The Case for Extant Life on Mars and Its Possible Detection by the Viking Labeled Release Experiment

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. Astrobiology 16, 798-810.

The potential science and engineering value of samples delivered to Earth by Mars sample return

“…Two Viking landers carried out a series of biological experiments, including the labeled release experiment, which was designed to detect metabolic activity. In this experiment, simple 14 C‐labeled substrates, water, and Martian soil were combined and monitored for the evolution of radioactive gases (Levin and Stratt ) as evidence that microorganisms had metabolized the substrate. Viking instruments detected 14 C labeled gas; however, it is widely accepted that those data were due to oxidizing agents in the regolith rather than microbial activity (Lasne et al.…”

Prerequisites to Human Activity on Mars: Scientific and Ethical Aspects

“…The most interesting results came from the Labelled Release Experiment (LR) which showed reactivity similar to that expected from microorganisms. 8 However, it is generally held that the reactions in the LR instrument and the other results from Viking can be explained by the chemistry of perchlorate now known to be on Mars. 9 However, the conclusion that the surface of Mars is devoid of life is tentative.…”

LDM (Life Detection Microscope): In Situ Imaging of Living Cells on Surface of Mars

“…Past trial of direct detection of life on Mars by the 1970's Viking mission resulted in a negative conclusion, 1) whereas numbers of circumstances provided by recent exploration missions in the last decade indicated that there are good reasons to perform another life detection program. 2) Recent explorations have provided evidence for 1) the existence of large bodies of ancient surface water (paleo-ocean/lakes), [10][11][12] 2) a limited but certain period of wet and warm paleo-climate probably suitable for life, 13) and 3) the existence of strong magnetic field that could have protected the atmosphere from being quickly eroded away in the earliest stage of the Mars history (Noachian: 4.5 Ga to ~4.2 Ga). 14) These would lead one to argue that the surface environment (e.g., hydrologic activity) in ancient Mars was not very different from that for Earth.…”

“…1) Since then, numbers of new finding provided by recent Mars exploration missions indicate that there are good reasons to perform another life detection program. 2) The sensitivity of the GC-MS (mass spectrometer) onboard the Viking lander was not high enough to detect <10 6 microbial cells in 1 gram soil. 3,4) Here we propose Life Detection Microscope (LDM) that has the potential sensitivity much higher than the instrument onboard Viking.…”