All Viking results can be explained by autotrophic microbes living on the Martian surface
Cite as: Benner, S. A. (2023) “Why does the NASA Culture Still Get Viking 1976 Wrong?”. Primordial Scoop, e20231113. https://doi.org/10.52400/OMNN6244
My last post noted that all three Viking 1976 life detection results are compatible with a model for autotrophic microbes that have evolved a lifestyle adapted to Martian environments where water and organic carbon are scarce. That model specifies that:
• The microbes make reduced carbon biomass by using energy to fix CO2 (or CO) to give reduced carbon (Creduced), a process that on Earth would be called “autotrophy”.
• That process must generate O2; this conclusion is unavoidable after one balances the chemical equation.
• Like Earth’s photosynthetic autotrophs, Martian autotrophs likely also exploit respiration, the oxidation of Creduced by O2 to recover energy.
• Unlike Terran photosynthetic autotrophs, however, Martians cannot easily obtain O2 from the atmosphere to serve as a bio-oxidant for later respiration.
• Thus, Martian surface microbes must store the O2 that they make during autotrophy.
• Water, its hydrogen atoms and their electrons, are limiting resources on the Martian surface.
• Thus, Martian autotrophs pre-collect CO2 (or CO) to be ready should scarce H2O come along.
Now to the Viking results
How might they be explained by this model for Martian near-surface autotrophs? Interpreting those results according to the model:
• The O2 released in the “gas exchange experiment”, where water was added to the soil without food, is the O2 that these microbes have stored to support respiration.
• For the “label release experiment”, enzymes in the autotroph that catalyze respiration in the normal autotrophic life cycle catalyzed the release of 14CO2 from radiolabeled food fed by Viking in water. The stored O2 served as the oxidant to make14CO2 from radiolabeled food.
• The uptake of 14CO2 in the “carbon fixation experiment” represents the pre-collection of an abundant resource (CO2) in preparation for a low probability encounter with a scarce resource (H2O), analogous to the “dark reaction” in Terran photosynthetic autotrophs.
We need not specify the source of the energy that the hypothesized Martian autotrophs use to drive carbon fixation. It can come from the Sun. It may come from the reaction of trace gasses. The ability of the model to explain the Viking results does not change.
Further, only ~30% of the bio-stored O2 was evidently needed to account for the amount of 14CO2 released from Viking’s radiolabeled food in the LR experiment. The model implies that some O2 was also released when the food and water was added to the Martian soil in the LRE. However, the LRE did not itself measure O2 release.
Why did Viking scientists conclude, oppositely, that Viking sites held no life?
Mission logs and subsequent commentaries hold no evidence that the Viking team considered this model. Instead, in its 1977 commentaries, the Viking scientists concluded that life was entirely absent in the soil samples taken at the Viking sites. Further, they concluded that the Martian soil must contain a strong oxidant, one so kinetically powerful that it converted the Viking-delivered food to CO2 without needing any biological catalysis.
The consequences of this conclusion for Mars exploration were dramatic. Exploration ceased entirely, for a quarter century. Only the 1996 discovery of “fossil microbes” in the Allan Hills meteorite, and the inability of NASA to answer the question reportedly posed at the time by President Bill Clinton (“Is this life or not?) created a new NASA discovery program for Mars, together with the NASA Astrobiology Institute.
However, the conclusion remained consequential for subsequent astrobiology research within that Institute, and in the Mars “community” design of missions to Mars. Under the belief that the Martian surface was self-sterilizing, “the Mars community [remained] not convinced that a mission to attempt (re?)detection of extant Martian life is a high priority.” [1]
Instead, NASA made the search for water and past habitability its top priority. Rovers were specifically directed away from sites that might contain extant life, in part for “planetary protection” issues. NASA ruled out missions where the detection of extant life was the declared objective. Flagship-level funding for Mars was put into a mission to collect and return samples from deltas arising from ancient water, away from near surface ice at mid latitudes that might contain life living today.
