Viking Missions 1976

•Gas Exchange Experiment

•Pyrolytic Release Experiment

•Labeled Release Experiment

Also carried a Gas Chromatograph Mass Spectrometer

Gas Exchange

Water and Organic Compounds (19 amino acids and over a dozen growth factors, plus numerous inorganic salts )

Mars soil

The GEX experiment partially submerged a 1-cc sample of soil in a complex mixture of compounds the investigators called "chicken soup". The soil would then be incubated for at least 12 days in a simulated Martian atmosphere of CO2, with helium and krypton added. Gases that might be emitted from organisms consuming the nutrient would then be detected by a gas chromatograph -- this instrument could detect CO2, oxygen (O2), CH4, hydrogen (H2), and nitrogen (N2).

Gas Exchange ResultsThis gas exchange experiment (GX) was based on the assumption that life consisted of heterotrophic micro-organisms requiring the presence of or direct contact with organic substrates and possibly various organic growth factors for their metabolism, and that metabolism would involve the uptake or release of metabolic gases. Therefore, this experiment called for a thick mixture consisting of many organic compounds both in the solution and in the vicinity of the solution and tested for the evolvement of gas from the sample. This experiment was also designed to distinguish between those gases that emerged from non-biological processes from those that emerged form biological processes.

The GC results that every gas except O2 exhibited the same level as the control indicating that no change had occurred. The increase in O2 seemed to indicate that some heterotrophic organism produced it upon contact with the thick nutrient medium.  ProblemsAnother viable reason for the evolution of more O2 was the presence of peroxides and superoxides in the soil. Upon contact with moisture, these compounds could have produced O2 and are therefore not evidence of life. In addition, the rapidity of the gas evolvement seems indicative that the reaction was a chemical one and not a biological one.

Pyrolytic ReleaseMars soil

Of the three Viking biology experiments, this was the only one to attempt to detect signs of life in the complete absence of water and organic nutrients. It was assumed that any organisms on Mars would have developed the ability to assimilate carbon dioxide and carbon monoxide from the atmosphere and convert these, in the absence of water, to organic matter. Therefore, the PR experiment exposed a small sample of Martian soil to quantities of these two gases which had been labeled with radioactive carbon-14 for detection purposes. After 120 hours of incubation under an artificial sun (a xenon arc lamp), the soil chamber was heated to about 625°C to break down (pyrolize) any organic matter and release the volatile organic products for subsequent testing by a radiation counter. Since any organisms present would be expected to carry out metabolic processes during which they would take in carbon-14 from the gas in the chamber, detection of carbon-14 would be a positive result. It would not, however, be conclusively biological, since a first peak of radioactivity might equally be due to purely chemical processes. In order to rule out this possibility, other samples, serving as controls, were sterilized by heating before the carbon source was admitted

PR ResultsThe data show that a fixation of atmospheric carbon occurs in the surface material of Mars under conditions approximating the Martian ones. Although the amount of material was small relative to that which organisms on Earth produced, it was still more significant than the margin of error.   ProblemsDue to the lack of organic material as detected by the GC/MS, the probability of there existing such organic material was slim and made the results hard to believe. In addition, the argument was brought up that any Martian organisms would have been killed under the lamp energy as it provided heat that greatly exceeded its normal climate while the sample tested positive after being heated. Therefore, the material detected must have been the product of the nonbiological reactions.

Another explanation is related the existence of peroxides and superoxides; the CO could have been reduced by H2O2 to produce the organic material that the detector was testing for.

Labeled ReleaseWater and Organic Compounds (formate, glycolate, glycine, D-alanine, L-alanine, D-lactate, and L-lactate)

Mars soil

After moistening, the sample would be allowed to incubate for at least 10 days, and any microorganisms would hopefully consume the nutrient and give off gases containing the carbon-14, which would then be detected. (Terrestrial organisms would give off CO2, carbon monoxide (CO), or methane (CH4).)

Labeled Release Results

Success?? Did we detect life!

1)      There appeared a uniform production of gas issues when the nutrient was placed on Martian soil.2)      The reactant in the Mars soil is completely inhibited by heating the soil to 160CTherefore, one would suggest that this experiment did indeed find life on Mars.

Labeled Release ProblemsMany discrepancies were detected between the experiment and other known facts about Mars and the assumptions the experiment was based on:

•No organic compounds were found in Martian soil analyzed by the Viking Gas Chromatograph Mass Spectrometer (GCMS).

•H2O2 , chemically formed in the upper atmosphere, was thought to descend to the soil and, directly or through forming complexes or compounds, to oxidize the LR substrates to evolve labeled gas. For example, the reaction of formic acid (present in nutrient) and hydrogen peroxide (H2O2) produces water and carbon dioxide which would be detected as radioactive.

