While some scientists suggest that the water might somehow have been blown off the planet, most believe it is still there, locked in ice under the surface or trapped in clay minerals. One of the tasks of Observer and the missions that follow is to find the water and to help reconstruct the planet's history. Future missions that reach the surface could examine areas where water is abundant to search for fossils of past life forms. The Mars 94 mission, to be launched next year in November, will continue the search for water. It includes two probes that will penetrate the planet to a depth of 18 feet or more to see what's underneath.
Scientists hope the penetrators detect ice.
Although humans may dream of someday visiting and even inhabiting Mars, it is by Earth's standards a forbidding place. Summer high-noon temperatures at the equator might reach a pleasant 68 degrees Fahrenheit, but because the planet's carbon dioxide atmosphere is so thin, nighttime temperatures can plunge a couple hundred degrees or more. At the poles in winter the mercury hovers at -220 degrees Fahrenheit. Researchers hope that with Mars Observer and later missions they will be able to understand Mars'ssevere climate and perhaps learn to predict its weather. The most dramatic feature of the Martian climate is that the atmospheric pressure changes by an astonishing 30 percent twice a year with the seasons.