Speculation that life exists on Mars has decreased this week even though the Viking spacecraft that landed on the planet more than two weeks ago relayed data back to Earth indicating Martian soil samples were emitting large quantities of oxygen.
Elso S. Barghoorn, Fisher Professor of Natural History and a member of the exobiology panel of the American Academy of Science's Space Sciences Board that was established in 1958 to advise NASA, said yesterday, it is "certainly an inorganic reaction" which is causing the release of oxygen.
The oxygen could not have been produced by photosynthesis which can only occur in the presence of light because light was absent from the experiment which detected the oxygen, Barghoorn said. He added that water was present when the oxygen was produced.
Richard M. Goody, Mallinckrodt Professor of Planetary Physics, who is chairman of the Space Sciences Board, said yesterday scientists have realized the presence of hydrogen peroxide in small amounts on Mars could explain the high oxygen content of the soil.
"This does not rule out life," Goody added because the explanation cannot be confirmed without first-hand observation on the surface of Mars. But, he said, scientists are more inclined to believe a chemical explanation rather than a biological one because life is so improbable.
Barghoorn said the production of oxygen "is a mystery." At two meetings of the exo-biology panel last year and this past March at which possible problems with the biology experiments on board the spacecraft were discussed there was never any suggestion that oxygen would be released.
The presence of oxygen was detected by the pyrolytic release experiment which was designed to test for the occurence of photosynthesis by exposing a soil sample to radiation from a xenon lamp. The oxygen was produced before the lamp was switched on.
Two additional experiments are included in the biology package on board Viking. The gas exchange looks for evidence of respiration by adding some moisture and nutrients to the soil to determine if the soil is "breathing."
The third experiment, the so-called "chicken-soup experiment," involves innoculating the soil with a complex nutrient broth that provides substrates for many biological activities. The soil is then incubated to encourage the growth of life.
Goody said the latter two experiments are not showing any reactions that require a biological explanation. Despite conditions which "would be amenable to life," Barghoorn said, no evidence of life has yet been found.
Barghoorn added that it is possible that life once existed on Mars but is now extinct. The only way to detect that possibility would be to bring rocks from Mars back to Earth. He said we now have the technology for such a mission but it will probably not be launched for at least another decade.
Send Chicken Soup, Quick
Barghoorn said Mars seems to be the only body other than Earth in the solar system which could support life. But some scientists have recently suggested that life might exist on Titan, the largest moon of Saturn, because it has a dense atmosphere.
The mission so far has lived up to the best expectations, Barghoorn said. Problems have occurred with the seismometer which was intended to measure tremors and volcanic activity on Mars.