Jan Jackson, age 11, of Muncie, Indiana, for her question:

Where do all the meteors come from?

Billions of tiny meteors were left by passing comets, strewn like delicate dust across the path of the orbiting earth. We see them at certain times of the year, swooping through the sky like falling sparks. The origin of these meteors has been traced by computing the dates and paths of comets that came our way. But they are not related to the various other meteors that swoop through our skies.

No one is certain how these originated, though several theories have been suggested. Some of them may be the fragments from a planet that shattered asunder, though this has not been proved. I lost astronomers suspect that they are fragments of debris, strewn around when the Solar System was formed. Perhaps our Pioneer spacecrafts will tell us more about meteors on their grand tours to the outer planets.