MARK GARLIC / SCIENCE PHOTO LIBRARY MARK GARLIC / SCIENCE PHOTO LIBRARY
Illustration of the shower of particles produced when cosmic rays enter the Earth's atmosphere, and the detection of muons. Cosmic rays are high-energy particles that originate from events in space. Earth is constantly bombarded by this radiation. The particles collide with atoms in the atmosphere, producing showers of secondary particles. A high-energy proton collides with an atmospheric atom, producing pions, protons and neutrons. These decay further into gamma rays (waves) and muons, heavier counterparts to the electron. The muons are relatively stable, and can be detected by airborne balloons (top right) and ground-based detectors (bottom right), and even underground.
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