National Geographic : 1967 Dec
Evidence of seasons: As the polar cap recedes, between the Martian months of May (left) and July (right), a wave of darkening sweeps toward the equator, increasing the con trast between bright and dark areas. Seeking signs of intelligent life on Mars, Percival Lowell peers into a 24-inch telescope at Flagstaff, Arizona, in this old photograph. The observatory he founded there in 1894 has long been a leading center of Mars study. Mysterious areas of darkness show up in nonseasonal changes. From the dark center patch of Syrtis Major in March, 1954 (left), a curving band extends toward the lower left. The feature was barely discernible in April, 1907 (right). on flybys that will approach within 2,000 miles of Mars (page 825). One important ex periment will measure the polar temperature. What happens when the icecaps disap pear? The Mariner IV photographs-which cover less than 1 percent of the Martian sur face-show no clear and prominent sign of water-erosion features, such as river valleys. We expected this. Mars has no open bodies of liquid water today, and the thin polar caps simply vaporize rather than melt. Mars No Longer Shows Original Face However, even the largest craters on Mars have been significantly eroded and filled, probably by wind-blown dust, by expansion and contraction under huge daily tempera ture changes, and by new craters. Because of the erosion, we can no longer see the original surface of Mars. Perhaps in earlier eons oceans of a sort lapped Martian shores. In any case, large bodies of liquid water are not required for the origin of life; in many respects, shallow pools or underground lakes 832 provide better environments. We cannot ex clude the possibility that even today, below the arid Martian surface, lies a layer of per mafrost, with liquid water still deeper. Could life exist on Mars, in the apparently hostile environment we have described? People have thought so for several hundred years. One of the arguments, advanced about the beginning of the century, hinged on the fact that people looking through telescopes thought they detected green areas. This is now known to be partially an optical illusion. Also, green does not prove vegetation-nor does lack of it prove there is none. Plants, if any, on Mars may be a different hue. Another argument centers about the fa mous "canals." In the 1870's and 1880's Schia parelli discovered through his telescope a net work of delicate dark lines that occasionally stood out "like the lines on a fine steel etch ing," as a later observer described them. The lines seemed straight and proceeded for hun dreds of miles across bright areas, connecting distant dark regions with one another.