Mars: An Update for Biologists

Abstract

IMANY ASTRONOMERS OF THE 1950s shared the optimistic view of the life-on-Mars hypothesis. Astronomer Gerard de Vaucouleurs (1953) wrote, All in all the plant-life hypothesis so far seems to provide the most likely explanation of the dark regions. (The dark regions-often called mariashow regular and distinct coloration changes during the various seasons of the year). Most biologists, however, felt that life on Mars was only a very remote possibility. It was not until the early 1960s that biologists, probably influenced by the growing U.S. space program, began to reevaluate their stand on the life-onMars hypothesis. Biologist Frank Salisbury (1962), in an article entitled Martian Biology, attempted to provide models of biological systems that could possibly survive in an environment similar to that of Mars. During this period numerous experiments in environmental simulation chambers indicated that simple Earth life forms, bacteria for example, could survive on Mars. In 1965, the American spacecraft Mariner 4 flew past Mars and transmitted back to Earth a series of 22 photographs showing the surface to be pitted with craters. With no evidence in the photographs of such Earth-like tectonic features as mountain chains, valleys, or volcanos, it was assumed that Mars was a very ancient planet and that conditions believed necessary for the beginning of life never did exist. Despite the fact that only one percent of the surface had been photographed by Mariner 4, there developed a general consensus among many scientists that life on Mars was absent. But the future exploration of Mars by spacecraft held some surprises. In 1969 two American spacecraft, the Mariner 6 and the Mariner 7, took hundreds of photographs as they approached and flew past Mars. The photographs, in contrast to the dismal photographs of Mariner 4, now showed a surface with features other than ancient craters. For example, there were large featureless plains (the desert known as Hellas on maps of Mars based upon telescopic observations) with no evidence of craters and there were other areas, termed chaotic, which resembled a terrain of jumbled ridges. Despite their better quality these photographs still offered no visible evidence that tectonic processes were at work.