Did we find life on Mars and then wipe it out?

When the Viking 1 and 2 landers scanned the Martian sands for microbial life in the late 1970s and early 1980s, the results were…inconclusive. Some of the experiments tested positive for microorganisms that survived the harsh conditions – today, not just in the ancient past – but others did not. It was puzzling then and it still is today. Most scientists have since concluded that the positive results were wrong, because neither lander found abundant organic material in the soil. How could there be microbes without organic matter, the building blocks of life? But perhaps there is another possibility. And if there they were microbes, but soil tests on rovers accidentally destroyed them in the process?

That theory has been around for a while. Astrobiologist Dirk Schulze-Makuch has revisited this intriguing idea in a new post for Think big on June 27, 2023.

4 experiments to search for life on Mars

The Viking landers performed four basic experiments. The landers conducted them on soil samples that they excavated from the ground. Each lander collected samples in its onboard laboratory. While not as sophisticated as laboratories on Earth, they were considered capable enough to detect living microbes, if they existed.

The labeled release experiment looked for signs of metabolism, chemical reactions in organisms that sustain life processes. This includes converting the energy in food into energy available to run cellular processes; the conversion of food into the building blocks of proteins, lipids, nucleic acids and some carbohydrates; and the elimination of metabolic waste.

The pyrolytic release experiment looked for evidence of organic synthesis. This is the intentional construction of organic compounds.

Those first two experiments seemed to yield positive results. But the third experiment, the Gas Exchange Experiment, no. First, he added small amounts of water to the samples. This was an attempt to see if any dormant microbes would be revived by the moisture, since Mars is now so dry. He also added a “chicken soup” broth containing 19 amino acids, vitamins, other organic compounds, and few inorganic salts. Would any microbes eat this delicious meal?

Where are the organics?

The scientists were excited by the early positive results of the labeled release experiment and the pyrolytic release experiment. However, there was one big problem. The Vikings also searched for organic matter in soil with their fourth experiment, the Gas Chromatograph-Mass Spectrometer instrument. Without organic substances, there could be no life. All they found were tiny traces of chlorinated organic matter. These are organic compounds containing at least one covalently bonded chlorine atom. Since only that and no other organic material was found, mission scientists concluded that it was most likely terrestrial contaminants on the landers. They weren’t products of life and probably didn’t even originate on Mars.

The lack of other organic matter was a major blow to the possibility of life inhabiting the Martian sands. As Schulze-Makuch wrote:

Viking landers also included an instrument for detecting organic compounds. He saw traces of chlorinated organic matter, which at the time was interpreted as the result of contamination from the Earth. This led Viking project scientist Gerald Soffen to utter his famous words: “No bodies, no life.” In other words, there could be no Martian life without organic compounds. So Soffen concluded, like most other scientists of the time, that the Viking project was negative as regards the presence of life, or at best inconclusive.

Organics on Mars, after all

As it turned out decades later, there I am organic on Mars. And they’re native to the planet, not contaminants that spacecraft from Earth have brought there. The Curiosity and Perseverance rovers have now confirmed them beyond doubt. Previously, the Phoenix Mars Lander was the next mission after Viking to recover organics.

Just as Viking discovered, organic matter is chlorinated. It is also now known that Martian soil contains perchlorates, which can destroy organic molecules. This could also help explain the very low abundance of organic matter in which the Viking landers sampled. Most of the more recently found organic substances have been preserved in rocks.

Just add water

One of the key goals of the Viking experiments was to add small amounts of water to soil samples. The idea was that the microbes in the soil might be dormant due to the extremely dry and freezing conditions. Adding water could rejuvenate them to get active again. Schulze-Makuch speculated, like others, that this may have been too good a thing. Instead of just providing moisture for microbes to absorb or drink, it he drowned them. All Martian microbes would by now be well adapted to the hostile and extremely dry conditions. Schulze-Makuch wrote:

Now let’s ask ourselves what would happen if we poured water on these dry-adapted microbes. Could it overwhelm them? In technical terms, we would say we are overhydrating them, but in simple terms, it would be more like drowning them. It would be like an alien spacecraft finding you wandering half dead in the desert, and your would-be saviors deciding, “Humans need water.” Let’s put the human in the middle of the ocean to save him!’ That wouldn’t work either.

Hygroscopic life on Mars?

Perhaps the Martian microbes could be like those on Earth in Chile’s Atacama Desert who live only on salts, without liquid water, such as rain. They use a process called hygroscopicity, where certain salts in the soil absorb water directly from the relative humidity in the air.

As noted by Schulze-Makuch, the soil at the Viking landing sites was low in salts. However, it did contain perchlorates and hydrogen peroxide. Both are highly hygroscopic by nature. Additionally, Viking orbiters have seen fog in the valleys from orbit. This means that the relative humidity in the morning and evening should have been high enough to allow access of the moisture in the mist to the microorganisms.

Hydrogen peroxide: another possibility for life on Mars

The results of the Viking experiment were really frustrating for scientists. Some of the results seemed to indicate life while others did not. Then there was the lack of abundant organics. Most scientists now think the findings could be explained by non-biological chemical reactions. But there is also another possibility.

Schulze-Makuch and his colleague Joop Houtkooper of the University of Giessen in Germany had previously proposed a new biological explanation for the Viking findings. What if Martian microbes had hydrogen peroxide in their cells? Hydrogen peroxide can be deadly in large quantities, but there are actually microbes on Earth that use and produce it. These include Neisseria dry, Haemophilus signis, Streptococcus AND Lactobacillus.

On Mars, in theory, microbes with hydrogen peroxide in their cells could suck up tiny amounts of water directly from the atmosphere. It would also help prevent water from re-freezing inside the microbes and damaging their cells.

Schulze-Makuch argues that such hydrogen peroxide microorganisms could explain Viking’s puzzling results. The gas chromatograph-mass spectrometer, by design, heated soil samples before analyzing them. The scientists wanted to see if any biological compounds would be released in the process. But in hindsight, this may have actually destroyed any microbes present. If the microbes contained hydrogen peroxide, the intense heat would likely have killed them. So in this scenario, the heat would have killed the microbes instead of the water. Furthermore, the hydrogen peroxide would have reacted with the organic compounds to produce carbon dioxide. And maybe it was a coincidence, but that’s exactly what the gas chromatograph’s mass spectrometer detected.

Gilbert Levi

On a related note, Gilbert Levin, who was the principal investigator for the tagged release experiment for both Viking landers, said we’ve found life on Mars. He outlined his position in an opinion piece in American scientist on October 10, 2019. He passed away in 2021 at the age of 97.

We may never know with absolute certainty whether Viking landers found life — or not — but the puzzling results may help scientists better plan future life-detection missions. There is still a lot to learn, especially in hindsight, as scientists like Schulze-Makuch remind us.

Bottom line: Did Viking landers from a few decades ago find microbial life on Mars after all? Astrobiologist Dirk Schulze-Makuch presents the case Think big.

Via Big Think

Related: Did Viking landers find life on Mars in 1976?