Nasa investigating earth's mysteriously weakening magnetic field amid concerns over satellites and spacecraft

'Dent' or anomaly is small but getting bigger, scientists warn

SpaceX Starlink satellites are pictured in the sky seen from Svendborg on South Funen, Denmark 21 April, 2020 (Reuters)

Nasa is monitoring a "small but evolving dent" in the Earth's magnetic field that could cause major problems for satellites and spacecraft.

The Earth's magnetic field wraps around our planet, bouncing away charged particles that come to us from the Sun. But there is an unexplained gap in it, where the magnetic field is weak, hovering over South America and the southern Atlantic Ocean.

What's more, the region is spreading and continuing to weaken, leading to fears that the problem could get worse.

Researchers refer to the gap as the "South Atlantic Anomaly, or SAA", and fear that it could cause significant problems for equipment that is used on Earth. Within the anomaly, particles are able to get closer to the surface than usual, meaning that satellites and computers that pass through it could be hit by problems.

That has led Nasa to devote resources to tracking the dent, in an attempt to better understand where it is and what could be causing it.

At the moment, there is no obvious consequence of the SAA for anyone living on Earth. But detailed observations have suggested that it is getting more extreme and that it is expanding to the west, as well as splitting so that there are two points at which the anomaly is least strong.

The Earth's magnetic field – and the changes it undergoes – are happening beneath our feet. Underneath the Earth, in its outer core, metals are churning that create electric currents that then go on to produce the important magnetic field.

Over time, those conditions within the core change, and so does the magnetic field. It is those changes that lead to phenomena such as the SAA.

But the greatest concern about the magnetic fields for the time being is it effects on equipment away from Earth's surface. Ordinarily, the magnetic field keeps the satellites that are around the Earth safe – including inhabited ones like the International Space Station – but the changes mean they lack the protection as they fly through the area covered by the SAA.

At the moment, operators are forced to shut down specific components as they pass through the area. That is one of the reasons that tracking the SAA is important to Nasa, since it needs to know exactly where it is so that those changes can be made most accurately.

With better data in the future, Nasa hopes to be able to more accurately predict how the SAA could be changing and therefore what danger it might pose to satellites and the instruments on them. Future missions will better inform those models, Nasa says, and can also be used to better understand the processes in the Earth that are leading to the changes.