Pathfinder Strengthens Case for Warmer, Wetter Mars
(From the March/April 1998 issue of StarDate magazine)
Mars Pathfinder's studies of Martian rocks and soil and photographs of its surroundings seem to confirm what scientists have long suspected: Mars was once much more like Earth, with a warmer, wetter atmosphere and torrential rivers flowing across its surface.
Images from Mariner 9 and the Viking 1 and 2 orbiters of the 1970s revealed structures that look like riverbeds and lakebeds. But before Mars Pathfinder, no craft had ever analyzed the composition of Martian rocks or viewed the planet from inside a suspected flood channel.
Pathfinder landed in Ares Vallis, a wide channel that scientists suspect was carved by a great flood several billion years ago. Images revealed possible "conglomerate" rocks -- smooth, rounded pebbles held together by clay or sand. Running water would be an efficient way to polish the pebbles and deposit them in beds of clay or sand. Some of the larger rocks at Pathfinder's landing site appear to be volcanic, according to project scientists.
"The high silica or quartz content of some rocks suggests that they were formed as the crust of Mars was being recycled, or cooled and heated up, by the underlying mantle," scientists reported in the December 5 issue of Science.
Atmospheric measurements indicate that the planet's rotation rate changes slightly as the seasons change because the ice caps at the north and south poles grow and shrink at different rates.
When it is summer in one hemisphere, much of that hemisphere's polar ice cap vaporizes, and the liberated carbon dioxide flows outward, thickening the atmosphere.
At the same time, atmospheric carbon dioxide in the opposite hemisphere freezes onto the ice cap. If one ice cap shrank and the other grew at the same rate, the planet's rotation rate (which governs the length of a day) would not change. But Pathfinder found that the rotation rate changed with changes in atmospheric pressure -- an indication that the process is unbalanced. -- — Damond Benningfield
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