Vignette B The Viking Landers

Ask any newspaper reporter. There are some stories that just never die. They take on a life of their own, seemingly forever hovering in the background, always ready to be dressed down for one more airing. The saga of the biological experiments carried aboard the Viking Landers that touched down on the surface of Mars in 1976 is one such apparently never-ending story. What exactly did the experiments reveal? Was Martian life actually identified? Is there an official NASA cover-up of the results? The questions are endless, and there is much confusion about the results of the biological survey. Let us, therefore, give the story of the Viking Landers one more brief reading.

Viking 1 (Figure 4.16) touched down in the Golden Field region (Chyse Planitia) of Mars on 20 July 1976. About a month and a half later, on 3 September, the Viking 2 Lander touched down in Mars' Nowhere Plain (Utopia Planitia). Each Lander carried an identical biological experiment package consisting of four subcomponents. The first experiment was designed to identify the various chemical elements and molecular species present in the sampled Martian soil. The second experiment was designed to detect any gases that might be given off by an incubated soil sample.

To set the latter experiment in motion, a liquid complex of both organic and inorganic nutrients were added to the soil samples and a gas chromatograph was used to measure the concentrations of oxygen, carbon dioxide, nitrogen, hydrogen, and methane.

A third experiment, the Labeled Release test, produced the most controversial results and is the focus of much debate. In this

Figure 4.16. Model of the Viking 1 Lander. A robotic arm (seen in the center of the image, pointing downward toward the left) was used to capture and place soil samples into the various biological experiment bays. Image courtesy of NASA.

test, a sample of Martian soil was fed a drop of nutrient solution that had been specially tagged with radioactive carbon-14 (14C) and sulfur-35 (35S). The experiment consisted of measuring the amount of radioactive gas in the sample chamber. The key point is that any increase in the radioactivity of the gas in the chamber would indicate that one or more of the nutrients had been metabolized by Martian microorganisms.

Three variants of this test were performed. In the first experiment the soil sample was tested without prior heating; the second and third tests were made on soil samples that were heated to 50°C and 160°C, respectively. The point behind these variant experiments was that by heating the soil some (at the 50°C temperature) and then all (at the 160°C temperature) of the microbes should be killed off, and this would be reflected in the radioactivity levels measured in the experimental chamber. In the latter case, for example, there should be no radioactivity detected at all. The final experiment was again a tagged radioactive carbon-14 experiment. In this case, however, a Martian soil sample was exposed to tagged carbon monoxide (CO) and carbon dioxide (CO2) brought from the Earth. The aim of this experiment was to see if any of the CO or CO2 would become incorporated into the soil as biomass.

Well, to cut a long (and complex) story short, the only experiment that produced consistent results that satisfied the control criteria for the detection of Martian microbes was the Labeled Release experiment (number three in our list). The other three experiments either gave null results (i.e., no organic molecules were detected with the first experiment at either Lander site) or inconsistent results. So, the NASA researchers were left with a confusion of findings, some consistent with the detection of life, others not. The conclusions drawn, therefore, correctly aired on the side of caution, and it was announced that no Martian microbial life had been found at either of the Viking Lander sites. The positive results, from both the Landers, in the Labeled Release experiments were interpreted as being due to some unexpected (and still unexplained) nonbiotic chemical reaction.

Given the spread of results between the various experiments, it is hardly surprising that there were dissenters who rejected the NASA panel's conclusion that no Martian life had been detected. Sir Fred Hoyle and Chandra Wickramasinghe, whose panspermia ideas we described at the end of Chapter 3, have, for example, openly rejected the NASA panel findings. They argue that the experimental results can be made consistent if the Martian microbes have a thermophilic (heat-loving) physiology and a highly efficient free-organic molecule-scavenging system. Other researchers have focused on conducting laboratory experiments to show how the Viking Lander results are consistent with the presence of Martian microbial life.

Gilbert Levin, a Viking scientist team member who helped design the Labeled Release experiment, has long been a strong advocate for the positive detection of life on Mars, and at a recent seminar presented at the Carnegie Institution in May of 2007 he argued that researchers ''should re-focus the analysis of the Viking mission results to working out the broadest physiological details required by the organisms in Marciana.''6 By using the term Marciana, Levin is, in fact, arguing that a new biosphere has been discovered, that is, that of Mars, and he is also adopting the nomenclature recently proposed by Argentinean neurobiologist Mario Crocco (Hospital Borda, Buenos Aires). Indeed, following a reappraisal of the Viking data,7 Crocco has argued that by any reasonable standards, life on Mars has most definitely been detected, and accordingly he has proposed the new domain Jakobia (named in honor of German-born neurobiologist Christfried Jakob (1866-1956) who

Table 4.4. The division of organic life within the Solar System as suggested by Mario Crocco.

Biosphere

Domain(s)

Genera/species

Terrestria

Bacteria, Archaea, and Eukaria (see

Many millions known

Figure 3.12)

Marciana

Jakobia

Gillevinia straata

worked for much of his life in Buenos Aires, Argentina) to complement the three domains (Bacteria, Archaea, and Eukaria; see Figure 3.12 and Table 4.4) that codify all life on Earth. Crocco has also proposed the name Gillevinia straata (in honor of Gilbert Levin and co-experimenter Patricia Straat) for the microorganisms purportedly detected by the Viking Lander Labeled Release experiment.

Adding a twist to the Viking Lander story, researchers Joop Houtkooper (Justus-Liebig University of Giessen, Germany) and Dirk Schulz-Makuch (Washington State University, US) have recently suggested that Martian extremophiles might have evolved to use a hydrogen peroxide/water (H2O2/H2O) mixture instead of salty water as their intercellular fluid.8 The advantage of this mixture is that it only freezes at temperatures well below —50°C, which is a definite advantage on the freeze-dried surface of Mars. Hout-kooper and Schulz-Makuch also suggest that the hydrogen peroxide/water mixture can explain the otherwise anomalous results recorded by the Viking biology experiments.

So the debate continues. Needless to say, and in spite of Croc-co's recent positive reevaluation of the Viking data, not everyone is convinced. Indeed, it will probably require new and overwhelming results before the majority of researchers are convinced of the presence of contemporary life on Mars. One of the key experiments that will be carried aboard the recently launched Phoenix mission (see Figure 3.3), which touched down on Mars in mid-2008, is the thermal and evolved gas analyzer (TEGA), which is a modern-day, more sensitive version of the first experiment carried aboard the Viking Landers. This new instrument will provide data concerning the detailed chemical makeup of the Martian soil, and it will also test for the presence of organic molecules within the soil at levels as small as ten parts per billion.

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