Klein, Harold P.

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(b. New York, New York, 1 April 1921; d. Palo Alto, California, 15 July 2001),

microbiology, origin of life, astrobiology.

Klein was a microbiologist who worked on lipid and carbohydrate metabolism in a wide range of microbes. But he is best known for his work as an administrator at the National Aeronautics and Space Administration’s (NASA) Ames Research Center for more than twenty years, where he supervised work on the origin of life and on instruments to search for life on other planets. He served as scientific leader of NASA’s Viking Biology Investigation on the Viking 1 and 2 Mars landers, coordinating the development, construction, and execution of all the biology experiments aboard the spacecraft.

Harold (or “Chuck” as he was known to colleagues) Klein was born to Hungarian immigrant parents just a month after their arrival through Ellis Island into New York City. He received a BS in chemistry from Brooklyn College in 1942 and a PhD in microbiology from the University of California, Berkeley, in 1950. Klein served in the U.S. Army from 1943 to 1946, researching the effect of molds on electrical equipment in the humid South Pacific. In 1955, he joined Brandeis University in Waltham, Massachusetts, becoming associate professor in 1956 and full professor 1960 to 1963. He was chair of the Biology Department at Brandeis from 1956 to 1963, with the exception of 1960 to 1961 while on leave from Brandeis, when Klein was visiting professor of bacteriology at the University of California, Berkeley. Klein saw NASA’s advertisement for the initial position at Ames and felt it would be an extraordinary challenge to be in on the development of a historic scientific and technological enterprise such as looking for life on other planets. NASA had begun to fund such research with the creation of its Life Sciences Office in March 1960; by 1962 a whole new research lab was being set up at Ames, to conduct in-house research, in addition to the studies by university scientists at their home institutions. In the heady days of the early “space race,” NASA had high levels of funding from Congress for all its research goals; cuts did not begin until the late 1960s. After retiring from Ames he became scientist-in-residence at Santa Clara University, Santa Clara, California, as well as senior research scientist at the SETI (Search for Extraterrestrial Intelligence) Institute from 1985 until his death.

Science Administrator . As a young microbiologist, Klein studied the biochemical metabolism of carbohydrates and lipids in various microorganisms, from bacteria to yeast. During 1950 to 1951 he was a research fellow at the Biochemical Research Institute of Massachusetts General Hospital in Boston, working in Fritz Lipmann’s research group there, just prior to Lipmann’s receipt of the 1953 Nobel Prize. From 1951 to 1954 Klein was an instructor in the Department of Microbiology at the University of Washington, Seattle; he became assistant professor there from 1954 to 1955. Beginning with his start as chair of the Brandeis University Biology Department, however, Klein soon discovered that his greatest talents were as a science administrator and organizer. Thus, when he was approached by NASA in January 1963 and invited to become the division chief of a new set of labs in an exciting new science—exobiology—Klein felt the potential to be in on the beginnings of a major new field of exploration sufficient to overcome his reservations about leaving the freedom of academia for a bureaucratic civil service job. While he continued many of his former lines of research at NASA’s Ames Research Center, this turning point marked the beginning of his work to coordinate an entirely different kind of investigation: designing, building, and operating devices to search for life on other planets, most of all Mars.

Validating his sense of his abilities as a science administrator, in less than a year at NASA, Klein was promoted to assistant director of all Life Sciences at Ames, by 1968 rising to director. Klein’s twenty-one-year tenure at Ames encompassed the “boom days” of NASA, when the Apollo program was in full swing and planetary missions began to multiply, including Mariners to Mars and Venus, Pioneers and Voyagers to the outer planets, and Vikings to Mars.

Klein participated in the National Academy of Sciences workshop at Woods Hole, Massachusetts, in the summer of 1965, on scientific prospects for finding life on Mars. He oversaw the construction of a new laboratory building (completed in December 1965) and the training of many National Research Council postdoctoral scientists; in addition Klein presided over a time when a great many staff scientists were hired as civil servants. In the exobiology (soon to be called Planetary Biology) division of Life Sciences alone, there were three bureaucratic branches: Chemical Evolution, Biological Adaptation, and Life Detection Systems. Some of the talented young scientists Klein spotted and hired included microbiologist Ruth Mariner Mack, chemist Fritz Woeller, chemist Katherine Pering, biochemist Donald DeVincenzi, and geochemist Keith Kvenvolden. Thus, Klein’s administrative abilities led to and catalyzed a large amount of research on the origin of life (overseen until 1971 by Cyril Ponnamperuma in the Chemical Evolution section), adaptations of living systems to extreme environments, and the design of actual instruments to search for life in the cosmos.

