A weak spot in Earth’s magnetic field is developing over the South Atlantic Ocean, according to more than a decade of satellite data collected by scientists.
The magnetic field surrounding Earth protects the planet from cosmic radiation and charged particles from the sun. Scientists believe it is generated by Earth’s outer core, according to a press release from the European Space Agency. The ESA said the “global ocean of molten and swirling liquid iron” in this layer of the planet creates electric currents that generate the magnetic field.
The weak spot, known as the South Atlantic Anomaly, was first identified in the 19th century, the ESA said. It is southeast of South America and southwest of Africa. In this area, the planet’s magnetic field decreases, according to NASA. Satellites flying over it are hit by higher doses of incoming radiation, which can cause technical problems and even power outages.
ESA (Data source: Finlay, CC et al., 2025)
The ESA studied the spot for 11 years, from 2014 to 2025. Three different satellites, known as Swarm, precisely measured the planet’s magnetic signals during this period. The data was published in the journal Science Direct.
Satellite data showed that the South Atlantic anomaly had expanded over an area “nearly half the size of continental Europe”, or about two million square miles. The rate of weakening of the area has accelerated since 2020, the ESA said, with different parts of the anomaly evolving at different rates.
“The South Atlantic anomaly is not just one lump,” says lead author Chris Finlay, professor of geomagnetism at the Technical University of Denmark, in the ESA press release. “The situation is developing differently towards Africa and towards South America. Something special is happening in this region which weakens the field more intensely.”
ESA (Data source: Finlay, CC et al., 2025) 
Finlay said magnetic field lines emitted by the core bounced back there. It’s unclear why this happens, but it contributes to the weakening of the anomaly in these areas, the ESA said.
ESA satellites have discovered other changes in the Earth’s magnetic field. In the southern hemisphere, there is another area where the magnetic field is particularly strong. Two other anomalies exist in the northern hemisphere: one near Canada and one over Siberia. Both are stronger than the rest of the pack. However, the one near Canada decreased by an area equivalent to that of India, while the one located over Siberia increased by an area equivalent to that of Greenland, the ESA said.
Medialab ESA/AOES 
Satellites will continue to study the planet’s magnetic field in the coming years, the ESA said.
“It’s truly wonderful to get a bird’s-eye view of our dynamic Earth through Swarm’s extended time series,” Swarm mission manager Anja Stromme said in a statement. “The satellites are all healthy and providing excellent data, so we hope to be able to extend this record beyond 2030, when the solar minimum will provide unprecedented information about our planet.”
