Vikings  1 and 2 found life on Mars, but some academicians are difficult to convince

Article from National Geographic, author Ker Than

"A fresh look at NASA data suggests that a robotic mission uncovered microbial life on Mars—more than 30 years ago. In 1976 NASA sent two space probes, Vikings 1 and 2, to Mars to determine whether life exists on the red planet. The probes carried three experiments specially designed for the task, one of which was called the Labeled Release (LR) apparatus. The LR experiment worked by scooping up a bit of Martian soil and mixing it with a drop of water that contained nutrients and radioactive carbon atoms. The idea was that if the soil contained microbes, the life-forms would metabolize the nutrients and release either radioactive carbon dioxide or methane gas, which could be measured by a radiation detector on the probe.  

A number of control experiments were also performed, including heating some Mars soil samples to different temperatures and isolating other samples in the dark for months—conditions that would kill microbes that are photosynthetic or that rely on photosynthetic organisms for survival. These control samples were also mixed with the nutrient solution. To the delight of many biologists at the time, the LR experiment came out positive for life, and the control experiments came out negative. "The minute the nutrients were mixed with the soil sample, you got something like 10,000 counts" of radioactive molecules—a huge spike from the 50 or 60 counts that constituted the natural background radiation on Mars, said study team member Joseph Miller, a neurobiologist at the University of Southern California and a former NASA space shuttle project director. Unfortunately, the LR experiment results were not backed up by the probes' other two experiments, both of which came out negative for life, so the space agency dismissed the possibility. Now, after running Viking's LR data through a mathematical test designed to separate biological signals from nonbiological signals, Miller's team believes that the LR experiments did indeed find signs of microbial life in Martian soil. "It's very possible that if you have microbes, they're living a couple of inches beneath the soil, close to water ice," he said. For the study, Miller and mathematician Giorgio Bianciardi, of Italy's  University of Siena, used a technique called cluster analysis, which groups together similar-looking data sets. "We just plugged all the [Viking experimental and control] data in and said, Let the cluster analysis sort it," Miller said. "What happened was, we found two clusters: One cluster constituted the two active experiments on Viking and the other cluster was the five control experiments." To bolster their case, the team also compared the Viking data to measurements collected from confirmed biological sources on Earth—for example, temperature readings from a rat—and from purely physical, nonbiological sources. "It turned out that all the biological experiments from Earth sorted with the active experiments from Viking, and all the nonbiological data series sorted with the control experiments," Miller said. "It was an extremely clear-cut phenomenon."

http://news.nationalgeographic.com/news/2012/04/120413-nasa-viking-program-mars-life-space-science/
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