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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 at the first site, but showed a higher level of possible microbial activity. Jastrow and several other scientists feel that this weakens the argument that peroxides were responsible for the results of the first gas exchange experiment and leaves biology as the logical alternative.
To Gilbert Levin, principal Viking investigator in the microbe experiment, the evidence from the lander experiments strongly suggests biology: "Certainly whatever they have shown cannot easily be explained otherwise." Chief Project Scientist Gerald Soffen is less certain. "It is possible," he notes, "to formulate chemical equations to describe all the results we've had." Whether these are the right equations, though, remains to be determined. Adds Soffen: "It's not a question of finding a chemical explanation; we must find the chemical explanation, and we need a natural as opposed to a blackboard explanation."
There is good reason for Soffen's —and NASA's—caution; the implications of discovering any form of life on Mars are so staggering that no scientist can afford to be wrong. But the ambiguities surrounding the Viking biology tests may soon be resolved. Now that Mars has re-emerged from behind the sun—which blocked transmissions between Viking and the earth for more than a month late last year—scientists have "reawakened" the sleeping laboratories and instructed them to run a new round of experiments.
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 on Mars."
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 of the tiny, potato-shaped Martian moon.