High above the South Atlantic, an invisible weak spot in Earth’s defences is quietly spreading, reshaping how we think about spaceflight.
Earth’s magnetic field usually acts as a planetary force field, steering away charged particles from the Sun. Yet new satellite data show that this shield is thinning in a vast region, forcing engineers and space agencies to rethink how they protect spacecraft and people in orbit.
A shield with a growing crack
For decades, scientists knew that the magnetic field was weaker over the South Atlantic. They even gave this region a name: the South Atlantic Anomaly. What recent research shows is that this weak patch is expanding and deepening faster than expected.
Using measurements from the European Space Agency’s Swarm mission – three satellites launched in 2013 to map Earth’s magnetism – researchers tracked the evolution of the anomaly between 2014 and 2025.
The weak zone now covers about 1% of Earth’s surface, an area of roughly 5 million square kilometres – about half of Europe.
Inside this area, the field intensity drops to about 22,000 nanoteslas, compared with 40,000 to 60,000 nanoteslas in many other regions. Since 2014, the minimum has fallen by a further 336 nanoteslas, a clear sign that the problem is not static.
Geological records show that magnetism over this part of the globe has been unstable for around 11 million years. Yet the speed and scale of the current change stand out on human timescales. Swarm data also reveal that the weakening is not uniform: the field drops faster in the eastern part of the anomaly, to the south-west of Africa, than over South America.
Satellites crossing a dangerous corridor
The South Atlantic Anomaly matters because it affects the orbital highway used by many satellites. Low Earth orbit, from roughly 400 to 1,000 kilometres up, is crowded with weather probes, imaging satellites, navigation systems and crewed vehicles.
When these craft pass through the anomaly, they meet more high‑energy particles than elsewhere at the same altitude. The weakened magnetic field deflects fewer charged particles, so more of them slam into spacecraft.
In this zone, satellites face a higher risk of electronic glitches, corrupted data and, in some cases, permanent hardware failure.
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Electronics are especially at risk from events called “Single Event Disruptions”. A single energetic particle can flip a bit in memory, lock up a processor, or trigger a false signal. Engineers already know this corridor is troublesome: operators of Earth‑observation and communication satellites routinely report extra anomalies when their craft transit the South Atlantic.
How operators respond in practice
To cope, many missions use a mix of tactics:
- Switching off or putting sensitive instruments in safe mode while crossing the anomaly
- Using radiation‑hardened components in critical systems
- Adding extra shielding around key electronics
- Designing software that can detect and correct corrupted data
- Adjusting orbits and schedules to reduce time spent in the weak zone
All these measures have a cost. Hardened components are heavier and more expensive. Extra shielding adds mass, cutting into payload capacity. More complex operations planning raises mission budgets.
Astronauts are not immune
The problem goes beyond machines. The International Space Station (ISS) flies at about 400 kilometres and passes through the South Atlantic Anomaly several times a day.
During these crossings, the radiation level around the ISS rises. Astronauts are shielded by the station’s hull, but not as well as people on the ground, who benefit from both the magnetic field and the thick atmosphere. Medical studies on ionising radiation suggest that repeated exposure, even at relatively modest doses, can damage DNA and raise lifetime cancer risk.
For long missions, extra radiation from the anomaly becomes one more factor limiting how often and how long crews can safely work in low orbit.
Mission controllers already schedule some activities to avoid anomaly crossings. Sensitive experiments may be paused. Future commercial stations and tourist flights in low orbit will need similar precautions, even for short‑stay visitors who are less trained than professional astronauts.
Clues from deep inside Earth
This space safety story begins far below the surface. Earth’s magnetic field comes from a natural dynamo in the outer core, about 3,000 kilometres down, where liquid iron flows around the solid inner core. Motion in this conductive fluid generates electric currents, which in turn create a global magnetic field.
In the region beneath the South Atlantic, Swarm data show unusual structures called “reversed flux patches”. In these patches, the direction of the magnetic field bends back into the core instead of emerging outward. That reversal cancels part of the surrounding field and creates local minima at the surface.
One such patch appears to be sliding slowly westward under southern Africa. As it moves, it deepens the magnetic “dip” that spacecraft experience above the South Atlantic. This supports broader geophysical models that point to a restless boundary between the liquid core and the solid mantle above it.
