There is a region in Earth’s orbit where our magnetic field is weaker, and as a result satellites and spacecraft are more vulnerable to solar storms and cosmic radiation. The area, known as the South Atlantic Anomaly, has earned the nickname “Space Bermuda Triangle”, in reference to the North Atlantic region where more than 50 ships and 20 aircraft have disappeared since the middle of the 19th century.
“I don’t like the nickname, but in this region the lower intensity of the geomagnetic field ends up resulting in a greater vulnerability of the satellites to energetic particles, to the point that damage to spacecraft occurs as they traverse the region”, explains the professor of geophysics at the University of Rochester , John Tarduno, in a magazine interview All About Space.
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. Typically, 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.
“Thus, the satellites that pass through this region experience higher amounts of radiation to the point of damage. Like a sudden electrical discharge. With more radiation received, a satellite can be overloaded and suffer serious damage,” says 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.
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
This “attack” affects the electronic systems on board the spacecraft, which makes it difficult for these objects to operate and for space agencies and other satellite operators to shut them down or put them in “safe mode”. Even the Hubble telescope is a frequent victim: it passes through the region ten times a day, and is unable to collect astronomical data during these times (which represent 15% of its activity time).
The anomaly also appears to affect astronauts. The International Space Station is especially strengthened in its most frequented areas, such as galleries and dormitories. Some of the occupants have already reported seeing strange white lights flashing before their eyes when passing through the region. Since then, astronauts have used devices that measure their personal exposure to ionizing radiation in real time, and send out a warning if they reach dangerous levels.
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
In addition, the movement of the liquid metal that flows in the Earth’s core (and that generates the magnetic field) makes the poles not permanent. At the moment, for example, the magnetic field is weakening in the area of the anomaly, causing it to grow and, according to some studies, to divide into two cores.
This increase is worrisome, as it not only makes problems with electronic equipment more frequent, but it can also lead to a higher prevalence of cancer. According to data from the European Space Agency (ESA), the magnetic field in the region has lost about 15% of its strength in the past 150 years. Before 1994, the magnetic north pole was moving at 10 km per year, but has accelerated to about 65 km per year since 2001.
This animation shows the decrease in the magnetic field strength 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
Researchers are also concerned with a possible geomagnetic reverse. In this phenomenon, the north and south poles change position (that is, the magnetic north will be close to the geographic south, and vice versa), although there is no consensus among scientists whether we are going through this process or not. About 183 reversals have occurred in the past 83 million years, with the most recent 780,000 years ago.
“The disappearance of the Earth’s magnetic field is not a concern for many billions of years in the future,” says Tarduno. “Even during times of magnetic reversals, there is a magnetic field, although much weaker and much more complex than the present. The rapid decline in the strength of the dipolar magnetic field over the past 160 years and the decay pattern of some support regard it as it is a possibility, but in a short time this is still speculation “, completes the professor.