The Stardust Revolution

by Jacob Berkowitz

  This view dominated, even though there was some evidence to the contrary. In 1937, Mount Wilson astronomers had produced an unusual stellar light fingerprint using the observatory's new high-resolution spectrograph. The stellar light fingerprint had a single prominent line that caught the eyes of two spectroscopists in Belgium. The line is clearly produced using a Bunsen burner to heat not a single element but a molecule: carbon hydride. It's as simple a molecule as there is, a single carbon atom in an electron-sharing dance with a single atom of hydrogen. For astronomy, though, this little molecule was a giant leap forward—it was the first interstellar molecule.

  Like radio waves, interstellar molecules weren't supposed to be there. More importantly, as with cosmic dust, astronomers had no way of incorporating them into their understanding of the cosmos. But by 1942, astronomers and chemists had identified two other molecules. The Canadian astronomer Andrew McKellar had spotted the light fingerprint of cyanogen—a carbon atom bound to a nitrogen one—in interstellar space; and in the scientific backwater of Saskatoon, Saskatchewan, the molecular spectroscopist Gerhard Herzberg—who'd barely escaped Nazi Germany, arriving in Saskatoon with only his wife, five dollars, and his spectroscopy equipment—identified another light fingerprint in the Mount Wilson spectra as that of the positive carbon hydride ion, or carbon and hydrogen minus one electron. Yet, rather than opening the door to exploration for more molecules, these discoveries reinforced most astronomers' view of an atomic cosmos. It appeared that only the most bare-boned two-atom molecules—a single carbon atom married to either a hydrogen or a nitrogen atom—existed in the dark interstellar void. It wasn't until December 1968, while all eyes were on the Apollo 8 lunar orbit, that a renegade radio telescope tuned in on a small molecule with one atom more. Just three atoms, but these three together make a universe of difference: water.

  COSMIC WATER MAN

  In the 1960s, NASA's Apollo Moon missions provided the first live television images of the Earth's closest cosmic neighbor, and it wasn't just sleepy-eyed kids in pajamas who were hoping for the ultimate full-Moon revelation: signs of lunar life. With the first images, these ancient dreams shriveled, no more so than when it came to that defining ingredient of life, water. The sense was captured in the view of the lunar landing site from the Eagle, the Apollo 11 landing module. For all its watery allusion, the Sea of Tranquility appeared to half a billion television viewers as Buzz Aldrin described it, a “desolate beauty.” Neil Armstrong left a first footstep that would never be erased by wave or rain. Any glimmers of hope for lunar life evaporated with that first small step by man on what appeared to be a bone-dry Moon.

  This lunar view of a parched universe beyond Earth's borders was the follow-up punch to the first-ever close-up images from Mars, provided by NASA's 1964 Mariner Mars orbiter. Regardless of Mariner's seafaring moniker, the images the probe beamed back from the red planet revealed a barren, rock-strewn, and, above all, dry Martian surface. The images sank a century of sometimes jubilant speculation about a possible diverse Martian canal system and the civilization that must have built it. Mariner and other research also showed that even the Martian polar caps, long thought to hold vast amounts of water, were in fact mostly frozen carbon dioxide, with only trace amounts of icy water. The red planet appeared to be a dry and, more important, dead planet.

  For those hoping that these inaugural journeys into our cosmic backyard would reveal hints of alien neighbors, the results were enormously disappointing. After all, NASA's mantra in the search for extraterrestrial life then as now is “Follow the water.” Where there's life, there's liquid water. On Earth, this is a truism. Whether it's at the bottom of the world's deepest gold mines miles underground or in the eternal darkness at the bottom of the Pacific Ocean, wherever we've looked on our planet, if there's liquid water, there's usually life. Liquid doesn't mean an ocean, a lake, or even a puddle; liquid can be just a layer, no more than microns thick, a boundary layer of just less than solid ice, its melting caused by the friction as a mile-thick Greenland glacier moves over granite bedrock. Even in this unbelievably remote, extreme, and shifting environment, microbes spring into action, in what to them is the liquid of life as much as the Pacific is home to Tahitians.

