Given the pace with which they were finding molecules, the question now was how widespread they were. Before announcing the water results, they decided to look elsewhere, including in the famous Orion Nebula. Townes was hosting a Christmas-week party for his research group when he got the call. It was from Al Cheung, whose PhD would be based on the work. The sound of a buoyant party made it difficult to hear, but Townes knew Cheung was up at Hat Creek, not letting the holiday get in the way of his search. “It must be raining on Orion,” Cheung shouted. “It has a very strong water line.” In the Berkeley foothills, water—in the form of champagne—was raised in celebration. They'd later calculate that the water line from Orion was twenty times stronger than that from Sagittarius B. More than discovering cosmic water, it was the cause of this powerful molecular signal, hitting them like blast from a fire hose, that would reverberate to Townes's core. “It turns out I didn't invent the maser,” Townes tells me. “They have been out there for billions of years and nobody knew it.”
Townes had the Nobel Prize, but when all was said and done, Nature had beat him to it. His team had found the first astronomical water maser, a natural maser formed when starlight excites vast clouds of water molecules, causing them to beam an intense, amplified microwave signal. Hundreds of water masers have since been discovered, some pumping out more energy than the Sun, all along the 1.35-centimeter wavelength, making them the most powerful molecular radio stations in the universe. For Townes, a lifelong Christian and in his later years a proponent of intelligent design, it was as if creation was winking at the boy from North Carolina, as if to say, Yes, it had been here all the time, you just had to look. Or, maybe, to say that it was only the beginning of what the search would reveal.
THE COSMIC SEA
The discovery of water beyond our Solar System unleashed a flood of research that has reshaped and continues to influence astronomers' view of the universe. Water—the popular marriage between the most common element to emerge from the big bang, hydrogen, and the most common element formed by stars, oxygen—is one of the three most abundant molecules in the universe, after molecular hydrogen and in an unclear photo finish with carbon monoxide. When we look into the dark depths of the night sky now, we know that the Earth, rather than a watery oasis, is a tiny blue drip in a cosmic sea.
Few single discoveries of the Stardust Revolution have so dramatically changed our view of the universe. In fifty years, we've gone from looking out at what we thought was a bone-dry cosmos to seeing one that's wet in every crevice and corner. Now knowing how to look, astronomers find water almost everywhere they search for it, the vast majority of it in the form of very cold gas or ice. The cosmos is dripping from the very edge of time to today; it's at times raining or snowing around newborn stars and dying ones; it's swirling in vast, gaseous torrents on the violent shores of massive black holes at the hearts of galaxies; it's icing over the dust grains in the cold, dark clouds that are stellar nurseries; and, in our Solar System, it's frozen into moon-sized ice balls around Saturn and Jupiter—even vaporized on the surface of the Sun. NASA's “follow the water” mantra in the search for alien life has taken on cosmic proportions.
Townes's team first heard cosmic water's radio splash, but astronomers found that it is also very visible in the infrared. Seeing water in space, however, requires getting above the Earth's water-vapor-laden atmosphere, which absorbs cosmic water's signal. It wasn't until the launch of the European Space Agency's Infrared Space Observatory (ISO) in 1995 that astronomers began to realize the extent of the cosmic sea. When ISO trained its infrared spectrometer on the Orion Nebula star-forming region where Townes had first detected cosmic water, the instrument revealed that what Al Cheung had called rain was in fact a deluge. Scientists at ISO determined that—over a region with a diameter about a hundred thousand times the Earth–Sun distance—the Orion Nebula region is producing enough water to fill Earth's oceans sixty times every day. That works out to twenty-one thousand Earth oceans a year. For millennia.
