Bengaluru: NASA has announced that its researchers are actively tracking the South Atlantic Anomaly, a large but slowly widening weak spot in the Earth’s magnetic field over the Atlantic Ocean. The region extends from South America to Southwest Africa, over the Atlantic Ocean.
The Earth’s magnetic field acts like a protective bubble around the planet, shielding its inhabitants from harmful radiation from the Sun. But it is not completely uniform or stable due to changes over time with Earth’s outer core rotation.
The dent in the magnetic field does not affect life on the surface, but does put satellites passing through the region at a higher risk of instrument damage or data loss from radiation.
Earth’s magnetic field
Earth’s magnetic field originates more than 2000 km inside its interior and extends several thousand kilometres into the space, where it interacts with charged particles emanating from the Sun in the form of solar wind. The field is sustained by electric currents that are in turn caused by the rotating outer core of Earth — the mixture of molten iron, nickel, and rock in our core spins, generating a dynamo-like effect and producing the magnetic field.
The magnetic field covers all of Earth and is shaped like a teardrop, with a tail that points away from the Sun. It helps keep in the atmosphere liquid water, warmth, and supports the survival of life on this planet.
Approximately 640 km above the ground begin the Van Allen radiation belts, which are concentric belts of magnetic lines that capture and hold charged particles from the Sun and cosmic rays. These belts extend up to 58,000 km, and are mainly divided into the inner and outer belts. Other transient belts are also formed from time to time, but do not persist.
In the South Atlantic Anomaly (SAA) region, the innermost Van Allen belt has been observed to drop down to 200 km from the surface, bringing with it charged particles that penetrate the atmosphere.
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Earth’s magnetic dipole
The magnetic dipole axis of Earth, which determines the geomagnetic north and south poles, is tilted about 11 degrees relative to our rotational axis, which is tilted at 23.5 degrees. The dipole axis is considered to be a hypothetical bar magnet on Earth, acting like any other magnet. But since its north aligns to the North Pole of Earth, the magnetic north pole is actually considered to be the south pole of the Earth’s magnetic field because all magnets on Earth turn their north towards it.
Owing to the changing nature of the core spin over time, the magnetic dipole of the Earth moves slowly but constantly. These changes also cause ripple effects in the Earth’s magnetic field, and the Earth’s geomagnetic poles move over time.
As of 2015, the Earth’s magnetic North Pole was located at approximately 80°22′12″N 72°37′12″W, over Ellesmere Island, Canada, but it is now drifting away from North America and toward Siberia.
These changes lead to uneven strength in magnetic fields, and caused the SAA, which the American space agency describes as a “pothole in space”.
The region sees the passage of several low-Earth orbit satellites, whose non-essential instruments are shut down when passing through SAA for safety. The International Space Station (ISS) also passes through the region. Though the ISS crew is safe within, components mounted externally on the station are thought to be at risk for damage or data loss.
Close monitoring of the SAA is being performed by multiple agencies and authorities in an effort to understand Earth’s evolution as well as for keeping future satellites safe.
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