NASA investigates mysterious South Atlantic Anomaly

Scientists at NASA are investigating the mysterious South Atlantic Anomaly, a region of weakness in the Earth's magnetic field that is growing in size.

On average, the planet's magnetic field has lost almost 10% of its strength over the last two centuries - but there is a large localised region of weakness stretching from Africa to South America.

Known as the South Atlantic Anomaly, the field strength in this area has rapidly shrunk over the past 50 years just as the area itself has grown and moved westward.

Over the past five years, a second centre of minimum intensity has developed southwest of Africa, which researchers believe indicates that the anomaly could split into two separate cells.

The weakness could expose the planet to danger, as the Earth's magnetic field repels and traps dangerous solar radiation, but this weak spot means that these particles are dipping closer and closer to the surface.

Without the protection of the magnetic field this radiation could directly harm life, as well as destroy computers on board ships and aircraft. It's already causing technical difficulties for satellites orbiting the Earth.

Such weaknesses have occurred in the past.

During what is known as the Laschamp event the reduction in the strength of the Earth's magnetic field was so severe that the planet was bombarded with more cosmic rays than usual.

This is something that can be detected today in ice cores dated to this period which have far more radioactive elements in them than usual.

Terry Sabaka and Wijia Kuang, geophysicists at NASA, are observing using the European Space Agency's SWARM satellites to investigate how the South Atlantic Anomaly is changing.

"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," Dr Sabaka said. "Because that's what helps us make models and predictions."

The anomaly is caused by processes inside of the Earth where the magnetic field originates, in the outer core where molten metal, rich in iron, churns 1,800 miles (2,900 km) below the surface.

At the moment, to avoid satellites being hit by a high-energy proton, which can cause it to short circuit - or potentially worse if a key component is hit - operators shut down non-essential components in their satellites as they fly through the area.

NASA's satellite the Ionospheric Connection Explorer regularly travels through the region so the team is forced to keep track of the anomaly's position and strength.

Although the International Space Station is well-protected, as it has to be due to the astronauts living there, there are instruments on board which are so sensitive they are impacted by passing through the anomaly.

According to Bryan Blair, the Global Ecosystem Dynamics Investigation (GEDI) mission on the ISS has its power boards reset about once a month when it passes through the anomaly.

"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."

One speculation is that the weakening of the field is a sign that the Earth is heading for a pole reversal - in which the north and south magnetic poles flip.

This flip doesn't happen immediately, but instead would occur over the course of a couple of centuries during which there would be multiple north and south magnetic poles all around the globe.

"Such events have occurred many times throughout the planet's history," said ESA, noting "we are long overdue by the average rate at which these reversals take place (roughly every 250,000 years)".