Apollo Expeditions to the Moon

CHAPTER 15.4


ANCIENT TRACKS OF RADIATION

What are the principal effects of the Sun upon the Moon, and how do they differ from the effects of the Sun on Earth? Protected by Earth's atmosphere, we are not directly exposed to the lethal part of the Sun's radiations. But the airless Moon is starkly exposed. By a neat twist, this situation gives us a way of checking up on the Sun's activity over the past few million years. Cosmic rays from the Sun and galaxy leave tracks in the soil grains and rock surfaces on which they impact; these tracks can be enhanced by etching, and counted. The track intensities indicate the intensity of the radiation to which the materials were exposed. By analyzing the rate at which lunar material is brought out onto the surface and then later buried again, it is possible to estimate the times when different layers in the lunar regolith were exposed, and for how long. Thus sample cores of the lunar regolith taken by the Apollo astronauts enable us to look back in time at the radiation environment experienced by the Moon. No significant changes in galactic cosmic radiation are seen, but there is a suggestion that there might have been variation in solar cosmic rays over the last one to ten million years. This would imply changes in solar activity, which in turn may have had effects on Earth.

Is there life on the Moon? Some of the bitterest exchanges took place over this question If there were life, no matter how primitive, we would want to study it carefully and compare it with Earth life. This would require very difficult and expensive sterilization of all materials and equipment landed on the Moon, so as not to contaminate Moon life with Earth life. Also there was the question of contamination of Earth by Moon life, possibly a serious hazard to us on Earth. So difficult, time-consuming, and expensive quarantine procedures were urged. On the other side of this argument were those who pointed to the hostile conditions on the Moon: virtually no atmosphere, probably no water, temperatures ranging from 150° C during lunar night to more than 120° C at lunar noon, merciless exposure to lethal doses of solar ultraviolet, X-rays, and charged particles. No life, they argued, could possibly exist under these conditions. The biologists countered: water and moderate temperature conditions below ground might sustain primitive life forms. And so the argument went on and on, until finally Apollo flew to the Moon with careful precautions against back contamination of Earth, but with limited effort to protect the Moon.

It turns out that there is no evidence that indigenous life exists now or has ever existed on the Moon. A careful search for carbon was made, since Earth life is carbon based. In the lunar samples one hundred to two hundred parts per million of carbon were found; of this no more than a few tens of parts per million are indigenous to the lunar material, the rest being brought in by the solar wind. None of the carbon appears to derive from life processes. As a consequence, after the first few Apollo flights, even the back-contamination quarantine procedures were dropped.