Did NASA's Viking landers kill Martian life in 1976?

In 1976, NASA launched the Viking 1 and Viking 2 landers, which performed four distinct experiments to explore the Martian landscape for signs of life.
Rizwan Choudhury

Astrobiologist Dirk Schulze-Makuch from Technical University Berlin has put forward a controversial argument that NASA's Viking landers could have unintentionally destroyed microbial life on Mars almost 50 years ago. His hypothesis, published in a June 27 article for Big Think, has lately caused a divide amongst experts and reignited debates surrounding the scientific process of searching for life beyond Earth.

The Viking missions

In 1976, NASA launched the Viking 1 and Viking 2 landers, which performed four distinct experiments to explore the Martian landscape for signs of life. These experiments were the gas chromatograph mass spectrometer (GCMS), the labeled release experiment, the pyrolytic release experiment, and the gas exchange experiment.

Did NASA's Viking landers kill Martian life in 1976?
Viking lander.

Each sought to understand the metabolic, photosynthetic, and respiratory mechanisms that could exist in Martian soil. Yet, the outcomes of these tests have confounded scientists for decades. Some, like the labeled release and pyrolytic release experiments, hinted at metabolic activities, while others, notably the gas exchange experiment, yielded negative results.

The water conundrum

Schulze-Makuch posits that the Viking landers, designed with an Earth-centric perspective, could have oversaturated the Martian samples with water. On Earth, water is often considered a universal solvent for life; however, on Mars, where conditions are markedly different, too much water might have been detrimental.

Schulze-Makuch cites the Atacama Desert in Chile—home to extreme microbes that thrive in arid conditions—as a possible Earthly analog. These organisms flourish in hygroscopic rocks, which absorb minimal atmospheric moisture. Similar rocks are believed to exist on Mars, which led Schulze-Makuch to question whether the Viking landers might have annihilated any potential Martian microbes by drowning them in water.

According to him, a lot has changed in the half-century since the Viking missions. More landers and rovers have explored the Martian surface in greater detail, revealing indigenous organic compounds in a chlorinated form. This discovery raises questions about whether these compounds derive from biological processes or abiotic chemical reactions.

Contradictory views from the scientific community

As per Live Science, Alberto Fairén, an astrobiologist at Cornell University and co-author of a 2018 study, supports Schulze-Makuch's theory, stating that excessive water could have spelled the demise of Martian microbes, thereby explaining Viking's inconsistent results.

On the other side of the debate, an astrobiologist at NASA's Ames Research Center, Chris McKay, argues that subsequent missions like NASA's Phoenix lander have provided alternate explanations. McKay cites the discovery of perchlorates—a class of chemicals also found on Earth—as sufficient evidence to dismiss any speculation about Martian life.

Earlier theories and existing skepticism

This is not the first time experts have debated the possibility of Viking's experiments affecting Martian life. In 2018, researchers posited that heating the soil samples during the experiments could have initiated a chemical reaction, thereby killing any microbes. However, most scientists remain skeptical of these theories, standing by the consensus that Viking did not discover life on Mars.

While Schulze-Makuch's claim has been deemed provocative by many, it nonetheless brings to light the significant challenges and implications of searching for life on other planets. Whether the Viking missions did indeed come into contact with—and subsequently destroy—Martian life forms remains a contentious issue, necessitating further investigation and potentially more sophisticated methodologies in future Mars missions.

As experts debate the interpretation of decades-old data, the question remains: Could we have been closer to discovering extraterrestrial life than we ever realized, and have we learned enough to avoid repeating the same mistakes? Only time—and perhaps future missions to the Red Planet—will tell.

Schulze-Makuch has suggested that we require a new Mars mission that focuses on detecting life to test various hypotheses. This mission should investigate possible habitats on Mars, particularly in the Southern Highlands, where life could exist in salt rocks near the surface. The biggest benefit of this mission is that we may be able to access these rocks without drilling, which would significantly reduce engineering complexity and cost. I am eagerly anticipating the start of this mission.

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