The show starred a young astronomer named Carl Sagan, who rode his “Spaceship of the Imagination” through the psychedelic wonders of the universe. With the help of wild special effects, he spun among the stars, cruised through the “snowballs of Saturn,” and turned his body into a silhouette of pink lasers. He jumped forward and back through time, crawled inside a giant human brain, and floated across treetops, often to a melody of trippy music. My sister and I would stare wide-eyed then doze off to sleep, to be carried up to our cribs as the credits rolled.
To say that Cosmos was a phenomenon would be an understatement. Sagan eventually reached into the homes of more than half a billion viewers across the globe. He’d already started building a public presence by writing for a large audience, but Cosmos was what made him truly famous. He appeared regularly on Johnny Carson, surrounded himself with celebrities, smoked lots of marijuana, and exasperated his colleagues. He was a turtlenecked, freewheeling prophet of science, happy to sign an autograph. For the first time since Percival Lowell, a single individual was the face of Mars science. For the last forty years, no name has been more closely associated with Mars, or the search for life generally, than Sagan. In fact, you’d be hard-pressed to find a modern scientist who cut a higher profile or had a stronger influence over the popular imagination.
A few years before Cosmos aired, with an iconoclastic confidence that would foreshadow his rise to stardom, Sagan daringly suggested there might be turtle-like creatures on the Red Planet. In 1974, he had submitted a short piece to the journal Icarus, in which he concluded that “large organisms…are not only possible on Mars; they may be favored.” It was a tremendous leap, of course, but Sagan, like many visionaries, saw the possibilities in precise detail. These creatures, he speculated, might be plodding about with tough silicate shells to protect them from UV radiation. He conceded that because no visible vegetation had been detected on Mars, it was difficult to imagine the creatures’ food source. Even so, he suggested that some among them, which he called “crystophages,” might be tapping into the icy permafrost to fight the aridity, while others, the “petrophages,” might be drinking hydrated minerals from the rocks themselves. Sagan pointed out that desolate tracts of land on Earth long thought to be barren of large animals were now understood to be habitats, home to polar bears and their kin. He reasoned that substantial size would reduce the ratio of surface area to volume, thereby enabling large creatures to conserve heat and moisture in a cold, dry climate. A graphic artist from Time magazine rendered a gigantic sprawling octopus to convey Sagan’s vision to the public. It was all a stretch, as Sagan undoubtedly knew, but that wasn’t his point. His point was that the case against large, loping creatures—“macrobes,” he called them—simply hadn’t been made, so why would we want to constrain our imaginations? Why not macrobes? Why not even silicon-based giraffes? As with so many things in Sagan’s life, it was a highly unconventional argument, and an inspiring one. It was also an early flourish of the genius he would later show for communicating with nonscientists.
At the time, NASA was preparing spacecraft that would finally land on the surface of Mars. The 1976 Viking mission would conduct the very first life detection experiments on the Red Planet. Sagan was part of the mission’s imaging team, and he worked to ensure that anything in the vicinity of the two identical landers would have its portrait taken in color, black and white, infrared, and even stereo. And he was up to his old tricks: When a reporter pointed out that a fast-moving creature would only “show up as a streak,” Sagan didn’t miss a beat. “But we can always look at the footprints,” he replied.
Sagan had always had an extravagant, limitless imagination. He’d grown up in a small apartment in Brooklyn, and after reading Edgar Rice Burroughs’s A Princess of Mars, with its Virginian hero mysteriously finding himself on the Red Planet, he’d rushed headlong into a nearby field, his arms resolutely outstretched, imploring Mars to ferry him there. As a ten-year-old, he’d sketched block-letter headlines from the future: SPACESHIP REACHES MOON!!! and LIFE FOUND ON VENUS, even a pair of astronauts advertising voyages on INTERSTELLAR SPACELINES.
He’d devoured pulp science-fiction magazines throughout his adolescence, and at fifteen he’d happened to notice an advertisement for Arthur C. Clarke’s Interplanetary Flight: An Introduction to Astronautics. Unlike Clarke’s fanciful short stories, Interplanetary Flight was a short technical volume, outlining everything that was known in 1950 about orbital dynamics and rocket design. Sagan was astounded by the possibilities Clarke laid out for sending probes to other planets and perhaps even sending them soon.
He raced off to the University of Chicago the next year, at just sixteen years old. The demands were high, and Sagan was nothing if not intense. He was soon suffering from chronic pain that would stay with him for his entire adult life. He drove the lonely highway to the Mayo Clinic by himself, embarrassed that he could no more than nibble at food without fear of choking. He was diagnosed with achalasia, literally “failure to relax.” It was a condition of the esophagus that made it difficult to breathe and swallow, which his sister speculated was the result of his mother’s obsessive, neurotic influence. The doctors tried to stretch his esophagus, unsuccessfully, just as they failed with surgery years later, leaving his lung cavity filled with blood.
