Home Table of Contents What's New Image Index Copyright ScienceViews Search

On Mars: Exploration of the Red Planet. 1958-1978
 
 
LIFE OR NO LIFE?
 
 
 
[409] Soffen's disappointment was shared by others on the biology team. For years, they had discussed the scientific possibilities of discovering life or the prerequisites for life on the Red Planet, and Soffen recalled the long debates with his colleagues on the subject. Some, like Wolf Vishniac, had argued that a negative result-that is, no life-was as important scientifically as the discovery of life. But such a discovery had not proved very exciting. Before the Viking landings, Soffen had been very careful in all his public statements to say that they would likely find nothing on the planet, but personally he had wanted to find life.
 
While Soffen believed that it was possible for life to have developed on Mars, he also thought it likely that the biology instrument, for a host of reasons, had not been designed properly to detect it. However, he was also very confident that if organic compounds had been present, the GCMS would have detected them. For that reason, he had fought for the instrument throughout the evolution of the Viking project. Soffen could have accepted a negative biology result, if there had been a positive measurement of organic compounds. But positive biology results could not be interpreted as indicating the existence of life in the absence of organics. Others have argued that perhaps Viking landed at the wrong places on the planet. Nearer the poles where there was a higher moisture content in the soil and atmosphere, life might exist. Or perhaps, as suggested by Carl Sagan and Joshua Lederberg, there are Martian microenvironments where in small oasislike areas life has evolved and survived. Soffen thought this unlikely since the homogenizing effects of wind and dust storms would have likely distributed any organic material all over the planet. He reluctantly concluded that life on Mars was unlikely. 69
 
The apparent absence of life on the Red Planet had a far-reaching philosophical and emotional impact on members of the biology team. The team had never been a cohesive group of investigators, and the results of the biology and GCMS experiments served to accentuate their differences. Norman Horowitz came to the opinion that there is no life elsewhere in the solar system. While he did not rule out the possibility in theoretical terms, he believes, practically speaking. that scientists will never be able to prove the existence of life on another planet. Horowitz noted:
 
[410] There are doubtless some who, unwilling to accept the notion of a lifeless Mars, will maintain that the interpretation I have given is unproved. They are right. It is impossible to prove that any of the reactions detected by the Viking instruments were not biological in origin. It is equally impossible to prove from any result of the Viking instruments that the rocks seen at the landing sites are not living organisms that happen to look like rocks. . . . .The field is open to every fantasy. Centuries of human experience warn us, however, that such an approach is not the way to discover the truth. 70
 
One man who is still not convinced is Gil Levin. He cannot rule out the biological interpretation of the Viking biology experiment results. "The accretion of evidence has been more compatible with biology than with chemistry. Each new test result has made it more difficult to come up with a chemical explanation, but each new result has continued to allow for biology," Furthermore, Levin believed that all of the life-seeking tests showed reactions that "if we had them on earth, we would unhesitatingly have described as biological." 71 But other members of the biology team were not as easily convinced.
 
Vance Oyama, who fathered the gas-exchange experiment, publicly stated in early 1977 that "there was no need to invoke biological processes" to explain the results obtained from the experiments. While far from being accepted by all his colleagues, Oyama's opinion is one more example of the extent to which differing explanations can be made to account for the puzzling data acquired by the biology experiments. Should Oyama's explanation turn out to be valid, it would affect more than the biology experiments. It would also help explain the nature of the magnetic particles that adhered to the magnets on the sampler head, the interactions between the atmosphere and the surface, and the early evolution of the planet. His theory begins with a simple photochemical effect in the atmosphere: the intense solar ultraviolet radiation breaks down atmospheric carbon dioxide (CO2) into activated carbon monoxide (CO) and single atoms of oxygen (O). As the ultraviolet radiation continues to bombard the atmosphere, some of the carbon monoxide is further reduced to its constituents, carbon and oxygen. Some of this single-atom carbon combines with carbon monoxide to produce carbene (C2O). The carbene in turn combines with carbon monoxide to form the first key element in Oyama's theory, carbon suboxide (C3O2). Oyama postulated that the carbon suboxide molecules were united to form a carbon suboxide polymer. Intriguingly, the resulting polymer has a reddish cast.
 
