Curtis Behling, age 7, of Pewaukee, Wisconsin, for his question:

Do asteroids have any gravity?

Young space agers know that the earth has a built in force of gravity. This pulling force is very strong becauee the earth is so very massive. The moon is not so massive as our planet. So its built in gravity is less than the earth's. Giant Jupiter is more massive than the earth and its gravity is stronger. Experts tell us that the biggest aster¬oids are only a few miles wide. Most of them are not nearly as massive as our big moun¬tains. But all of these junior members of the sun's family have their built in share of gravity.

The mass of an asteroid is the amount of material packed into its small body. This mass decides the strength of its gravity. Its share of gravity is not strong enough to hold a spaceman and stop him from escaping. But it is there. Even an asteroid no bigger than a grain of sand has its proper share of gravity. Experts tell us that a fair share of gravity is built into every speck of dust in the whole universe.