The quest for extraterrestrial life has fascinated humanity for centuries.
Mars, our red neighbor, particularly arouses this curiosity.
But what if, in our eagerness to discover signs of life, we had accidentally destroyed the evidence we were looking for?
This troubling question emerges in light of new analyzes of the Viking missions of the 1970s.
These pioneering missions, the first to land gently on Mars, had the ambitious objective of detecting traces of life. Fifty years later, scientists are questioning the methods used and the conclusions drawn. A fascinating debate is opening, mixing hope and regret, on what we could have discovered if we had better understood the Martian environment.
The Viking missions: a giant leap for Martian exploration
In 1976, the NASA achieves an unprecedented feat: placing two probes on the surface of Mars. The missions Viking 1 et Viking 2 mark the beginning of a new era in space exploration. For the first time, humanity has eyes and ears on Martian soil.
These missions had several objectives, but the most ambitious was undoubtedly the search for life. Scientists of the time designed a series of sophisticated experiments to detect biosignaturesthese molecular traces which betray the presence of living organisms.
Pioneering but controversial experiences
Among the onboard instruments, the gas chromatograph coupled to a mass spectrometer (GCMS) was considered the technological flagship. This complex device's mission was to analyze the chemical composition of Martian soil in search of organic molecules, the building blocks of life.
The results obtained by the GCMS have been a source of intense debate in the scientific community. The instrument has detected chlorinated organic compounds. At the time, these molecules were attributed to terrestrial contamination, likely due to cleaning products used to sterilize the probes before their departure.
This conclusion had a considerable impact on the perception of Mars. For decades, the Red Planet was considered a barren desert, devoid of any complex organic chemistry.
A fresh look at old data
Nearly 50 years after the Viking missions, our understanding of Mars has evolved considerably. Recent missions, such as Curiosity et Perseverancerevealed a planet much more complex and potentially hospitable than we imagined.
In light of this new knowledge, scientists are re-examining data from the Viking missions. Their conclusion is surprising: the chlorinated organic compounds detected in 1976 are indeed of Martian origin. This revelation challenges the initial interpretation of the results and opens new perspectives on the possibility of life on Mars.
Dirk Schulze-Makuch's provocative hypothesis
L’astrobiologiste Dirk Schulze-Makuch from the Technical University of Berlin goes even further. He puts forward a bold theory: what if the Viking experiments, designed to detect life, had actually destroyed it?
Schulze-Makuch points to two experiences in particular:
- The experience of marked release
- The experience of pyrolytic release
These tests consisted of adding water to Martian soil samples to stimulate possible metabolic or photosynthetic processes. The idea seemed logical at the time: on Earth, water is synonymous with life.
But Schulze-Makuch points out a major flaw in this reasoning. Mars is an extremely arid planet. The life forms that could have developed there would probably be adapted to these conditions of extreme drought. By flooding the samples with water, scientists may have unintentionally destroyed these hypothetical organisms.
The neglected clues: a re-reading of the Viking results
The Schulze-Makuch theory is not mere speculation. It is based on a careful analysis of Viking data, in particular those from the pyrolytic release experiment.
Curiously, this experiment gave more convincing results when it was carried out on dry samples, without adding water. At the time, these results were considered anomalies and largely ignored. Today they take on a new meaning.
The hypothesis of a life adapted to aridity
Schulze-Makuch offers a fascinating scenario: what if Martian life had evolved to use hydrogen peroxide (H2O2) rather than water? This molecule, present on Mars, could play a role similar to that of water in terrestrial biochemistry.
This hypothesis would explain why the Viking experiments gave more promising results with dry samples. It is consistent with what we know about the Martian environment: a cold, dry world bathed in ultraviolet radiation.
Rethinking the search for life on Mars
The thoughts of Schulze-Makuch and other scientists invite us to reconsider our approach to the search for extraterrestrial life. It is not just a matter of looking for analogues to terrestrial life, but of imagining radically different forms of life, adapted to environments that we consider hostile.
New avenues for future missions
Schulze-Makuch offers several recommendations for future missions to search for life on Mars:
- Focus on the hydrated and hygroscopic compoundssuch as salts, which could harbor microorganisms
- Study areas where liquid water might exist transiently
- Develop instruments capable of detecting non-water-based life forms
- Design experiments that respect Martian ecology, without disturbing samples with excess water
The complex legacy of Viking missions
The Viking missions remain a remarkable technological and scientific feat. They paved the way for all the Martian missions that followed and considerably enriched our knowledge of the red planet.
However, interpreting their biological results illustrates the challenges of searching for extraterrestrial life. We are constantly torn between our desire for discovery and the risk of projecting our earthly expectations onto radically different worlds.
A call for a new life detection mission
Schulze-Makuch and many other scientists are calling for the launch of a new mission dedicated to detecting life on Mars. Nearly 50 years after Viking, our understanding of the Martian environment has been considerably refined. We are better equipped to design relevant experiments and interpret their results.
Such a mission could finally provide a definitive answer to the question that has haunted us for so long: are we alone in the universe?
Towards a new era of Martian exploration
The history of the Viking missions reminds us of the importance of scientific humility. Our certainties today may be called into question tomorrow. This lesson is particularly relevant as we prepare for a new phase of Martian exploration.
Current and future missions, such as the rover Perseverance from NASA or the mission ExoMars of ESA, benefit from the lessons learned from Viking. They take a more nuanced approach, aware of the complexity of the Martian environment and the forms of life that could exist there.
As we prepare to send humans to Mars in the coming decades, the question of Martian life takes on new urgency. If life forms exist on the Red Planet, we must discover and study them before human presence irremediably disrupts their environment.
The story of the Viking missions reminds us that the line between failure and success in science is often thin. What we consider today to be a missed opportunity could well be the first chapter of a revolutionary discovery. As we continue to scan the Martian soil for signs of life, let's keep in mind that the biggest discovery might be one we didn't anticipate.
