Viking 1 surveys the “Big Joe” rock at Chryse Planitia. NASA image.

Throughout the 1970s, pop culture references to “life on Mars” were inescapable. The late David Bowie sang about it on his album Hunky Dory, and musician Dexter Wansel even made a sci-fi funk album called Life On Mars, released in 1976 (the year of Viking). Science fiction, of course, had bandied about the possibility of “little green men” on our neighboring planet for decades.

But did Viking really discover life on Mars, in any way, shape, or form? Did the “little green men” exist on a microbial level? This debate continues to this day. Read on, and make your decision:

Point: Viking Didn’t Discover Life On Mars 

There were three biology experiments aboard each of the Viking landers: the pyrolytic release (PR) experiment (principal investigator: Norman Horowitz, Caltech), the gas exchange (GEX) experiment (PI: Vance Omaya, NASA’s Ames Research Center), and Labeled Release (or LR, whose PI was Gilbert Levin of Biospherics Inc.). A fourth experiment, the “Wolf Trap” developed by Dr. Wolf Vishniac of the University of Rochester, was axed due to budget cuts in 1972.

Let’s focus mainly on the results from the LR experiment. The January 1977 issue of National Geographic explained how LR worked: “[A] radioactive nutrient is added to a soil sample in the hope that something will digest it and give off radioactive carbon dioxide. A count is made to determine any background radiation prior to the test. Martian atmosphere and soil are added to the chamber, and the latter is sprayed with tiny drops of nutrient. As with the gases in the PR experiment, these carbon compounds contain radioactive carbon 14. As the soil incubates, a detector looks for a rise in radioactivity, indicating Martian organisms are metabolizing. After a week or two the soil is squirted with a second course of nutrient. The detector continues its watch.”

Viking’s biology package. NASA graphic.

Within weeks of Viking 1’s July 20^th landing, both the GEX and LR experiments showed hopeful results that some kind of abundant microbial life might exist upon the Red Planet. LR especially suggested that a form of “exotic” life had taken root on Mars, as the experiment initially yielded high counts of radioactive carbon dioxide. But this excitement soon faded; Nat Geo reported, “…[B]oth the LR and the GEX leveled off.” The PR experiment, too, initially showed promising results, but later no organic compounds were detected. (For a more detailed recollection of LR findings, please check out this link.)

Tim Mutch, leader of the Viking Imaging Team, wrote in the 1978 NASA publication The Martian Landscape:

Since all three of the experiments designed to test metabolic activity of a microbiota yielded “positive” results, it is tempting to conclude that life exists on Mars. …We now recognize that the biological results can be explained by inorganic surface reactions in the absence of any living forms. Strengthening this conclusion is the absence of organic compounds, documented by a gas chromatograph mass spectrometer (GCMS) experiment.

Counterpoint: Viking May Have Discovered Life On Mars

But Mutch also added:

…Surely this does not prove the absence of life on Mars, only its absence at two localities purposely chosen to be bland and featureless. It remains possible – perhaps unlikely, although statistics in this instance have little validity – that life exists elsewhere on Mars in some special environmental niche – or that it existed millions of years ago.

Remember that Mars’ exploration was still (and is still) very much in its stages of infancy, and as Mutch pointed out, the Viking landers only had surveyed two small areas (Chryse Planitia and Utopia Planitia). More modern robotic explorers, both orbiting and roving Mars, continue to search for signs of past and/or present life, and evidence of water.

In addition, the results of the LR experiment are still subject to debate. Gilbert Levin, LR’s principal investigator, insists the Viking findings require further review to this day. He asserts that microbes in the samples observed may have been killed by the experiment itself. An email from Levin published in the July 2016 issue of Air & Space partially stated:

What actually happened on Mars was that the LR gave positive tests for life. Loss of activity of the soil occurred while the soil sat over two- and three-month periods at about 20 degrees Celsius (68 degrees Fahrenheit), strongly indicating that the organisms in the soil, isolated from their environment, in the dark, and at a high temperature for them, had died. A variety of other test and control runs by the Viking LR all indicated life over chemistry. But because another Viking instrument did not find organic matter in Martian soil, scientists concluded life was not present.

Levin added passionately, “It is time to re-examine the Viking LR data, which I contend did show extant microbial life in the topsoil of Mars.” Who knows; perhaps there’s life – literally, and figuratively – left yet in the Viking program.

Do you think the Vikings found life on Mars? Feel free to discuss your thoughts in the comments.

Sources/Recommended Reading:

1. Gallentine, J. (2015). Infinity Beckoned: Adventuring Through the Inner Solar System, 1969-1989.Lincoln, NE: University of Nebraska Press.

3. Levin, G. (2016, July). Life on Mars: Did We Miss It? [Letter to the editor]. Air & Space/Smithsonian, 31(2), 6.
4. Mutch, T. (1978). The Martian Landscape. Washington, D.C.: NASA Scientific and Technical Information Office. 

Emily Carney is a writer, space enthusiast, and creator of the This Space Available space blog, published since 2010. In January 2019, Emily’s This Space Available blog was incorporated into the National Space Society’s blog. The content of Emily’s blog can be accessed via the This Space Available blog category.

Note: The views expressed in This Space Available are those of the author and should not be considered as representing the positions or views of the National Space Society.