Jim Liggett, age 11, of College Station, Texas, for his question:

What is meant by an asteroid belt?

Recently some of us got into a tizzy about an asteroid named Icarus. This little space traveler was due to make a close U turn around the sun along a path very close to the earth. With bated breath we waited for Icarus to fall into the sun or bash into the earth. But neither collision occurred.

For a long time, astronomers assumed that the one and only asteroid belt was the wide open stretch of space roughly between the orbits of Mars and Jupiter. The major part of this celestial territory is a spacious doughnut, approximately 966 million miles wide with a central hole about 282 million miles wide. This asteroid belt is populated with uncounted asteroids. Each one is a solid little heavenly body busily orbiting around the sun along its own path at its own particular speed.

The motions of an asteroid are almost exactly like those of a bulky planet. Both travel in orbits around the starry sun at the center of our Solar System. Their positions and orbits are governed by the gravity of the sun and by the same cosmic traffic laws. A planet, however, is bigger, much bieger than an asteroid. It also rotates on its axis. We know that the larger asteroids also rotate but the smaller ones may or may not spin around as they swoop around their orbits.

Actually, the asteroids are small planets and we often call them "Planetoids." There is room between the orbit of Mars and Jupiter for a sizable planet and many astronomers have pondered why this is so. The news that this planetless tract is occu¬pied by a belt of asteroids merely poses another problem. We wonder why all these little space travelers are not bulked together to form one orbiting planet. Perhaps they are building blocks that plan to merge and add_another planet to the Solar System at some distant time in the future. Perhaps they are fragments from an ancient planet that shattered asunder.

At present, we do not know enough to prove either of these theories.    But recently we discovered that this asteroid belt that orbits the sun like a swarm of golden bees is not the only one of its kind. There are zillions more asteroids out near the rim of our Solar System. In uncounted numbers they swarm along the orbit of Pluto and  far out beyond it. They also pursue planetary paths governed by the rules of our Solar System. This outside asteroid belt also belongs to our solar family and extends its outer limits way beyond the orbit of Pluto.

A few asteroids have eccentric orbits and sometimes zoom way out df bonrids among the planets. But most of them travel well within definite belts  an inner belt beyond Mars and an outer belt beyond Pluto. We cannot say why this is so. But when two such happenings occur in our Solar System, we wonder. We know that other suns have families of planets. It seems more than likely that these other solar systems also have asteroid belts similar to those in our own solar family.