NASA tracks the South Atlantic Anomaly, a weakened region in the magnetic field that stretches 1,800 miles. (Image Credit: NASA Goddard/YouTube)
For years, NASA researchers have been keeping a close eye on a weakened part of the magnetic field called the South Atlantic Anomaly (SAA), which stretches between South America and Southwest Africa. Although the SAA doesn't pose a risk to Earth's life, it can affect the electronics and hardware in satellites and spacecraft, including the International Space Station.
Scientists believe the source of the magnetic field is a churning molten iron ocean within Earth's outer core. As this mass moves, it produces electric currents, generating the magnetic field. The African Large Low Shear Velocity Province, a massive, dense rock formation located 1,800 miles beneath the African continent, interfered with the field's generation, making it significantly weaker.
"The observed SAA can be also interpreted as a consequence of weakening dominance of the dipole field in the region," said Weijia Kuang, a geophysicist and mathematician in Goddard's Geodesy and Geophysics Laboratory. "More specifically, a localized field with reversed polarity grows strongly in the SAA region, thus making the field intensity very weak, weaker than that of the surrounding regions."
NASA uses fluxgate magnetometers aboard low Earth orbit satellites to detect changes in the South Atlantic Anomaly. These magnetometers have coils wound around ferromagnetic cores to measure the Earth's magnetic field strength and structure. When an electric current flows through the coil, the internal metal core repeatedly switches its magnetic state. That switching interacts with the Earth's magnetic field, generating a signal in the sense coil. Afterward, that signal is amplified and processed to determine the magnetic field's strength and orientation.
Additionally, these satellites are equipped with particle detectors and radiation monitors that monitor the flux of high-energy solar particles, like protons and electrons, penetrating deeply at the weakest part of the magnetic field in the atmosphere. With this data, NASA can quantify how radiation affects spacecraft in the anomaly. Those high particle fluxes can interfere with electronics functionality, damage equipment, and potentially harm astronauts.
For instance, the CESES-01 satellite is equipped with a HEPD-01 detector that precisely maps the SAA's charged particle environment by measuring protons and electrons over a wide energy range. This helps to track particle flux changes and the anomaly shifting location over time. HEPD-01 operates in burst and survey modes, collecting high-res data to track particle flux changes and the geographic shift of the anomaly's center.
All the satellite data are combined with ground-based measurements and geomagnetic models to monitor field changes and predict future developments. This technique produces a more precise geomagnetic environment model, such as the High Definition Geomagnetic Model (HDGM), as it's updated and validated in real-time from satellite and ground observatory data. NASA also analyzes data from the ESA's Swarm satellites that provide a detailed map of Earth's magnetic field. It also shows how the SAA has developed and evolved.
Although researchers haven't fully grasped the anomaly and what it could mean, they always get new insights into this phenomenon. A 2016 study showed that the SAA gradually shifts around, which was verified by CubeSats, which tracked it. The SAA doesn't just move. In 2020, researchers discovered that it's splitting into two lobes. Each one marks a distinct zone of lowest magnetic intensity within the broader anomaly. It's not clear what this could represent for the SAA in the future, but evidence suggests the anomaly isn't new.
Have a story tip? Message me at: http://twitter.com/Cabe_Atwell
