Mars and the Viking Mission: A Discovery of Life?
Between August 14 and 15, 1965, the U.S. probe Mariner 4 completed a seven-and-a-half-month journey to Mars, passing at a minimum distance of 9,846 kilometers from the planet. As it transmitted the first images of the Martian surface to Earth, excitement among scientists quickly turned to disappointment. Many expected to find a planet that was “alive,” possibly even with traces of vegetation. Instead, the images revealed a barren, cratered landscape resembling the Moon’s surface. The dream of finding a Martian civilization or advanced life seemed dashed.
Despite the lack of evidence for advanced life, scientists clung to the hope that microbial life could still exist on Mars. That question was left to be answered by NASA’s Viking missions—two highly ambitious projects launched in 1975. The twin probes, Viking 1 and Viking 2, each consisted of an orbiter and a lander. Viking 1 entered orbit around Mars on June 19, 1976, and Viking 2 followed on August 7 of the same year. Both landers successfully touched down on the Martian surface, taking the first close-up images of the planet and conducting chemical experiments to detect signs of life.
Search for Life: The Viking Experiments
The Viking landers were equipped with mechanical arms to collect Martian soil samples, which were then analyzed in small on-board laboratories. NASA designed three experiments to detect life:
1. Gas Exchange: Nutrient broth was added to soil samples, with the expectation that microbial metabolism would produce gases like oxygen, nitrogen, or carbon dioxide. Interestingly, oxygen emissions were detected, but the results remained inconclusive.
2. Labeled Release (LR): In this experiment, radioactive carbon was added to the nutrient broth. If microbes were present, they would metabolize the carbon, releasing detectable radioactive carbon dioxide. Both Viking landers returned positive results, but the scientific community was divided on whether this indicated life or an unknown chemical process.
3. Carbon Dioxide Assimilation: Soil samples were exposed to radioactive carbon dioxide and strong light to see if Martian organisms, like photosynthesizing plants on Earth, would absorb carbon. The results were partially positive, though still inconclusive.
Despite promising results, NASA ultimately concluded that Mars was a biologically dead planet due to the lack of detectable organic material. However, Gilbert V. Levin, who led the LR experiment, remained convinced that the Viking experiments had found evidence of Martian microbial life.
A Controversial Conclusion
Levin, along with his colleague Patricia Ann Straat, spent years analyzing the Viking data and replicating the experiments in Earth’s extreme environments, such as Antarctica. In 1997, Levin publicly declared that the Viking missions had, in fact, detected microbial life on Mars. He argued that further discoveries, such as the presence of perchlorates (toxic salts) found by the Phoenix lander in 2008, supported his hypothesis. Perchlorates could explain why Viking’s spectrometer failed to detect organic molecules—by heating the soil samples, the perchlorates could have burned the organic material.
In recent years, the Viking mission’s results have been revisited by scientists like Joseph D. Miller, who found that carbon dioxide emissions followed a circadian rhythm similar to biological processes on Earth. These findings have only added to the ongoing debate about whether the Viking landers did indeed discover life on Mars.
NASA’s Reluctance to Revisit the Search for Life
One of the most puzzling aspects of the debate is NASA’s reluctance to include life-detection instruments in subsequent Mars missions. Levin suggested that the discovery of microbial life could have triggered international “planetary protection” treaties, halting future missions and potentially jeopardizing NASA’s funding.
While NASA’s Perseverance rover, which recently landed on Mars, is not equipped for biological research, future missions like the European Space Agency’s ExoMars are designed specifically to search for life and explore the Martian subsurface. This probe, however, has faced delays and is not expected to arrive on Mars before 2023.
As we await new missions, Levin’s conviction remains strong. In his own words, “I believe we found life on Mars, but NASA was not ready for the world to know.” Whether this is true or not, the search for life beyond Earth remains one of humanity’s greatest scientific quests.