That's a lot of water, but it was only a hint of things to come. Cosmic water making in vast quantities has been going on for a very long time, and now astrophysicists are in a cosmic water fight to see who can find the oldest water. In 2008, a research team using a German radio telescope announced the detection of a water maser around a massive black hole whose light had traveled for 11.1 billion years, situating this watery signal 2.5 billion years after the big bang. This record took the plunge in 2011, when radio telescopes in Northern California and then Hawaii picked up the steamy hiss of water vapor from twelve billion years ago. Not only is this the oldest body of water ever found, it's the largest. The American astronomers estimated that the gaseous ocean they'd spotted spanned hundreds of light-years. And it held 140 trillion times the water in Earth's oceans.
Much closer to home, the news has been similar. From its status as the only water bearer in the Solar System fifty years ago, Earth has dropped to middling class. At least four other Solar System bodies contain more water. Jupiter's moons make the Earth seem puddle-like: Ganymede has thirty-six times as much water as the Earth, and Europa has almost three times as much. The water on the surface of these Jovian moons is all solid ice. However, most planetary scientists think there are deep liquid seas below these icy crusts. Similarly, recent lunar sampling has revealed that the once seemingly parched Moon has abundant subsurface ice and thick water ice in craters at the lunar north and south poles—ice that could one day supply water for the inhabitants of a lunar colony. And, in the past decade, a series of NASA robotic missions to Mars has revealed that the red planet harbors abundant water ice reserves, and images of the Martian surface show rivulets possibly made by meltwater.
The presence of all this water has made astrophysicists turn to figuring out where it comes from. Few kids make it out of elementary school without drawing the Earth's water cycle—the endless movement of water evaporating from oceans; condensing in clouds; and falling back to the Earth's surface in rain, sleet, and snow to run back to the seas, where the cycle begins once again. Children of the Stardust Revolution can draw the cosmic water cycle. One big difference is that, whereas the terrestrial water cycle assumes the presence of water, the cosmic water cycle involves its formation from atomic scratch. And astrophysicists have discovered that, rather than cosmic water having a single wellspring, it is made in a myriad of ways. It appears that the cosmos pumps out water wherever it can. Whether the astrophysical environment is hot or cold, and whether stars are dying or being born, oxygen and hydrogen find each other and bond, sometimes for eternity.
There are at least four ways and environments in which hydrogen and oxygen meet and bond to form water. Just as older stars churn out dust and minerals, they also spout water. When the Herschel space telescope turned its sensitive infrared eye on the star CW Leonis in the constellation Leo, astronomers saw what was previously thought to be impossible. CW Leonis is a pulsating red giant star, also dubbed a carbon star for the amount of sooty carbon this elderly star emits. The astronomers expected to see lots of carbon, not steam. But there, deep in the star's atmosphere, was hot water vapor at a scalding 1,300°F. It had previously been thought that water wouldn't form around these carbon-rich stars because, before the oxygen could hook up with two hydrogen molecules, it would bind with the abundant carbon. Now it's believed that the water is formed when energetic rays of ultraviolet light from the star cleave molecules of carbon monoxide or silicon monoxide, liberating an atom of oxygen that then hooks up with the abundant hydrogen streaming by. It appears that CW Leonis is typical of stars between one and eight times the mass of the Sun: at the end of their lives, as they lose mass in the form of dust and molecules, much of what's poured out is water. In this way, the star both produces the oxygen and acts as the energetic matchmaker in catalyzing the formation of water.
And water is not just formed around dying or embryonic stars. The cold, dense molecular clouds in which stars are born also turn out to be ideal for m
aking water. Water in turn repays the favor; like dust, it radiates heat in the infrared, enabling a collapsing cloud of dust and gas to continue collapsing. It's also thought to form in interstellar space, when molecular hydrogen is zapped and cleaved by a cosmic ray, the hydrogen then interacting with atomic oxygen.