Viking Biology Leader . Nineteen sixty-eight saw the beginning of plans for the Viking Mars lander mission, and NASA advertised a competition among all submitted life-detection schemes, to decide which four experiments would be chosen to actually get built and sent to the Martian surface on the two Viking spacecraft. In December 1969, from more than fifty submissions the four experiments chosen were Norman Horowitz’s pyrolytic release (PR), Gilbert Levin’s labeled release (LR), Vance Oyama’s gas exchange, and Wolf Vishniac’s light scattering experiment. A committee was appointed by NASA to oversee the development of a workable Viking Biology Experiment Package, including all four experiments. Committee members included the four experimenters, but also micro-biologist Joshua Lederberg and microbiologist Alexander Rich, scientists who it was believed could be more objective because they did not have experiments of their own at stake.

Vishniac was the first chair, but it soon turned out that he was too relaxed, willing to let everybody have his say. So work on the project bogged down amid disagreements; each experimenter thought his own approach the most important, yet all the experiments had to function in a common environment inside the same instrument. Horowitz, for example, argued that the design of all the other experiments was based on Earth-like conditions far too warm and wet to be realistic for Mars. He argued that the temperature inside the experiment package should be kept as low as possible; because his experiment did not involve any liquid water, he had no qualms about advocating a temperature of 0 degrees Celsius or less, despite the fact that this would render almost useless the other three largely aqueous experiments.

The tension between egos and differing experimental ideas led to regular deadlocks of the committee until Klein was asked to take over as new chair. He brought the same capable administrative talents that he had brought to directing the Ames Exobiology Program and then all of Life Sciences at Ames. Klein’s managerial style worked, and though the Viking Biology Committee was noted by many as one of the most contentious groups of people ever assigned to work jointly, he managed to keep the group together and the project moving forward, if notoriously behind schedule and over budget. Klein’s key talent in this context was as a diplomatic moderator more than as a scientist. His levelheaded calm would turn out to be most important of all in the days and weeks after Viking landed on Mars, and after results from the experiments began to come in.

Indeed, problems with the biology instrument were not limited merely to the difficulties of getting the team to work together. Fearing the complexities of getting all four experiments to function problem-free in a single instrument, NASA’s Viking project manager issued a directive on 1 July 1971 declaring a new project policy that no single malfunction should cause the loss of data return from more than one scientific investigation. In November and December 1971, the instrument contractor, TRW, and NASA Ames personnel under Klein worked to simplify the biology instrument. It simply had too much going on in the space allotted. In 0.027 cubic meters—a box about the size of a gallon milk carton— were forty thousand parts, half of them transistors. Several items were eliminated.

By January 1972 administrators from NASA headquarters met with people from the Viking Project Office and the contractors to discuss the problems and especially the cost, which had escalated to $33 million for the biology package alone. Soon NASA headquarters concluded that one of the four biology experiments would have to be dropped. Klein, Lederberg, and Rich, the biology team members who did not have a stake in any one of the experiments, met to discuss priorities; shortly afterward, by mid-March 1972 NASA headquarters had decided that Vishniac’s light scattering experiment was based on the least Mars-like conditions and therefore it should be the one to be sacrificed. The entire Viking Biology Team met immediately, and showed rare cohesiveness in criticizing the decision at headquarters to drop Vishniac’s experiment. But in the event, Viking carried only the remaining three biology experiments.

By the time the Viking 1 and 2 spacecraft launched from Cape Kennedy, on 20 August and 9 September 1975, the team had written a description of the experiments for Nature. A special issue of the journal Origins of Life was also in preparation, describing the experiments in much greater detail. These articles clearly convey the scientists’ sense of the historic nature of their enterprise; but also their awareness of how complex the experiments were and how limited their ability from Earth to check up on ambiguous results or run additional controls. Klein wrote an overview of the biology package and its development (Klein, 1976a). Knowing the sensational nature of the mission, Klein seemed to feel more than most the responsibility to educate the press and the public about a cautious, scientific attitude toward the experiments.

