Patricia Strayer, age 9, of Fairfield, Corm., or her question:

How do the planets stay in place?

The nine planets are held in the Solar System by the gravity of the sun. This mighty pull keeps them from flying away into outer space. But, if the sun can pull so hard, why does it not pull all the planets down into its blazing furnace? There must be something which pulls in the opposite direction from the sun's gravity, And so there is.

This opposite pull is centrifugal force. The planets get it from the speed at which they travel around their orbits. Each planet is in the middle of a heavenly tug of war. The sun's gravity exactly balances the centrifugal force. The tug of war is a draw, with each planet staying so far and no farther from the sun.