Lecture 8 Flashcards
How did the microbiological experiments on the two Viking landers work?
they searched for metabolic reactions in the samples
Which Viking experiment delivered results that were exactly as expected for the presence of living microbes in the soil sample?
The Label Release (LR) experiment
Which measurement performed by Viking, which was not part of the microbiological experiments, convinced most scientists in the late 1970s that Viking had not found life on Mars?
the absence of any detectable amount of organic compounds in the soil samples
If life ever emerged on Mars, what is the most likely place for it to exist today?
In the subsurface where it is protected against the harsh UV radiation
What did Viking carry?
a Gas Chromatograph Mass Spectrometer (GCMS) that could measure the composition and abundance of organic (carbon containing) compounds in the Martian soil.
The Labeled Release (LR) Experiment
The LR experiment moistened a 0.5-cc sample of soil with 1 cc of a nutrient consisting of distilled water and organic compounds. The organic compounds had been labeled with radioactive carbon-14.
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.
The Gas Exchange Experiment (GEX)
The GEX experiment partially submerged a 1-cc sample of soil in a complex mixture of compounds
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
The Pyrolytic Release Experiment (PR)
In this experiment, a 0.25-cc soil sample was incubated in a simulated Martian atmosphere of CO2and CO labeled with carbon-14
After 5 days, the atmosphere was flushed and the sample heated to 625 degrees C (1157F) to break down, or pyrolyze, any organic material, and the resulting gases were passed through a carbon-14 detector to see if any organisms had ingested the labeled atmosphere.
Viking’s Biological Experiments Results (Earth)
GEX : failed
LR : failed
PR : failed
Viking’s Biological Experiments Results (Mars)
GEX : oxygen emitted
LR : failed
PR : carbon emitted
Martian microfossils?
The case of signs of life in AHL 84001 is heavily contested and no longer considered as compelling enough!
Methane on Mars?
There has been detection of Methane on Mars and it is seasonal (Summer and Autumn)
How does methane release on Mars?
Subsurface water, carbon dioxide, and the planet’s internal heat combine to release methane that had been trapped in the ice.