This conclusion continues to guide planning out to 2040. For example, in the most recent Decadal Survey, the only extant life detection concept, outlined by a team led by Amy Williams, was constrained by budgetary considerations. So constrained, it could not possibly deliver conclusive results.
A single misinterpreted mass spectrometry result constrained community analysis
The questions that concern us are simple to ask:
• Why did the Viking team and, subsequently, the “Mars Community”, conclude that the Viking results did not indicate an active Martian biosphere, at least to the point of putting a “low priority” on missions to detect it at easily accessible sites?
• Why did it not consider, and still does not consider, a model for the lifestyle of possible Martian autotrophs, one of which is outlined above, or any of a number of other biological explanations for the complete collection of Viking results?
• Indeed, the mission logs suggest that no one in the Viking mission team sought to create a model for the lifestyle of a Martian biosphere that might explain the Viking results in an integrated fashion, one compatible with the local Viking environment. Why not?
Given the density of the record, it is not difficult to answer these questions. In real time as the experiments were done, the label release result was interpreted as favoring the presence of life. The gas exchange experiment result was interpreted as opposing the presence of life. The carbon fixation result was considered to be ambiguous, because carbon fixation did not have any simple correlation to sample illumination.
Thus, the interpretations might be summarized by three words: “Yes”, “No”, and “Dunno”.
So how did the Mars community move from ” Yes” + “No” + “Dunno” to a clean “No”?
Again, the record is clear. The logic was driven by a fourth set of results.
These results were delivered by a gas chromatography-mass spectrometry (GC-MS) instrument. That instrument was not designed to be a life detection instrument. Nevertheless, once operational, the GC-MS generated results that were interpreted as showing the absence of organic molecules in the Viking soil.
This result drove the following logic that was stated in the 1977 mission reviews.
• Life requires organic compounds, a general principle.
• The Martian soil contains no organic compounds, a (mis)interpretation of the GC-MS results.
• Therefore the Martian soil contains no life.
The (mis)interpretation of the GC-MS result became stronger as other issues were raised. Organics come to Mars via meteorite, just as they do to Earth. Indeed, before Viking flew, the GC-MS experiment was criticized under the view that it would simply detect meteoritic organics, which (it was argued) could not be distinguished from indigenous bio-organic molecules.
But, because of the (mis)interpretation of the GC-MS results, the Mars community now felt obligated to find an unnamed “mystery” oxidant strong enough not only to oxidize the Viking food without biological catalysis, but also to destroy meteoritic organics. And that requirement drove the conclusion that the Martian surface would destroy all organic molecules.
The logic was then carried forward. As this mystery oxidant was evidently able to oxidize Martian food in hours to days, and destroy grams of meteoritic organics that would be expected in a square meter of Martian surface, it must be hostile to all life. After all, life requires organic molecules.
In the language that followed, the Mars community concluded that the Martian soil is “self-sterilizing”. Life could not possibly be present at the Viking sites and, as the argument developed, anywhere on the near surface of Mars.
But Martian soils do contain organic molecules
Now, it has been established beyond doubt that the Martian soil contains organic molecules. It is clear beyond clarity that the real time belief that the GC-MS result showed that organics were absent from the Viking results was a misinterpretation. In fact, the GC-MS results showed the opposite.
The sequence by which the GC-MS results were shown to be misinterpreted began in 1999, with our paper [2] that showed that the Viking GC-MS could not have detected likely meteoritic organics even if it were sitting on a pile of them. In the following decade, after perchlorate was discovered in the Martian soil, Chris McKay and his team showed that the GC-MS results could be entirely explained by perchlorate oxidation of indigenous organics at the high temperatures used in the GC-MS experiments [3]. In this interpretation, the GC-MS results required organics to have been present in the Viking samples.
