In 1977, the Viking Mars Exploration Program concluded that biological analyzes of the soil and atmosphere showed no signs of life on Mars. But what if they were wrong? Here are the discoveries scientists made in the largest astrobiological experiment in history.
Is there life on Mars?
In May 1977, the largest astrobiological experiment in history was completed, which even to this day has not been successful: the search for the smallest traces of biological activity on the arid surface of the red planet. This was carried out by two twin Viking spacecraft, which landed 5,000 km apart on the Martian surface.
Both spacecraft carried a set of specific experiments, chosen from among 150 proposals: on the one hand, an analysis of the soil through a chemical experiment and three biological experiments, complemented by another designed to analyze the atmosphere to detect gases biological origin in significant quantities.
Astrobiological experiments
According to muyinteresante.es , the chemical experiment was carried out with GCMS (Gas Chromatograph-Mass Spectrometer) – a hundred times more precise than biological ones – and was supposed to find organic compounds in the samples taken by both probes. But it detected nothing. The three biological experiments gave ambiguous results: it seemed that there might be “something” on its surface.
In the first (PR, pyrolytic release), carbon dioxide and carbon monoxide were injected into Martian soil samples to see if microorganisms could convert these gases into organic substances through photosynthesis. Photosynthesis was detected, but in very small amounts and did not follow the classical exponential course for living organisms.
In the second (LR, labeled release), a nutrient composed of 7 molecules and labeled with radioactive carbon was used to find out if something like respiration or fermentation was taking place. Carbon dioxide was produced, but this too was not exponential and ceased within a few hours.
And in the third (GEX, gas exchange), life was looked for on the basis of two different hypotheses: first, to see if the metabolism was somehow stimulated by the addition of a few drops of water; second, to see if something similar was happening, but using a nutrient with 19 organic compounds that the researchers called “chicken soup.”
In both cases, the gases were analyzed for oxygen, carbon dioxide, methane and nitrogen. Oxygen, nitrogen and very little carbon dioxide were formed.
The three biological experiments represented a different approach to the problem of life
Thus, LR was developed from a research project to detect bacterial contaminants in city water pipes, GEX looked for the by-products of a certain type of metabolic action, and finally PR was based on the assumption that a microorganism would be could develop the ability to assimilate CO or CO2 and transform them into organic matter.
The latter made the fewest prior assumptions about the type of life that might be found on Mars, except that it must be carbon-based. All represented the practical application of what was known about life at the time. With the results of the experiments in hand, NASA’s official conclusion was that Mars was not teeming with the life we had always imagined.
And if life was found on Mars?
However, over time, many voices have emerged. In 2016, former head of the LR experiment, Gilbert Levin, together with biologist Patricia Ann Straat, published an article in the journal Astrobiology in which they argued that experimental evidence from Viking suggests that there are microorganisms on the surface of the Red Planet that have managed to survive in the conditions harsh Martian environment.
For both researchers, who are part of a small group of scientists who disagree with the conclusions reached by NASA in 1978, Mars is a planet with life.
Planet Mars
Mars didn’t make things easy, and Martian scientists discovered that the solution wasn’t black and white, but a whole wide range of grays. Preliminary reports published in October 1976 stated that two of the biological experiments gave “probably positive results” and the third showed some kind of oxidative process.
Were we facing the first evidence of life on Mars? It certainly would have been, but there was one problem: chemical analysis of the soil found no organic molecules in amounts greater than three parts per billion, a result that would be considered “the most surprising discovery of the entire mission.”
Day after day, researchers received amazing data. Only one thing was clear to them: “All three experiments indicate that the Martian surface is chemically and biochemically active.” Essentially what they were saying, without being very clear, was that it looked like there was something alive up there, but the more data they got, the less conclusive the results were.
Ten weeks later, in the journals Science and Nature, the scientists responsible for each of the experiments revealed the results of their analyzes in more detail: with them in hand, “no conclusion can be drawn about the existence of life on Mars.”
Life on Mars: the first firm conclusions
After eight and a half months and 26 experiments, the first firm conclusions were reached: PR gave positive results, LR results were ambiguous, and GEX showed no evidence of biological activity. The confusion was such that the three responsible researchers, Gilbert Levin (LR), Norman Horowitz (PR) and Vance Oyama (GEX) could not reach an absolute consensus.
While Horowitz, the creator of the only experiment that yielded positive results, stated that “these could be interpreted as non-biological”, Levin did not fail to argue that the biological interpretation is the most plausible. In the end, scientific conservatism prevailed over Levin’s opinion, and until his death in 2021, he continued to argue that the LR results proved the existence of life on Mars.
Perhaps the most rational would have been to say that no definitive conclusion could be reached, but was it difficult to explain to the public that after spending almost a billion dollars to search for life on Mars, it was still not clear? And this despite the fact that, before the launch, NASA scientists had reached an agreement: a positive result in any of the three experiments would mean that life had been found.
With this in mind, what they failed to define precisely was what they meant by “positive result”. Thus, finally, Harold Klein, head of biological experiments on Viking, announced to the world that Mars is a lifeless planet. And he asked Levin, who disagreed, to be silent.
