A total of four Martian samples, one surface and one subsurface sample at each of the two Viking landing sites, Chryse Planitia and Utopia Planitia, have been analyzed for organic compounds by a gas chromatograph-mass spectrometer. In none of these experiments could organic material of Martian origin be detected at detection limits generally of the order of parts per billion and for a few substances closer to parts per million. The evolution of water and carbon dioxide, but not of other inorganic gases, was observed upon heating the sample to temperatures of up to 500 C. The absence of organic compounds seems to preclude their production on the planet at rates that exceed the rate of their destruction. It also makes it unlikely that living systems that behave in a manner similar to terrestrial biota exist, at least at the two Viking landing sites.

The search for organic substances and inorganic volatile compounds in the surface of Mars

The Sample Analysis at Mars (SAM) investigation of the Mars Science Laboratory (MSL) addresses the chemical and isotopic composition of the atmosphere and volatiles extracted from solid samples. The SAM investigation is designed to contribute substantially to the mission goal of quantitatively assessing the habitability of Mars as an essential step in the search for past or present life on Mars. SAM is a 40 kg instrument suite located in the interior of MSL’s Curiosity rover. The SAM instruments are a quadrupole mass spectrometer, a tunable laser spectrometer, and a 6-column gas chromatograph all coupled through solid and gas processing systems to provide complementary information on the same samples. The SAM suite is able to measure a suite of light isotopes and to analyze volatiles directly from the atmosphere or thermally released from solid samples. In addition to measurements of simple inorganic compounds and noble gases SAM will conduct a sensitive search for organic compounds with either thermal or chemical extraction from sieved samples delivered by the sample processing system on the Curiosity rover’s robotic arm.

/pdf/the-sample-analysis-at-mars-investigation-and-instrument-3posc554ox.pdf

The Sample Analysis at Mars Investigation and Instrument Suite

The current status of geochemical, mineralogical, petrological interpretation of refined Viking Lander data is reviewed, and inferences that can be drawn from data on the composition of Martian surface materials are presented. The materials are dominantly fine silicate particles admixed with, or including, iron oxide particles. Both major element and trace element abundances in all samples are indicative of mafic source rocks (rather than more highly differentiated salic materials). The surface fines are nearly identical in composition at the two widely separated Lander sites, except for some lithologic diversity at the 100-m scale. This implies that some agency (presumably aeolian processes) has thoroughly homogenized them on a planetary scale. The most plausible model for the mineralogical constitution of the fine-grained surface materials at the two Lander sites is a fine-grained mixture dominated by iron-rich smectites, or their degradation products, with ferric oxides, probably including maghemite and carbonates (such as calcite), but not such less stable phases as magnesite or siderite.

Geochemical and mineralogical interpretation of the Viking inorganic chemical results

GC-MS on the Viking 1976 Mars 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.

/pdf/the-missing-organic-molecules-on-mars-20d9qn7kgq.pdf

The missing organic molecules on Mars.

On the possibility of chemosynthetic ecosystems in subsurface habitats on Mars.

Three different types of biological experiments on samples of martian surface material ("soil") were conducted inside the Viking lander. In the carbon assimilation or pyrolytic release experiment, 14CO2 and 14CO were exposed to soil in the presence of light. A small amount of gas was found to be converted into organic material. Heat treatment of a duplicate sample prevented such conversion. In the gas exchange experiment, soil was first humidified (exposed to water vapor) for 6 sols and then wet with a complex aqueous solution of metabolites. The gas above the soil was monitored by gas chromatography. A substantial amount of O2 was detected in the first chromatogram taken 2.8 hours after humidification. Subsequent analyses revealed that significant increases in CO2 and only small changes in N2 had also occurred. In the labeled release experiment, soil was moistened with a solution containing several 14C-labeled organic compounds. A substantial evolution of radioactive gas was registered but did not occur with a duplicate heat-treated sample. Alternative chemical and biological interpretations are possible for these preliminary data. The experiments are still in process, and these results so far do not allow a decision regarding the existence of life on the plonet Mars.

http://science.sciencemag.org/content/sci/194/4260/99.full.pdf

The Viking Biological Investigation: Preliminary Results

A fixation of atmospheric carbon, presumably into organic form, occurs in Martian surface material under conditions approximating the actual Martian ones. The reaction showed the following characteristics: The amount of carbon fixed is small by terrestrial standards; highest yields were observed in the light, but some dark activity was also detected; and heating the surface material to 90°C for nearly 2 hours had no effect on the reaction, but heating to 175°C for 3 hours reduced it by nearly 90%. New data from Mars do not support an earlier suggestion that the reaction is inhibited by traces of water. There is evidence of considerable heterogeneity among different samples, but different aliquots from the same sample are remarkably uniform in their carbon-fixing capacity. In view of its thermostability it is unlikely that the reaction is biological.

/pdf/viking-on-mars-the-carbon-assimilation-experiments-d0mnyaz924.pdf

Viking on Mars: The carbon assimilation experiments

A synthesis of organic matter from atmospheric carbon monoxide or carbon dioxide, or both, appears to take place in the surface material of Mars at a low rate. The synthesis appears to be thermolabile and to be inhibited by moisture.

http://science.sciencemag.org/content/sci/194/4271/1321.full.pdf

The viking carbon assimilation experiments: interim report.

The carbon-assimilation experiment: The Viking Mars Lander

A method is described for the measurement of 14CO2 assimilation by microorganisms in soils. A determination involves exposing soil to 14CO2, pyrolyzing the exposed soil, trapping the organic pyrolysis products on a column of firebrick coated with CuO, combusting the trapped organics by heating, and measuring the radioactivity in the CO2 produced in the combustion. The detection of significant levels of 14C in the trapped organic fraction appears to be an unambiguous indication of biological activity. The 14CO2 which is adsorbed or exchanged into soils by nonbiological processes does not interfere. The method easily detects the 14CO2 fixed by 102 to 103 algae after light exposure for 3 to 24 hr. Assimilation of 14C is also demonstrable in dark-exposed soils containing 105 to 106 heterotrophic bacteria. Possible applications of the method in the biological exploration of Mars are discussed. Images

George L. Hobby

Papers

The Viking Biological Investigation: Preliminary Results

Viking on Mars: The carbon assimilation experiments

The viking carbon assimilation experiments: interim report.

The carbon-assimilation experiment: The Viking Mars Lander

Measurement of 14CO2 Assimilation in Soils: an Experiment for the Biological Exploration of Mars