What is the main difference between a comet and an asteroid?

Fact

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Comets are small bodies rich in ice, dust and rocky materials. When they approach the Sun, their ices sublimate and form a hair as well as tails of gas and dust. Asteroids are generally more rocky or metallic, although the boundary between the categories is not always absolute. A shooting star is neither a comet nor a star: it is the light trail of a meteoroid entering the atmosphere. Dust dropped by a comet in its orbit can cause a meteor shower when Earth passes through this stream, but the comet itself does not become a shooting star.