In 1975, NASA sent two probes on an 11-month journey to Mars to conduct studies of the red planet's geographical features and composition of Martian surface and atmosphere. The probes, Viking 1 and Viking 2, also conducted experiments that looked for signs of microbial life in the Martian soil.
In the 40 years since the experiments were performed, the general consensus among scientists is that the landers did not find conclusive evidence of life on Mars albeit the life-detection experiments had contradictory results.
One experiment showed the Martian soil was positive for metabolism while another experiment did not find trace of organic material in the soil.
In the Labeled Release experiment, scientists mixed soil picked up by the Viking probes with nutrient-rich water. The scientists hypothesized that if the soil contains signs of life, the microbes of the soil would metabolize the nutrients in the water. The microbes were metabolized releasing radioactive molecules, which suggest that the soil of Mars contained life.
Other Viking probe experiments, however, did not find signs of life. Since the landers did not find any trace of organic material, scientists wondered about the purpose of metabolism if there were no organic materials in the Martian soil. Scientists then concluded that metabolization could be attributed to nonbiological processes.
Now, two researchers have urged the scientific community to take another look at the 40-year-old studies of the soil on planet Mars.
Researchers Gilbert Levin from Arizona State University and Patricia Ann Straat from the U.S. National Institutes of Health contend that the NASA robots may have found signs of life on the red planet decades ago.
Levin and Straat said that the LR experiments must be re-examined in light of recent findings on the red planet, saying that biological processes could be responsible for the results of the LR experiments. NASA's recent findings of water, methane and other organic molecules in Mars, for instance, support the idea that biological processes are behind the results of the LR experiment.
"The absence of a nonbiological agent that satisfies all Viking findings, and in view of environmental evidence that Mars may well be able to support extant life, it seems prudent that the scientific community maintain biology as a viable explanation of the LR experimental results," the scientists wrote in the journal Astrobiology on Oct. 1.
"Biology should be held in the forefront of possible explanations for the LR results," they added, saying that in the interest of astronauts' health and safety, microbial life should be considered especially since the scientific community is set on exploring Mars.
Findings of the Viking landers are crucial in that other Mars experiments face potential contamination by previous landers. The Viking probes provided the only pristine Martian life-detection experiments.
