Word: soils
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Dates: during 1970-1979
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...those who hold similar views base their judgment not on new evidence but on an analysis of the biology experiments conducted by the Viking landers. The gas exchange test, based on the fact that terrestrial organisms give off gases as waste products, involved dropping a pinch of Martian soil into a warm, moist test chamber. The aim was to determine whether the sample would give off carbon dioxide, as animals would, or oxygen, as plants do. Scientists were surprised when the sample began releasing oxygen far more rapidly than plants would be expected to do. But they noted that...
More encouraging results came from a second test, in which a sample of Martian soil that had been moistened with a nutrient broth showed a rapid release of carbon dioxide. The result might mean that some kind of microbe was metabolizing the food provided by Viking. But cautious scientists noted that certain peroxides in the soil might also have caused the reaction to occur...
Tests did not find organic, or carbon-based, molecules in the Martian soil. Terrestrial soil is laden with such molecules, which are the remains of living organisms. But scientists agree that this negative finding does not necessarily weaken the case for Martian biology. There may simply have been too few of these molecules in the soil to be detected by the gas chromatograph-mass spectrometer designed to look for them. The picture is complicated by the biology tests run at the second Mars landing site. In the gas exchange test, the soil released substantially less oxygen than the sample...
These tests will allow Martian soil samples to incubate longer in order to give any microbes present a better chance to grow. The experiments will be run at temperatures closer to the frigid levels that prevail on Mars. Also, in a search for life that may have burrowed deeper into the Martian soil to escape ultraviolet radiation bombarding the surface, one of the landers will try to dig 30.5 centimeters (1 foot) deep for a soil sample. Explains Klein: "We want to play out our whole set of cards before we make our best judgment on the question of life...
Upholding Einstein. In other new experiments not concerned with biology, one of the landers will pick up and analyze a pebble (only soil has been examined to date) to get a better idea of the planet's geology. Scientists will also continue monitoring Viking 2's seismograph (the one aboard Viking 1 is disabled), which earlier picked up what may have been the only Marsquake to have occurred so far during the mission. They also plan to maneuver one of the Viking orbiters to within 50 kilometers (31 miles) of Phobos in order to get high-resolution pictures...