In 1976, two Viking landers became the first US spacecraft from Earth to touch down on Mars. They took the first high-resolution images of the planet, surveyed the planet’s geographical features, and analyzed the geological composition of the atmosphere and surface. Perhaps most intriguingly, they also performed experiments that searched for signs of microbial life in Martian soil.
Overall, these life-detection experiments produced surprising and contradictory results. One experiment, the Labeled Release (LR) experiment, showed that the Martian soil tested positive for metabolism—a sign that, on Earth, would almost certainly suggest the presence of life. However, a related experiment found no trace of organic material, suggesting the absence of life. With no organic substances, what could be, or seem to be, metabolizing?
In the forty years since these experiments, scientists have been unable to reconcile the conflicting results, and the general consensus is that the Viking landers found no conclusive evidence of life on Mars. However, a small minority of scientists argues that the Viking results were positive for life on Mars.
One prominent proponent of this view is Gilbert Levin, Experimenter of the Viking LR experiment. At first, Levin thought that the LR results were unclear, and stated merely that the results were consistent with biology. However, in 1997, after many years of further experiments on Earth, along with new discoveries on Mars (which NASA has now declared “habitable”), and the discovery of microorganisms living under conditions on Earth as severe as those on Mars, he and his Viking Co-Experimenter, Dr. Patricia A. Straat, have argued that the Mars results are best explained by living organisms. More.
Their recent Astrobiology article is here. Note: The image above shows the Viking 2 Lander site, showing frost on the ground (NASA).
Rob Sheldon, our favorite physics commentator (and physics colour commentator), has long believed that Viking did find such evidence on Mars. He comments,
When the two Viking spacecraft landed on Mars in 1976, one of their experiments–the Labelled Release Experiment–dug up some dirt, added radioactive sugar broth, and waited for radioactive carbon dioxide to come out, which would be a sign of bacterial life. It worked. They then heated the soil to 300 degrees, cooled and added the sugar broth. Nothing. They did this 8 times, and it worked like a champ.
But the Principle Investigator, Gil Levin, was a civil engineer, and the other “looking for life experiment” with 6 PhD’s on it including Carl Sagan saw nothing. NASA ordered Gil not to claim he had found life, and began to make a series of objections that this could be done by non-life. Each time, Gil would show that the objection didn’t work.
(a)UV light sterilizes the soil (Gil got some dirt from under a rock). (b) super metallo-peroxides in the soil of mars (no peroxides ever seen on mars) (c) perchlorate in the soil (unstable). In the end NASA told the world that Mars was too dry, which from 1976 to 2006 was the standard story. This despite the fact that in 1976 NASA studied snow on mars. Then came the pictures of water flowing down the walls of a crater, and NASA had to backtrack, but still maintained Gil’s data was false, because no other signs of life existed.
Then came the European announcement of methane on mars (an organic molecule), and the 3-yr delayed announcement that Mars Curiosity rover had seen chloromethane (another organic molecule).
Bit by bit, Gil is being vindicated, and the old guard at NASA retiring. Gil turns 88 this year, perhaps he will live long enough to get the Nobel he deserves.
The story is complex and messy, as many such are. It’s a complete mystery to some of us why NASA would keep the find quiet. Why would Carl Sagan matter so much more to the agency than its own future? That remains a more profound puzzle than the evidence.
See also: Ethan Siegel at Forbes: Was life found on Mars 40 years ago?
Rob Sheldon reflects on the hunt for water on Mars
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