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.
