Scientists are keeping a close eye on a growing “dent” in Earth’s magnetic field over a swath of the Atlantic Ocean that stretches from South Africa westward into Brazil.
In this zone, known as the South Atlantic Anomaly, the magnetic field — the invisible shield that protects the planet from radiation and charged particles from the sun — is weaker than normal. Though it’s not thought to be dangerous to humans, experts say the weak spot could cause glitches or permanent damage to Earth-circling satellites that are exposed to energetic particles as they fly through the region.
“Those particles can wreak havoc on satellite instrumentation, so it’s good to track the South Atlantic Anomaly, and especially its changing shape, so that we can take preventative actions,” Terence Sabaka, a geophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said.
Scientists have known about the weak spot in Earth’s magnetic field for several decades, but new research suggests that the South Atlantic Anomaly is growing, spreading further west toward the Pacific Ocean, and is further weakening.
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“Satellite measurements, as well as theoretical modeling, predict that the area will be larger in the next five years or longer, and the strength of the magnetic field in that area will be even lower,” Weijia Kuang, a geophysicist and mathematician at NASA Goddard’s Geodesy and Geophysics Laboratory, said.
Kuang added that the weak spot also appears to be splitting in two, though it’s not yet known what specifically is driving that process.
Earth’s magnetic field is generated by the constant motion of liquid metal in the planet’s iron-rich outer core, roughly 1,800 miles below the surface. As these molten deposits slosh around, they produce electric currents that power Earth’s magnetic field and effectively turn the planet into a giant bar magnet.
But the constant churning in the outer core means the magnetic field is tilted, which is why the magnetic poles aren’t perfectly aligned with Earth’s geographic North and South poles. These dynamics deep inside the planet also create fluctuations and instability in the magnetic field.
In general, the magnetic field is strongest at the poles and weaker at the equator, but more research is needed to understand the precise cause of the South Atlantic Anomaly.
“It’s like a weakness on top of a weakness,” Sabaka said, adding that although other spots exist where the magnetic field is less intense, the one over the Atlantic is by far the largest and most significant.
Sabaka and Kuang have been mapping the South Atlantic Anomaly, but more data will help them finesse their models and build more accurate forecasts of how the weak spot could change over time.
Kuang said these insights will not only help protect satellites and other spacecraft in orbit around Earth, but could also give scientists a better understanding of processes that have unfolded deep inside the planet over hundreds of thousands or millions of years.
“This provides a very, very important window for us to probe the interior properties of the Earth,” he said, “and to understand the Earth as a whole over its evolution.”