A Planetary Pothole
Deep beneath southeastern Brazil lies a vast expanse of ancient volcanic rock that contributes to a growing "dent" in Earth's magnetic field. This feature, known as the Paraná magnetic anomaly, comes from the Paraná-Etendeka traps, a massive flood basalt province that erupted between 136 and 132 million years ago. This immense volcanic event, linked to the breakup of the supercontinent Gondwana, spewed out over 1.5 million cubic kilometers of lava, blanketing an area of 1.5 million square kilometers. The main pulse of these eruptions occurred over a remarkably short period, possibly less than one million years.
The igneous rocks of the Serra Geral Formation, which can be up to 1,700 meters thick, have specific magnetic properties that interfere with the Earth's geomagnetic field. This geological feature contributes to the much larger South Atlantic Anomaly (SAA), a region where the Earth's magnetic field is exceptionally weak. Here, the inner Van Allen radiation belt, a zone of energetic charged particles, dips down to an altitude of just 200 kilometers, much closer to the planet's surface than anywhere else.
This weakness in the magnetic shield has tangible consequences. The SAA is drifting westward at a rate of about 0.3 degrees per year and has been expanding. For satellites and spacecraft, passing through this region is a perilous part of their orbit.
The Satellite Menace
The increased flux of high-energy protons within the South Atlantic Anomaly poses a significant threat to orbiting technology. When these particles strike a satellite's sensitive electronics, they can cause "single event upsets" (SEUs)—glitches that can corrupt data, disrupt operations, or even cause permanent damage. NASA has reported that modern laptops have crashed when Space Shuttle flights passed through the anomaly.
To mitigate these risks, satellite operators often power down non-essential systems when their orbits cross the SAA. The Hubble Space Telescope, for instance, suspends its observations when passing through this hazardous zone. The International Space Station is also exposed to higher levels of radiation in this region. Astronauts have even reported seeing peculiar "shooting stars," which are actually phosphenes—light flashes inside the eye caused by cosmic rays interacting with their optic nerves.
The anomaly's effects are a modern problem. It is believed to have caused false alarms on Skylab's solar flare sensor and contributed to the failure of Globalstar network satellites in 2007. Data from the European Space Agency's Swarm satellite constellation, which has been mapping Earth's magnetic field since 2013, shows the anomaly is growing but also splitting into two distinct minimum points, further complicating satellite navigation and safety. The persistent weakness links deep-time geology and the challenges of our technological age.