earth's Magnetic Field

High above our planet, where satellites orbit and astronauts glide through space, there's a strange region unlike any other. It's not a hole in the ozone layer, nor a gap in the atmosphere—but a disturbance in Earth’s magnetic field itself. Scientists call it the South Atlantic Anomaly (SAA), and it’s been puzzling geophysicists for decades.

But in recent years, something has changed. The anomaly is not only growing, but shifting and splitting, raising questions—and concerns—about what’s happening beneath our feet and above our heads.

What Is the South Atlantic Anomaly?

The South Atlantic Anomaly is a large area above South America and the southern Atlantic Ocean where Earth’s magnetic field is significantly weaker than elsewhere. In this zone, the strength of the magnetic field can dip as low as 22,000 nanoteslas, compared to an average of 60,000 nanoteslas in other regions.

This weak field allows high-energy particles from the Sun and cosmic rays to penetrate closer to Earth than usual. As a result, satellites and spacecraft passing through the region are exposed to elevated levels of radiation, which can interfere with onboard electronics, corrupt data, and even cause permanent damage.

The International Space Station (ISS) also passes through this region, prompting astronauts and engineers to power down sensitive equipment during these crossings to avoid malfunctions.

A Known Phenomenon with New Behaviors

Scientists have been aware of the anomaly since the 1960s, when early satellite missions noticed unexpected radiation spikes in this region. But in the past few decades, the anomaly has grown in size, moved westward, and—most notably—begun to split into two separate zones.

In 2020, researchers from the European Space Agency (ESA) published new findings using data from the Swarm satellite constellation, a mission launched in 2013 to monitor Earth’s magnetic field. One of the lead scientists, Jürgen Matzka of the German Research Centre for Geosciences (GFZ), noted:

"The South Atlantic Anomaly is evolving. It’s not only expanding, but showing behavior that we haven’t observed before."

This shifting and splitting has sparked global interest, with many wondering what it could mean for Earth's future—and its core.

Deep Earth Clues: The African Low-Velocity Zone

To understand the SAA, scientists look not just at the sky—but deep into the planet’s interior.

Earth’s magnetic field is generated by the movement of molten iron in the outer core, a process known as the geodynamo. But this system is affected by the materials and structures in the mantle above it.

One such structure is the African Low-Shear-Velocity Province (LLSVP)—a massive, dense zone located beneath the African continent. This region was highlighted in studies like that of Sarah L. Lekić from the University of Arizona, who suggested that such deep anomalies can disturb the normal flow of molten metals and impact the magnetic field above them.

As it happens, the SAA lies directly above this African mantle anomaly.

A Sign of a Pole Reversal? Not So Fast

Some media reports have connected the South Atlantic Anomaly with the idea of an imminent geomagnetic pole reversal—a process where the magnetic north and south poles swap places.

Indeed, Earth’s magnetic poles have reversed multiple times throughout geological history, with the last full reversal occurring around 780,000 years ago during the Brunhes–Matuyama event. Partial and temporary excursions, like the Laschamp event around 42,000 years ago, have also been documented.

But while the SAA’s behavior is unusual, most scientists don’t believe a reversal is imminent. In a 2020 paper in Nature Geoscience, geophysicist John Tarduno from the University of Rochester warned against drawing quick conclusions:

"Although the weakening of the magnetic field in the South Atlantic is significant, we have seen similar fluctuations in the past without a full pole reversal."

That said, the anomaly remains a critical region to monitor, as it gives us clues about how the magnetic field evolves over time.

A Challenge for Space Technology

The South Atlantic Anomaly presents practical challenges for today’s space-based infrastructure:

Hubble Space Telescope routinely powers down instruments while crossing the SAA to protect its systems.

Satellites from both NASA and ESA have reported increased radiation exposure and occasional malfunctions while in the region.

Communications satellites, navigation systems, and military equipment may also experience disruptions when orbiting through the anomaly.

To mitigate risks, satellite operators now design orbits and shielding with the SAA in mind. Some missions even avoid the area altogether, if possible.

A Planet That’s Always Changing

The South Atlantic Anomaly reminds us that Earth is not a static planet. Beneath our feet, the liquid iron of the outer core swirls and shifts, creating a magnetic field that protects all life—but is also subject to mysterious changes.

From deep mantle structures to solar particles in the sky, the SAA is a meeting point of geophysics and space weather, of ancient planetary processes and cutting-edge technology.

And though it doesn’t pose an immediate threat to humans on the ground, it continues to challenge our satellites, test our understanding of Earth's interior, and inspire scientific curiosity.

Perhaps, in the anomaly’s shifting patterns, we are witnessing the heartbeat of a living planet.