NASA investigating unusual ‘dent’ in Earth’s magnetic field over South America

18 Aug 2020

Illustration of Earth's magnetosphere. Image: © cosmicvue/

Despite its small size, an evolving dent in Earth’s magnetic field could cause headaches for orbiting satellites.

While it doesn’t appear to affect life down here on the surface of Earth, an anomaly in our planet’s magnetic field is posing a problem to our satellite technology.

The protective magnetic field around Earth repels and traps charged particles from the sun, but there is an unusually weak ‘dent’ in the field over South America and the southern Atlantic Ocean.

Referred to as the South Atlantic Anomaly (SAA), the dent allows these particles to get closer to the planet’s surface than elsewhere and is capable of knocking out the onboard computers on satellites and interfering with their ability to collect data.

As a result, NASA is now investigating what’s causing the SAA. Recent observations and forecasts have shown it to be expanding westward and continuing to weaken in intensity. It also appears to be splitting into two lobes, creating additional challenges for satellite missions.

Preparing future satellites

The SAA is the result of the tilt of the planet’s magnetic axis and the flow of molten metals within its outer core almost 3,000km beneath our feet. These churning metals act like a massive generator, called the geodynamo, creating electric currents that produce the magnetic field.

Over time, dynamical processes in the core ripple outward to the magnetic field surrounding the planet, generating the SAA and other features in the near-Earth environment. These include the tilt and drift of the magnetic poles, which are moving over time.

Typically, our planet is protected from the outflow of solar particles by the Van Allen Belts – two doughnut-shaped belts that trap or repel the particles. However, when a particularly strong storm of particles from the sun reaches Earth, the Van Allen Belts can become highly energised and the magnetic field can be deformed, allowing the charged particles to penetrate the atmosphere.

“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,” said Terry Sabaka, a geophysicist at NASA’s Goddard Space Flight Center. “Because that’s what helps us make models and predictions.”

By tracking this slowly evolving dent in the magnetic field, researchers can better understand the way our planet is changing and help prepare for a safer future for satellites.

Colm Gorey was a senior journalist with Silicon Republic