Life on Mars Controversy . Every one of the biology experiments yielded evidence of activity from the very first run on the Martian surface. The PR experiment gave one reading consistent with production of organic matter (e.g., by photosynthesis), and the reading was high enough, compared to his earlier-stated requirements, that even Horowitz was briefly shaken about his doubts over the existence of life on Mars. But this result was not repeatable. When wetted in the gas exchange experiment, the Martian “soil” (regolith) released significant amounts of oxygen. Heating the sample to 145 degrees Celsius for

3.5 hours reduced the amount of oxygen released by about 50 percent. There was a slow evolution of carbon dioxide when nutrient was added to the soil. However, by three days into the first run, the gas production had decreased considerably, leading some to suspect that the reaction was chemical rather than biological. That is, it may have been produced by a potent reactant present in the sample that was used up via chemical combination with the water or nutrients.

Levin’s LR experiment showed the most potent reaction of all three. A nutrient solution added to the soil sample contained a mixture of the following acids: formic, glycine, glycolic, D-lactic, L-lactic, D-alanine, and L-alanine, each uniformly labeled with carbon-14, which would be detected as radioactive carbon dioxide (CO2) gas if metabolized by microbes. There was an immediate peak of labeled CO2 release in the first minutes after the nutrient solution was added, followed by a slow, continued release over many days as measurements continued. The amount of CO2 released amounted to what would be expected if a single carbon atom had been cleaved at the same spot from the entire pool of a single substrate (see Figure 1). The plot of data looked somewhat like a bacterial growth curve (though it lacked an initial lag phase); furthermore, if the soil was first heated to 160 degrees Celsius for three hours the activity was completely destroyed. The effect was partially destroyed by incubating the soil at 40 to 60 degrees Celsius, and the activity was relatively stable for short periods at 18 degrees Celsius, but lost after long-term storage at 18 degrees C. All of these data seemed to Levin to be almost completely consistent with what one would expect from a biological reaction. He was tentative at first, but the subsequent controls convinced him that the best explanation of the LR results could well be the existence of microbial life on Mars.

Because results were being released to the press on practically a daily basis, the nation, indeed the world, was getting the chance to observe science in process in a new way. Viking officials, especially Klein, worked hard to explain the slow, deliberate process by which the experiments had to be checked, different kinds of controls tried,

and so on. But the results were simply too unexpected; at each new trial that should have brought clarity in choosing between a chemical or biological explanation of the results, the ambiguity stubbornly persisted. Unused to doing science with an audience looking in at every step in the process, the scientists were exasperated at having to explain complex and ambiguous experimental results to a public and press corps that wanted to know simply: has Viking found life on Mars?

Shortly after, the gas chromatograph–mass spectrometer (GCMS) aboard each Viking spacecraft sent back the stunning results of its chemical analysis of the Martian soil: there were no detectable organic molecules of any kind. For most of the scientists, that immediately ruled out any possibility of life in those soil samples. In a press conference in which the GCMS results were announced, Klein also told the press about a new theory. This was that ultraviolet light getting from the Sun to the surface of Mars produces hydrogen peroxide, which oxidizes any organic compounds. Some laboratory experiments were carried out simulating Martian conditions; the result was that the half-life of any organic compound was at most two months. A team at the University of Maryland added peroxide to a sample of Levin’s nutrient mixture that Klein sent them; they found a very similar response and amount of CO2 evolution to what was seen in the Mars LR experiment. Oyama and his coworkers proposed, after some lab work, that γFe2 O3 was the most likely oxidant, rather than hydrogen peroxide.

The data from further control experiments were as confused and ambiguous as ever, having some “chemical” and some “biological” features. But with so much at stake, not only life on Mars but the possibility of seeming impetuous, unscientific, or insufficiently cautious before a world audience, the double-sided nature of the public relations aspect of “Big Science” of the post–World War II period was visible in sharp relief. Particularly in the case of exobiology, to speak of the science artificially extracted from the public relations context that served as such nourishing soil for its development would be arbitrary indeed.