Oyama's theory is consistent with data from the three biology experiments. Looking first at the pyrolytic-release experiment, Oyama noted that the carbon-14 isotope was an important factor in explaining the results observed from this instrument. The decay of the carbon- 14 isotope into nitrogen- 14 released a beta particle. The resulting energy was more than sufficient to fracture carbon-carbon, carbon-hydrogen, and carbon-oxygen [411] bonds. The breakdown would activate the red carbon suboxide polymer, allowing it to incorporate the available carbon monoxide. Heating that same polymer to about 625°C during pyrolysis would produce about four percent of the original carbon suboxide, with a carbon- 14 label. This single carbon suboxide molecule (monomer) would tend to stick to the pyrolytic release experiment's organic vapor trap and with subsequent heating would be released as the critical "second peak" the specialists observed in the experiment's data. Taking this another step, Oyama reported that the presence of water vapor when the sample was exposed to the labeled atmosphere would lower the second peak. 72
 
In Oyama's laboratory gas-exchange tests, the prominent release of oxygen was also less the second time. But as Oyama said, the reason was very different. In the Martian atmosphere, the same photochemical breakdown (photodissociation) that led to the formation of carbon suboxide also led to the creation of activated oxygen atoms, albeit by a different route. When these oxygen atoms struck alkaline earths (for example, oxides of magnesium or calcium), they united to form superoxides that would release oxygen upon exposure to water vapor. Oyama argued that less oxygen was released at the Utopia site than at the Chryse site because the greater amount of water vapor in the more northerly landing site had previously freed some of the oxygen in the superoxides near the surface.
 
In describing the reasons for the results observed in the labeled-release experiment, Oyama presented the following scenario. Hydrogen peroxide formed photochemically in the atmosphere reacted with a catalyst on the soil-grain surfaces to release oxygen, which diffused into the grains, reacting with the alkaline earths and metals to form other superoxides. Atmospheric water vapor could readily convert the superoxides to peroxides, which in turn could combine with water in the nutrient to form hydrogen peroxide, H2O2, which would oxidize the labeled components of the nutrients to release the labeled CO2. John Oro of the molecular analysis team also suggested very early that the results from the gas-exchange tests and labeled release were due to the presence of peroxidelike materials in the surface of the planet. To explain the process, Oyama used the example of chemical reactions in human beings. When hydrogen peroxide (H2O2), a commonly used disinfectant is applied to a wound, it bubbles. This, Oyama said, is caused by the presence of iron in the enzyme catalyst. When the iron combines catalytically with the hydrogen peroxide, it releases bubbles of oxygen. Oyama believed that a similar process is at work on the surface of Mars.
 
Having searched for possible Martian catalysts, Oyama concluded that there is one likely candidate-a form of iron oxide known as gamma Fe2O3, or maghemite. On Earth, this is usually found only around the edges of hydrothermal or magnetic activity, where the temperatures range between 300° to 400°C. The abundance of water on Earth has converted much of the maghemite into a noncatalytic form, but on Mars this material has [412] survived virtually unaltered. Oyama thinks that it probably was produced either by an episode of volcanic heating or by heating that accompanied a period of meteoritic impacts. While this probably occurred early in the planet's history, he believes that it took place after the large quantities of water others suspect once existed had disappeared. Otherwise, the maghemite would have been rendered non-catalytic, just as it has been here on Earth. This explanation is a complex one, but as Jonathan Eberhart, writing for Science News , has reported: "Oyama's theory will have to stand the test of time, additional data and competing theories. But it does show that looking for life on other worlds has the potential for making valuable contributions in other fields as well." 73
 
That there is still disagreement over the Viking biology results has caused some hard feelings among members of the biology team. Summarizing the situation after the results were in, Jerry Soffen said that he would expect the following responses if Horowitz, Oyama, Levin, and he were asked to participate in another Mars-bound biology investigation: Horowitz would not want to participate; Viking had satisfied his curiosity on the subject. Oyama would probably take part, but he would not expect to discover life. Gil Levin still believed that life may be discovered on the Red Planet. He had started with the goal of proving that there was life on Mars, and for him it was an engineering problem: How do you prove that there is life on Mars? To some of his colleagues, this was the attitude of an engineer, not the professional skepticism of the scientist. Examining his own position, Soffen said that he had never been certain about the possible existence of life on Mars, but he had hoped that it might be found. At no time, however, had he committed himself to proving that it actually existed. Horowitz, on the other band, had always had such strong doubts about finding life that on several occasions members of the team wondered aloud why he had remained with the group. For Soffen, disappointments aside, he would like to return to Mars and look beyond the horizon shown in the lander photos-looking not for life but for whatever was there. 74
 
Biology team leader Chuck Klein also had some thoughts on the search for life. "Before we landed on Mars we had a variety of opinions, ranging from those who expected to see no life on Mars to those who expected to see a rather flourishing-maybe not terribly advanced, but at least a flourishing life on Mars." Judging from all the Viking mission's findings, there is no visible flourishing life. But Klein suggested that the scientists must look more carefully at Mars "and ask whether the sophisticated biology and the chemistry instruments have given us clues as to whether there might be some less obvious kind of life on Mars." Klein believed that they could reject their pre-Viking model of Martian microbial life, "namely the Oyama model, which says that Mars should have micro-organisms similar to large numbers of soil bacteria on this planet." At neither site was there any indication to support that kind of concept of Martian biology. That means that either there are no organisms or any existing organisms do not fit that model.
 
