1. Spacecraft from the United States and from Russia have been to the moon, and men have walked upon its surface. Rock and soil samples and information of many other kinds have become available in recent years. Yet with all we know about the moon, there is even more that we don't know.
2. Following the end of the Apollo space program, the National Geographic Society published an excellent set of articles about the moon. Here, in shorter form, are some questions and answers from one of these articles. For the full story, see the September, 1973, issue of National Geographic.
Were scientists right about what the moon would be like?
3. Many were, of course, but many were mistaken. One said there was no lava on the moon. Another said that the moon material would explode as soon as an astronaut's boot touched it. One said there would certainly be water on the moon. Many felt there was a chance that the astronauts could bring back to earth some strange infection. These ideas are now known to be incorrect, and no doubt we are still wrong about many other things, also.
Is the moon like the earth?
4. Yes and no. It is more like it than many scientists thought before Apollo. Like the earth, the moon is in layers, with a crust on the outside and a deep mantle below. It may also have a core, as the earth does. However, the crust is almost four times thicker than the earth's crust. We do not know much yet about the moon's mantle, that section of superheated rock which goes down hundreds of miles below the crust. We think-but we are not sure-that the moon has a center core which includes molten rock, as the earth does.
5. In other ways, of course, the moon is very different. There is no life, and there is no water. The makeup of its atmosphere is very different; the earth creatures cannot breathe in it.
Of what is the moon made?
6. Definitely not green cheese. It has the same chemical elements as have the earth and the rest of the solar system but in very different amounts-more of some, less of others. Carbon, which is a very important part of living things on the earth, is rare on the moon.
Is the moon hot or cold?
7. Most scientists agree that some of the moon was hot for at least a time. Rocks from the moon show that they were once melted. Right now there seems to be heat someplace inside the moon, possibly a great deal of it. On the surface, however, there is no sign of heat-no volcano, for example. The surface itself ranges from heat of 230℉ to cold of minus 290℉,depending upon where the sun is.
Where did the moon come from?
8. We don't know. The three main theories (ideas) are (1) that the moon was born from the earth, (2) that the earth and the moon were born together at the same time from the same cloud of gas and dust, and (3) that the moon was born someplace else in the solar system and then captured by the earth's gravity. So far, none of these theories has been proved to be either right or wrong. Professor George W.Wetherill of the University of California in Los Angeles says that he would give the first two theories each a 10 percent chance and the third theory a 20 percent chance. The other 60 percent he would give to "things we haven't thought of yet."
9. In spite of all we have learned from space flights, the moon is still a riddle from the distant past-and will be for a long time to come. Although we know much more now, we find that, somehow, for every answer new questions spring up.