Levin and his coworker Patricia Straat continued to make the case that the interpretation of the biology results from Viking, at least the results from their LR experiment, were still open. By 1979, however, almost all other scientists concluded that the chemical explanation was more likely. In that context, Levin and Straat were viewed as being intransigent; they were rapidly marginalized. By the 1990s Straat was no longer writing on the subject, but Levin became still more convinced after results from the 1997 Mars Pathfinder spacecraft showed that water might exist in significant quantities not far below the surface of Mars; thus life was more likely. Similarly, he considered that the August 1996 announcement of the discovery of putative microfossils in a Martian meteorite gave broad support for the case for Martian biology, even if those possible organisms were from over three billion years in the past. Levin raised the possibility that Earth biota could have been seeded by Mars meteorites long ago when Mars was still habitable, or vice versa, now that it was recognized that meteorites were in fact moving at least in the Mars to Earth direction.

In 1997 a popular book appeared, championing Levin’s cause and presenting him as a scientific genius suppressed by the Establishment. Levin’s former Viking colleagues and the new generation of exobiology researchers had largely ignored Levin’s writings for the previous fifteen years; however, the new book caused Harold Klein sufficient irritation that he felt compelled to respond (Klein, 1999), hoping to silence the argument once and for all.

Klein pointed out that Levin’s argument consisted of two main propositions; only one of these had been properly and directly addressed, he said. The two main arguments were, as he saw them, first that the responses seen on Mars were practically indistinguishable from those shown by a variety of Earth microbes and second, that laboratory attempts to reproduce the LR results, based on nonbiological mechanisms, could not account for the results. Klein said all rebuttals had concentrated on the second argument, while little attention had been paid to the first. He went on to outline a number of characteristics the presumed Martian microbe or microbes must have, in order to fit with the data. First, they needed to live in an anaerobic environment devoid of liquid water at temperatures averaging (even at a sheltered depth of 5 centimeters below the surface) between –33 and –73 degrees Celsius.

Secondly, the organisms must survive after being brought from that ambient environment and placed in a storage container at an average of 15 to 18 degrees Celsius within the Viking lander. The samples were held at that temperature for eight days, at which time they were placed in an incubation chamber at 10 to 13 degrees Celsius. Two days later, ten days after being scooped up and dumped into the spacecraft, 0.115 milliliters of an aqueous solution of the organic carbon sources was added to the sample. After being put through those changes, the microbial species must immediately release gas (within the first four minutes, as the first measurement showed substantial gas already released by that time). Klein emphasized that the reaction took off immediately without the lag phase characteristic of most microbial growth curves. Then it leveled off after about twenty-four hours and ceased when an amount of carbon approximately equivalent to one of the added carbon atoms was released, while more than 90 percent of the added nutrients remained unaffected. Klein noted the further improbability for a living organism that had done all of the above: next, when the sample was treated with a second dose of nutrient solution, no further release of radioactive gas was seen. After still further criticisms, Klein insisted that to claim terrestrial organisms could reproduce all aspects of the LR data was not a plausible conclusion.

Not long after Klein’s rebuttal, the case for life on Mars perked up with a prominent article in the Proceedings of the National Academy of Sciences, which argued that the Viking GCMS would have been unable to detect some of the most likely organic compounds delivered to the Martian surface by meteorites. In retrospect there is reason to believe that the GCMS was too insensitive to detect organic matter in amounts found in the number of cells suggested by Levin’s interpretation of the LR data; it had merely been assumed in the instrument’s design that if cells were able to grow, higher levels of organics must be present all around them. Further discoveries of subsurface water ice by Mars Odyssey in February and March 2002 continued to reveal, much like the observations of Mariner 4 did in 1965, that Mars is a sufficiently complex place to repeatedly overturn past scientific certainties. The stunning discoveries at terrestrial hydrothermal vents, of the “third kingdom” of Archaea, and of the endosymbiotic behavior of bacteria that later turned into mitochondria, chloroplasts, and other cell organelles could suggest more caution than Klein displayed in predicting what microbes might and might not be capable of. At bottom, this turns upon a basic attitude toward the degree of adaptability of living organisms; what is more unlikely, life on a harsh planet such as Mars or Europa, or life (even complex multicellular animals) at many atmospheres of pressure and temperatures approaching 150 to 200 degrees Celsius near undersea hydrothermal vents? Though it may be a considerable time yet before any final answers about present or past life on Mars, Klein’s role as scientist, and even more importantly as science administrator, was crucial for bringing the scientific investigation of the subject to its present state. Klein was the recipient of the NASA Exceptional Scientific Achievement Medal (1977), the NASA Medal for Outstanding Leadership (1981), and the Presidential Meritorious Service Award (1981).


