The Earth’s magnetic field is weakening in hot spots around the globe, affecting navigation for ships. Projects are under way to improve our understanding of the issue and create more reliable navigation systems
On 31 May 2020, Liberia-flagged oil tanker Willowy was sailing in the South Atlantic Ocean, west of the South African city of Cape Town, travelling eastwards, when something strange happened. At 1 am local time, the ship swung violently to starboard and began to steer in circles. Officers were called to the bridge; it transpired that four other nearby vessels were doing the same, and all the while, converging. Was it sabotage or a cyber attack?
Not quite. Instead, a long-standing weakness in the Earth’s magnetic field – known as the South Atlantic Anomaly (SAA) – was throwing the ship’s primary gyrocompass off-kilter. The anomaly, dubbed the ‘Bermuda Triangle of space’, is well known to seafarers. However, this strange phenomena is known to occur in areas off South America, not in the South Atlantic Ocean. In fact, the SAA has grown. It is now threatening to split into two distinct areas of magnetic interference: one centred and radiating outwards from Paraguay; and another off the west coast of South Africa, bringing with it navigational interference on a key leg of the Cape Route – one more than treacherous enough without it.
The Earth’s magnetic field is generated by the movement of molten metal inside the core, which acts like a colossal magnet. Perpendicular to the polar gradient of the magnet are the Van Allen Belts, two doughnut-shaped high-radiation zones.
Low-Earth-orbit satellites, on average, are exposed to about 50 Gray or 50,000 millisievert radiation dose per year from these belts, which attacks and degrades electronics; the reason why most constellations have a limited lifespan of less than 30 years. However, the SAA allows the belts to dip closer to the Earth’s surface, and satellites have to be specially shielded and protected against the acute radiation.
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