Labels: text | machine | wheel OCR: MARS: GENERAL INFORMATION MARS'S SATELLITES The polar caps Beside Mars's frozen subsoil, the planet has another reserve of water-its polar caps. The southern cap is subjected to high temperatures in summer and a long cold winter, so it expands and recedes with the seasons much more than the northern cap. In summer, its diameter does not exceed 350 kilometers, much smaller than its northern counterpart. It is even thought the southern cap disappeared entirely during the summer of 1969. In late winter, however, the southern cap spreads as far north as 50" latitude; by way of comparison, if the Earth's Antarctic underwent the same expansion in winter, the Falkland Islands and Auckland, New Zealand would be icebound. Mars's northern cap is about 1000 kilometers in diameter; it has a spiral shape and valleys several hundred meters in depth. During the winter, both polar caps are composed of frozen carbon dioxide, as much as 50 centimeters thick. The northern cap that subsists in summer is undoubtedly composed of water ice, but we cannot evaluate exactly how much water this represents. MARS BETAT
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