<P> A meteoroid (/ ˈmiːtiərɔɪd /) is a small rocky or metallic body in outer space . </P> <P> Meteoroids are significantly smaller than asteroids, and range in size from small grains to one - meter - wide objects . Objects smaller than this are classified as micrometeoroids or space dust . Most are fragments from comets or asteroids, whereas others are collision impact debris ejected from bodies such as the Moon or Mars . </P> <P> When a meteoroid, comet, or asteroid enters Earth's atmosphere at a speed typically in excess of 20 km / s (72,000 km / h; 45,000 mph), aerodynamic heating of that object produces a streak of light, both from the glowing object and the trail of glowing particles that it leaves in its wake . This phenomenon is called a meteor or "shooting star". A series of many meteors appearing seconds or minutes apart and appearing to originate from the same fixed point in the sky is called a meteor shower . If that object withstands ablation from its passage through the atmosphere as a meteor and impacts with the ground, it is then called a meteorite . </P>

What is the average size of a meteor