Extraterrestrial Civilizations by Isaac Asimov Page A

quarter hours of dark, the temperature could be as low as –100° C (–150° F).
    In short, it looked as though the temperature of Mars was too low for water to exist as anything but ice, except in a narrow region around the equator and for brief times around midday. Elsewhere, the climate on Mars was colder than that in Antarctica.
    Worse yet, the great difference between dawn temperatures and noon temperatures meant that the Martian atmosphere was probably thinner than had been thought till then. An atmosphere acts as a blanket, absorbing and transferring heat, and the thinner it is the more rapidly temperatures go up and down.
    What’s worse is that a thin atmosphere does not absorb much of the energetic radiation of the Sun. On Earth, the relatively thick atmosphere acts as an efficient blanket absorbing the energetic radiation that bombards our planet from the Sun and elsewhere.
    All these energetic radiations would be fatal to unprotected life if they fell upon Earth’s surface in full strength. Mars is farther from the Sun than we are and it receives a smaller concentration of ultraviolet light, for instance. However, that smaller concentration reaches the Martian surface in far greater quantities, it would appear, than it reaches the terrestrial surface.
    By the 1940s, it became possible to analyze the infrared radiation from Mars to analyze the content of its atmosphere. This was done in 1947 by the Dutch-American astronomer Gerard Peter Kuiper (1905–1973). He found that what little there was of theMartian atmosphere was almost entirely carbon dioxide. There was very little water vapor and apparently no oxygen at all.
    Considering the frigidity of Mars, some astronomers began to wonder if there was any water on Mars at all. Might the ice caps not be frozen water, but frozen carbon dioxide instead?
    Taking all things into consideration—a thin atmosphere of carbon dioxide, ultraviolet light bombarding the Martian surface, temperatures of deep frigidity—it seemed unlikely that the kind of complex life forms one would expect to have developed intelligence would have evolved on Mars.
    The feeling grew that if the canals existed at all, they were natural phenomena, not the product of a race of advanced engineers.
    But then, if not intelligent life, what about primitive life? On Earth, there are bacteria that can live on chemicals poisonous to other forms of life. There are lichens that can grow on bare rock, and on mountaintops where the air is so thin and the temperature is so low that one might almost imagine one’s self to be on Mars.
    Beginning in 1957, experiments were conducted to see if any simple life forms that were adapted to severe conditions on Earth might survive in an environment that, as far as possible, duplicated what was then known of the Martian environment. Over and over again it was shown that some life forms would survive.
    Perhaps, in that case, we ought not abandon all hope of complex life forms either. After all, life on Earth has evolved to fit the terrestrial environment. To us, therefore, conditions on Earth seem pleasant, and conditions that are considerably different from those on Earth seem unpleasant. On Mars, however, life forms would have evolved to suit the conditions there, and it would then be those conditions that would seem pleasant to them.
    The question appeared moot right into the 1960s.
MARS PROBES
    In the 1960s, rocket-powered probes were being launched that were intended to pass near the planet and send back information (like the ones I have already mentioned in connection with Mercury and Venus).
    On November 28, 1964, the first successful Mars probe,
Mariner 4
, was launched. As
Mariner 4
passed Mars it took a series of twenty photographs that were turned into radio signals beamed back to Earth, where they were turned into photographs again.
    What did they show? Canals? Any signs of a high civilization or, at least, of life?
    What the photographs showed turned out to