Douglas C. Padgett, age 10, Of Farmersvi11e, Calif., for his question:

Why has the moon no atmosphere like ours?

Our huge atmosphere is held by the gravity of the massive earth. Its assorted gases press down upon the surface with an average weight of more than 14 pounds per square inch. Its total weight is enormous, and the earth has held it captive for countless ages. But if such an atmosphere were placed around the moon, its gases would soon escape off into space.

The earth's gravity can prevent the escape of molecules speeding up to 25,000 miles an hour..    It is six times stronger than the Moon's gravity, where gases traveling at some 5,000 miles an hour could escape its pull. Heat gives speeding energy to gases, and the lunar day may be hot enough for its gases to get enough speed to escape and go off onto space. Even if we gave the moon a blanket of air like ours, the satellite would be too weak to hold on to it.