The missing organic molecules on Mars

Abstract

GC-MS on the Viking 1976Mars missions did not detect organic molecules on the Martian surface, even those expected from meteorite bombardment. This result suggested that the Martian regolith might hold a potent oxidant that converts all organic molecules to carbon dioxide rapidly relative to the rate at which they arrive. This conclusion is influencing the design of Mars missions. We reexamine this conclusion in light of what is known about the oxidation of organic compounds generally and the nature of organics likely to come to Mars via meteorite. We conclude that nonvolatile salts of benzenecarboxylic acids, and perhaps oxalic and acetic acid, should be metastable intermediates of meteoritic organics under oxidizing conditions. Salts of these organic acids would have been largely invisible to GC-MS. Experiments show that one of these, benzenehexacarboxylic acid (mellitic acid), is generated by oxidation of organic matter known to come to Mars, is rather stable to further oxidation, and would not have been easily detected by the Viking experiments. Approximately 2 kg of meteorite-derived mellitic acid may have been generated per m 2 of Martian surface over 3 billion years. How much remains depends on decomposition rates under Martian conditions. As available data do not require that the surface of Mars be very strongly oxidizing, some organic molecules might be found near the surface of Mars, perhaps in amounts sufficient to be a resource. Missions should seek these and recognize that these complicate the search for organics from entirely hypothetical Martian life.Viking ͉ organic compounds ͉ exobiology ͉ astrobiology

Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group

“…We know that ancient organic molecules will preserve only if buried in sediments and long-term preservation will occur only if buried organics are shielded from oxidizing fluids. On Mars, surface oxidants and UV radiation will have altered or destroyed organic molecules (Benner et al, 2000;Navarro-Gonzâlez et al, 2006;Sumner, 2006). On Mars, surface oxidants and UV radiation will have altered or destroyed organic molecules at or near the surface (Benner et al, 2000;Navarro-Gonzâlez et al, 2006;Sumner, 2006).…”

“…On Mars, surface oxidants and UV radiation will have altered or destroyed organic molecules (Benner et al, 2000;Navarro-Gonzâlez et al, 2006;Sumner, 2006). On Mars, surface oxidants and UV radiation will have altered or destroyed organic molecules at or near the surface (Benner et al, 2000;Navarro-Gonzâlez et al, 2006;Sumner, 2006). If we can identify generic features that can be used to characterize potential landing sites with respect to the presence or absence of specific taphonomic windows, then we can help maximize the chances of successful analyses by MSL.…”

Astrobiology and habitability studies in preparation for future Mars missions: trends from investigating minerals, organics and biota

“…No organic matter and no proof of life were found although detection limits of the GC-MS were in the ppb range (Biemann 1979). It is possible that the Viking GC-MS failed to detect certain types of organic material present in the Martian soil (Benner et al 2000;Glavin et al 2001;Navarro-González et al 2010).…”

“…Oxidizing species may also be created directly in the soil, by Fenton-type reactions (Liang et al 2006) and superoxide radicals (Yen et al 2000). Organic material arriving on the Martian surface via small bodies may be converted to carboxylic acid derivatives (Benner et al 2000). The large number of laboratory experiments performed in atmospheric Mars chambers has provided supporting material to our understanding of organic degradation and the viability of micro-organisms on Mars.…”

Astrobiological instrumentation for Mars – the only way is down

“…These rapidly oxidize surface biomolecules to carbon dioxide and unrecognizable residues (Stoker & Bullock 1997). The OH radical reacts with most organic molecules to yield benzenecarboxylic acid derivatives from kerogen (the most abundant organic material in meteorites), metastable oxalic acid derivatives of amino acids, phthalic acid and other carboxylic acid derivatives of PAHs, and perhaps the carboxylic acid derivatives of alkanes (Benner et al 2000). These derivatives, particularly carboxylic acids such as acetic acid may be stable to further degradation and such derivatives would not have been detectable by the Viking GCMS instrument due to the pyrolyic degradation process involved in its operation.…”