Further, the Curiosity and Perseverance Rovers on Mars actually found organic molecules at their respective sites. As one example, benzoic acid was found in the Bagnold dunes [4]. Interestingly, the scientists who found it there reported that they hesitated to look for organics in the dunes because they had been influenced by the misinterpretation of the Viking GC-MS results; they thought from those results that that looking for organics in the dune sample would be futile.
These facts came long after the Viking mission closed shop. The logic before 1999 appeared to demand that the Mars community find a non-biological oxidant in the soil sufficiently strong to explain the label release experiments and the planet-wide destruction of meteoritic organics.
O2 would not be a sufficiently powerful as an oxidant to explain the rate of oxidation of the Viking food. Nor would perchlorate, or even hydrogen peroxide (H2O2) without a catalyst, either biological (an enzyme) or abiological. None of these oxidants, when mixed with the food presented in the label release experiment, could generate CO2 at the rate seen by Viking. And none of them seemed to be active enough to destroy all meteoritic organics, even over long periods of time, again without catalysis. So the community decided that it must be dealing with an unknown oxidant, a “mystery oxidant”.
If one assumes that organics were absent from the Viking soil samples, and they are not there because a mystery oxidant is there, the “Yes”, “No”, and “Dunno” results move the burden of proof away from neutrality. The “Yes” conclusion bore it. The “No” conclusion did not. And so, in the absence of further information, “No” wins the day. This is what the phrase “burden of proof” means.
Now, the release of O2 in the gas exchange experiment was seen to be a manifestation of that mystery oxidant. Harold “Chuck” Klein from NASA Ames, the head of the Viking Biology Team, opined (in real time) thus:
“[W]e must be wary of [biological interpretations of the label release experiment] in the face of information indicating that all of the samples tested yielded O2 in the [gas exchange] experiment upon introduction of water. The evidence for strongly oxidizing chemicals in these samples is quite convincing.”
Only because Klein accepted the misinterpretation of the GC-MS result did Klein did not explain the evolution of O2 in the gas exchange experiment in the simplest way (“the soil contained O2“). After all, O2 is not a strong enough oxidant to explain the absence of organics in the soil sample.
Rather, because he accepted the misinterpretation of the GC-MS result, Chuck was driven to conclude that the soil contained a strong oxidant, one strong enough to release 15% of the easily released carbon in the food at low temperatures over 10 days at the Viking sites as CO2. And one strong enough to destroy all organic compounds that might arrive to Mars via meteorite.
The search for the Mystery Oxidant
But what was this mystery oxidant? In real time, Vance Oyama, a leader of these experiments, suggested a mechanism that involved some (or all) of these steps [5]:
• Solar UV breaks down atmosphere CO2 to give CO and atoms of oxygen (O).
• Solar UV breaks down CO to give C and O atoms.
• Some of the C-atoms combine with CO to give C2O.
• C2O reacts with CO to give C3O2, which makes a polymer.
• This is the 14C fixation observed in the carbon fixation experiments (the “Dunno” result).
• Photochemical breakdown giving C2O also gives activated O atoms.
• O atoms hit MgO or CaO, giving superoxides that release O2 with water (the “No” result)
• They also give “peroxide-like materials” in the Martian soil that oxidize the food (reinterpreting the “Yes” result as a “No” result, even though these “peroxide-like materials” were not specified).
As far as we can tell, few (and possibly none) of these steps occur on Mars. The overall process has never received much experimental support here on Earth.
However, because the misinterpretation of the GC-MS result had been accepted, the burden of proof in the Mars Community did not lie with the Oyama mechanism. Those seeking to conclude that the Viking soils were sterile had no burden to identify the mystery oxidant that caused the Viking food to be oxidized, released O2 upon wetting, and destroyed all meteoritic organics. Rather, the burden fell on the other side, to prove that such an oxidant did not exist.
