The Case for Extant Life on Mars and Its Possible Detection by the Viking Labeled Release Experiment
To cite this article:
Levin Gilbert V. and Straat Patricia Ann. Astrobiology. October 2016, 16(10): 798-810. doi:10.1089/ast.2015.1464.
Published in Volume: 16 Issue 10: October 1, 2016
Online Ahead of Print: September 14, 2016
Author information
Gilbert V. Levin1 and Patricia Ann Straat2
1Arizona State University, Tempe, Arizona.
2National Institutes of Health, Bethesda, Maryland (Retired).
Both authors were affiliated with Biospherics Incorporated, Rockville, Maryland, throughout the development and execution of the Viking Labeled Release experiment.
Address correspondence to:
Gilbert V. Levin
10709 Blossom Dr.
Goodyear, AZ 85338
E-mail: gilvlevin@gmail.com
Submitted 31 December 2015 Accepted 16 June 2016
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ABSTRACT
The 1976 Viking Labeled Release (LR) experiment was positive for extant microbial life on the surface of Mars. Experiments on both Viking landers, 4000 miles apart, yielded similar, repeatable, positive responses. While the authors eventually concluded that the experiment detected martian life, this was and remains a highly controversial conclusion. Many believe that the martian environment is inimical to life and the LR responses were nonbiological, attributed to an as-yet-unidentified oxidant (or oxidants) in the martian soil. Unfortunately, no further metabolic experiments have been conducted on Mars. Instead, follow-on missions have sought to define the martian environment, mostly searching for signs of water. These missions have collected considerable data regarding Mars as a habitat, both past and present. The purpose of this article is to consider recent findings about martian water, methane, and organics that impact the case for extant life on Mars. Further, the biological explanation of the LR and recent nonbiological hypotheses are evaluated. It is concluded that extant life is a strong possibility, that abiotic interpretations of the LR data are not conclusive, and that, even setting our conclusion aside, biology should still be considered as an explanation for the LR experiment. Because of possible contamination of Mars by terrestrial microbes after Viking, we note that the LR data are the only data we will ever have on biologically pristine martian samples.
Key Words: Extant life on Mars—Viking Labeled Release experiment—Astrobiology—Extraterrestrial life—Mars.
Key Words: Extant life on Mars—Viking Labeled Release experiment—Astrobiology—Extraterrestrial life—Mars.
Astrobiology 16, 798–810.
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