Extraterrestrial Civilizations - Isaac Asimov [28]
One American astronomer, Edward Emerson Barnard (1857–1923), was a particularly keen observer. In fact, he is often cited as the astronomer with the sharpest eyes on record. In 1892, he discovered a small fifth satellite of Jupiter, one that was so small, and so close to the brightness of Jupiter itself, that to see it required eyes of almost superhuman keenness; yet Barnard insisted that no matter how carefully he observed Mars, he could never see any canals. He said flatly that he thought it was all an optical illusion; that small, irregular patches of darkness were made into straight lines by eyes straining to see objects at the very edge of vision.
This notion was taken up by others. An English astronomer, Edward Walter Maunder (1851–1928), even put it to the test in 1913. He set up circles within which he put smudgy irregular spots and then placed schoolchildren at distances from which they could just barely see what was inside the circles. He asked them to draw what they saw, and they drew straight lines such as those Schiaparelli had drawn of the Martian canals.
Meanwhile, astronomers continued to study the habitability of Mars. As the twentieth century advanced, instruments were devised that could detect and measure tiny quantities of heat. If these heat detectors were placed at the focus of a telescope and the light from Mars were allowed to fall upon it, the temperature of Mars could be deduced.
This was first done in 1926 by two American astronomers, William Weber Coblentz (1873–1962) and Carl Otto Lampland (1873–1951). From such measurements, it seemed that at the Martian equator the temperature would rise above the melting point of ice at times. In fact, it was even possible for the equatorial temperatures to rise as high as 25° C (77° F) on rare occasions.
The temperature dropped sharply during the night, however. There was no way of following the temperature at night, for the night side of Mars was always on the side away from Earth. However, the temperature of the early morning could be taken at the western edge of the Martian globe where the surface of the planet was just emerging from night and into the dawn. After twelve and 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 the Martian atmosphere was almost entirely carbon dioxide. There was very