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A planet's radiation belt is a region of high energy particles (e.g., electrons and ions moving at high speed) surrounding the planet due to the planet's magnetic field interacting with particles entering, such as the stellar wind. (This use of the word radiation does not mean electromagnetic radiation, but largely consists of some types of particles also produced by radioactivity and has analogous dangers.) The magnetic field changes the velocity (including direction) of particles, trapping them, producing a cloud of such particles. If a strong magnetic field produces a substantial belt, it can glow in the microwave due to synchrotron radiation. Within the solar system, remaining within the radiation belt is dangerous to spacecraft and humans. The belt is also protective of the planet underneath, trapping some such particles arriving from elsewhere that would otherwise descend on the planet. The size and strength of the belt can vary with the host star's wind. Example radiation belts include the Earth's Van Allen belts, and Jupiter's radiation belt, which is far stronger and more damaging due to Jupiter's strong magnetic field. The other planets with any significant magnetic fields have lesser radiation belts: Mercury, Saturn, Uranus, and Neptune. A radiation belt has been identified around at least one extra-solar body.