These deep patterns are difficult to constrain, because scientists cannot access the core directly. Instead, they combine satellite data, ground observatories and computer simulations of fluid motion and heat flow inside Earth.
No sign of an imminent pole reversal
Whenever the magnetic field changes, one question surfaces: are we heading for a flip of the poles? Geological records show that north and south magnetic poles have swapped hundreds of times in Earth’s history. The last full reversal happened about 780,000 years ago.
Current data do not indicate that such an event is about to happen. Researchers view the South Atlantic Anomaly as a regional feature superimposed on a field that is constantly fluctuating on timescales of decades to centuries. Models suggest that the present changes fit within that natural variability, even if they bring new challenges for satellites.
An asymmetric field with real-world consequences
Swarm’s maps reveal that Earth’s magnetic field is lopsided. The simple “bar magnet” picture, with neat lines running from pole to pole, does not match the actual structure.
In the southern hemisphere, only one major high‑intensity region stands out. In the northern hemisphere, two strong zones dominate: one over Canada and another over Siberia. These areas are moving and changing strength in different ways.
| Region | Trend since 2014 | Approximate change |
|---|---|---|
| Canada high‑intensity zone | Weakening and shrinking | −801 nanoteslas, area reduced by 0.65% (almost the size of India) |
| Siberia high‑intensity zone | Strengthening and expanding | +260 nanoteslas, area growth similar to Greenland’s size |
This imbalance helps explain why the magnetic north pole has been racing toward Siberia since the 19th century, with an acceleration noted from the early 2000s. That drift affects navigation systems that rely on magnetic north, from aircraft compass calibrations to some military and maritime procedures.
Why space agencies care about every nanotesla
Changes that sound modest on paper can translate into big operational shifts. A few hundred nanoteslas of weakening may mean more radiation exposure in key orbital bands, especially when solar activity spikes.
Space weather – driven by solar flares and coronal mass ejections – already threatens satellites with sudden blasts of charged particles. A weaker magnetic field in a specific region makes that region a choke point, where the same solar event does more damage. For constellations of small satellites with limited shielding, the cumulative effect is a shorter working life and higher replacement rates.
The South Atlantic Anomaly acts as a natural stress test for satellite design, pushing engineers to build hardware that can survive harsher conditions than the historical average.
This has knock‑on effects for insurance, launch cadence, and the economics of mega‑constellations that aim to provide broadband from orbit. Operators must budget for both routine radiation hits and occasional extreme storms that may exploit the weakened shield.
Key terms that shape the debate
Two technical ideas help frame what is at stake.
Single Event Disruption (SED). This term covers glitches triggered when a single particle disturbs an electronic component. On the ground, Earth’s atmosphere filters out most of these particles. In orbit – and especially over the anomaly – they arrive in far greater numbers. Designers use redundancy, error correction and radiation‑tolerant chips to reduce the risk.
Geomagnetic secular variation. This describes the slow change in Earth’s magnetic field over years to centuries. The South Atlantic Anomaly is part of this long‑term evolution. Tracking secular variation helps agencies update navigation charts, plan satellite orbits and refine models of the core.
Scenarios for the next few decades
Based on Swarm observations and numerical models, scientists expect the South Atlantic Anomaly to keep changing. Several scenarios are on the table for the coming decades:
- Continued growth of the weak zone, affecting more orbital tracks used by Earth‑observation and communication satellites
- Splitting of the anomaly into multiple weaker patches, which would spread risk across a larger area
- Partial recovery of field strength if core flows reorganise, easing pressure on spacecraft in the region
Space agencies are preparing for the most demanding case: an anomaly that grows and intensifies. That approach encourages conservative design margins and long‑term monitoring. The European Space Agency is already considering extending Swarm beyond 2030, ideally overlapping a period of low solar activity. That timing would help separate internal magnetic changes from solar disturbances more clearly.
For now, the South Atlantic Anomaly does not threaten daily life on the ground. For the space sector, though, it acts as a reminder that Earth’s magnetic shield is a living, shifting system – and that space safety depends as much on what happens 3,000 kilometres below us as on what happens 400 kilometres above.
Originally posted 2026-03-02 18:10:33.