A meteoroid is a piece of stone, metal, or dust that travels through space and sometimes enters the Earth's atmosphere.
Most meteoroids burn when they enter the atmosphere, and some reach the Earth's surface. When a meteoroid is large enough to be seen when it burns in the Earth's atmosphere, it is called a meteor.
Every day, about 200,000 meteors (or shooting stars) are visible on Earth, and 100 tons of meteoroid material are added to our planet's atmosphere every day. But only about 150 meteoroids reach the Earth's surface in an average year. When they do, they are called meteorites.
Very large meteorites have crashed into the Earth, creating huge craters. However, the largest meteorite ever discovered in one piece was found in Namibia. This block of outer space material was 2.70 metres wide and weighed about 59 tonnes!
A meteoroid in outer space that measures more than 10 metres is called an asteroid.
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