A box of Klein’s personal papers donated to this author before Klein’s death has been deposited at the NASA History Office.


With Michael Doudoroff. “The Mutation of Pseudomonas putrefaciens to Glucose Utilization and Its Enzymatic Basis.” Journal of Bacteriology 59 (1950): 739–750.

“Fructose Utilization by Pseudomonas putrefaciens.” Journal of Bacteriology 61 (1951): 524–525.

With Fritz Lipmann. “The Relationship of Coenzyme A to Lipide Synthesis: I. Experiments with Yeast.” Journal of Biological Chemistry 203 (1953): 95–99.

With Orr E. Reynolds. “The Utility of Automated Systems in the Search for Extraterrestrial Life.” Proceedings of the Second International Symposium on Basic Environmental Problems of Man in Space, Paris, 14–18 June 1965, edited by Hilding Bjurstedt. New York: Springer-Verlag, 1967.

“Problems Involved in the Detection of Life on Extraterrestrial Bodies.” Proceedings of the Tenth International Congress for Microbiology 241 (1970).

“Potential Targets in the Search for Extraterrestrial Life.” In Exobiology, edited by Cyril Ponnamperuma. Amsterdam: North Holland, 1972.

With Joshua Lederberg and Alex Rich. “Biological Experiments: The Viking Mars Lander.” Icarus 16 (1972): 139–146. “Automated Life-Detection Experiments for the Viking Mission to Mars.” Origins of Life and Evolution of the Biosphere 5 (1974): 431–441.

“General Constraints on the Viking Biology Investigation.” Origins of Life and Evolution of the Biosphere 7 (July 1976a): 273–279. Klein’s advance description of the Viking Biology Instrument package and its concept and design constraints.

“Life on Mars?” Trends in Biochemical Sciences 1, no. 8 (August 1976b): N 174–N 176.

With Norman Horowitz, et al. “The Viking Biological Investigation: Preliminary Results.” Science 194 (17 December 1976): 1322–1329. A report on the earliest experimental data in the first weeks after the Vikings landed.

With Joshua Lederberg, et al. “The Viking Mission Search for Life on Mars.” Nature 262 (July 1976): 24–27.

“The Viking Biological Investigation: General Aspects.” Journal of Geophysical Research 82 (30 September 1977): 4677–4680. A more complete article on the Viking biology results a year after the experiments first began sending back data.

“The Viking Biological Experiments on Mars.” Icarus 34 (1978a): 666–674. The definitive discussion of the Viking biology experiments.

“The Viking Biological Investigations: Review and Status.” Origins of Life and Evolution of the Biosphere 9 (1978b): 157–160.

“Simulation of Viking Biology Experiments: An Overview.” Journal of Molecular Evolution 14 (1979): 161–165. A review of laboratory attempts to simulate the Viking results, in order to choose between biological vs. chemical explanations as the best fit for those data.

A Personal History. Mountain View, CA: privately printed, 1998. Klein’s personal and scientific autobiography.

“Did Viking Discover Life on Mars?” Origins of Life and Evolution of the Biosphere 29 (1999): 625–631.


Benner, Steven, Kevin Devine, Lidia Matveeva, et al. “The Missing Organic Molecules on Mars.” Proceedings of the National Academy of Sciences of the United States of America 97: (2000) 2425–2430.

Dick, Steven J., and James E. Strick. The Living Universe: NASA and the Development of Astrobiology. New Brunswick, NJ: Rutgers University Press, 2004.

DiGregorio, Barry. Mars, the Living Planet. Berkeley, CA: Frog, 1997.

Ezell, Edward C., and Linda N. Ezell. On Mars: Exploration of the Red Planet, 1958–1978. NASA Special Publication 4212. Washington, DC: Scientific and Technical Information Branch, National Aeronautics and Space Administration, 1984.

Fry, Iris. The Emergence of Life on Earth: A Historical and Scientific Overview. New Brunswick, NJ: Rutgers University Press, 2000.

James E. Strick