- Earth’s magnetic field protects the planet from deadly solar radiation, but it isn’t static.
- It has gotten 9% weaker, on average, in the last 200 years.
- Satellites that keep tabs on the field show that one weak spot over the southern Atlantic Ocean has continuously grown over the last 50 years.
- This weakening of the magnetic field can cause malfunctions in satellites and and spacecraft.
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In the last 50 years, a weak spot in the Earth’s magnetic field has gotten bigger.
This chink in the planet’s armour of geomagnetic energy is located above the southern Atlantic Ocean, so scientists have appropriately dubbed it the South Atlantic Anomaly. For people, it isn’t cause for concern: The protective field still shields the planet from deadly and destructive solar radiation. But the weak area does affect spacecraft and low-orbit satellites passing through the region, since more charged solar particles can seep through and cause malfunctions onboard.
Additionally, scientists at the European Space Agency (ESA) recently reported that in the last five years, the anomaly may have split in half. One area of magnetic weakness has developed over the ocean southwest of Africa, while another sits east of South America.
“The new, eastern minimum of the South Atlantic Anomaly has appeared over the last decade and in recent years is developing vigorously,” Jürgen Matzka, from the German Research Centre for Geosciences, said in a press release last week.
The weak spot is expanding and weakening further
The South Atlantic Anomaly has weakened by 8% since 1970. This mirrors what’s happening to the magnetic field as a whole:According to the ESA, the entire field has lost around 9% of its strength on average over the last 200 years.
ESA researchers use a set of three satellites, collectively nicknamed Swarm, to keep tabs on what’s happening to Earth’s changing magnetic field.
The animation below shows changes in the anomaly from April 2014 to August 2019. The white dots on the map indicate instances in which the satellites detected radiation – you can see their frequency increase over time.
Matzka and his colleagues aren’t sure what prompted the anomaly to cleave in two; their models can’t account for the bifurcation.
“The challenge now is to understand the processes in Earth’s core driving these changes,” he said.
What happens in the Earth’s core determines what happens to its magnetic field
Earth’s magnetic field exists thanks to swirling liquid iron in the planet’s outer core, some 1,800 miles beneath the surface. Anchored by the north and south magnetic poles (which tend to shift around and even reverse every million years or so), the field waxes and wanes in strength, undulating based on what’s going on in the core.
Periodic and sometimes random changes in the distribution of that turbulent liquid metal can cause idiosyncrasies in the magnetic field. If you imagine the magnetic field as a series of rubber bands that thread through the magnetic poles and the Earth’s core, then changes in the core essentially tug on different rubber bands in various places.
Those geomagnetic tugs influence how strong or weak certain parts of the field are, or cause the magnetic north pole to shift its location from one year to the next.
In the last five decades, the South Atlantic Anomaly has moved west at a rate of roughly 12 miles per year, the ESA reported. It has also grown.
A growing weak spot is bad news for satellites and spacecraft
A weaker field enables more charged particles from deadly solar winds to make their way through the Earth’s protective shield. If spacecraft and satellites in low-Earth orbit (within 1,200 miles of the planet’s surface) get bombarded with these particles, they can go haywire.
The particles can cause problems with onboard electronic systems, interrupt data collection, and lead expensive computer components aboard on spacecraft like the Hubble Space Telescope to age prematurely. The ESA noted that satellites flying through the region are “more likely to experience technical malfunctions,” like brief computer glitches that can disrupt communications.
Hubble passes through the anomaly in 10 of its 15 orbits around Earth each day. The orbiting observatory spends nearly 15% of its time in this “hostile region,” according to NASA.
The International Space Station, too, could be affected by the South Atlantic Anomaly. According to one 2018 study, when spacecraft pass through the anomaly, they – and the humans they carry – are exposed to “several minutes of strong radiation each time.”
“This is a well-known area where all different types of satellites – not just a space station with people, but normal communication satellites and others – have problems,” former NASA astronaut Terry Virts told the BBC. “You want to kind of get through there as fast as you can on the way to the moon, or wherever you’re going.”
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