  Why is water so critical to life? We think of ourselves as solid beings, flesh and bone. But we're really made up of trillions of bags of water—our cells. When you step on the scale to weigh yourself, more than half of the answer, about 55 percent, is pure water. Water is the medium of our living interaction with the world. We pee out waste products, drink in dissolved nutrients, and breathe out water, a by-product of respiration, the burning of chemical energy that gives our cells the energy of life. It's why chemists call water the universal solvent. Life on Earth is immersed in, depends on, and originated in water.

  As Earthlings watched successive Apollo astronauts bound across the desertlike lunar surface and let handfuls of dry lunar regolith—the Moon's powdery surface material—sift through their gloves, they silently received one clear message: in the search for extraterrestrial life, there appeared to be no watery tracks to follow. However, in Houston on that historic day in July 1969, there was one scientist who knew that the grainy black-and-white television images didn't tell the whole story. As the chairman of NASA's Apollo Science and Technology Advisory Committee, Charles Townes had a front-row seat for the lunar landing, seated beside Apollo project leader George Mueller and watching the touchdown on a large TV screen. Like the others, Townes could see that Eagle hadn't spied cosmic water, but he knew that he just had.

  Charles Hard Townes was around that NASA table because, when it came to physics in the second half of the twentieth century in the United States, no one was more respected and accomplished than Professor Townes. He'd suggested the Apollo Science and Technology Advisory Committee several years earlier in his role as provost, or academic chief, of the Massachusetts Institute of Technology. Yet, for those around the NASA table, it wasn't only Townes's academic administrative achievements that gave him scientific street cred. As Neil Armstrong positioned a mirror on the lunar surface, it was thanks to Townes that this mirror would be used to measure the distance from the Earth to the Moon, by reflecting a laser beamed from Earth. Townes coinvented the laser and its predecessor, the maser—a molecular version of the laser—for which he shared the 1964 Nobel Prize in Physics.

  For all his establishment credentials, Townes was a scientific rebel—of the nicest kind. He was a sought-after team player and could adroitly play that role to great end. But he was truly his happiest—blissful, really—when working alone or with a small team of passionate comrades at the misty, labyrinthine frontiers of the unknown. So, two years before the Apollo Moon landing, he'd quit his provost post, packed up his family, and moved from relatively staid Cambridge, Massachusetts, to the hotbed of 1960s activism: the University of California campus in Berkeley.

  Some friends thought he was crazy. “Charlie, how could you move to Berkeley? That's the most sinful city in the whole United States!” chided his friend, the retired US admiral Chester Nimitz, namesake of the Nimitz-class aircraft carriers. While others in tie-dyed T-shirts and headbands were heading to the West Coast for anti–Vietnam War sit-ins and San Francisco's atmosphere of free love, it was another kind of freedom that drew Townes—the freedom to do whatever research he wanted. Another university suitor had tried to pin him down as to his research plan, but Townes balked. More liberal Berkeley offered him the no-holds-barred position of professor-at-large, including $100,000 to equip his lab and, given his Nobel-laureate status, a coveted campus parking spot. Berkeley had one other, less obvious, thing that Townes wanted: a radio telescope. As tear gas wafted across the Berkeley commons, Townes had what most astronomers considered a radical and foolhardy idea: he wanted to search for molecules between the stars.

  The likelihood of finding interstellar water was considered akin to the chance that Neil Armstrong would report back that the Moon was made of cheese. The universe—m
uch like that view of the lunar regolith—was generally believed to be a dry, cosmic desert. In the two decades following the discovery of how stars create elements, one thing hadn't changed—astronomers still thought the universe was primarily elemental. While on Earth atoms join to form molecules—as occurs with water, carbon dioxide, and sugars, for example—astronomers believed that the rest of the universe was too diffuse and energetic a place for molecules to form and survive. We might be stardust, but we were fundamentally different from the rest of the cosmos. “We are complex; it is simple,” went the thinking.

