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Mariner's most remarkable finding came in the south polar region. Astronomers had long been convinced that the southern polar cap consists largely of frozen carbon dioxide, and that it vanishes completely in the Martian summer only to reappear during the following winter's freeze. Closeup pictures show that in fact Mars retains a small cap near the south pole that is 200 miles in diameter even at the height of summer. Judging from the configuration of the cap—for example, its sharp edges —some scientists deduce that it may be composed of frozen water.
Wobbling Axis. If water is indeed locked inside the Martian polar caps, its presence could have profound biological implications. Since the axis of the planet slowly wobbles, or precesses, as Mars travels around the sun, the polar regions are alternately exposed to increased doses of sunlight. As a result, every 25,000 years, ice in the polar regions may well melt, releasing moisture into the Martian atmosphere and causing rains that could turn the planet's arid surface into a morass of fast-flowing rivers and streams, lakes and perhaps even short-lived seas. A more favored theory is that flash-flooding could occur when ice in the Martian soil is melted by volcanic heat. In either case, the flowing water could account for some of the canyons and perhaps even for what looks like a wave-eroded edge around Nix Olympica. Even more intriguing, the water might in the past have remained on the surface long enough in liquid form for rudimentary life to develop.
Another reading, made by Mariner's ultraviolet spectrometer, also raised hopes that some life, however simple, could exist on Mars. The instrument confirmed the presence of atmospheric ozone, the three-atom form of oxygen that is also found in the upper layers of the earth's atmosphere and acts as a crucial life-saving shield against the sun's searing ultraviolet radiation. Presumably, the ozone could play the same protective role on Mars. Indeed, the U.S. Geological Survey's Harold Masursky, a member of the Mariner team, was so excited by these discoveries that he talked openly last week of looking for fossils when men or their robot envoys finally begin to prowl the surface of the red planet.