A weak spot in Earth's magnetic field over the South Atlantic Ocean has ballooned in size since 2014, satellite data reveals.

The region, known as the South Atlantic Anomaly, has grown by an area nearly half the size of continental Europe, sprouting a lobe in the direction of Africa where the field is weakening the fastest.

And the anomaly, linked to mysterious fluctuations near Earth's outer core, could pose a risk to satellites passing over the region, according to a study published in the November issue of the journal Physics of the Earth and Planetary Interiors.

"The South Atlantic Anomaly is not just a single block," study lead author Chris Finlay, a professor of geomagnetism at the Technical University of Denmark, said in a statement. "It's changing differently towards Africa than it is near South America. There's something special happening in this region that is causing the field to weaken in a more intense way."

Researchers first detected the South Atlantic Anomaly in the 19th century. Inside its boundaries, the magnetic field that radiates away from Earth's interior dips down to an altitude of about 120 miles (200 kilometers) above the planet's surface, which is much lower than the field's average altitude of about 400 miles (650 km).

This poses a threat to satellites and other spacecraft. Earth's magnetic field shields the planet and objects in low Earth orbit from charged solar particles and incoming X-ray and ultraviolet radiation, so spacecraft traveling over the South Atlantic Anomaly are exposed to more of these impacts. This could lead to malfunctions or damage in hardware, and even blackouts, according to the statement.

Finlay and his colleagues think the South Atlantic Anomaly is growing and spreading eastward due to strange fluxes at the limit between Earth's mantle and outer core, the layers of the planet sandwiched between Earth's crust and inner core.