The planet’s magnetic shield, usually a reliable guardian against cosmic radiation, is showing signs of fatigue in one key region — and that slow-motion change is starting to affect satellites, astronauts and our understanding of Earth’s deep interior.
A shield with a growing crack
Earth’s magnetic field works like a giant, shifting force field. It deflects charged particles from the Sun and from deep space, steering most of them away from the surface and from low‑orbit spacecraft. Where the field weakens, that protection thins.
Over the South Atlantic and parts of southern Africa, this thinning has become striking. Scientists call it the South Atlantic Anomaly, or SAA. It is not new in geological terms, but satellite data from the European Space Agency’s Swarm mission show that the anomaly has grown larger and deeper over the last decade.
The South Atlantic Anomaly now covers roughly 1% of Earth’s surface — an area about half the size of Europe — and continues to evolve.
Between 2014 and 2025, the region of markedly weak field intensity expanded by around five million square kilometres. Inside that zone, measurements have dropped to about 22,000 nanoteslas, far below the 40,000 to 60,000 nanoteslas typically recorded elsewhere at similar latitudes.
That decline, by a few hundred nanoteslas in just over ten years, may sound modest. For satellites that rely on a predictable radiation environment, it makes a real difference.
Why space agencies are paying attention
Low‑Earth orbit is crowded with hardware. Weather satellites, Earth‑observation platforms, navigation systems and the International Space Station (ISS) all pass through or near the anomaly several times a day.
Inside the SAA, the weakened field lets more energetic particles, especially from the Van Allen radiation belts, dip closer to Earth. These particles can punch through satellite shielding and hit sensitive electronics.
When one particle is enough to glitch a mission
Many spacecraft operators now know the SAA as a trouble zone. Engineers see an uptick in what are called single‑event effects: radiation hits that briefly or permanently disturb electronics.
- Single Event Upset (SEU): a bit flip in memory or processors, causing software glitches or corrupted data.
- Single Event Latchup (SEL): a current surge inside a component that can overheat and destroy it if not cut off quickly.
- Single Event Burnout (SEB): permanent damage to power electronics, sometimes ending the life of an instrument.
Spacecraft designers try to anticipate this. They “radiation‑harden” electronics, adding shielding, redundancy and error‑correction routines. Some instruments are switched off whenever a satellite passes through the SAA to avoid damage or false readings. That can mean regular, predictable data gaps over an entire portion of the planet.
For certain low‑orbit missions, the South Atlantic Anomaly is no longer a marginal nuisance; it is a planning constraint baked into every orbit and instrument schedule.
The ISS crew also feels the impact. Astronauts already receive higher radiation doses than people on the ground. When the station moves through the anomaly, that dose rate spikes. Mission planners use shielding, careful tracking of individual exposure and operational rules — for example, timing spacewalks away from high‑radiation periods.
What the anomaly says about Earth’s core
The SAA is not just a space‑weather story. It is a window into the churning metal 3,000 kilometres below our feet.
Earth’s magnetic field originates in the outer core, a vast ocean of liquid iron and nickel surrounding a solid inner core. As this conductive fluid moves, it generates electric currents. Those currents give rise to the geomagnetic field through a process known as the geodynamo.
Swarm measurements suggest that under the South Atlantic lies a patch where the core field is partially reversed. Instead of magnetic flux emerging strongly from the core, some of it dives back in.
Beneath southern Africa, researchers have identified “reversed flux patches” — blobs where the magnetic field points in the opposite direction and cancels part of the surrounding field.
These reversed patches drift slowly, roughly westward, and appear to deepen the local minimum in field strength. Their behaviour matches geophysical models that point to complex interactions at the boundary between the liquid outer core and the overlying solid mantle.
Seismic studies already show that this boundary is not smooth. There are dense, chemically distinct regions deep under Africa and the Pacific. These may steer convection in the outer core, focusing irregularities in particular longitudes. The South Atlantic Anomaly could be the surface fingerprint of that deep structure.
Is a pole flip coming?
