The South Atlantic Anomaly is a region located between the coast of the African continent and South America, where the Earth’s magnetic field – which serves as a shield against solar radiation – is particularly weak. Dubbed the “Space Bermuda Triangle”, the area is particularly dangerous for satellites and spacecraft, which end up being more vulnerable to solar storms and cosmic radiation.
For this reason, NASA scientists, divided into geomagnetic, geophysical and heliophysical research groups, have been observing the anomaly to monitor and predict future changes that could affect the Earth’s atmosphere and serve as an indicator of what is happening to the planet’s magnetic fields. .
The lower intensity of the magnetic field in the region that extends from Chile to Zimbbue allows the Earth’s radiation belt, the Van Allen Belt, to approach the surface. Normally, the belts extend at an altitude between 1,000 km and 60,000 km, but in this area, the sun’s rays reach 200 kilometers in height, and the more intense solar radiation results in an increase in the flow of energetic particles.
This animation shows the decrease in the strength of the magnetic field on the Earth’s surface from 2014 to 2020, based on data collected by the Swarm satellite constellation. Video: ESA / Division of Geomagnetism / DTU Space
The radiation from these particles can damage the on-board computers and interfere with the collection of data from the satellites that pass through it – one of the main reasons why NASA scientists want to track and study the anomaly.
Satellites that pass through this region experience higher amounts of radiation to the extent that damage occurs. as a sudden electrical discharge. With more radiation received, a satellite can be overloaded and suffer serious damage “, explains the professor of geophysics at the University of Rochester, John Tarduno.
In the South Atlantic Anomaly, objects in orbit are bombarded by protons that exceed the energies of 10 million electron volts at a rate of 3,000 “hits” per square centimeter per second. Currently, the anomaly does not create visible impacts on daily life on the surface. However, recent observations and forecasts show that the region is expanding to the west and continues to weaken in intensity.
White dots on the map indicate individual events when instruments recorded the impact of radiation from April 2014 to August 2019. Video: ESA / Division of Geomagnetism / DTU Space
But what causes the South Atlantic Anomaly? The shape of the Earth is one of the factors. The planet is not perfectly round (but it is far from flat or concave), but slightly flattened at the poles and wider at the equator. In addition, the magnetic dipole field is displaced from the center by about 500 km. It is in this difference that the cosmic rays manage to get closer to the surface and the isolation of the interplanetary space is less.
Earth radiation belts with the South Atlantic Anomaly (“South Atlantic Anomaly”, or SAA) indicated. Image: ESA
As the movement of the Earth’s core changes over time – due to the complex geodynamic conditions inside it and bordering the solid mantle above – the magnetic field also fluctuates in space and time. These dynamic processes propagate to the magnetic field around the planet, generating anomaly and other characteristics in the environment close to Earth – including the inclination and drift of the magnetic poles.
“The magnetic field is actually a superposition of fields from many sources,” explains geophysicist Terry Sabaka of the Goddard Space Flight Center. The forces in the core and the inclination of the magnetic axis together produce the anomaly, the area of weakest magnetism – allowing charged particles trapped in the Earth’s magnetic field to dive closer to the surface.
The International Space Station, which is in orbit around the Earth, also passes through the anomaly. The base and its astronauts are well protected from damage, but the ISS has other passengers affected by the highest radiation levels: Instruments such as the Global Ecosystem Dynamics Investigation (GEDI) mission.
“The anomaly blinks GEDI detectors and resets the instrument’s power panels about once a month,” says Bryan Blair, deputy mission researcher and instrument scientist at Goddard. “This causes a few hours of loss of data, but it only happens every month or more “, he adds.
In addition to measuring the strength of the South Atlantic Anomaly’s magnetic field, NASA scientists also analyze particle radiation in the region. A study led by heliophysicist Ashley Greeley used two decades of data to show that the anomaly is slowly but steadily drifting in a northwest direction.