  Townes, however, had come of age intellectually in the denouement of the great discoveries in quantum physics and the new era of its application. In the mid-1930s, he had earned his PhD at Caltech, where he talked physics on weekend hikes up Mount Wilson with the affable and brilliant young professor Robert Oppenheimer, who'd soon go on to lead the building of the first atomic bomb. When he graduated Caltech in 1939, Townes was disappointed that he couldn't get an academic post that would enable him to pursue his own research. He settled for an applied research job with the Bell labs, which turned out to be an ideal incubator for a man who would learn to talk with cosmic molecules. At the outbreak of World War II, Townes was assigned to the army of scientists tasked with developing new and better ways to see and therefore destroy the enemy. His job was to develop air force radar-guided bombing systems to enable pinpoint targeting, the equivalent of today's laser-guided smart bombs. As Townes and his colleagues developed one prototype after another, air force officials kept pushing them for more compact, lighter radar systems for planes. Townes worked on systems in the microwave region, first using a 10-centimeter wavelength, then 3 centimeters, and ultimately a measly 1.25 centimeters, about half the diameter of a US penny.

  It was at this final level that Townes tuned in to something larger. He recalled that a decade earlier, a team of American researchers had discovered that when microwaves were beamed through ammonia gas, the molecules absorbed the microwave radiation right at the 1.25-centimeter wavelength. Radar designers were not concerned about this blocking their radar signals because there's very little ammonia in Earth's atmosphere. But there's lots of water in the atmosphere, and other radar researchers cautioned that water molecules were predicted to absorb at around the same wavelength.

  For Townes, this caution wasn't so much a warning as a revelation. He saw that down in this largely unexplored netherworld of microwaves of around a centimeter in length was a whole new language, a way to communicate with molecules. Radar's sensitive microwave receivers could do more than lock on enemy targets; they could tune into otherwise invisible molecular targets. And just as radar could reveal information about a target—its speed, what it was made of—so microwaves could also reveal information about molecules, from their structures to their temperatures.

  During his free time, Townes pursued the other side of his radio passion. Inspired by Karl Jansky's discovery of cosmic radio waves, he began pondering the physical atomic processes that might create them. After the war, first at the Bell labs and then as a professor at Columbia University, Townes set to work pioneering a new field, microwave molecular spectroscopy, investigating the invisible light fingerprints of molecules.

  A molecule's unique light fingerprint, Townes and others realized, isn't caused by energy released and absorbed by electron quantum jumps or drops, as with single atoms, but because a free-floating molecule rotates, vibrates, or both. What's remarkable is that just as with the defined quantum jumps of electrons, this rotating and vibrating takes place only in discrete amounts, or quanta, at energies in the infrared and microwave. For example, Townes's favorite molecule, ammonia, is an amalgam of three hydrogen atoms in a pyramidal pattern around a central nitrogen atom. When the molecule is energized by a colliding particle or photon, it vibrates, the nitrogen going up and down like the surface of a trampoline, and the whole molecule repeatedly inverts itself like an umbrella turned endlessly inside out and back again—about twenty-four billion times a second. It's this vibrating, like the head of a molecular drum, that causes ammonia to emit a steady resonant beat at the microwave length of 1.25 centimeters.

  Similarly, water's microwave signal is the result of one or more of three possible rotational movements the molecule makes, particularly one that emits a microwave signal at a wavelength of 1.35 centimeters, just a little down the microwave scale from ammonia. With microwave ovens we use this phenomenon in reverse, firing microwaves to get water molecules in potatoes, milk, or soup, for example, rotating en masse, hitting one another and everything around them, and in the process heating up our dinner.

  By 1955, Townes and his Columbia University colleague and brother-in-law Arthur Schawlow had probed and prodded enough molecules with microwaves to write Microwave Spectroscopy, still the bible of the field. In this book, they outlined the theory, laboratory practices, and microwave molecular fingerprints that have guided subsequent generations of molecular spectroscopists. It was through these molecular insights that Townes envisaged the MASER (microwave amplification by stimulated emission of radiation), the first of which used the coordinated emission of microwaves by ammonia to create an energetic beam. It was just a jump along the electromagnetic spectrum for Townes, and others, to envision the laser, an optical light version of the maser.