Yet Sagan had a resilience that ran deep. Despite his self-consciousness and pain, he fearlessly approached important scientists to ask his questions. By putting himself on the line, he cultivated a series of brilliant mentors. He studied physics and wrote an undergraduate thesis on the origin of life, supervised by Nobel Prize winner Harold Urey. He worked in the summers with top scientists around the country, then decided to stay on at the University of Chicago to complete a PhD in astronomy and astrophysics, commuting in a blue-and-white Nash-Hudson station wagon over to the school’s observatory in Williams Bay.
Although his primary PhD research was on the physical properties of planets, Sagan soon found himself at the epicenter of the nascent field of exobiology—back doing research about the origin, evolution, and presence of life in the universe. In the late 1950s, one of Sagan’s mentors invited him to help the National Academy of Sciences with some “spadework, mainly consultation, on the generalities of biological probes.” Sputnik had just launched, and the Soviets were hastily preparing landers for the moon. American scientists were beginning to worry about the secretive program, about whether the Russians were paying sufficient attention to things like sterilization, whether they might be risking humanity’s chance to study life beyond Earth. NASA was already laying plans to protect the moon from contamination, and it seemed like a good time to begin thinking about other planets too.
Sagan’s move was an auspicious one. It placed him for the first time in contact with the luminaries directing the American space program, at the beginning of what would ultimately become a watershed moment in Mars science: the shift from looking for life in photographs to looking for life in ways that couldn’t possibly show up on film. It would require new instruments, new miniaturization, and, most important, actual scientific experimentation on the surface of the planet itself. But landing on a planet was very different from flying by it or orbiting around it. We could learn so much more, which inevitably meant that more was at stake, professionally and personally, for all involved.
The realignment of Mars science began as soon as the National Academies panel coalesced. The participants—including young Sagan as a PhD student—divided themselves into an East Coast group, EASTEX, and a West Coast group, WESTEX. The panel’s first order of business was to set a path for their efforts, and at one of the earliest EASTEX meetings, one of the group members bombastically lamented that no devices had been invented that could be used for life detection. What was needed, he felt, was a simple contraption that would register “yes, there’s life in this sample!” or “no, no life.” It was a compelling, and ultimately transformative, call to arms.
Young Vishniac had grown up in Berlin, culturing algae at home, which he in turn fed to fairy shrimp, which he in turn fed to seahorses. He set sail for America in 1940 aboard an American Export Lines steamer with his family and eighty other Jewish refugees. Despite speaking little English, he landed a spot at Brooklyn College the following year, then went on to Stanford. As a young professor at Yale, he made a name for himself by working out some details of photosynthesis and investigating how microbes used sulfur as an energy source, before moving on to the University of Rochester.
Despite their rather divergent scientific proclivities, Vishniac and Sagan became dear friends. They had been trained very differently: Sagan, the astronomer, with his cameras and spectrometers, and Vishniac, the biologist, with his slides and test tubes. Vishniac loved to tinker and had a knack for engineering, whereas Sagan was butterfingered. And their personalities also set them apart. Vishniac had a quiet nature. While he could sometimes be found talking to his local Kiwanis chapter, members of the police department, and other luncheon groups, Sagan had the world as his pulpit. But each, in his own way, was startlingly imaginative, and each made profound contributions to Mars exploration.
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IN 1959, AROUND the time Sagan was starting a postdoctoral fellowship at Berkeley, Vishniac received a grant of $4,485 for what he dubbed the “Wolf Trap,” mocking his own first name. It was a life detection concept for Mars that was based on the idea that microbes would change the environment as they grew. Vishniac envisioned that after a soil sample was sucked up from the ground through a nozzle and dumped into nutrient-rich water, growing Martian microbes would produce changes in the culture media that could be measured, allowing scientists on Earth to see what was happening. A change in acidity could be picked up by a pH probe, and increased cloudiness—an indication of rapid growth—could be detected with optical sensors. Together the measurements would provide an independent check on each other. Exponential increases—a skyward swoop of the curve—would be particularly indicative of the proliferation of small microorganisms.
Within two years, Vishniac had a working model of the Wolf Trap, a huge scientific achievement and a shockingly quick response to the EASTEX challenge. Yet not everybody was impressed—including Vishniac’s father-in-law. As a postdoc, Vishniac had fallen in love with and married Helen Simpson, the daughter of one of the most influential paleontologists and evolutionary biologists of the twentieth century. The elder Simpson had little regard for life detection. He’d publicly taunted biologists for agreeing that the first and foremost task in space science should be the search for alien life. He teased them about their “new science of extraterrestrial life, sometimes called exobiology,” deeming it “a curious development in view of the fact that this ‘science’ has yet to demonstrate that its subject matter exists!”
