Science & Technology

The South Atlantic Anomaly Is the Bermuda Triangle of Space

Outer space is a dangerous place: If the deep cold doesn't get you, the cosmic rays will. Luckily, Earth has its own pair of radiation belts that shield us from the kinds of high-energy particles that would wreak havoc on living things and delicate electronics the first time they had the chance. But there's an area of our planet where those protective belts turn on us. That area is known as the South Atlantic Anomaly.

The Van Allen Belts

In 1958, James Van Allen led a project to send the United States' first satellite into space with some simple equipment: a Geiger counter to detect radiation and a tape recorder to, well, record sound. That project — and several after — led to the discovery that our planet is surrounded by two donut-shaped masses of high-energy particles. Those particles are leftovers of cosmic rays shooting in from outside our solar system that become trapped in the Earth's magnetic field. They exist in that belt configuration because the magnetic field follows a telltale pattern, one you know if you've ever seen iron filings sprinkled around a magnet. Though the high-energy particles would be dangerous on their own, when they're trapped in the Van Allen Belts, they shield the Earth from any other dangerous particles that might elbow their way in.

Earth's poles of rotation don't line up with the poles of its magnetic field.

Here's the Catch

Thanks for protecting us, Van Allen Belts! Well, don't be too grateful just yet. The poles of Earth's magnetic field don't line up perfectly with its poles of rotation; they're actually tilted by 11 degrees. That means the Van Allen Belts are tilted too. This leads the inner donut-shaped mass of deadly high-energy particles to dip dangerously low to the Earth's surface — as close as 124 miles (200 kilometers) at some points over the South Atlantic and Brazil. That's well below the path of many satellites, which are forced to pass through the belt and get pummeled by protons. And we're talking pummeled: Every square centimeter is hit 3,000 times per second. That abuse can cause all sorts of problems, from data glitches to electronic damage. As a result, engineers tell their satellites to power down as they pass through the anomaly in hopes that their data will be protected.

But why doesn't Earth's magnetic field line up with its physical poles? It might be because Earth's magnetic field is getting ready for a reversal. Scientists say the main cause of the South Atlantic Anomaly is a strange patch of the core-mantle boundary — the place where the Earth's iron outer core meets the slightly stiffer mantle, which lies beneath the crust — that sits right below southern Africa. The polarity in this area is reversed from what you see everywhere else on the planet: If you could stick a compass that far beneath the Earth's surface and direct it north, it would point south. Computer simulations have shown that full geomagnetic reversals — that is, a complete flip of the magnetic field that turns compasses upside down — often begin with the appearance of strange patches just like the one discovered beneath southern Africa.

What's more, this already weak area of the planet's magnetic field appears to be getting even weaker. Unfortunately, scientists can't predict what will happen next. Will we have a complete magnetic reversal, or will the magnetic field continue to weaken over the centuries? Only time will tell.

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Written by Ashley Hamer January 24, 2017

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