In 1976, two lander “Viking” became the first American spacecraft from Earth that landed on Mars. They made the first high-quality pictures of the planet, studied the geographical features of the planet and analyzed the geological composition of the atmosphere and surface. But most interesting is that they also conducted experiments in search of microbial life in the Martian soil.
Overall, these experiments to detect life has produced unexpected and controversial results. One of the experiments Labeled Release (LR) showed that the Martian soil gives a positive result on metabolic process on Earth that almost certainly would have assumed that the presence of life. But no trace of organic material was detected, and therefore life. How do we get the metabolism, if there was no organic?
Since these experiments forty years have passed, but scientists still can’t agree. The General consensus is that landers “Viking” is not found convincing evidence of life on Mars. However, a small group of scientists claims that the results of the Viking speak in favor of life on Mars.
One of the prominent supporters of this view is Gilbert Levin, who led the experiment LR. At first Levin thought the LR results is unclear and argued that the results are consistent with the biology. But in 1997, after many further experiments on Earth and from the new discoveries on Mars and the detection of the microorganisms living on Earth in conditions similar to the Martian, he and his colleague Patricia Straat claim that the Mars results are best explained by living organisms.
Not long ago, Levin and Straat published a long article in the journal Astrobiology, in which he reviewed the results of the LR experiment of “Viking” in light of recent discoveries on Mars and the recent suggestion that inorganic substances can mimic the observed metabolic processes. They stated that none of the proposed processes non-living matter does not explain the results of the Viking, and Martian microbes are still the best explanation of the results.
How was organized the Labeled Release experiment
In the experiment, the LR both spacecraft “Viking-1 and Viking-2” has collected samples of Martian soil, introduce them to a drop of dilute solution of nutrients, and then watched the air above the soil, expecting to see signs of metabolic by-products. Because the nutrients were tagged with radioactive carbon 14 if organisms in the soil have metabolisable nutrients, they had to produce radioactive byproducts like radioactive carbon dioxide or methane.
Before spacecraft launch, scientists tested the experimental Protocol, a variety of terrestrial soils in inhospitable locations, from Death Valley to Antarctica. In each case, the experiments gave a positive result, have found life. Then, as a control, the researchers heated the sample to 160 degrees Celsius to kill all forms of life, and again checked. In each case, the experiments gave a negative result now. To confirm that the experimental procedure does not give false-positive results, scientists tested it in a sterile soil. Lunar soil and volcanic soil from the island of Surtsey, as expected, were negative.
In addition, it seemed that the source of metabolism was relatively fragile, since metabolic activity was significantly reduced by heating the sample to 50 ° C and was completely absent in the soil storage in the dark for two months at a temperature of 10 degrees. Levin and Straat believe that these results confidently say that in the Martian soil was life.
Non-biological candidates
Since then, as experiments were made, scientists were in search of other types of non-biological chemicals that could produce identical results.
In his new work of Levin and Straat consider some of these suggestions. One of the possible candidates is a formate, formic acid is a component found on Earth in natural conditions. In 2003, the experiment on the type of LR showed that the formate in the sample soils from the Atacama desert in South America gave a positive result, despite the fact that the soil there contains no microorganisms. However, this study was not conducted in a sterile control, and the concentration of formate in the Atacama desert probably much higher than on Mars.
Another potential candidate is the perchlorate or one of its decomposition products. In 2009, the mission on Mars Phoenix found perchlorates in the Martian soil. Although perchlorates could give a positive result, because the produce gas in the interaction with some amino acids, they are not destroyed at a temperature of 160 degrees and will give positive results even after the sterile control.
Research from 2013 suggests that cosmic rays and solar radiation can cause perchlorates decompose to sodium hypochlorite, which should give a positive result and, unlike the perchlorates, is destroyed by heating to 160 degrees. For these reasons, hypochlorite is the best candidate to explain the LR results.
However, Levin and Straat write that the hypochlorite had not experienced at a temperature of 50 degrees (at which the activity of the Martian soil was significantly reduced) or after prolonged storage in the dark (which produced a negative result for the Martian samples). Thus, at the moment none of the non-biological agent was not satisfied with all the results of the LR.
Biological candidates
Mars
Today, scientists know more about Mars than 40 years ago. One of the biggest discoveries happened in 2014, when the lab Rover “Curiosity” was first discovered organic molecules on Mars.
Over the past two years laboratory SAM found methane, chlorinated hydrocarbons and other organic molecules. Scientists suspect that the organic material could have formed on Mars or to be listed there through meteorites.
The discovery of organic matter on Mars raises the question of why an experiment of the Viking found no organic matter in 1976. As Levin explains, there are several possible reasons for the negative results of the Viking.
“We have long pointed out the problem with gas chromatography-mass spectrometer Viking (chromas core facility), says Levin. “Even his experimenter Dr. Klaus Beeman often said that the chromas core facility was not an experiment to detect life. He needed at least one million microbial cells in order to find any organic matter. In addition, the instrument often failed during tests on the Ground. Later it was stated that the perchlorate in the soil have destroyed organic matter. Nevertheless, I am wary of this statement because there is no evidence of perchlorate in the places of the landing of the Vikings.
In light of recent findings, Levin and Straat think it’s important to review the results of the LR as having a biological origin. Other scientists supporting this view, suggested that Martian life might take the form of methanogens (microorganisms that produce methane as a by-product), halophila (which can withstand high salt concentrations, the moderate radiation and low oxygen content) or “cryptobiotic” organisms that remain dormant until activated, e.g., by using nutrient solution, which was in the LR experiment.
Problems publishing
To publish a work about life on Mars is, of course, is not what to publish some typical research. For many years, the Levine study included low-calorie sweeteners, pharmaceutical drugs, safe pesticides, and wastewater treatment processes, among other things. It took about 20 years to Levin and Straat published a paper on the topic of revision of results of the LR experiment of “Viking”.
“Since I first came to the conclusion that LR found life (in 1997), major journals refused to accept our publications,” said Levin Phys.org. “I and my sexperimentation, Dr. Patricia Ann Straat, published mainly in the section of astrobiology in SPIE Proceedings after showing work at the annual conventions of SPIE. At the meeting of the Canadian space Agency, I met Dr. sherry Cady, editor of Astrobiology. She invited me to submit a paper for peer review. I did, and it immediately rejected. Together with Pat we decided to prepare a work that will withstand scientific criticism. It took years of countless revisions and additions revisions in response to the myriad reviewers, but we stubbornly went to his goal. We think that the publication has been so thoroughly refined that it is impossible to find fault”.
What’s next?
Levin and Straat think that the assumption of the presence of life on Mars could seriously affect future research.
“It seems reasonable that the scientific community supports biology as a suitable explanation of the experimental results LR”, the scientists write. “It seems inevitable that astronauts will one day explore Mars. For the sake of their health and safety, biology is considered as the main possible explanation of the results of the LR”.
Levin and Straat suggest that carefully designed experiments can help to answer the question about the existence of life on Mars. In particular, the experiments, the LR-type can answer questions of biological or chemical origin of metabolism. It is also important to continue the search for organic molecules like amino acids, simple hydrocarbons, lipids, proteins and DNA. Further experiments may allow to study the Martian soil under the microscope.
And yet, all future experiments will have an inevitable disadvantage: possible contamination left by previous descent devices. In this respect, the “Viking” was a unique opportunity to study a pristine Mars.
