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P A Straat

Publications and source records attributed to P A Straat.

6 recordsLinked to original sources
PubMed1979

Completion of the Viking labeled release experiment on Mars.

The final Labeled Release (LR) cycle on each Viking lander tested a surface sample that had been stored for several months at approximately 10 degrees C prior to the onset of the active sequence. At each lander site, activity was strongly diminished. This thermal sensitivity of the active agent on the surface of Mars is consistent with a biological explanation of the LR experiment. At the end of one of these cycles, the incubation mixture was heated to 50 degrees C to release any radioactive gas trapped in the sample matrix. The results suggest that more than one carbon substrate is involved in the LR reaction on Mars. The thermal data from the stored samples, coupled with data from previous cycles, have formed the basis for evaluation of the thermal decomposition of the Mars active agent. The slope of the resulting Arrhenius plot has been used to test the fit of other flight data and to calculate the activation energy for thermal decomposition of the Mars agent. The results and their interpretation still leave unresolved the question of whether the Mars LR data were generated by biological or chemical activity.

Carbon Radioisotopes↗
PubMed1979

Laboratory simulations of the Viking labeled release experiment: kinetics following second nutrient injection and the nature of the gaseous end product.

Injection of 14C-labeled nutrient onto Mars soil produced an evolution of 14C gas in the Viking Labeled Release (LR) experiment. However, a second injection of nutrient seven days later was followed by an abrupt diminution of the amount of radioactive gas in the test cell. Simulation experiments performed in the LR Test Standards Module (TSM) have yielded a plausible explanation for this diminution. Radioactive carbon gases were injected into the TSM test cell in the presence and absence of two Mars analog soils. After equilibration, water was injected and its effect observed. The results indicate that the flight data following second nutrient injection can be explained on a physico-chemical basis involving a carbon dioxide/water/soil equilibrium in the test cell. The results also suggest that the gaseous end product of the Labeled Release reaction on Mars is more likely carbon dioxide than carbon monoxide.

Carbon Radioisotopes↗
PubMed1977

Life on Mars? The Viking labeled release experiment.

Viking radiorespirometry ("Labeled Release" [LR]) experiments conducted on surface material obtained at two sites on Mars have produced results which on Earth would clearly establish the presence of microbial activity in the soil. However, two factors on Mars keep the question open. First, the intense UV flux striking Mars has given rise to several theories postulating the production of highly oxidative compounds. Such compounds might be responsible for the observed results. Second, the molecular analysis experiment has not found organic matter in the Mars surface material, and therefore, does not support the presence of roganisms. However, sensitivity limitations of the organic analysis instrument could permit as many as one million terrestrial type bacteria to go undetected. Terrestrial experiments with UV irradiation of Mars Analog Soil did not produce Mars type LR results. Gamma irradiation of silica gel did produce positive results, but not mimicking those on Mars. The life question remains open.

Carbon↗
PubMed1977

Evidence for incorporation of thymidine into deoxyribonucleic acid in airborne bacterial cells.

As part of an effort to discover whether bacteria might propagate within airborne particles, we studied the incorporation of thymidine into the trichloroacetic acid-insoluble fraction of airborne cells of Serratia marcescens to seek evidence of the possible formation of new DNA. Two aerosols, one of S. marcescens and another of [3H]thymidine ([3H]dT) suspended in growth medium were caused to aggregate in air just prior to directing the aerosols into rotating-drum aerosol storage chambers. The age of the S. marcescens culture and other conditions for maximizing ([3H]dT) uptake were selected on the basis of prior in vitro trials. With 10-h cultures and addition of 2-deoxyadenosine to the [3H]dT, we showed that [3H]dT is incorporated into the trichloroacetic acid-insoluble fraction of cells recovered 6 h after aerosols were stored under the conditions of high humidity and 30 degrees C. Tests conducted in the same manner with Formalin-killed S. marcescens ruled out the possibility of adsorptive carry-over of [3H]dT. As much as 20 times more activity was found in the trichloroacetic acid-insoluble fraction of live cells than of dead cells.

Aerosols↗