Life detection experiments of the Viking Mission on Mars can be best interpreted with a Fenton oxidation reaction composed of H₂O₂ and Fe²⁺ and iron-catalysed decomposition of H₂O₂

Abstract

: The findings of the life detection experiments carried out during the Viking mission to Mars were reinterpreted with a chemical hypothesis. The labelled release (LR), pyrolytic release (PR) and gas exchange (GEx) experiments were interpreted with Fenton chemistry. Oxygen and carbon dioxide evolution from Martian soil upon wetting and nutrient addition could be attributed to competition reactions between the Fenton-type oxidation of organic nutrients with the aqueous (hydrogen peroxide+Fe(II)) combination and the iron-catalysed decomposition of hydrogen peroxide. A substantial evolution of radioactive gas upon addition of labelled organic nutrient solution to soil, whereas the ceasing of this gas with a heat treated sample in the LR experiments, was attributed to Fenton oxidation and hydrogen peroxide thermal decomposition, respectively. The peculiar kinetics of LR and PR experiments -that cannot be fully explained by other chemical or biochemical scenarios -were easily explained with this new hypothesis, i.e. limitation of the Fenton reaction may arise from the depletion of reactants, the build-up of ferric hydroxide on soil and excessive scavenging by the organic nutrients of the generated hydroxyl radicals. Reabsorption or adsorption of evolved or introduced CO 2 may involve the formation of carbonate compounds (e.g., magnesium carbonate and bicarbonate) on the surface of alkalinized soil as a result of the Fenton reaction.A critical evaluation of the recent biological hypothesis assuming the utilization of a hydrogen peroxide-water intracellular fluid by putative organisms (Houtkooper & Schulze-Makuch 2007) is also made.

The principle of detailed balancing, the iron-catalyzed disproportionation of hydrogen peroxide, and the Fenton reaction

“…If we disregard this concern, the consequences of this illegal loop in a mass-action mechanism can be explored by performing simulations of the loop based on the mechanism and parameters of a publication by Lin and Gurol 1998. 176 17,21,23,26,33,95,99,133,[176][177][178][179][182][183][184]187,189,190,193,195,197,198,200,203,204,206,207,211,218,219,[223][224][225]228 One of these shows the steps in the loop but then excludes them from the final model. 200 There are a few publications that use the inverse acid dependence in the first step of the loop (non-mass-action kinetics).…”

Physical and chemical mechanisms that impact the detection, identification, and quantification of organic matter and the survival of microorganisms on the Martian surface – a review

“…Superoxide disproportionation was proposed as the most likely source of oxygen, because it decomposes into O 2 in contact with water and tolerates heating to 145 °C (Oyama et al ., 1977; Ballou et al ., 1978). Likewise, H 2 O 2 can disproportionate into O 2 and H 2 O through reactions catalysed by transition metals (Fe and Cu) present in the Martian regolith (Apak, 2008). H 2 O 2 per se should not be degraded by heating to 145 °C (Levin and Straat, 1979), but if H 2 O 2 is produced only after the addition of water, then the production of O 2 would depend on the heat stability of the H 2 O 2 precursor rather than on the heat stability of H 2 O 2 itself.…”

“…A chemistry-founded interpretation of the results is also supported by the detection of ROS that can serve as sources of O 2 as well as oxidants of organic compounds, which would lead to the production of CO 2 (Ponnamperuma et al ., 1977; Oyama and Berdahl, 1979; Quinn and Zent, 1999; Apak, 2008). However, as ROS are unstable in the presence of metal ions such as Fe 2+ or Fe 3+ , that both are present in the Martian regolith, and as H 2 O 2 would be degraded by exposure to UV radiation, it is most likely that the oxidants are produced from precursors that are present on mineral surfaces (Zent and McKay, 1994), either as primary products (Bak et al ., 2017 a ) or through secondary processes (Quinn and Zent, 1999).…”