Pierre Auger Observatory

On the trail of Cosmic Bullets - Symmetry - Oct/Nov 2007

By Kurt Riesselmann

Argentina’s Pampa Amarilla is a rather remote place, a dry plain stretching thousands of miles against the spectacular backdrop of the rugged, snowcapped peaks of the Andes. Like every other place on Earth, the yellow pampa is bathed in a constant shower of cosmic rays—protons and atomic nuclei that fly through the universe at close to the speed of light. While some are known to come from the sun, most take a meandering path that gives no clue to where they came from. Once in a while, an unusually powerful cosmic ray strikes the Earth’s atmosphere with almost as much energy as a bullet. Fortunately, such a projectile is no danger to human life. Entering the atmosphere, it loses energy and creates showers of lower-energy particles, which can spread across more than 15 square miles by the time they hit ground.

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