Cite as: Benner, S. A. (2023) “The BARSOOM Model for Life on Mars”. Primordial Scoop, e20231118. https://doi.org/10.52400/USVX5880
Jan Špaček yesterday criticized a post that I made last week about life on Mars. There, I presented a model for how microbes may have evolved to live today at sites on Mars that were visited in 1976 by Viking. That model hypothesized that these microbes are bacterial autotrophs respiring with oxygen stored for use in their overnight metabolism. That gives the acronym BARSOOM, which is most appropriate for Mars. After all, John (Jan?) Carter was the first human to visit Mars.
For those who are uncertain about whether Viking encountered life living today on Mars, the hypothesized BARSOOM lifestyle has two important virtues:
• The model is entirely consistent with biochemistry expected for life adapted to the very dry (by Earth standards) environments where Viking landed, based on biochemical first principles. The model hypothesizes that pre-organization of CO2 and storage of biosynthesized O2 prepare the microbes to respond rapidly when they encounter resources (liquid water, reduced carbon) that are very scarce in near surface Mars, day or night.
• The hypothesis accounts for every observation that Viking made, including the respiration of Viking food with CO2 release, the partial loss of respiration at 46 °C, the release of O2 when the soil is treated with water without food, the loss of activity upon prolonged sample storage, and the “fixation” of carbon, among others.
Thus, the value of the BARSOOM model, and the reason why it should impact NASA culture (which still generally denies the possibility of extant life on Mars at the Viking sites [1][2]), come from its combination of both first principles that predict how “clever” evolution would drive organisms to adapt to Martian near-surface environments, and the observations made by the experiments that Viking actually did there.
Thus, Jan should be happy with the BARSOOM model, since it wraps the final line of his post. There, he writes that “[a]n explanation without an experiment is doomed”. The experiments that provide the first level testing of the BARSOOM model were done. Viking did them. Twice, at two different sites.
Curiously, Jan thinks that it is relevant to the BARSOOM discussion to recite different lifestyles that are used by bacteria living in Earth environments that are partial analogs of the Viking sites. I have no argument with this recitation. The many ways life uses different strategies in different environment axiomatically represent the “cleverness” of evolution acting to adapt life living at those Terran sites. But none of them explain the Viking observations.
Thus, it is true that bacteria living in dry Antarctic locales can make a living by oxidizing trace H2 or CO. Microbes exploiting an analogous metabolism might be present at the partially analogous Viking sites. But their presence would not explain the Viking experimental results.
Likewise, Martian microbes might exist that reduce CO2 with H2S, Fe2+, elemental sulfur, ammonia, or any of the other reductants that Jan suggests. But none of those alternative ways to fix CO2 explain observations made by the Viking experiments.
And yes, Martian life might exploit the 0.13% O2 present in the Martian atmosphere to do respiration when respiration is needed. But this life would not generate the Viking observations.
Now, and it is appreciated, Jan concedes that the BARSOOM model explains all of the Viking observations. Jan agrees that BARSOOM is consistent with chemical principles. Nor does Jan dispute the proposal that BARSOOM is a plausible lifestyle for organisms “cleverly” evolving to be adapted to the Viking sites on Mars.
So what is Jan’s objection? Well, he objects to one “flaw” in the BARSOOM “story”. The point where I wrote that CO2 fixation “must generate O2” (his emphasis).
Now, I prefer the words “hypothesis” or “model” over “story.” But otherwise, I agree. Which is why I wrote in my first piece, “Viking showed that the Martian soil contains O2, or something that generates O2 when treated with water without food [emphasis added]”. I wrote: “Let us call it “O2” in quotation marks.” That is, of course, the “O2” generated during the day and stored to be able for the microbe to respire to stay alive during the night.
I continued thus: “Our Martian friends need not store O2 as a gas in bubbles. They can store it as we do, complexed to iron. We use iron in hemoglobin…. They may use something else.”
But I did note from first principles that the way in which “O2” is stored must make it available for respiration to give back energy. That constrains the bio-storage chemistry by thermodynamic principles. I wrote: “For now, let me simply note that ‘O2‘ cannot be an energy ‘sink’”’, so stable that respiration using it does not retrieve energy.”
For example, chemistry where CO2 is reduced by sulfur to make sulfate as an oxygen sink does not offer the needed biochemistry in this environment. Sulfate does not oxidize reduced carbon to return energy.
Thus, I have not exactly told a “story”. I have asked the question: “Can we construct a model for a life form that might, by first principles, be adapted to the Viking environments, a model that can also explain the Viking results?” The answer is “Yes, we can.” Curiously, this does not seem to have been done previously, although I am always open to education, and this piece is open for comments, below.
However, as always [3], Jan’s analysis forces me to think. And ask this question: “How might clever evolution adapt bio-systems to store “O2” in a way most fit for the Viking Mars environments?” That question deserves to be explored, and that exploration will come in another post.
References
[1] Rummel, J. D., Conley, C. A. (2017) Four fallacies and an oversight: Searching for Martian life. Astrobiology 17, 971–974.
[2] 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.
[3] Benner, S. A. (2021) NASA: The Gatekeeper of “Consensus Science”? Primordial Scoop, 2021, e1029. https://doi.org/10.52400/UZJZ9163
