By 
February 21st, 2025
NASA Viking missions to Mars of the 1970s.
Credit: NASA
Back in 1976, the dual NASA Viking landers came to full stop on the Red Planet.
Their life detection experimental findings still reverberate within the scientific community – fueling the on-going discussion on a key question: Is there life on Mars?
Fast forward to today, a new paper tackles and reconsiders the results of the Viking Biology experiments.
NASA 1976 Viking 2 lander image of the Mars Utopian Plain.
Credit: NASA/JPL-CalTech
Perchlorate finding
The most significant change since those 1970’s experiments were conducted was the discovery of high levels of perchlorate on Mars. Perchlorate, plus abiotic oxidants, explains the Viking results and there is no requirement to postulate life on Mars.
“The discovery of perchlorate on Mars by the Phoenix mission has provided a basis for explaining the results of the Viking Landers,” the newly issued paper notes. “Thermal decomposition of perchlorate in the ovens of the [Viking] instrument can explain the lack of organics detected. Accumulation of hypochlorite in the soil from cosmic ray decomposition of perchlorate can explain the reactivity seen when nutrient solutions were added to the soil in the Viking Biology Experiments.”
However, the paper adds, “a non-biological explanation for the Viking results does not preclude life on Mars.”
Credit: NASA/Ben Clark
Revisit the results
The just-released paper — The Viking biology experiments on Mars revisited – has been authored by noted Mars researchers Christopher McKay, Richard Quinn and Carol Stoker. All three authors are from the space science division of NASA’s Ames Research Center at Moffett Field, California, near San Francisco.
“With Mars sample return on the horizon and the prospect of future missions to Mars, perhaps even including life detection instruments, it may be timely to revisit the results of the Viking Biology Experiments,” the research team suggests. “Since Viking landed on Mars, many things have changed, and many things have not. What has not changed in the past 50 years is our understanding of the limits of life in cold and dry environments.”
In a communiqué with Christopher McKay, he told Inside Outer Space: “It is important to note that we are not saying that the Viking results imply ‘no life on Mars.’ Nor are we saying the Viking results imply there is life on Mars.”
The first photo from the surface of Mars shows one of the Viking 1 lander’s footpads.
Credit: NASA/JPL
McKay said that their core point is that the Viking results are saying there is perchlorate and other oxidants on Mars, “and that is what the Viking biology experiments responded to.”
What this means is that the results of the Viking Biology experiments can’t be used to justify an approach to astronaut health and safety or a sample and/or astronaut quarantine policy for return to Earth that assumes no life on Mars.
New data
In their paper for the scientific journal, Icarus, the research trio explains that there have been big changes resulting from missions to Mars. “The most important new data, by far, was the surprising discovery from the Phoenix Mission that the soils of Mars contain about 0.5% perchlorate,” they observe. “This incredibly high concentration of perchlorate is still not adequately explained but the implications for the Viking results are profound.”
NASA Phoenix lander.
Credit: NASA/JPL
The space scientists in their paper explain that the perchlorate model and the resultant conclusion that Viking did not detect life in the surface soils of Mars will factor into any discussion of sample return or astronaut return from Mars.
“The Outer Space Treaty prohibits “adverse changes in the environment of the Earth resulting from the introduction of extraterrestrial matter.” Future experiments are needed to better understand the chemistry of martian soils and the possibility of life persisting there,” McKay and colleagues add.
Good targets
In summing up their research paper, they conclude that the perchlorate model for the Viking results “does not prove that there is no life on Mars, nor does it imply that the continued search for evidence of life on Mars, past or present, is pointless.”
Indeed, as the research team suggests, “we strongly argue for the search for evidence of extant life in future missions. Good targets are salt deposits and polar ground ice.”
The Red Planet as seen by Europe’s Mars Express.
Image credit: ESA/D. O’Donnell – CC BY-SA IGO
For access to the full paper – “The Viking biology experiments on Mars revisited” – go to:
https://www.sciencedirect.com/science/article/pii/S0019103525000132?via%3Dihub
Posted in Space News
For all the Mars aficionados out there, the perchlorate results reported by McKay et al. in their recent 2 1/2 page paper “The Viking biology experiments on Mars revisited” was already reported on and refuted in 2011 by Biemann himself:
Biemann, K., and J. L. Bada (2011), Comment on “Reanalysis of the Viking results suggests perchlorate and organics at midlatitudes on Mars” by Rafael Navarro-González et al., J. Geophys. Res., 116, E12001, doi:10.1029/2011JE003869.
https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JE003869
“Here we read that during cruise to Mars, each GCMS instrument was subjected to a test run in which one of the three ovens was heated to 500°C. As can be seen from Biemann et al. [1977, Figure 3, top], so much adsorbed water was expelled that the effluent divider (ED) went into the 1:8000 ratio mode, which caused the valve to the MS to close at about scan 25. Thus, any CH3Cl that may have been present would have been completely vented into space. After the water had passed through the GC column, at about scan 40, the ED opened again up to full transmission into the MS, permitting detection of the Freon-E and any CH2Cl2, if it would have been present. Because the oven had been heated to 500°C, it was completely dry when it was later filled with Martian soil and
heated to 200°C.
Conclusions
[17] The assertion by Navarro-González et al. [2010,
paragraph 33] that “the Viking Landers did detect the presence
of organics in the soil” of Mars, based on the detection
of CH3Cl with one of the two samples of the VL-1 site and
of CH2Cl2 with both of the VL-2 samples is not supported
by the experimental data. In order to validate their assertions
the experimental date were searched specifically only for
these two molecules but neglecting any other chlorinated
aliphatic or aromatic hydrocarbons. Similarly, the kinetic
modeling included only rate expressions (in the gas phase)
for the conversion of CH4 to CH3Cl and CH2Cl2 but not the
continued chlorination to CHCl3 and CCl4 or for the chlorination
of benzene or other hydrocarbons. Equally questionable
is the suggestion that in situ life detection missions
to Mars be initiated immediately. In fact, what is urgently
needed are well designed experiments to analyze the surface
of the planet for the presence of specific organic molecules,
in order to ascertain what types of organic material may be
present, if any. We know that meteoritic infall is disseminating
such organic material continuously although radiolysis
may compromise its long-term survival at the surface
[Kminek and Bada, 2006]. If the meteoritic material cannot
be found, it must be that destructive processes prevail, which
at the same time would destroy any prebiotic chemistry long
before it reaches the point of the “origin of life” chemistry.”
——————————————–
Of course with the landings of the Curiosity and Perseverance rovers on Mars we now have abundant data about complex organics from the rocks, soil and atmosphere of Mars that would seem to rule out organic molecules being destroyed by perchlorates.
Thus, the case of the Viking Labeled Release experiment remains open as it has been for nearly fifty years.
Barry DiGregorio