The Stardust Revolution

by Jacob Berkowitz

  Where once there was obscuring dust, there are now sparkling crystals. About a dozen astrominerals have been identified on the basis of their infrared light fingerprint, including graphite, moissanite (silicon carbide), and a green one called olivine. We know it's green because olivine is one of the most common minerals on Earth: it is found in the gemstone peridot, gives a green tint to some Hawaiian beaches, and is one of the dominant minerals in the Earth's core. Olivine is creating a green-hued sparkling crystal shower around newborn stars throughout the Milky Way, and it now appears that some of the crystals are the result of a kind of stellar blast furnace. Olivine is part of the silicate family of minerals, the most abundant minerals on Earth, a family that includes silicon dioxide, or silica, the main ingredient in glass. It forms at temperatures as hot as lava, and while this might occur in the shock wave of a supernova, the crystal might also be getting cooked up in stellar blasts from young stars that heat amorphous silicate dust, creating more organized crystalline forms. In before-and-after images from a prolonged period of stellar blasts, Spitzer scientists noticed a marked increase in the amount of crystalline material in the dust disk around a young star.

  In the young field of astromineralogy, the one finding that has created perhaps the most buzz is the discovery of an astromineral that, here on Earth, is associated with the extremes of love, wealth, and strife: diamonds. The cosmos' first diamonds didn't form deep inside planets. They formed around stars. These symbols of eternal commitment were likely the universe's first crystals. At the very edge of time, glittering in the cosmos' first starlight, there were diamonds. On first glance, diamonds and graphite, or pencil lead, have nothing in common. But they're actually twins; both are pure carbon, just in different forms. Rearrange the carbon atoms, and graphite from a red giant star becomes astro-bling. These stellar diamond grains wouldn't impress most fiancées, at least not without a scanning electron microscope at hand. Stellar nano-diamonds aren't measured in carats but rather in carbon atoms; there are about a thousand atoms in a typical grain. Yet they are out there, possibly condensed from stellar outflows in a process analogous to the way artificial diamonds are made here on Earth; perhaps shocked into being by supernovas or maybe formed by the blast-furnace burps of newborn stars. As much as a third of the carbon dust from red giant stars emerges in the form of nano-dia monds. One way or another, the cosmos is a vast mine of them.

  In one of the greatest about-faces in science, cosmic dust has gone from an astronomical nuisance to a critical missing link in our evolutionary journey from the stars. It's the great connector—we are indeed all connected through cosmic dust billions of years back and into eternity. While astronomers focused on the stars, it was in the cosmic dust that we'd find our gritty beginnings. The saying “dust to dust” starts with the stars. The bad news on the cleaning front is that you can't have our kind of universe without dust. Forget string theory, branes, and alternate universes. Without cosmic dust we wouldn't even have the universe we call home. Cosmic dust is essential for the birth of Sun-like stars, and it's the cosmic raw material for everything that we think of as “stuff,” from meteorites to planets and from me to you. The dark bits are the universe's great element-recycling depots, the origins of stars and planets and, ultimately, people. A new breed of cosmic-dust scientists has shown that we're not just made of stardust; it's the ship for our collective epic cosmic odyssey.

  Today in the Stardust Revolution, the talk about dust isn't focused on light extinction but on its role in the origin of life. In a 1962 article that started a new way of seeing—turning the haze between stars into stardust—Fred Hoyle and Chandra Wickramasinghe reflected on the cosmic ecological consequences of a universe full of tiny graphite flakes. They suggested that these tiny graphite grains might be the multitudinous equivalent of cosmic test tubes, ideal locales for interstellar chemistry and the formation of carbon-based molecules. Each grain of stardust might be a microscopic world, a tiny terra nova, a stage on which the next chapter of the Stardust Revolution could play out. But for this new view of stardust to develop required yet another new way of seeing.

  The surface of the Earth is the shore of the cosmic ocean. From it we have learned most of what we know. Recently, we have waded a little out to sea, enough to dampen our toes or, at most, wet our ankles. The water seems inviting. The ocean calls. Some part of our being knows this is from where we came. We long to return.