Any mention of a weakening magnetic field often triggers the same question: are we heading for a flip of Earth’s magnetic poles?
Over geological time, full reversals — where north and south magnetic poles swap places — have happened hundreds of times. During a reversal, the field weakens and becomes more complicated, with multiple poles emerging before a new configuration settles in.
Current data, though, do not show the pattern expected at the start of a global reversal. The weakening is strong in some regions, such as the South Atlantic and parts of Canada, but other areas, especially over Siberia, have strengthened. The overall field has declined slightly in the last century, yet not at an exceptional rate when seen against the long geological record.
| Region | Recent trend | Approximate change since 2014 |
|---|---|---|
| South Atlantic Anomaly | Weaker and larger | −336 nanoteslas, area +1% of Earth’s surface |
| Canada high‑field zone | Weaker and shrinking | −801 nanoteslas, area −0.65% of Earth’s surface |
| Siberia high‑field zone | Stronger and expanding | +260 nanoteslas, area roughly the size of Greenland |
This asymmetric pattern helps explain why the magnetic north pole has been racing from Canada toward Siberia since the 19th century. Navigation systems that rely on magnetic north — from aircraft to smartphone compasses — need regular updates to match that shift.
An asymmetric, restless magnetic field
School textbooks often sketch Earth’s field as a neat bar magnet, centred on the planet. Reality is messier. The field is lopsided, with blobs of high and low intensity scattered across the globe and at different altitudes.
Swarm’s trio of satellites, flying at slightly different heights, separate the contributions from the core, the crust, oceans and ionosphere. That layered view shows that the core field is changing noticeably on timescales of just a few years.
The magnetic field is not slowly fading in a uniform way; it is reorganising, moving its strong and weak regions around the globe like weather systems in slow motion.
Numerical simulations of the geodynamo run on supercomputers reproduce this behaviour. They show patches of reversed flux forming, merging and disappearing, and polar regions that wander. The current South Atlantic Anomaly looks like one episode in that ongoing rearrangement, not a unique catastrophe.
What this means for future missions and everyday life
For most people on the ground, the SAA is not a direct health threat. Atmosphere and residual magnetic shielding still block the bulk of high‑energy particles.
The main stakes sit in orbit and, indirectly, in the services that depend on space hardware. Satellite designers and operators are already adjusting to a more hostile patch of near‑Earth space. Some key trends are emerging:
- More shielding and smarter software for satellites expected to regularly cross the anomaly.
- Orbit planning that minimises time spent in the highest‑risk zones, where mission constraints allow it.
- Continuous monitoring of the geomagnetic field to update radiation models used by airlines and space agencies.
There is also a cost angle. Hardened electronics are heavier and more expensive. Additional shielding means more mass to launch. For commercial operators working on tight margins, a slowly changing magnetic field becomes another risk to model into business plans.
Key terms and scenarios that help make sense of it
A few concepts help frame what is happening:
- Geomagnetic field: the magnetic field generated primarily by Earth’s core, distinct from short‑term variations caused by space weather.
- Space weather: disturbances in the near‑Earth environment driven by the Sun, such as solar flares and coronal mass ejections.
- Radiation belt: torus‑shaped regions of trapped charged particles surrounding Earth, known as the Van Allen belts.
Scientists often run “what if” simulations that combine long‑term core‑field evolution with bursts of solar activity. One scenario looks at a strong solar storm hitting while the anomaly has expanded further. In that case, the flux of particles through the SAA could jump, shortening satellite lifetimes and forcing operators to temporarily shut down services to protect hardware.
Another line of research tests how aviation at high altitude might react to a shifting field. Routes over the South Atlantic already see modest radiation increases during major solar storms. If the field there weakens further, airlines may need more flexible flight‑level planning, similar to what already happens on polar routes.
For now, the changing field is a reminder that Earth is not a static rock with a fixed magnetic label stuck on top. The same deep processes that keep the core molten and the geodynamo working also reshape our near‑space environment — and with it, the safety margins of the machines and people we send above the atmosphere.