[413] Even though two of the biology experiments gave indications that could be interpreted on first inspection as being the result of some simple organisms being present, the molecular analysis team found no detectable organic compounds in the soil samples. The absence of organics made the biology team very suspicious; the weak-to-moderate signals in the two experiments might not be due to biological processes at all. "However, the lack of organics, in and of itself, does not rule out the possibility of organisms but makes that whole idea much less attractive," said Klein. As was noted by other Viking scientists, there is evidence that the surface material of Mars contains chemicals that are highly oxidizing and could interfere with the biological tests and mimic them. "Just as a living organism can, let us say, decompose a steak by eating it and digesting it, the steak can also be decomposed by being thrown into acid, with roughly the same end products." The equivalent to the sulfuric acid in the case of the Viking biology experiments could be an inorganic non-biological oxidizing material. Since this kind of nonorganic material seems to be present on Mars, it could be the cause of the confusing experiment results. "We tried a few tricks on Mars to see if we could devise some experiments that might definitely rule out the possibility that the decomposition seen is due to biology. We have nor been able to do that so far." Although the two landing sites were more hostile than the biologists had anticipated, Klein points out that the Viking data do not really say there is no life on Mars.
 
We can certainly say that it is not rampant, but we can't be sure there isn't some scraggly form of life for which we just haven't found the right nutrients or the right location or the right incubation temperature or the right environment within which to show its presence. That's why it's going to be very difficult for me, at least, to come out and say that there is no life on Mars. l think that would not be a scientific conclusion.
 
Klein, for one, wanted logo back to Mars. 75
 
The planetary scientists agree that Mars is a fascinating place, and Soffen believes it is significant that no one has criticized Viking or the men who brought it about because life was not found there. Philip Abelson, editor of Science, stated categorically in February 1965 that "we could establish for ourselves the reputation of being the greatest Simple Simons of all time" if NASA pursued the goal of looking for extraterrestrial life on Mars. 76 His editorial in Science in August 1976 that reported on the initial results of Viking 1 did not repeat this complaint, however, nor did he make it in either of the two subsequent issues that dealt with the Mars findings. 77 Some writers complained that the Martian microbes had not been given a decent chance-after all, the same ultraviolet radiation that caused the various photochemical reactions postulated by Oyama could also have destroyed the organic remains of many if not all of the Martian microbes- but none faulted the space agency for having made the search. 78
 
A November 1976 editorial in the New York Times was typical of the press reaction. Noting that Mars had gone behind the sun earlier in [414] November, interrupting for a time communications between Earth and the Viking spacecraft, the editorial suggested that the "temporary halt in the receipt of new data permits a preliminary evaluation of what has been accomplished since last summer's historic landing." It appeared that "the whole field of Martian studies has been revolutionized and provided with an abundance of new data that will take years to assimilate fully." Findings on Mars would, in turn, force a reconsideration of the hypotheses concerning the origins of life on Earth. Referring to the postulated superoxides in the Martian soil, the Times noted, "Now the possibility is being discussed that such a superoxide existed here on Earth in the primeval years and that it is this weird substance that provided the oxygen that now makes Earth such a hospitable planet for human and other familiar life forms. The classic explanation that the plant life produced most of earth's free oxygen is now being re-examined." Even the experiments of Miller and Urey in the early 1950s regarding the synthesis of prebiotic molecules could be questioned in light of the Viking investigations, "....the data from Mars have reminded scientists that electric discharges and accompanying ultra-violet radiation can also break down and destroy complex organic molecules as well as form them. All of a sudden the conventional wisdom about the development of life on Earth seems neither so certain nor so inevitable as it did before the Viking landings last summer." Although most scientists would not agree that the results of Viking were sweeping away the foundations for the studies of the origins of life, they would agree that "the Viking experiments have already been even more fruitful than their backers expected." 79 Perhaps the basic reason that there were no serious complaints about the Viking missions was that Mars had turned out to be a far more interesting place than anyone had predicted and more exciting than generations of scientists had expected.