But what really gets the scientists of the Stardust Revolution excited is the final place water is thought to both form and remain during its interstellar odyssey: on cosmic dust. During the advent of research on cosmic dust in the early 1960s, speculation arose from an analysis of their light fingerprints that these rocky or carbonaceous grains were iced over. Today we know that interstellar dust grains are in fact dirty molecular ice balls—bits of dust glued together with ice and encrusted with it. In interstellar space, it appears that dust plays the matchmaker in providing a surface that helps oxygen and hydrogen both meet and bond. In 2009, scientists reported that in a laboratory in France they'd pelted a mock interstellar grain with atomic beams of oxygen and hydrogen under interstellar conditions, and voilà, water had formed on the grain surface. Other researchers have found similar results and have discovered that grains ice over much faster than previously thought possible.
The combination of cosmic ice and dust might sound about as exciting as coming out of your house to find your car windshield covered with hard frost on a January morning, but for stardust scientists the combination of water and a solid surface is molecular paradise. Water was dubbed “the universal solvent” long before its cosmic origins were discovered. “Universal” pays tribute to water's ability to dissolve most things—to get molecules to mix and meet in its watery matrix, such as inside the human body. Water is life's matrix. Thus an icy interstellar grain becomes much more than just a dirty cosmic iceberg; it's the perfect place for something that was once thought to take place only on Earth: chemistry.
JOINING HEAVEN AND EARTH
Charles Townes's detection of cosmic water and ammonia involved more than the discovery of two molecules in outer space; it was the breaking of a cosmic molecular barrier. Water and ammonia aren't esoteric ionized molecules that can be dismissed as molecular space oddities; they are among the most familiar molecules on Earth, ones that until just then almost no one had thought could exist in interstellar space. And the number of atoms in cosmic molecules was marching upward. Water has three atoms; ammonia, four; what else was out there? Wherever they were, radio astronomers, and soon infrared astronomers as well, began tuning their telescopes for the messages from potential cosmic molecules. In the process, they transformed themselves into a new breed of astronomers: astrochemists.
When Townes pioneered the search for molecules in space, these scientists christened their nascent research niche “molecular astrophysics.” A decade later, the field had matured from fanciful science fiction to peer-reviewed science—the transformative discipline of astrochemistry. The very term astrochemistry captures the philosophical phase shift that is the Stardust Revolution. Etymologically it's an oxymoron. Though the word's origins are debated, one possible source for chemistry derives from the ancient Egyptian word keme (chem), meaning “black earth”; it is also the name given to Egypt itself. By its very nature, chemistry is terrestrial; it's of and about the Earth. It relates to the very small, to atoms and molecules. In contrast, astronomy is about the nature of the stars, the largest bodies in the universe. With astronomy we look away from Earth, to the beyond; with chemistry we've conventionally looked inward at ourselves and the Earth. The new field of astrochemistry literally joins heaven and Earth as one system.
This transformation came just in time for Lucy Ziurys, now an astrochemist at the University of Arizona and director of the Arizona Radio Observatory's 12 Meter Telescope. “It was in 1977, [as] I began to write graduate school applications, that I read about the discovery of the first interstellar molecules. This just caught my imagination,” recalls Ziurys, who entered Berkeley's astronomy department as a PhD student in 1978 to work in the new field that Townes and others were pioneering.
Ziurys is a child of the Stardust Revolution. Few have a more visceral sense of the grand hopes and sometimes false promises and dead ends that are the stuff of revolutionary science and technology. She grew up on the knee, literally, of the dream of space travel. Born on May 6, 1957, she was barely five months old when the Soviet Union's Sputnik 1 satellite rocketed into space, the satellite's rhythmic and ethereal beep, beep, beep audible on shortwave from the Ziurys's Annapolis, Maryland, home. It was the Soviets' message to the world that the space age had begun. Eighteen months later, US president Dwight D. Eisenhower threw the Cold War space race into high gear with the creation of NASA, the National Aeronautics and Space Administration.
