Scientists Say: Muon

These heavy cousins of electrons constantly rain down on every part of Earth’s surface

A photo of the doughnut-shaped magnet that was used with the Muon g-2 experiment.

Physicists are using the Muon g-2 experiment at Fermilab to study the magnetic properties of muons. Researchers do this by watching how muons wobble as they move through a doughnut-shaped magnet (pictured).

Ryan Postel/Fermilab

Muon (noun, “MYOO-ahn”)

A muon is a type of fundamental particle. That means it is one of the basic building blocks of the universe. Like electrons and the quarks that make up protons and neutrons, muons cannot be split into smaller pieces.

Muons are in the same family of particles as electrons. Like electrons, muons carry a negative electric charge. But muons are about 200 times as heavy as electrons.

A shower of muons constantly hits every part of Earth’s surface. These muons form high in the sky, when particles from space called cosmic rays smash into Earth’s atmosphere. The muons raining down on Earth easily pass through many substances. In fact, a muon zips through your thumbnail about once per minute. 

But muons can also lose energy as they burrow through materials. The denser a material is, the fewer muons make it through. So measuring how many muons have passed through an object can reveal how dense that object is — and expose any empty spaces inside. This has allowed researchers to use muons to map the insides of volcanoes and Egyptian pyramids.

Since muons have electric charge, they also tend to lose energy when passing through thunderstorms. So muons have helped scientists probe the electricity inside storms, too.

In a sentence

In 2017, muons revealed a mystery void inside the Great Pyramid of Giza.

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Maria Temming is the assistant editor at Science News Explores. She has bachelor's degrees in physics and English, and a master's in science writing.

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