Elaine Kihn, age 11, of Garfield Hts., Ohio, for her question:

Could the moon possibly be hollow?

You can tell whether a box is full or empty by hefting it in your hand. Its weight, of course, is related to its size. In somewhat the same way we can be sure that the inside of the moon is not an empty hole. If it were hollow, it would weigh less for its size. Naturally, of course, scientists did not reach this conclusion by hefting the moon like a box. However, it was estimated from a number of basic facts learned from the weights and sizes of everyday objects here on the earth.

One factor is the force of gravity, with its relationship to mass and distance. The moon's mass is the amount of matter in its size, or volume. These and other complex factors were computed together. The results indicate that the moon is solid, though made of lighter materials than the earth. The earth is 50 times larger and about 82 times heavier. The lunar astronauts left seismograph experiments which we hope will reveal details of the deeper layers. If they report that the moon has a hollow inside, the world of science will be downright stunned.