National Geographic : 1967 Dec
springtime darkening, we may still believe that life can exist on Mars. For one thing, we do not expect that signs of life would be visible over interplanetary distances. The Mariner IV photographs of Mars do not detect features much less than two miles across. Weather-satellite photo graphs of earth, at about the same resolution, show virtually no signs of life on our planet. For another thing, experiments in a num ber of laboratories suggest that the Martian environment does not rule out life. In our own laboratories, for example, we have designed special chambers where we can simulate the Martian environment. They are, of course, called "Mars jars." With earthly organisms, mainly bacteria, in the jars, we have repro duced the daily temperature variations, the low atmospheric pressure, the composition of the Martian air, and the ultraviolet radiation. Earth Life Survives Martian Conditions Most of the organisms quickly die. But in every sample of terrestrial soil we have found varieties of micro-organisms that survive the Martian conditions, some indefinitely. They find the lack of oxygen and the tem perature extremes to their liking. They find perfect safety, under small particles of soil, from the deadly ultraviolet light. When the subsurface water content in creases slightly, they thrive in the seemingly hostile environment, just as do such strange earthly creatures as iceworms that live on glaciers, algae that survive in scalding hot springs, or brine shrimp that easily take to the intense salinity of salt lakes.* So it takes no great stretch of the imagina tion to believe that some earthly organisms would grow on Mars. And if terrestrial organ isms can at least survive, native creatures should get along very nicely, for what seems to us to be a rigorous environment may not be rigorous at all for Martian life. If there are Martian organisms-and scien tists do not agree on this matter-we must expect adaptations there that do not occur here, because the histories of life on the two planets must have been widely divergent. It may be that the oxygen bound in limo nite is used for respiration. Perhaps some Martian enzyme is able to use the water chem ically bound in the iron-rich soil. In fact, so much water is tied to the limonite that if the chemical bonds binding the water to the li monite can be tapped by Martian organisms, the bright areas on Mars may for them be oceans rather than deserts! 838 Sealed off from his work, a technician sol ders by using gloves built into an airtight plastic tent. At Denver, the Martin Marietta Corporation develops methods of repairing space parts under sterile conditions, since microbes, riding Voyager to Mars, could mis lead life detectors and possibly set off a plague among any Martian life. Aside from showing that life on Mars is within the realm of possibility, the Mars-jars experiments underline the problem of biologi cal contamination of the planet. Suppose an unsterilized spacecraft from earth crash-lands on Mars. Micro-organisms such as bacteria easily survive the crash. They escape and adhere to grains of surface mate rial; winds spread them over the planet. Some may find themselves in favorable environments, with neither competitors nor predators; they reproduce rapidly. In this way, descendants of just one micro-organism could, in theory, give Mars in a few years as many microbes as exist on earth. *See "Life in a 'Dead' Sea-Great Salt Lake," by Paul A. Zahl, NATIONAL GEOGRAPHIC, August, 1967.