Extraterrestrial Civilizations - Isaac Asimov [29]
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 be completely unexpected, for as they were received, astronomers saw what were clearly craters—craters that looked very much like those on the Moon.
The craters, at least as they showed up on the Mariner 4 pictures, seemed so many and so sharp that the natural conclusion was that there had been very little erosion. That seemed to mean not only thin air, but very little life activity. The craters shown in the photographs of Mariner 4 seemed to be the mark of a dead world.
Mariner 4 was designed to pass behind Mars (as viewed from Earth) after its flyby, so that its radio signals would eventually pass through the Martian atmosphere on their way to Earth. From the changes in the signals, astronomers could deduce the density of the Martian atmosphere.
It turned out that the Martian atmosphere was even thinner than the lowest estimates. It was less than 1/100 as dense as Earth’s atmosphere. The air pressure at the surface of Mars is about equal to that of Earth’s atmosphere at a height of 32 kilometers (19 miles) above the Earth’s surface. This was another blow to the possibility of advanced life on Mars.
In 1969, two more rocket probes, Mariner 6 and Mariner 7, were sent past Mars. They had better cameras and instruments, and took more photographs. The new and much better photographs showed that there was no mistake about the craters. The Martian surface was riddled with them—as thickly, in places, as the Moon.
The new probes, however, showed that Mars was not entirely like the Moon. There were regions in the photographs in which the Martian surface seemed flat and featureless and others where the surface seemed jumbled and broken in a way that was not characteristic of either