After all, “the GC-MS results showed that the soil contained no organics!“
Others subsequently took up the challenge of identifying the “mystery oxidant”. For example, Quinn et al. [6] examined the impact of cosmic rays on perchlorate (ClO4–). They used a cobalt-60 radiation source to deliver 500,000 grays of radiation dosage to a simulated sample. They found that this irradiation generated, among other products, HOCl and Cl2O (“oxychloro compounds”). They suggested that these compounds generated on the surface of Mars explained all of the Viking results.
These oxychloro compound are indeed “strong oxidants”. The reaction of HOCl (bleach) with Viking foods is well studied; bleach can indeed release CO2 from some of the foodstuffs. Thus, these oxychloro compounds, if present in adequate amounts, would release some of the label from the 14C-labeled food.
However, their amounts in Viking soil samples would depend on the rate at which they were formed, minus the rates at which they were destroyed. Quinn et al. showed that these were also destroyed. Some numbers therefore come into play.
The rate of the formation of these oxidants should depend on the amount of radiation at the Martian surface. It turns out that the amount of radiation used by Quinn et al. was 1011 times more than the estimated radiation dose on Mars. For actionable amounts of bleach to have accumulated to explain the Viking label release results, the rate of loss of these oxychloro compounds must be negligible. However, Quinn et al. observed their loss in real time. While the question is still open, it appears that the steady state concentrations of these oxidants in the Viking soils was likely to be miniscule. If so, they would not likely be abundant enough to explain any of the Viking results, neither in terms of their rates nor their stoichiometries, neither the oxidation of Viking food nor the release of O2.
But that did not matter. The burden of proof was not borne by those seeking a chemical that might be the mystery oxidant. “Might be” was sufficient, given the placement of that burden. The Quinn et al. experiments would be assumed to be correct absent “proof” that they were not.
The misinterpretation persists in NASA’s culture
We often teach students that culture has a larger impact than facts and logic on the development of a field in science. Culture is what one thinks when one is not thinking. It determines what facts you select to analyze, which hypotheses you choose to test, which arguments you reflexively choose to credit, and which positions bear the burden of proof.
We also teach the students that they themselves are not immune from this. Training in science is in large part developing the discipline to not deceive oneself. We therefore encourage students to write out their thinking in long form, a process that helps reveal deficiencies in their thinking processes. And then we encourage them to observe how scientists, some very famous, fail to escape from their cultural view, even long after it cannot be sustained by facts or logic.
The Viking results, nearly a half century later, provide an excellent example. In 2021, NASA assembled a committee to define “community standards” to be used to judge claims by those who thought that they may have detected alien life. It was directed by Victoria Meadows, an astronomer and professor at the University of Washington, and Heather Graham, a geologist at the Goddard Space Center and Catholic University. Over 300 scientists applied to participate in the workshop. A total of 82 were admitted by the co-chairs and an advisory committee. Thus, the workshop might be considered to represent the crème de la crème of the NASA community.
In January 2022, a draft “Community Report” emerged [7]. Soon thereafter, NASA brought the Report to the Space Studies Board at the National Academy of Sciences for its imprimatur.
What did this Report say about the Viking 1976 results? Here it is, with internal references removed:
“One of the most famous claims for the possible detection of extant life on Mars is based on the results of Labeled Release (LR) experiment carried on the NASA Viking Landers. The LR experiment tested for the presence of life by adding carbon-14 labeled (14C) organics to Mars regolith in a sample cell while monitoring for production of 14C-gas that might be indicative of microbial metabolism, and in some respects the results resemble what had been expected for a biological response. However, since Viking it’s been recognized that there are numerous possible non-biological explanations for the LR results. The results of the Viking Gas Exchange Experiment, which demonstrated that the regolith was chemically reactive, and the search for organics using the Viking Gas Chromatograph-Mass Spectrometer further support a non-biological interpretation of the LR results. Additionally, detections of oxychlorine compounds on Mars (perchlorate and chlorate) during the Phoenix and Mars Science Laboratory missions indicate the occurrence of processes that can explain both the Viking LR and GCMS results.”
