It is called the South Atlantic magnetic anomaly. An area located off the coast of Brazil, in the southern part of the Atlantic Ocean. Here, the earth’s magnetic field is not quite the same.
This natural phenomenon has been known for a long time, but a new study published in the journal Physics of the Earth and Planetary Interiors reveals disturbing details. In 2013, three small European satellites were put into orbit, together forming the Swarm constellation. They are responsible for measuring the Earth’s magnetic field, but also and above all its variations over time.
When they were put into service, these satellites were therefore able to see this anomalieswhich was not a surprise since it had been documented since the 19the century. It is due to the Van Allen belt, the area of the Earth’s magnetosphere that contains a large quantity of particles emanating from solar winds.
So far, nothing to worry about, the phenomenon is natural and under control. But Swarm saw something else: since the beginning of measurements in 2014, the area affected by this anomaly has grown. Impressive growth since in 2025, it will almost reach the coasts of South Africa! This corresponds to an increase of half the surface area of the European continent in just ten years.
Worse, the weakening of the magnetic field seems to have accelerated considerably since 2020. One of the authors of the study, Chris Finlay, specialist in geomagnetism at the Technical University of Denmark, specifies in an interview with the European Space Agency: “ The magnetic field is expected to flow out of the planet’s core. But at the level of the anomaly, we see unexpected areas where the magnetic field, instead of leaving the heart, returns there. »
It is in fact in this zone, at the level of the interaction between the coat rocky and the core of the planet that the magnetic field forms and evolves. And these are perhaps little-known phenomena underground which play a role in the weakening of the magnetic field in this region in particular.
The extremely precise data transmitted by Swarm made it possible to notice other, but less worrying, changes in the world, with a strengthening of the magnetic field in Siberia, to the detriment of Canada.
But this doesn’t just concern scientists and their research. Variations in the magnetic field, even locally, can have significant consequences on communications, locations GPS and, overall, for all the satellites which navigate above these areas more exposed to solar radiation.
Unfortunately, there are no ways to prevent these effects, only to know them better to be able to predict their consequences. But Swarm is undoubtedly reaching the end of its life, the primary mission was supposed to end in 2017, but the instruments have held up until then.
The authors hope that quality successors will be able to ensure continuity of observations in the years to come.
