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

The South Atlantic Anomaly is one of those pieces of space that are shrouded in mystery, and it has both intrigued and concerned scientists for years.

When it comes to outer space, it seems that the more we learn the less we know. Despite how far we’ve come, and the incredible advancements the scientific community has made over the last several decades, there are still many aspects of space that scientists don’t fully understand.

The South Atlantic Anomaly

The South Atlantic Anomaly (SAA) is a giant region of lower magnetic intensity in the Earth’s magnetic field that stretches between South America and Southwest Africa. NASA describes this phenomenon as a sort of “dent” in the Earth’s magnetic field, or like a “pothole in space”.

The SAA is complex and difficult to understand and is being actively monitored by NASA scientists. In order to begin uncovering its mystery, however, it is important to first understand the Earth’s magnetic field, and how it’s generated.

According to Terry Sabaka, a geophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, regions outside the solid earth contribute to the observed magnetic field, but most of it comes from the core.

“The magnetic field is actually a superposition of fields from many current sources,” he explained [2].

The forces in the Earth’s core together with the tilt of the magnetic axis produce the area of weaker magnetism, allowing charged particles that are trapped in the earth’s magnetic field to dip closer to the Earth’s surface.

An Ocean of Molten Iron

The main source for the magnetic field appears to be a swirling ocean of molten iron, which is located thousands of miles below the Earth’s surface inside the Earth’s outer core. Here, there is also a vast reservoir of dense rock called the African Large Low Shear Velocity Province. It rests between the hot liquid iron of the outer core and the stiffer, cooler mantle, and seems to be disturbing the iron, which generates the magnetic field [3].

NASA Goddard geophysicist and mathematician Weijia Kuang says that the SAA can also be interpreted as a consequence of the weakening of the dipole field in the region.

“More specifically, a localised field with reversed polarity grows strongly in the SAA region, thus making the field intensity very weak, weaker than that of the surrounding regions,” he said [2].

Causing the Earth’s Poles to Flip?

Initially, scientists thought that the SAA was an irregularity of modern history and that it could be a precursor or trigger to the entire planet’s magnetic field flipping, however, a recent study found that this is not the case. Instead, researchers at the University of Liverpool in the UK have determined that the SAA is a recurrent magnetic phenomenon that has affected earth for millions of years [4].

“Our study provides the first long term analysis of the magnetic field in this region dating back millions of years,” said lead author of the paper, University of Liverpool PhD student Yael Engbers. “It reveals that the anomaly in the magnetic field in the South Atlantic is not a one-off, similar anomalies existed eight to 11 million years ago.” [5]

The SAA is on the Move

A 2016 study revealed that the South Atlantic Anomaly is actually slowly drifting in a north-westerly direction [6]. Perhaps even more interestingly, it appears to be splitting in two.

Since the 1970s, the SAA has been growing and moving west at a speed of approximately twenty kilometers (twelve miles) per year. New readings from the European Space Agency’s (ESA) Swarm satellites have shown that a second center of minimum intensity has opened up with the SAA during the last five years [7].

This observation has led scientists to believe that the entire thing could be splitting up into two separate cells, with one centered above the middle of South America, and a new one off the coast of southwest Africa.

“The new, eastern minimum of the South Atlantic Anomaly has appeared over the last decade and in recent years is developing vigorously,” says geophysicist Jürgen Matzka from the German Research Centre for Geosciences. “The challenge now is to understand the processes in Earth’s core driving these changes.” [7]

How the SAA will develop from here, however, remains unclear.

Why NASA is Concerned

The Earth’s magnetic field acts as a kind of barrier that protects the Earth from solar winds and cosmic radiation. It also determines the location of the Earth’s magnetic poles, and any time its strength is reduced it needs to be monitored closely since it could have a significant impact on our planet.

Currently, however, the ESA says there is no reason to be alarmed. The most significant effects the SAA is exerting at present are mostly technical malfunctions onboard satellites and spacecraft as they pass through it during their orbit [7].

This, however, is cause for concern for NASA scientists, since spacecraft are exposed to charged particles from the sun when they pass through the SAA. These particles can cause systems onboard satellites to short-circuit and malfunction. 

This usually only causes low-level glitches, but there is the risk of significant data loss or permanent damage to key components to the spacecraft. For this reason, satellite operators routinely shut down spacecraft systems before they enter the anomaly zone [1].

Although scientists have been following the anomaly closely and have made some new discoveries regarding its cause and movement, there are still many large questions that are as of yet unanswered. 

“Even though the SAA is slow-moving, it is going through some change in morphology, so it’s also important that we keep observing it by having continued missions,” says Sabaka. “Because that’s what helps us make models and predictions.” [1]

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  1. NASA Is Tracking a Vast, Growing Anomaly in Earth’s Magnetic Field.” Scienc Alert. Peter Dockrill. August 18, 2020.
  2. NASA Researchers Track Slowly Splitting ‘Dent’ in Earth’s Magnetic Field.” NASA. August 17, 2020.
  3. NASA Researchers Track Slowly Splitting ‘Dent’ in Earth’s Magnetic Field.” Sience Alert. Peter Dockrill. March 6, 2018
  4. Elevated paleomagnetic dispersion at Saint Helena suggests long-lived anomalous behavior in the South Atlantic.” PNAS. Yael A. Engbers, et al. August 4, 2020.
  5. South Atlantic Anomalies existed 8 – 11 million years ago.” Livepool
  6. SAMPEX observations of the South Atlantic anomaly secular drift during solar cycles 22–24.” AGU Pubs. A. D. Jones, et al. November 21, 2016.
  7. The Mysterious Anomaly Weakening Earth’s Magnetic Field Seems to Be Splitting.” Science Alert. Peter Dockrill. May 26, 2020.