To adapt (with some exaggeration) the remarks made by Mary McCarthy of Lillian Hellman’s memoirs, every word in this statement is wrong, including “and” and “the”. The gas exchange experiment did not demonstrate that the regolith was chemically reactive. The search for organics using the GC-MS instrument did not support a non-biological interpretation of the LR results. Neither perchlorate nor chlorate can explain the Viking LR results. We still do not have a solid non-biological explanation for the LR results, and we certainly do not have “numerous” explanations.
In contrast, as noted in the previous post, one can readily generate a biological model for all of these results. That model hypothesizes that Viking encountered Martian autotrophic microbes adapted to the environments that Viking visited.
As Carol Cleland recently noted on these pages [8], the problem is not that non-life interpretations of the Viking results were not considered. Rather, the problem is that the GC-MS misinterpretation was so deeply embedded in the culture of the community that it refused to consider possible pro-life interpretations.
And that persists even today.
The need for private life detection missions to Mars
Paul Davies, the cosmologist and author of many books to explain science to the public, recently remarked on the focus at NASA on exoplanets as a place where extant life might be found, refusing to return to the “earthlike rocky planet right here in our neck of the cosmic woods”. As Paul writes:
“Disillusioned by NASA’s caution, several tech entrepreneurs have now begun expressing strong interest in seeking out extant life in the solar system. And a growing band of frustrated astrobiologists is outlining how to go about it.”
Just so.
The astrobiologists who know something about life in extreme environments are among the most frustrated. In 2019, Michael Meyer, the Mars guru at NASA Headquarters, assembled a workshop in Carlsbad to consider the possibility of extant life on Mars and where it might be living today. The resulting conference paper [9] had 60 co-authors. In the interests of full disclosure, I was one. It offered this summary, where we have added italics:
“A significant subset of conference attendees concluded that there is a realistic possibility that Mars hosts indigenous microbial life. A powerful theme that permeated the conference is that the key to the search for Martian extant life lies in identifying and exploring refugia (“oases”), where conditions are either permanently or episodically significantly more hospitable than average. Based on our existing knowledge of Mars, conference participants highlighted four potential Martian refugia: Caves, Deep Subsurface, Ices, and Salts. Within the context of these candidate environments, we identified a variety of geological search strategies that could narrow the search space. Additionally, we summarized a number of measurement techniques that could be used to detect evidence of extant life.”
However, in the years since, NASA has not moved. Its Mars-allocated resources are tied up in a sample return mission that, consistent with its culture, was premised on not seeking extant life. Being an organization that must respond to many constituencies, NASA’s next flagship mission will go to Titan, which offers little prospect of holding life, but gives the “outer world” constituencies “their turn”. Five of its eight new “Interdisciplinary Centers for Astrobiology Research” announced last summer focus on exoplanets, again without a path to unambiguous detection of alien life. And the latest Decadal Survey sees the search for extant life on Mars beginning in 2040 … maybe.
At the same time, as Paul notes, astrobiologists have provided tools that would detect Martian life [10]. Most importantly, these would detect Martian life “agnostically” and with high sensitivity [11]. Thus, even sparse Martian life with a core biochemistry quite different from that of Terran life would be found.
Thus, private societies are organizing to persuade private entities to do a focused mission to find life now living on Mars [12]. The model for an autotrophic Martian lifestyle was outlined in the previous post. Alternative lifestyles may be proposed for life living in the near-surface ice prevalent at mid-latitudes on Mars. These help guide the search that they are seeking entrepreneurs to provide.
Which raises the question: Which entrepreneur will seek to take credit for making what would arguably be, as Jodie Foster remarked, “the biggest discovery in the history … of history.”
References
[1] Rummel, J. D., Conley, C. A. (2017) Four Fallacies and an Oversight: Searching for Martian Life. Astrobiology 17, 971–974.
