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What are cosmic rays?

'Cosmic rayCharged atomic particles moving in space with very high energies (the particles travel close to the speed of light); most originate beyond the solar system, but some of low energy are produced in solar flares.' is the (confusing) name given to any kind of energetic particle that comes from outside the Earth. These particles could be single protonsA massive, positively charged elementary particle; one of the main constituents of the nucleus of an atom. A proton is 1836 times heavier than an electron., nuclei of different atomsThe smallest particle of an element that exhibits the chemical properties of the element. or electronsA negatively charged elementary particle that normally resides outside (but is bound to) the nucleus of an atom.. Cosmic rays are neither light nor beams of particles, so maybe they should be renamed energetic cosmic particles. Cosmic rays are often made when a star explodes. This is called a supernovaA stupendous explosion of a massive star, which increases its brightness hundreds of millions of times in a few days.. Some cosmic rays can be produced by the Sun and some can even come from as far away as other galaxies. These particles are very energetic, but also very small. They rarely directly hit anything as they travel through space, but if they do it can cause nuclear reactions with atoms. These reactions are similar to the activities in particle accelerators. The Sun's heliosphereThe region around the Sun where the solar wind dominates over the interstellar medium. protects the planets and other objects in the solar system from some of these dangerous particles. The Earth's magnetosphereThe region around a planet where particles from the solar wind are trapped by the planet's magnetic field. and atmosphereA gaseous envelopesurrounding a planet, or the visible layers of a star; also a unit of pressure(abbreviated atm) equal to the pressure of air at sea level on the Earth's surface. protect life on Earth from cosmic rays that make it through the heliosphereThe region around the Sun where the solar wind dominates over the interstellar medium.. Studying the heliosphere will help us to prepare adequate shielding during future space travel.

NASA Principal Investigator: Dave McComas
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Last Updated: 22 NOVEMBER 2010
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