  While working on molecules in uptown Manhattan, Townes always had one eye turned heavenward and his ear cocked for celestial microwaves. At an astrophysics meeting in Washington, DC, in 1953, much of the buzz in the seminar rooms and during hallway coffee chats was about the 1951 discovery of neutral hydrogen by its radio fingerprint, as predicted by Hendrik van de Hulst during the war. Based on his molecular spectroscopy work, Townes, an astronomy outsider, presented a paper that Fred Hoyle still remembered years later. Townes argued that, if they were there in the space between the stars, it should be possible to detect a suite of simple molecules, including hydroxide (the marriage of a single oxygen and hydrogen atom), carbon monoxide, ammonia, and water. Few astronomers paid any attention to his prediction. Not only did they think it was a fool's errand, but they also didn't have the wherewithal to begin to look for these molecules even if they'd wanted to.

  However, Townes infected one of his Columbia PhD students with enthusiasm for this stellar molecular mission. During the next half-dozen years, Alan Barrett risked his young career by searching for a molecule in space that everyone insisted wasn't there—until 1961, when Barrett and MIT's NASA-funded Lincoln lab engineer Sandy Weinreb detected a distinct cosmic microwave signal at eighteen centimeters, just the wavelength that Townes's group had predicted would be the cosmic molecular song of hydroxide. As the provost of MIT, Townes organized the celebratory press conference to announce the discovery. But while the cameras flashed and the journalists asked questions about this alien molecule that communicated in microwaves, Charles Townes was already moving on. His former student had doggedly pursued cosmic hydroxide and found it. Now Townes's own space mission was moving to launch.

  Although Townes had free rein to do whatever he wanted when he arrived at Berkeley in 1967, that didn't mean he'd be encouraged in his search for cosmic molecules. “The chairman of the department of astronomy here, George Field—a very good theorist, an excellent scientist—he kept telling me, ‘No, it can't be there. I can prove to you it can't be there,'” a ninety-four-year-old Townes told me in his chalkboard-dominated corner office on the top floor of Birge Hall at the University of California–Berkeley. By this time in his life, Townes was more than familiar with following his gut sense and his own eyes, when others thought that what he was doing was impossible. An example: on a walk in Copenhagen in the late 1940s, he'd described the idea for a maser to Niels Bohr. The revered father of quantum mechanics admonished his much younger colleague: “It's not possible, it's not possible.” With a twinkle in his eyes, Townes says of Bohr: “I don't think he understood what I was trying to describe.” Similarly, in 1945, Townes had gone to seek Ira Bowen
's advice on using radio waves in astronomy. Bowen, Townes's former professor at Caltech and now head of the Mount Wilson Observatory, said: “Well, I’m very sorry to tell you, but I don't think radio waves are ever going to tell us anything about astronomy.”

  But at Berkeley, Townes found an ally in Jack Welch, an engineer in the university's electrical engineering and computer science department who was involved with the nascent radio astronomy lab. Welch was less interested in astronomy dogma and more interested in how astronomers might use the new Hat Creek Radio Observatory twenty-foot antenna he'd just helped install in a mountain meadow near Mount Lassen in Northern California. Its maiden voyage would be the search for molecules. The question was, which one first? Townes considered trying to tune in to carbon monoxide, but its dominant microwave signal is at just above two millimeters, barely wider than a piece of paper is thick, and the Hat Creek antenna's surface was too rough for the job—the two-millimeter signal, if there, would be distorted in the antenna's surface irregularities.

  So Townes settled on trying to find an old friend: ammonia. With PhD student Al Cheung and postdoctoral fellow David Rank, he built an amplifier specially tuned to ammonia's 1.25-centimeter wavelength. In the early fall of 1968, Townes and his colleagues were set to go. They decided to begin their search in Sagittarius B, a mass of dark, dusty clouds near the center of our galaxy. As a reference point, they started by pointing their antenna toward the galactic center. Not a crackle. Then they moved it to point at Sagittarius B. From halfway across the Milky Way, in a region of space so different from Earth it's hard to imagine—a super-chilled -460° F—ammonia's microwave signal sprang to life in the Hat Creek Observatory's control room. Townes's 1.25-centimeter radar-guided bombing system had never flown, but, turned to the stars, he'd nailed his target on the first try. Cheung, Rank, and Townes had found interstellar ammonia. “How easy, and how exciting,” Townes later recalled. Given the ease with which they had tuned in to ammonia, the energized group thought about their next target. It quickly came into focus just up the microwave dial, at 1.35 centimeters: water. With just one look, the trio came up wet in Sagittarius B.