Understanding Microbial Respiration

In 1864, Louis Pasteur conducted an experiment that allowed microbes to develop in hay broth, leading to the formation of bubbles that he attributed to microbial respiration. This foundational work laid the groundwork for similar methodologies employed in laboratories today, including the Viking's LR experiment, which was adapted for Martian conditions.

The LR experiment included enhancements to test for unknown lifeforms, utilizing a thermostat to distinguish between biological and chemical reactions. The nutrient range was expanded, and radioactive carbon was employed to trace respiration.

Gavin and Patricia Ann Straat warned in an article in Icarus (1981) of the need to consider nonbiological reactions that might account for the positive LR results, especially given Mars's extreme environment.

However, when the Viking Molecular Analysis Experiment failed to identify organic compounds on Mars, the LR experiment's results were deemed inconclusive, leading NASA to conclude that the findings might have been a false indication of life.

Each LR experiment lasted seven days, with positive samples undergoing sterilization before re-testing. Despite numerous trials on Earth under varied conditions, where the respiration test consistently yielded reliable results, the true nature of the LR findings remains elusive.

The Quest Continues

Multiple missions, including Viking, Pathfinder, Phoenix, and Curiosity, have demonstrated that Mars has significant frozen water reserves, potentially capable of supporting simple life forms.

Following the Viking results, some speculated that ultraviolet light from the Sun might have caused false positives. Nevertheless, samples retrieved from Martian crust under rock formations—shielding them from UV exposure—exhibited similar respiration-like reactions.

Curiosity has identified complex organic molecules, such as kerogen, often linked to life on Earth, while both it and the Phoenix lander have uncovered indications that Mars might have once harbored a more temperate climate.

The Martian atmosphere's elevated carbon dioxide levels suggest the possible presence of biological activity, as ultraviolet light transforms CO2 into carbon monoxide. Researchers hypothesize that unknown processes, potentially involving microbes, could regenerate CO2, releasing it into the atmosphere.

The detection of high methane levels might also point to biological origins, akin to processes observed on Earth. A balance could exist between methane-producing bacteria and those converting methane back into CO2, explaining the fluctuating methane levels noted by Martian explorers.

It is conceivable that life from Earth may have reached Mars in the distant past due to interplanetary debris transfer. Some Earth microbes have demonstrated resilience against Mars's harsh conditions, thriving even in laboratory simulations. Tardigrades, known for their extreme survivability, may currently reside on the Moon following the Beresheet mission's crash.

Findings of methane flares, along with traces of formaldehyde and ammonia in the Martian atmosphere, could hint at biological processes, but definitive conclusions remain elusive.

Future Prospects

The allure of Martian life has captivated human imagination since before Lowell's time, inspiring countless works of fiction by authors like H. G. Wells and Ray Bradbury. An empirical investigation into this possibility awaited the Viking mission in 1976.

Levin and Straat propose a future experiment akin to the Viking LR, incorporating a new element known as chirality. Molecules can exist as mirror images, and biological systems typically favor one form over the other, which could indicate life.

A Chiral Labeled Release (CLR) experiment could confirm or extend the Viking findings, as global space agencies plan new missions to Mars, including NASA's Mars Helicopter. The ExoMars 2020 project—a collaboration between the European Space Agency and Roscosmos—will deploy the Rosalind Franklin rover, aimed at conducting in-depth analyses of Martian samples.

Despite the uncertainties surrounding the Viking results from 1976, NASA researchers are contemplating follow-up experiments. Christopher McKay from NASA Ames Research Center noted that previous Viking instruments might have overlooked low organic levels in Martian soil due to the presence of iron, suggesting future missions should employ non-heating extraction methods.

A small CLR prototype has been developed and tested successfully. As plans evolve to send humans to Mars, determining whether life exists on the planet becomes increasingly vital—not only to avoid potential contamination but also to respect any native species that may inhabit the Martian landscape.

The LR experiment aboard Viking raises profound questions about our existence in the universe: are we truly alone? We may not find the answer until another spacecraft lands on the Martian surface, embarking on the quest to uncover life on the Red Planet.

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