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NASA's Space Place

Earth’s Impenetrable Shield

Alex H. Kasprak
National Aeronautics and Space Administration

Sure, the sun is great. It’s nice to not live in a frozen wasteland, after all. But the sun is pretty terrifying, too. It sends a dangerous stream of fast-moving electrons, protons, and other even smaller particles, called photons, toward Earth.

You may have heard of one of the ways Earth shields itself—the ozone layer. The ozone layer, which is high in the atmosphere, blocks much of the sun’s damaging UV radiation, which comes from the photons. But there’s another shield further away. This takes care of the larger, fast-moving particles—the electrons and protons. And scientists have just discovered how strong this other shield is.

Two donut-shaped belts called the Van Allen belts surround our planet. Scientists have known about them for a long time. For the most part, the closer belt contains protons and the further belt contains electrons. Earth’s magnetic field shapes them and holds them in place.

Now, scientists have new information from a pair of NASA probes sent into orbit back in 2012. The big discovery is about the edge of the outer donut that is closest to Earth. It’s pretty much an unbreakable shield against the fastest moving particles thrown at us by the sun. Scientists have even called it “impenetrable.”

It’s pretty remarkable. These electrons and protons from the sun are traveling at nearly the speed of light. But when they reach the end of the first Van Allen belt, they stop moving toward Earth.

Scientists are still not sure how or why this powerful shield exists or even how it works. But we should sure be thankful it’s there. Without protection from the sun’s damaging particles, Earth would be a different place!

Learn more about this sun in Space Place’s latest “Space Place in a Snap” http://spaceplace.nasa.gov/sun-heat.

Diagram of the two Van Allen radiation belts. Credit: NASA/Goddard.

A fun comic! Download here: http://spaceplace.nasa.gov/review/partners/vanallenbelthero.jpg


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