All told, more than 1,000 scientists in 19 countries have been studying the Apollo samples—a priceless trove of 841 pounds of lunar rock and soil. And a third of a pound of lunar soil brought to earth by Russia’s unmanned Luna 16 and Luna 20 spacecraft has added importantly to the growing body of knowledge because it came from areas not sampled by Apollo.
There is a particular fascination in comparing some of our pre-Apollo ideas about the moon with what we know today. I recall, for example, a prominent scientist who told me in 1968, “I see no evidence for lava flows on the moon.” Another predicted that the moon material would explode the instant an astronaut’s boot touched it. A third asserted confidently that we would find water on the moon. Still others firmly maintained that the moon has always been a cold, dead body, a simple relic of the primitive solar system.
And the possibility of life on the moon led the National Aeronautics and Space Administration for a time to quarantine both the returning astronauts and their lunar rocks, lest pathogenic organisms infect the earth. Today none of these ideas is tenable. We have come a long way in understanding our satellite. And yet, as Dr. Robin Brett at NASA’S Lyndon B. Johnson Space Center near Houston notes, “The more we see of the moon, the more complicated we know it is.”
What we know—and what we still do not know—can perhaps best be summed up in six questions, six mysteries of the moon: 1. Is the moon like the earth? Yes, more so than many scientists thought before Apollo. Like the earth, it is layered, with a crust and mantle and possibly a core, and it “burns” with internal heat. Like the earth, it has had a dynamic history, although volcanic violence has given way to an occasional burp and the shivers of small quakes.
But in more obvious ways, the moon is unlike the earth. No hint of life has shown up in the moon samples, although some analysts find small quantities of substances that they consider the forerunners of amino acids, the building blocks of life. There is no free oxygen. The moon is dry, even though three of its flat maria, or “seas,” are named Humorum (moisture), Imbrium (rains), and Nubium (clouds). Rust stains in some Apollo samples may well have been caused by melted ice from comets or water in meteorites falling on the moon, although some scientists blame contamination within the spacecraft.
Apollo’s instruments detect tiny amounts of the gases argon, neon, and helium, much of which comes from solar wind. So the moon has an exceedingly tenuous atmosphere, though it is a high vacuum by earth standards. As Dr. John H. Hoffman of the University of Texas points out: “If you took all the molecules in a cubic centimeter of the moon’s atmosphere and lined them up end to end, they would fit on the tip of your pen. But if you did the same thing with the air you are breathing, the chain of molecules would reach to the moon and back with some left over!”