The Ziurys household was a space-age scientific incubator. Her father, Eugene Julius, was a member of the first generation of American rocket scientists. During the 1960s, Mr. Ziurys brought home stories of a world where the limits on the future were bound only by the imagination. After designing nuclear-powered commercial aircraft (which never, fortunately, took off), he became a project engineer with NERVA (Nuclear Engine for Rocket Vehicle Application), a program originated to use the power of the atom to blast humans into outer space. The program was supported by NASA and the even now futuristic-sounding Atomic Energy Commission Space Nuclear Systems Office. Ziurys's last job before he retired was working on the development of nuclear fusion, the still-unfulfilled dream of producing energy on Earth as it's done in stars. Lucy Ziurys followed her father's space-science path, enrolling at Rice University in Houston, Texas, an informal preschool for NASA's nearby Johnson Space Center. But in her senior year, she faced the dilemma of the bright and deeply curious: she was equally fascinated by astronomy, physics, and chemistry—her mother Genevieve was an industrial chemist who taught high-school chemistry. At this point in their budding academic careers, most students specialize in one discipline or another. Ziurys didn't want to let go of any of these interests. That's when she stumbled across a quiet scientific revolution. For the young Ziurys, interstellar molecules weren't about a dawning scientific transformation but a personal one. Here was a field where she could search for new interstellar molecules using all the subjects she loved: physics, astronomy, and chemistry.
“The whole term ‘astrochemist' used to be what astronomers considered a dirty word,” says Ziurys. “When I had my grand idea of combining chemistry, astronomy, and physics, a lot of people laughed at me and said, ‘Go into astronomy or work in the lab.' This idea of combining things wasn't very well accepted.”
Now one of the world's leading astrochemists, Ziurys has a tomboyish pluck, a demeanor that speaks to the business at hand. During my visit at the end of a fall term, one of Ziurys's PhD students stood in her adviser's doorway late one Friday afternoon and said she was leaving for the graduate-student Christmas party. “What about the paper?” asked Ziurys, eyebrows raised, smileless. “My whole dream as a graduate student was to detect a new molecule,” Ziurys says. “It never worked. So every time one of my graduate students finds a new molecule I just laugh. OK, you get to do what I didn't get to.” Since her 1984 PhD thesis, she's more than made up for it. Ziurys has discovered, along with colleagues and graduate students, almost two dozen cosmic molecules, one-seventh of all those found—possibly the world-record number of such discoveries.
RED GIANTS AND WHITE DWARFS
Ziurys takes a two-pronged approach in probing the cosmos' molecular nature: she sees what can be cooked up in the lab, identifies its molecular spectrum, and then, with molecular light fingerprint in hand, she heads to Kitt Peak and other radio telescopes to see if the molecules are out there. Through this detailed mix of laboratory and radio telescope work, Lucy Ziurys is among a group that's been able to do more than spot interstellar molecules. She has helped lead astrochemistry to a new level: not just describing the detection of molecules but also revealing how and where they're formed. In the past decade, Ziurys and others have made a remarkable discovery: some star
s make atoms on the inside and molecules on the outside. Just as Fred Hoyle, William Fowler, and the Burbidges described the process of how stars forge elements, Ziurys and other astrochemists are mapping out a spectacular, complicated process of stellar molecular synthesis. The same stars that fascinated Paul Merrill with their light fingerprints of heavy elements and Hoyle with their ability to make carbon are turning themselves into the molecules of life. “Organic chemistry starts back in the stars, where we have a carbon-rich environment,” says Ziurys. Organic chemistry, the chemistry based on the carbon atom, starts not on Earth but around the very stars that have forged that carbon atom in their hearts: red giants.
There's hardly an epic Norse saga, whether of mighty Odin or, later, Beowulf and the monster Grendel, that compares with the true tale of our ancestors who in their dying days rose up as red giants only to end as white dwarfs. Over the past century, astronomers have gradually pieced together the life history of stars, like our Sun, that have a birth weight between one and eight times the Sun's mass. For most of their billions-of-years-long lives, from birth through middle age, these stars have stable lives—a period dubbed the main sequence—during which they're fueled by burning hydrogen in their cores. But in the last moments of their lives, over the course of less than a million years, and with much of the activity occurring in only ten thousand years, these dying stars shed about 80 percent of their mass.
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