NASA Is Watching a Vast, Growing Anomaly in Earth’s Magnetic Field

NASA has been observing an unusual anomaly in Earth’s magnetic field: a vast region of reduced magnetic intensity stretching between South America and southwestern Africa.

Known as the South Atlantic Anomaly (SAA), this immense and evolving phenomenon has captivated scientists for years, particularly NASA researchers.

The weakened magnetic field within the anomaly makes NASA’s satellites and spacecraft especially vulnerable to solar-charged particles.

Described by NASA as a “dent” in Earth’s magnetic field or a “pothole in space,” the SAA does not generally affect life on Earth. However, orbital spacecraft, including the International Space Station, regularly pass through the region as they orbit the planet at low altitudes.

When spacecraft encounter this anomaly, the weakened magnetic field leaves their systems susceptible to high-energy protons from the Sun, which can cause short circuits and malfunctions. While these impacts are often minor, they pose risks of data loss or even permanent damage to critical components. To mitigate these risks, satellite operators often shut down systems before entering the anomaly zone.


NASA monitors the SAA not only to manage these hazards but also to study the anomaly as it offers a unique chance to understand a complex and elusive phenomenon. Thanks to its extensive resources, NASA is well-equipped to investigate this occurrence.

“The magnetic field is actually a superposition of fields from many current sources,” explained geophysicist Terry Sabaka from NASA’s Goddard Space Flight Center in 2020.

The primary source of this field is believed to be the swirling molten iron in Earth’s outer core, thousands of kilometers beneath the surface. This dynamic movement generates electrical currents that form the magnetic field, but its distribution is not uniform.

A massive reservoir of dense rock, called the African Large Low Shear Velocity Province, located approximately 2,900 kilometers (1,800 miles) beneath Africa, is thought to disrupt the field’s formation, amplifying the weakening effect. This is further influenced by the tilt of Earth’s magnetic axis.

“The observed SAA can also be interpreted as a consequence of the weakening dominance of the dipole field in the region,” said NASA Goddard geophysicist and mathematician Weijia Kuang in 2020. “More specifically, a localized field with reversed polarity grows strongly in the SAA region, making the field intensity very weak compared to surrounding areas.”

Although many aspects of the SAA remain unclear, researchers continue to uncover valuable insights. For instance, a 2016 study led by NASA heliophysicist Ashley Greeley revealed that the SAA drifts over time. This was later confirmed by CubeSat tracking in research published in 2021.

Remarkably, the anomaly also seems to be dividing. In 2020, researchers discovered it was splitting into two distinct cells, each representing a separate zone of minimum magnetic intensity within the anomaly.

NASA Is Watching a Vast, Growing Anomaly in Earth’s Magnetic Field
Satellite data suggesting the SAA is dividing. (Division of Geomagnetism, DTU Space)

What this division means for the future of the SAA is uncertain, but there’s evidence to suggest the phenomenon is not new. A 2020 study indicated that this may be a recurring magnetic event affecting Earth for at least 11 million years.

If true, this suggests the anomaly is not necessarily a precursor to a full planetary magnetic field reversal—a phenomenon that occurs but only over hundreds of thousands of years.

In another study from this year, researchers found that the SAA also influences auroras visible on Earth.

While significant questions remain unanswered, it’s reassuring that NASA continues to monitor this magnetic oddity closely.

“Even though the SAA is slow-moving, it is undergoing changes in morphology, so it’s crucial to keep observing it through ongoing missions,” Sabaka noted. “This is what helps us create models and predictions.”


NASA Is Watching a Vast, Growing Anomaly in Earth’s Magnetic Field

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