Forty years ago, NASA mistakenly burned the best evidence of life on Mars

In early June, NASA announced with great fanfare that Curiosity had discovered complex organic molecules, the bricks of life, on the surface of Mars. The news, long awaited, resonated in the main media of the world and was received as the best evidence found of the existence, present or past, of living beings on the red planet.

Now, however, a study just published in the Journal of Geophysical Research: Planets argues that another historic NASA mission, the Viking probes, could have made the same discovery more than 40 years ago. Only that their results were burned by NASA accidentally.

In 1976, in effect, the twin Viking lander modules carried out the first field experiments to search for organic matter on the neighboring planet. Even then, scientists were well aware that planets constantly receive a shower of carbon-rich micrometeorites and, often, more complex organic molecules, so they were convinced that Mars should be full of such substances. But the Vikings found nothing, leaving the scientists stupefied and with a span of noses.

"It was totally unexpected and inconsistent with what we knew," said Chris McKay, of NASA's Ames research center, and one of the authors of the study.

From that moment, numerous researchers have tried to find a logical explanation to the "enigma of lost molecules", but none of them ended up fitting. In 2008, however, NASA's Phoenix lander made a crucial discovery: found, near the North Pole of Mars, a strange salt known as perchlorate, a substance used to make fuel for rockets and fireworks. , because it becomes explosive when subjected to high temperatures.

Of course, on the icy surface of Mars that does not constitute a problem. But it turns out that the Viking, in their search for organic molecules, took samples of Martian soil to analyze them. Samples that contained perchlorate and that, when carrying out the experiments (in which a torch is used), incinerated without any organic element that could be in them. Which led to the scientists not finding anything in the results.

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Conclusive tests

After this discovery, McKay and some of his colleagues regained their conviction that, finally, there could be organic molecules on Mars. "Suddenly," says the scientist, "you acquire a new perception and realize that everything you thought was wrong." Despite this, there remained a marked division of opinion between those who thought that the Martian surface contained organic matter and those who held that it was completely sterile.

This being the case, the discovery of Curiosity arrived in June of this year. The rover finally provided conclusive evidence of organic matter on the red planet, which gave new wings to those who claimed the Viking experiments.

One of the keys to doing this was that, along with organic molecules, Curiosity also found chlorobenzene, a molecule that is produced when carbon atoms are burned with perchlorate. It was evidence, albeit indirect, of what happened forty years ago. And one more confirmation that the Viking probes had already detected organic molecules on Mars.

With all that data in hand, McKay and his colleagues, including Melissa Guzman, of the LATMOS research center in France, thoroughly reviewed the results obtained by the Vikings and discovered that these ancient probes had also detected chlorobenzene, a consequence more than probable from the involuntary burning of the organic material contained in the samples.

So, after all, the Vikings did not end up with their hands as empty as they thought, and this old case can be considered, more than four decades later, definitely closed. In addition, the more than likely finding of organic matter by the Viking, plus the recently announced Curiosity, show that this organic material is found not only in one, but in different areas of the planet. Which reinforces even more the possibilities of finding, at last, life.

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