[2] Benner, S. A., Devine, K. G., Matveeva, L. N., & Powell, D. H. (2000). The missing organic molecules on Mars. Proceedings of the National Academy of Sciences, 97(6), 2425-2430.
[3] Navarro‐González, R., Vargas, E., de La Rosa, J., Raga, A. C., & McKay, C. P. (2010). Reanalysis of the Viking results suggests perchlorate and organics at midlatitudes on Mars. Journal of Geophysical Research: Planets, 115(E12).
[4] Millan, M., Teinturier, S., Malespin, C. A., Bonnet, J. Y., Buch, A., Dworkin, J. P., … & Mahaffy, P. R. (2022). Organic molecules revealed in Mars’s Bagnold Dunes by Curiosity’s derivatization experiment. Nature Astronomy, 6(1), 129-140.
[5] Oyama, V. I., & Berdahl, B. J. (1979). A model of Martian surface chemistry. Journal of Molecular Evolution, 14, 199-210.
[6] Quinn, R. C., Martucci, H. F., Miller, S. R., Bryson, C. E., Grunthaner, F. J., & Grunthaner, P. J. (2013). Perchlorate radiolysis on Mars and the origin of martian soil reactivity. Astrobiology, 13(6), 515-520.
[7] Meadows, V., Graham, H., Abrahamsson, V., Adam, Z., Amador-French, E., Arney, G., … & Young, L. (2022). Community Report from the Biosignatures Standards of Evidence Workshop. arXiv preprint arXiv:2210.14293. This report was criticized by National Academy of Sciences for “consensus” approach to science as opposed to judging each hypothesis on its merits: National Academies of Sciences, Engineering, and Medicine. (2022). Independent Review of the Community Report from the Biosignature Standards of Evidence Workshop: Report Series—Committee on Astrobiology and Planetary Sciences.
[8] https://primordialscoop.org/2021/11/22/why-searching-for-extraterrestrial-life-with-a-universal-biosignature-detection-framework-is-a-mistake/
[9] Carrier, B. L., Beaty, D. W., Meyer, M. A., Blank, J. G., Chou, L., Dassarma, S., des Marais, D. J., Eigenbrode, J. L., Grefenstette, N., Lanza, N. L., Schuerger, A. C., Schwendner, P., Smith, H. D., Stoker, C. R., Tarnas, J. D., Webster, K. D., Bakermans, C., Baxter, B. K., Bell, M. S., Benner, S. A., Bolivar Torres, H. H., Boston, P. J., Bruner, R., Clark, B. C., Dassarma, P., Engelhart, A. E., Gallegos, Z. E., Garvin, Z. K., Gasda, P. J., Green, J. H., Harris, R. L., Hoffman, M. E., Kieft, T., Koeppel, A. H. D., Lee, P. A., Li, X., Lynch, K. L., MacKelprang, R., Mahaffy, P. R., Matthies, L. H., Nellessen, M. A., Newsom, H. E., Northup, D. E., O’Connor, B. R. W., Perl, S. M., Quinn, R. C., Rowe, L. A., Sauterey, B., Schneegurt, M. A., Schulze-Makuch, D., Scuderi, L. A., Spilde, M. N., Stamenković, V., Torres Celis, J. A., Viola, D., Wade, B. D., Walker, C. J., Wiens, R. C., Williams, A. J., Williams, J. M., Xu, J. (2020) Mars Extant Life: What’s Next? Conference Report. Astrobiology 20, 785–814.
[10] Špaček, J., & Benner, S. A. (2022). Agnostic life finder (alf) for large-scale screening of martian life during in situ refueling. Astrobiology, 22(10), 1255-1263.
[11] https://primordialscoop.org/2023/09/15/making-operational-the-polyelectrolyte-theory-of-the-gene-in-the-agnostic-search-for-martian-life/
[12] https://primordialscoop.org/2022/08/08/a-new-project-to-find-existing-life-on-mars-before-humans-arrive/
