Although the consensus among planetary scientists and biologists is that the existence of life on Mars, both present and past has not been proven, one investigator, who was the lead scientist during the Viking 2 mission, now disagrees with the majority opinion, and is citing his original work to prove his point.
While Gilbert Levin, who oversaw the LR experiment during the Viking 2 mission, initially thought that the Viking 2 findings were merely consistent with metabolic activity, he now contends in a new research paper that if several new lines of evidence are added to his original work, there is now “substantial” evidence that there is indeed microbial life on Mars.
In short, the Viking LR (Labelled Release) experiment involved adding some nutrient solution to a Martian soil sample, and if life were present, the signs of metabolic activity would be found both in the soil sample itself, and in the “atmosphere” of the container that held the soil sample. As it turned out, the original sample did yield signs of metabolic activity, but a related experiment performed at the same time did not confirm this finding.
Nevertheless, Levin now defends his opinion on the grounds that on Earth, there are many life forms that thrive under conditions that are far more severe than anything that occurs on Mars, in addition to the fact that one of the current Mars rovers discovered several organic compounds under a rock that was several billion years old. According to Levin, the organic compounds under rocks could only be explained by the presence of at least microbial life forms.
Other researchers, however, that include astronomers, physicists, cosmologists, and chemists have identified similar and other complex organic molecules and compounds (that include the precursors to amino acids) on meteorites, and in molecular clouds and other nebulous structures in deep space, the implication being that organic compounds are common in the Universe.
The next question then becomes; why did the Viking experiments not identify actual microorganisms, given the fact that organic material indisputably exists on Mars? There are several possible answers to this, and according to Levin, one possibility is the fact that since the gas chromatograph/mass spectrometer onboard the Viking craft was known to be defective, it could not be used to either eliminate or confirm the presence (or otherwise) of microbes.
That said, several other researchers point out that the gas chromatograph/mass spectrometer was neither designed, nor intended to be a “life detector”, since it required at least one million microbial cells to detect organic matter. Moreover, Levin claims that the presence of perchlorate in the Martian soil samples could have destroyed all life in the sample, but no other researcher has been able to identify perchlorate in either of the Viking landing sites, which incidentally, were several thousand kilometers apart.
Levin also points to the cyclical variations of methane in the Martian atmosphere as evidence of life on Mars, but the problem with that is the fact that inorganic rock chemistry is also known to produce methane, which means that the presence of methane proves nothing, one way or the other. In fact, all of Levin’s “proofs” of life on Mars can be explained either by inorganic chemical processes, or by organic processes that do not require life to be present.
Nonetheless, both sides of the “Life on Mars, or Not” debate are in the same proverbial boat, since neither side can conclusively prove their own arguments, or disprove the arguments of the other side. To settle the question conclusively, NASA is currently in planning stages of a mission dubbed ExoMars 2020, whose sole objective either would be to find evidence of life on Mars, or to disprove that life exists now, or has existed in the distant past.
The late Carl Sagan once said, “Extraordinary claims require extraordinary evidence”, and provided budget cuts and other disasters do not delay the launch of the ExoMars 2020 mission unduly, extraordinary proof of life (or proof to the contrary) on Mars may become available by about 2025.