In May 1977, the largest astrobiological experiment in history, still unsurpassed today, was concluded: looking for signs, however small, of biological activity on the arid surface of the red planet. It was carried out by the two twin Viking spacecraft, which landed at locations 5,000 km apart on the Martian surface. Both ships carried a group 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 , and completed by another aimed at analyzing the atmosphere in search of gases of biological origin. in significant quantities.
astrobiological experiments
The chemical was the GCMS (Gas Chromatograph-Mass Spectrometer) -a hundred times more precise than the biological ones- and it had to find organic compounds in the samples taken by both probes: it did not detect anything. For their part, the three biological experiments gave ambiguous results : it seemed that there could be “something” on its surface. In the first (PR, pyrolitic release), carbon dioxide and carbon monoxide were injected into samples of Martian soil to see if microorganisms could convert these gases into organic matter through some type of photosynthesis. This was detected, but in very small quantities and did not follow an exponential course, classic for living organisms. In the second (LR, labeled release) a nutrient made up of 7 molecules and marked with radioactive carbon was used to discover if something similar to respiration or fermentation took place. Carbon dioxide was produced, but it was not exponential either and ceased after a few hours. And in the third (GEX, gas exchange) life was sought from two different assumptions: the first, to check if the metabolism was stimulated in some way by adding a few drops of water; the second, if something similar happened but using a nutrient with 19 organic compounds that scientists had baptized with the name of ‘chicken soup’. In both cases the gases were analyzed for oxygen, carbon dioxide, methane and nitrogen. Oxygen, nitrogen, very little carbon dioxide and none of the rest were formed.
Let us realize that the three biological experiments represented a different approach to the problem of life: the LR was developed from a research project aimed at detecting bacterial contaminants in the water pipes of cities; the GEX looked for the by-products of some type of metabolic action and finally the PR started from the assumption that some microorganism could have developed the capacity to assimilate CO or CO2 to convert it into organic matter. The latter had the fewest previous assumptions about the kind of life that could be found on Mars, except that it must be carbon-based. All of them represented the practical application of what was known about life at that 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.
What if life was found?
However, over time, discordant voices have been raised. In 2016, the person responsible for the LR experiment, Gilbert Levin, published in combination with the biologist Patricia Ann Straat an article in the journal Astrobiology where he defended that the experimental tests of the Vikings indicate that on the surface of the red planet there are microorganisms that have been able to survive in the harsh conditions of the Martian environment. For both researchers, who are part of a small group of scientists who do not agree with the conclusions reached by NASA in 1978, Mars is a planet with life.
And it is that Mars had not made things easy and the scientists of the discovered that the solution was not black or white but that there was a whole range of grays. Preliminary reports published in October 1976 indicated that two of the biological experiments gave “presumably positive results” and the third showed some kind of oxidative process. Were we facing the first evidence that there was life on Mars? It certainly would have been so, but there was an insurmountable problem: the chemical analysis of the soil did not find organic molecules in amounts greater than three parts per billion, a result that would end up being considered “the most surprising discovery of the entire mission”.
Day after day the researchers received data that astonished them. Only one thing was clear: “The three experiments indicate that the Martian surface is chemically and biochemically active.” In essence, what they were stating without saying it clearly was that it seemed as if there was something alive up there , but the more data they obtained, the less conclusive the results were: if there were Martian microorganisms, they were playing cat and mouse with them. Ten weeks later, in the journals Science and Nature , the scientists responsible for each of the experiments revealed the results of their analysis in more detail: with them in hand “no conclusion could be reached about the existence of life in Mars”.
After 8.5 months and 26 experiments, the first firm conclusions were reached: PR had given positive results, LR’s were equivocal, 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) did not reach an absolute consensus: while Horowitz, the creator of the only experiment that gave positive results, stated that “ could be interpreted as non-biological”, Levin did not fail to defend that the biological interpretation was the most plausible. In the end , the proverbial scientific conservatism prevailed against the opinion of Levin, who until his death in 2021 continued to affirm that the LR results proved the existence of life on Mars.
Perhaps the most sensible thing would have been to say that a definitive conclusion could not be reached, but how to explain to the public that after spending almost 1,000 million dollars to search for life on Mars they were still not clear? And that taking into account 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 . Seen what was seen, what they lacked to define with precision was what they understood as “positive result”.
So in the end Harold Klein, the head of the Viking biological experiments, announced to the world that Mars was a lifeless planet. And he asked Levin, who disagreed, to keep quiet. In contrast, mission director Jim Martin snapped at him: “Damn it, Gil! Why don’t you get up and say you have detected life?”
References:
Levin G V, Straat P A. (2016) The Case for Extant Life on Mars and Its Possible Detection by the Viking Labeled Release Experiment, Astrobiology, 16(10):798-810, doi: 10.1089/ast.2015.1464.
Chambers, P (1999). Life on Mars; The Complete Story. Blandford
