Denise Wright, age 11, of Newport News, Virginia, for her question:     

How do meteors form?

We know that the spaces between the stars are strewn with countless meteors, large and small. Swarms of meteors also orbit around the outer limits of the Solar System. Scientists are not certain how all of them got there, but several likely suggestions have been made. They can explain the origin of meteor showers, those flocks of so called falling stars that occur on certain nights of the year. These are specks of matter left by passing comets.

We are less certain about the origin of the hordes of ordinary meteors. Some suggest that at least some of them may be the shattered remains of moons or planets that broke apart in the distant past. Amore popular theory suggests that they are debris formed when the Solar System was created. Most of these solid fragments collided and merged with the planets and moons. Others got lost in space, though millions of them are being grounded every day.