Bruce Vanischer, age 12, of Monroe, Michigan, for his question:

How does the atmosphere stay close to the earth?

Our wonderful universe operates with a set of forceful rules and regulations. Every particle of matter has a built in quota of gravitational force. Massive objects have more of this force. Our massive earth has enough gravity to hug us to its surface. It takes a tremendous amount of energy to break this grip and escape up and out into space. This same planetary force of gravity also exerts itself upon the gaseous air that surrounds the globe. This is what makes the atmosphere stay close to the earth.

But remember, there are forces strong enough to break the grip of the earth's gravity. We can use a mighty tbrust of energy to launch a rocket into space. Nature can use speed to break the grip. And in the miniature domain of gaseous particles, speed is related to heat. Heat from the sun can give a molecule enough speed to escape into space. A few of our air molecules do escape. The less massive moon has weaker gravity and more solar heat. There all the airy gases can escape    which explains why the moon is unable to keep an atmosphere.