A dent in Earth's magnetic field over South America and the c is expanding westward and continuing to weaken in intensity, according to recent observations by National Aeronautics and Space Administration (Nasa) scientists.

Currently, the dent has not created any visible impacts on daily life on Earth, but it could pose risk to satellites and spacecraft that pass through it, the US space agency said.

Earth's magnetic field acts like a protective shield around the planet, repelling and trapping charged particles from the Sun.

But over South America and the southern Atlantic Ocean, an unusually weak spot in the field — called the South Atlantic Anomaly, or SAA — allows these particles to dip closer to the surface than normal.

Particle radiation in this region can knock out onboard computers and interfere with the data collection of satellites that pass through it.

Recent data shows the South Atlantic Anomaly's valley, or region of minimum field strength, has split into two lobes, creating additional challenges for satellite missions.

Nasa scientists have also studied the particle radiation in the region with the Solar, Anomalous, and Magnetospheric Particle Explorer, or SAMPEX — the first of Nasa's Small Explorer missions, launched in 1992 and providing observations until 2012.

One study, led by Nasa heliophysicst Ashley Greeley as part of her doctoral thesis, used two decades of data from SAMPEX to show that the anomaly is slowly but steadily drifting in a northwesterly direction.

"These particles are intimately associated with the magnetic field, which guides their motions," said Shri Kanekal, a researcher in the Heliospheric Physics Laboratory at Nasa Goddard Space Flight Center in Greenbelt, Maryland.

"Therefore, any knowledge of particles gives you information on the geomagnetic field as well."

Greeley's results, published in the journal Space Weather, were also able to provide a clear picture of the type and amount of particle radiation satellites receive when passing through the South Atlantic Anomaly, which emphasized the need for continuous monitoring in the region.

The South Atlantic Anomaly arises from two features of Earth's core: The tilt of its magnetic axis, and the flow of molten metals within its outer core.

The International Space Station, which is in low-Earth orbit, also passes through the South Atlantic Anomaly.

It is well protected, and astronauts are safe from harm while inside, Nasa said.

However, the ISS has other passengers affected by the higher radiation levels: Instruments like the Global Ecosystem Dynamics Investigation mission, or GEDI, collect data from various positions on the outside of the ISS.

The SAA causes "blips" on GEDI's detectors and resets the instrument's power boards about once a month, said Bryan Blair, the mission's deputy principal investigator and instrument scientist, and a lidar instrument scientist at Goddard.

"These events cause no harm to GEDI," Blair said.

"The detector blips are rare compared to the number of laser shots – about one blip in a million shots – and the reset line event causes a couple of hours of lost data, but it only happens every month or so."

The South Atlantic Anomaly is also of interest to Nasa's Earth scientists who monitor the changes in magnetic field strength there, both for how such changes affect Earth's atmosphere and as an indicator of what is happening to Earth's magnetic fields, deep inside the globe..