Microbiology Experiments

Microbiology Experiments

Each Viking lander was equipped with a sample arm to acquire material from the surface and then slowly withdraw it into the innards of the spacecraft, transporting the particles on little hoppers like an electric train to five different experiments: one on the inorganic chemistry of the soil, another to look for organic molecules in the sand and dust, and three to look for microbial life. When the scientists look for life on a planet, they are making certain assumptions. They try, as well as they can, not to assume that life elsewhere will be just like life here. But there are limits to what they can do. We know in detail only about life here, on Earth. While the Viking biology experiments are a pioneering first effort, they hardly represent a definitive search for life on Mars. The results have been tantalizing, annoying, provocative, stimulating, and, at least until recently, substantially inconclusive.

Each of the three microbiology experiments asked a different kind of question, but in all cases a question about Martian metabolism. If there are microorganisms in the Martian soil, they must take in food and give off waste gases; or they must take in gases from the atmosphere and, perhaps with the aid of sunlight, convert them into useful materials. So we bring food to Mars and hope that the Martians, if there are any, will find it tasty. Then we see if any interesting new gases come out of the soil. Or we provide our own radioactively labeled gases and see if they are converted into organic matter, in which case small Martians are inferred.

Criteria of experimental success may be inadequate, but there is always a way to find a new criterion. Image : Pink Texture  by Elena

By criteria established before launch, two of the three Viking microbiology experiments seem to have yielded positive results. First, when Martian soil was mixed with a sterile organic soup from Earth, something in the soil chemically broke down the soup – almost as if there were respiring microbes metabolizing a food package from Earth. Second, when gases from Earth were introduced into the Martian soil sample, the gases became chemically combined with the soil – almost as if there were photosynthesizing microbes, generating organic matter from atmospheric gases. Positive results in Martian microbiology were achieved in seven different samplings in two locales on Mars separated by 5,000 kilometers.

But the situation is complex, and the criteria of experimental success may have been inadequate. Enormous efforts were made to build the Viking microbiology experiments and test them with a variety of microbes.