At the heart of the US space agency’s concerns is a geomagnetic phenomenon that is as fascinating as it is worrying: the South Atlantic Anomaly (SAA). This immense region is characterised by a significantly reduced magnetic intensity compared with the surrounding areas. Far from being a mere scientific curiosity, this weakness acts like a breach in our natural protective shield, allowing high-energy solar particles to come dangerously close to the Earth’s surface.

To understand AAS, we need to delve deep into the heart of our planet. Its origin is closely linked to geodynamics, the complex process that takes place in the Earth’s outer core. There, the movement of molten iron and nickel generates the magnetic field that envelops us. However, this generation is not uniform.

Two main factors contribute to the formation of the AAS. Firstly, the inclination of the Earth’s magnetic axis in relation to its axis of rotation plays a role. Secondly, the influence of a gigantic, dense structure known as the African province with low shear velocity, located almost 2,900 kilometres beneath the African continent, disturbs the generation of the magnetic field in this region. NASA geophysicists explain that the anomaly is also associated with a local polarity inversion within the Earth’s magnetic field, which further weakens the overall strength of the dipole field in this specific area. As Weijia Kuang from NASA’s Goddard Space Flight Center explains, a field of reversed polarity has developed in the region, creating a sort of “pothole” in the Earth’s magnetic armour.

A danger for space technology

This magnetic vulnerability is not without consequences. Satellites passing through the AAS are exposed to high levels of high-energy protons. These particles can cause what engineers call Single Event Anomalies (SEUs). These incidents can lead to temporary malfunctions, data corruption or even permanent damage if a critical system is affected.

Faced with this risk, many satellite operators are taking preventive measures, in particular by shutting down non-essential systems as they pass through the anomaly. The International Space Station (ISS) itself passes through the AAS during each orbit. While its shielding effectively protects the astronauts, the external instruments are more exposed. Bryan Blair, deputy principal investigator for the Global Ecosystem Dynamics Investigation (GEDI) instrument installed on the ISS, reports occasional “misfires” and resets, resulting in a few hours of data loss each month, an impact deemed manageable. Other missions, such as the Ionospheric Connection Explorer (ICON), are also closely monitoring the AAS and adapting their operations.

Far from being static, the South Atlantic Anomaly is a dynamic phenomenon. Recent data, notably from ESA’s Swarm constellation and historical measurements from NASA’s SAMPEX mission, confirm a number of worrying trends. The anomaly is slowly drifting north-westwards, expanding at the surface and, most notably since 2020, it is splitting into two distinct lobes, creating two centres of magnetic minimum. This bifurcation, corroborated by various studies, increases the number of dangerous zones for spacecraft and complicates the task of scientists developing predictive models of geomagnetic conditions. Understanding the changing morphology of the AAS is crucial for the safety of current and future satellites,” stresses NASA’s Terry Sabaka.

To refine their understanding and forecasts, NASA combines satellite data with simulations of the dynamics of the Earth’s core. This information is fed into global models such as the International Geomagnetic Reference Field (IGRF), which tracks changes in the Earth’s magnetic field. These models are essential not only for planning space missions, but also for gaining a better understanding of our planet’s internal structure. The approach is similar to weather forecasting, but on much longer time scales, making it possible to estimate Secular Variation, i.e. slow but persistent changes in the magnetic field over years and decades.

While the current evolution of the AAS is unprecedented on the scale of the space age, the geological record suggests that such anomalies are not exceptional over long periods of time. A 2020 study even suggests that similar anomalies may have existed 11 million years ago. It is important to stress that, according to the scientists, the current AAS is not a precursor of a magnetic pole reversal, a natural but rare phenomenon that takes place over hundreds of thousands of years. The study of the AAS therefore remains an active area of research, essential to protect our technologies in orbit and to deepen our understanding of the deep forces that drive our planet.

from:    https://farmingdale-observer.com/2025/04/29/nasa-is-growing-concerned-as-a-massive-anomaly-spreads-across-earth-scientists-believe-its-linked-to-deep-earth-forces/