The South Atlantic magnetic anomaly continues to expand. It’s bad news for space exploration

The South Atlantic magnetic anomaly (SAA) is an old acquaintance for space exploration: a wide region where the planet’s magnetic field is particularly weak. We have two problems with this anomaly. The first, that we do not know what causes it; the second, which is growing.

A deeper anomaly. This is what the latest annual report of the World Magnetic Model (WMM) stated: the SAA, far from correcting itself, has been deepening during the year 2023.

A problem that comes from afar. For years, various agencies have been closely monitoring the South Atlantic magnetic anomaly. This “dent” in the Earth’s magnetic field is located over an area that covers a good part of South America and the southern Atlantic, reaching the South African coast. The anomaly is of special interest to space agencies and operators of satellites in low Earth orbit that circulate in the area.

Our magnetic field not only protects those of us on the surface of the planet but also satellites, ships and space stations in low orbits. When they fly over the region they are unprotected from solar radiation and winds and other similar phenomena. This can cause problems in the operation of onboard systems as well as in communication with Earth.

A more intense fall. The annual report of the WMM warns of an anomaly that has become deeper in the past year. As the report explains, it is estimated that the magnetic field in this region has lost about 25 nanoteslas (nT) of intensity at the surface level. It is also indicated that the area where the field intensity is below 25,000 nanoteslas has grown by 7%.

If we contrast the minimum intensity in the last four years we will find a significant drop in the intensity of the field. If in 2020 the minimum intensity at the surface level was 22,232 nT, in 2024 it was 22,126 nT. A drop of 106 nT in these four years.

At 500 km high, near the area through which the International Space Station, the Thangong station, or the Hubble telescope orbit, the step has been from 18,428 nT to 18,349 nT. A drop of 79 nT, a slightly smaller drop in proportion to the surface view.

Westward. According to the report, the center of this anomaly has moved about 20 km in a westward direction during 2023. A displacement speed intermediate between 41 km/year at the north magnetic pole and 9 km/year at the south magnetic pole.

WMM. The WMM report goes beyond analyzing the state of the SAA. One of the objectives of the report is to contrast the model predictions with observations of the state of the Earth’s magnetic field.

This World Magnetic Model It is updated every five years, and its predictions are compared with other more current ones, such as those made from observations by the European Space Agency’s Swarm satellites.

The aim is to monitor the validity of this model year by year. Its latest iteration is 2020 (WMM2020), but according to the report its predictive capacity is still adequate.

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Image | NASA’s Scientific Visualization Studio / NASA, ESA, M. Kornmesser (ESA/Hubble)