But Vishniac persisted, and slowly he was joined by other microbiologists and biochemists who were thinking up new ways to miniaturize laboratory experiments to look for life on Mars. After the Wolf Trap, the next furthest along was an instrument dubbed “Gulliver”—an homage to Jonathan Swift, aptly named in its quest for Lilliputian life. Designed by a sanitation engineer, Gulliver sought to capitalize on one of the most common ways to detect microbes in swimming pools, oceans, and drinking water, particularly contaminants like fecal coliform. The idea was simply to monitor a culture for bubbles of carbon dioxide using a carbon-14 tracer. Some of the early designs envisioned tiny harpoons, fired like mortars from the base of the lander, trailed by seven and a half meters of kite line. The kite line would be coated in silicone grease to stick to soil particles, making them easy to reel back into the instrument to analyze.
By the early 1960s, NASA was funding nearly twenty life detection concepts, but notably, none of these instruments—not even Vishniac’s, the son of a microscope evangelist—were designed to take images. It was too complicated to prepare specimens and search glass slides for growth, and transmitting the images required too much data. Microscopy would have to go, and with that jettisoning, the search for life crossed a major threshold: For the first time, life would not be something you saw; it would be something you measured in an interplanetary laboratory.
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WHEN THE MARINER 4 mission began releasing findings in 1965, the new tribe of exobiologists was as stunned as the rest of the world. The extreme aridity, the extreme cold, the extremely low atmospheric pressure all raised serious doubts about how life could survive on Mars, and suddenly it seemed like they might be wasting their time. Until the exobiologists could articulate a theory for survival in such an inhospitable place, their hard work would look like a fool’s errand.
Naturally, it was Sagan and Vishniac who stepped to the plate. In response to the cratered images, Vishniac penned a moving letter to the Senate chairman of the Committee on Aeronautical and Space Sciences, arguing that craters might even contribute to “a diversification of the environment, with the creation of ecological niches favorable to colonization by living organisms”—that they might enable entry to deeper geological formations, protect organisms from radiation “in the shadows,” and provide a chance for essential elements to gather.
Meanwhile, Sagan scrutinized hundreds of photographs of Earth, trying to show that the Mariner results didn’t necessarily preclude life. He looked first to weather satellites: to TIROS-1 and Nimbus, which were just opening the door to space-based remote sensing. At one-thousand-meter resolution, he could see no roads or buildings, no rectilinear patterns, no life whatsoever over New York City, Moscow, Paris, or Peking, he pronounced. He then amassed eighteen hundred images snapped of Earth by the Apollo and Gemini astronauts, with ten times greater resolution. At one hundred meters a pixel, only a handful of the pictures showed even a trace of anything human. And even then, he argued, you had to know what to look for: A tilled field or a thin track of road would mean nothing to an observer who was unfamiliar with life on Earth. To such a newcomer, our human workings would be invisible, and the eighteen hundred images might lead to the erroneous conclusion that Earth was devoid of life. Our sense that we’d left an imprint, that we’d had a profound influence on the physical world, it was all wrong. So too was our assumption that if life existed on Mars, we would have spotted it by now: After all, if we were undetectable from above, Martian life might be as well.
Although Sagan wasn’t a biologist—his focus was on spectroscopy and imaging—he’d begun dabbling in the life sciences. Building on little-known experiments that had been conducted near San Antonio, Sagan began constructing “Mars jars,” which were small chambers simulating the inhospitable Martian surface and atmosphere. He filled the jars with terrestrial microbes, in temperatures ranging from minus 80 degrees Celsius at midnight to freezing by noon, under harsh ultraviolet light. What he discovered struck him as remarkable. As he wrote of the work, “There were always a fair number of varieties of terrestrial microbes that did not need oxygen; that temporarily closed up shop when the temperatures dropped too low; that hid from the ultraviolet light under pebbles or thin layers of sand.” In experiments where tiny amounts of water were present, he was delighted to find that the microbes actually grew. “I
f terrestrial microbes can survive the Martian environment,” he concluded, “how much better Martian microbes, if they exist, must do on Mars.”
At the same time, NASA embarked on its own effort to assess whether life could survive in harsh, cold conditions. It sent scientists down to the McMurdo Dry Valleys of Antarctica—the small sliver of the great white continent that is ice-free—to collect samples from one of the more Mars-like places on Earth and distributed samples to the researchers designing life detection instruments for calibration and testing. As part of the effort, a scientist named Norman Horowitz, said to resemble a fox terrier, tried every which way to culture life from the samples, but not a single bacterium grew under any of the treatment conditions. Horowitz published a Science article in 1969, swinging the ax. While the cold and barren Dry Valleys contained significant amounts of organic carbon molecules—the building blocks of life—vast tracts of land were in fact sterile. And if life couldn’t even survive in Antarctica, how could it survive on Mars?
This finding alarmed Horowitz, who was already deeply tied to the exobiology enterprise. In response, he led a last-minute effort to develop a different instrument concept. It co-opted the exact same detection principle as Gulliver, but whereas Gulliver moistened the soil with water and the Wolf Trap drenched it, Horowitz’s experiment was completely dry. There was to be a small lightbulb in the testing chamber, and if organisms similar to simple algae in the soil were able to pull any of the carbon-14 tracer from the chamber’s air into their bodies, it would be evident once the chamber was flushed and the sample baked.
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