Jo Ann M. Stipich, age 12, of St. Louis, Missouri, for her question:

What keeps the earth in a stable position?

In order to keep its proper place in the solar system, the earth must keep moving at a certain speed and at a certain distance from the sun. The feat is performed by a precise balancing trick. It depends on two opposing forces of equal strength, some¬what like two equally strong teams in a tug of war. One works to pull the earth toward the sun, the other works to keep it from falling.

Our planet is pulled toward the sun by the mighty force of gravity. Its traveling speed keeps it from falling straight down into the fiery furnace and bends its path into a curve. This curved path is the orbit that swings us around and around the sun. Our planet will keep its stable position in the solar system so long as it travels at the right speed and stays at the right distance from the sun. And nothing is likely to change these factors.