Cosmos - Carl Sagan [62]
Intelligent life on Earth first reveals itself through the geometric regularity of its constructions. If Lowell’s canal network really existed, the conclusion that intelligent beings inhabit Mars might be similarly compelling. For life to be detected on Mars photographically, even from Mars orbit, it must likewise have accomplished a major reworking of the surface. Technical civilizations, canal builders, might be easy to detect. But except for one or two enigmatic features, nothing of the sort is apparent in the exquisite profusion of Martian surface detail uncovered by unmanned spacecraft. However, there are many other possibilities, ranging from large plants and animals to microorganisms, to extinct forms, to a planet that is now and was always lifeless. Because Mars is farther from the Sun than is the Earth, its temperatures are considerably lower. Its air is thin, containing mostly carbon dioxide but also some molecular nitrogen and argon and very small quantities of water vapor, oxygen and ozone. Open bodies of liquid water are impossible today because the atmospheric pressure on Mars is too low to keep even cold water from rapidly boiling. There may be minute quantities of liquid water in pores and capillaries in the soil. The amount of oxygen is far too little for a human being to breathe. The ozone abundance is so small that germicidal ultraviolet radiation from the Sun strikes the Martian surface unimpeded. Could any organism survive in such an environment?
To test this question, many years ago my colleagues and I prepared chambers that simulated the Martian environment as it was then known, inoculated them with terrestrial microorganisms and waited to see if anybody survived. Such chambers are called, of course, Mars Jars. The Mars Jars cycled the temperatures within a typical Martian range from a little above the freezing point around noon to about – 80°C just before dawn, in an anoxic atmosphere composed chiefly of CO2 and N2. Ultraviolet lamps reproduced the fierce solar flux. No liquid water was present except for very thin films wetting individual sand grains. Some microbes froze to death after the first night and were never heard from again. Others gasped and perished from lack of oxygen. Some died of thirst, and some were fried by the ultraviolet light. But there were always a fair number of varieties of terrestrial microbes that did not need oxygen; mat temporarily closed up shop when the temperatures dropped too low; that hid from the ultraviolet light under pebbles or thin layers of sand. In other experiments, when small quantities of liquid water were present, the microbes actually grew. If terrestrial microbes can survive the Martian environment, how much better Martian microbes, if they exist, must do on Mars. But first we must get there.
The Soviet Union maintains an active program of unmanned planetary exploration. Every year or two the relative positions of the planets and the physics of Kepler and Newton permit the launch of a spacecraft to Mars or Venus with a minimum expenditure of energy. Since the early 1960’s the U.S.S.R. has missed few such opportunities. Soviet persistence and engineering skills have eventually paid off handsomely. Five Soviet spacecraft—Veneras 8 through 12—have landed on Venus and successfully returned data from the surface, no insignificant feat in so hot, dense and corrosive a planetary atmosphere. Yet despite many attempts, the Soviet Union has