•The amplitude and kinetics of the LR response from Mars was thought to be "too much too soon" for any putative Martian biology. •Although not a pre-mission criterion for life, a second injection of LR nutrient onto positive samples failed to re-invigorate the evolution of gas, as generally occurs with terrestrial soils. Instead, some of the gas evolved after the first injection appeared to be reabsorbed into the soil. •UV light from the sun was thought to activate soil particles, which then disrupted the LR nutrient upon contact, releasing labeled gas. Also, UV light's destructive effect was held to account for the reported lack of any organic matter on Mars. •Clays on Mars were proposed to react with the LR nutrient to release labeled gas.

GCMS

The Gas Chromatograph/Mass Spectrometer (GCMS) was designed to measure organic compounds in the martian soil. Organic compounds are present in space (for example, in meteorites), but the GCMS found no trace of them on the surface of Mars. Gilbert Levin believes, however, that the GCMS instrument sent to Mars could easily have missed biologically significant amounts of organic matter in the soil, as it had in a number of tests on Earth.

GCMS ResultsThe most important result for the detection of life came not from the biology experiment, but from the GCMS. It found no trace of any organic compound on the surface of Mars. Organic compounds are known to be present in space (for example, in meteorites), so this result came as a complete surprise. The GCMS was definitely working, however, because it was able to detect traces of the cleaning solvents that had been used to sterilize it prior to launch. The total absence of organic material on the surface made the results of the biology experiments moot, since metabolism involving organic compounds were what those experiments were designed to detect. However, the results from the biology experiments were sufficiently confusing to be worth examining.

ALH84001: The Case for Past Life on Mars?Image below shows possible elongated fossilized Martian cell on the surface of a clay mineral which fills veins or cracks in the meteorite.4 basic issues associated with claim meteorite had indicationsof past life.

1. Polycyclic aromatichydrocarbons (PAHs);2. Carbonates (compounds with both carbon andoxygen present);3. Magnetite (including iron sulfides) found; and4. Microfossils (size scale of above featuresaround 1 micron).Evidence consistent with life, but not proof of it.

1) PAHs

•PAHs are called “Kerogen” if they are the result of biological organic molecules

•PAHs are also the insoluble “leftover” products of non-biological organics.

2) Carbonates

The blebs are about 200 µm in diameter. The orange centers are relatively calcium and iron-rich, and the white rims are nearly pure magnesium carbonate. The black rim contains minute iron oxides and sulfides.

•Age of carbonate formation us disputed (>3.5 Ga or closer to 1.5 Ga??)

•Temperature of formation disputed. Some results show these formed in temps greater than 650° C.

3) MagnetiteThe iron sulfide and magnetite particles interspersed in carbonate which seems to be partially dissolved present an interesting problem. To produce these particles chemically, you need very alkaline conditions -- but you need acidic conditions to dissolve the carbonate. Thus it seems unlikely that the origin of these particles is entirely chemical. Some terrestrial bacteria, known as magnetosomes, are known to produce iron sulfide and magnetite particles, either inside themselves or (for some anaerobic bacteria) outside. The fossil remains of ancient magnetosomes, known as magnetofossils, are very similar in structure and composition to the particles of iron sulfide and magnetite found in the carbonate in ALH84001.

Magnetite and iron sulfide particles have been found in the carbonate globules. There are complicated inorganic explanations for the presence of these mineral grains, but as Kathie Thomas-Keprta explains, "The simplest explanation is that these are products from microorganisms on Mars." The magnetite particles are similar in shape and composition to the magnetite particles (magnetofossils) produced by terrestrial bacteria. However, one puzzling aspect of the magnetite crystals is that whereas certain Earth bacteria use them as a compass to navigate through sediments, the martian magnetic field is only 0.2% that of the Earth's.

Also it has been demonstrated that similar grains can be abiogenically produced.

Shock heating of carbonate??

4) Size

•Metabolism is dependent upon a cell’s S/V ratio

•Small cells with a 0.5 micron diameter have a S/V ratio 100-1000>Euk. Cell

•Bacteria can energetically outcompete Eukaryotes.

•Smaller than 0.5 microns and most cells don’t have more than a few free protons

•Liquid phase chemistry begins to break down smaller than 20nm (1E-9m) there is just no room left for basic cell functions (DNA/RNA, ribosomes, enzymes, etc.)

• A ribosome is 20-25 nm thick

•ALH84001 structures were 10-100nm thick. TOO SMALL