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There's a region of Earth's atmosphere known as the South Atlantic Anomaly, and it’s one of the most dangerous near-Earth areas of space, both for satellites and humans.

Hosted by: Reid Reimers

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Sources:

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Images:

https://www.nasa.gov/audience/forstudents/k-4/stories/nasa-knows/what-is-a-satellite-k4.html
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[♪ INTRO].

Despite our best efforts, satellites aren’t always the most predictable. Sometimes, they just up and reboot.

Or, occasionally, they misbehave for some unknown reason. As you might expect, these failures are a pain for scientists. Like, come on!

We’re trying to explore the universe out here. But, if nothing else, we can take comfort in the fact that we at least understand where some of these errors come from. In one 1980s study, engineers made a map of where many anomalies happened for two satellites, and they found something really weird:.

The vast majority of them happened in a region above South America and the Atlantic Ocean. This region is known as the South Atlantic Anomaly. And it’s one of the most dangerous near-Earth areas of space, for satellites and humans.

The story of the Anomaly starts with the Sun. All the time, electrically-charged particles from the Sun’s atmosphere stream off at supersonic speeds. Some of that material zooms by Earth, and when it does, it interacts with our planet’s magnetic field, because, well, that’s just what charged particles tend to do.

Some of the material gets directed into our atmosphere and causes the auroras, and some of it leaves the system. But most importantly for this story, some of that solar material gets trapped by the magnetic field and contributes to the Van Allen radiation belts: ring-shaped regions around Earth full of very high-energy particles. Despite the name, they’re not actually radioactive; space scientists use the term “radiation” differently than, say, doctors do.

But in general, engineers would still like to launch satellites so they never encounter these belts. Because those charged particles can pass right through a satellites’ computers, causing hiccups known as single-event upsets. The particles can hit a computer chip and change its memory; basically, flipping signals from “on” to “off,” or vice versa.

And that can cause anything from bad data to severe malfunctions or crashes. The problem is, depending on where you want to put your satellite, the radiation belts aren’t always easy to avoid. Because despite what you might be picturing, they’re not perfectly centered around Earth.

They’re a little skewed. Imagine you’re looking down at the North Pole. You can start by picturing the belts as a ring around the Earth’s equator.

Now, push that ring a little closer to Earth on one side, near North and South America. Then, tilt it a bit, so it gets closer to the Earth near South America, and a bit further away near North America. On average, that’s what the belts actually look like.

They’re like this because Earth’s magnetic field is tilted and shifted away from Earth’s geographic rotation axis, meaning the magnetic poles don’t line up with our geographic ones. Scientists think that’s because the magnetic field is generated by Earth’s core not rotating exactly the same as the rest of the planet. Because of this, there’s a region near South America, stretching from around 15 to 45 degrees south latitude, where the inner radiation belt is unusually close to Earth.

Typically, the belt is at least a few thousand kilometers above the surface, but here, it’s only about 600 kilometers up. That region is the South Atlantic Anomaly. And there, the inner belt is low enough to affect and damage satellites.

Now, it might seem like the obvious solution is to just not launch satellites that pass over South America. But it’s not that easy. For one, sometimes we want satellites there!

But even when it’s not necessary, it’s really hard to avoid this region because of how orbits work. Orbits are symmetric around the equator, so if you want a satellite to pass over a certain latitude in the northern hemisphere, it will also have to pass over the same latitude in the southern hemisphere. So, if you want your satellite to fly over somewhere specific, like NASA’s facility in Maryland at about 40 degrees north, your satellite will also have to pass over 40 degrees south.

Right through the South Atlantic Anomaly. Because of this, low, Earth-orbiting satellites often end up traveling through this spot for a few minutes every day. And as they do, they encounter those high-energy particles and the potential problems that come with them.

One way to protect spacecraft from this is to shield them with physical barriers. But since those can get heavy and therefore expensive to launch, we’ve had to find other workarounds. A common, and clever, one is to give a satellite multiple computers that can vote.

For instance, you might have three computers all running exactly the same code getting exactly the same information. And if at least two of them agree on an action, the satellite will do that. So, if one computer glitches, the mission will be okay.

This type of system wasn’t invented just for the Anomaly, but it still saves us a lot of trouble. But there’s another problem, too:. Because we currently launch most equipment and crew from Russia and its high latitudes, the International Space Station also orbits through the Anomaly.

That’s bad news, because high-energy particles can damage our DNA. So as we get exposed to more of them, the probability of getting cancer and other diseases goes up. NASA attempts to limit astronaut’s exposure to this as much as they can.

And thanks to things like physical shielding and careful spacewalk planning, they do a good job. But if we didn’t know about the Anomaly… things could be a lot worse. Exploration would be easier if the radiation belts were all nice and perfectly centered, but hey, that’s not the hand we’ve been dealt.

Instead, we’ve had to get creative with our engineering. And I like to think that that’s made us better explorers. After all, when we someday venture beyond near-Earth space, we’ll have to deal with all kinds of particles like this.

So, at least we can figure out the basics close to home. Thanks for watching this episode of SciShow Space! If you enjoyed it and want to learn more about satellites, you can watch our episode about how these things get and stay in orbit.

And if you have questions for us, we’d love to hear them. You can leave us a comment below or if you’re a patron, you send us a quick question in our patron inbox over at Patreon.com/SciShow. [♪ OUTRO].