  —Carl Sagan, Cosmos, 1980

  TUNING IN TO MOLECULES

  In more ways than one, the fifty-mile drive from the University of Arizona campus in Tucson to the Kitt Peak National Observatory is a journey from one world to another. Mostly it's the journey from Starbucks to stardust. The city of Tucson is a modern-day desert mirage—a spreading metropolis of low-level, cacti-gardened, upscale homes in the middle of a dusty desert fed by dwindling supplies of water from the distant Colorado River. Driving out of the city, as the last strip malls, gas stations, and warehouses give way, you enter the world as it was—the Sonora Desert. Tall saguaro cacti, the walking cacti, appear to march up the low, rounded hills that undulate across the desert. It's an expansive, mysterious landscape, populated with exotic creatures such as scorpions; rattlesnakes; and the small, wild, very hairy pigs known as javelina.

  Halfway to Kitt Peak, down Route 86 and about forty miles north of the Mexico–United States border, we pass a police checkpoint blocking the way. The police are searching for illegal aliens—Mexicans and other Latin Americans fleeing poverty and violence to enter this less-than-welcoming land of greater opportunity. The burly border-patrol guards, one holding back a sniffing German shepherd, wave us through. I’m traveling with two twentysomething astrochemistry graduate students from the University of Arizona's Steward Observatory. We're also searching for aliens, but of a different sort than what the guards and dogs are looking for.

  While the US border patrol now tries to keep out illegal immigrants, early peoples in this area weren't too keen on the arrival of the first European settlers. The Tohono O’odham people have occupied this area for thousands of years. To them, Kitt Peak, its reddish rock rising two-thirds of a mile from the desert floor, a wonder of altitude amid this horizontal expanse, is still part of their tribal lands and is part of a sacred mountain range known as I’itoi's Garden. I'itoi is also known as Elder Brother or Earth Maker—the creator. To the Tohono O’odham, Baboquivari Peak, a massive cubic outcrop of granite to the southeast of Kitt Peak, is the center of creation, the place where all life began.

  Standing atop Kitt Peak, you can believe it. In the cooler, greener mountain air, one feels a sense of otherworldliness looking out at an arid, barren landscape that appears to go on forever. For astronomers, Kitt Peak is also an ideal, scientifically sacred place to explore and contemplate the place where all life began. Situated high in the arid desert, the site has excellent “seeing” because the air column above it is often stable and dry. It also has excellent listening. The Kitt Peak National Observatory, which coordinates the cosmic viewing from the mountaintop, hosts a collection of more than twenty different telescopes, including the Arizona Radio Observatory's descriptively named 12 Meter Telescope. I’ve come to visit this “ear” to the cosmos.

  The white dome housing the 12 Meter Telescope looks like the kind of shell that covers optical telescopes, but what's inside looks like a giant satellite dish. There's no long tube with glass mirrors for focusing light; “12 Meter” refers not to length but to the diameter of the massive metallic dish that acts as a great ear to the universe. It doesn't matter whether it's day or night: this radio telescope sees not light waves but radio waves—whispers from the universe. Just as an optical telescope focuses light, the large dish focuses incoming radio waves, and a receiver in turn amplifies the signal and channels it to computers and the astronomers inside the control room.

  Just like the finely polished mirrors of an optical telescope, the 12 Meter's dish is a masterwork of fine-tuning. “There's only seventy-five micro
ns of bumpiness across the telescope's twelve-meter face,” says Bob Freund, the telescope's no-nonsense, long-time principal electrical engineer, as we stand looking up at the massive dish. That's less than half the width of a human hair and far smaller than the millimeter wavelengths at which the telescope “sees.” If anything out there is broadcasting in the 12 Meter's range, the radio telescope has a good chance of hearing it.

  If you're familiar with radio telescopes, it's probably because of their use in the search for extraterrestrial intelligence (SETI), particularly the giant, thousand-foot-wide Arecibo radio telescope in Puerto Rico. Perhaps you remember actress Jodie Foster, eyes wide with wonder, listening on headphones to an alien message via radio telescope in Contact, the movie based on Carl Sagan's 1985 book of the same name. The 12 Meter telescope is trying to make contact not with distant civilizations but with molecules. Radio telescopes have opened astronomers' eyes to another previously invisible part of the cosmos—its complex chemical nature.

  To give me a sense of just how chemically alive the universe is, Bob Freund asks the controller to point the dish randomly at 60° north. The huge dish pivots until it's pointed up and out across the desert into the intense blue of the afternoon sky. We wait a moment as the telescope tunes in. And then, there it is on the display screen—the telltale peaks and troughs, like those on a cardiac monitor measuring a heartbeat, of the signal from trillions of interstellar molecules light-years away, vibrating to the energy from distant stars and sending their radio story out through the universe.

  Later, as I drive with Freund back to Tucson, the setting Sun turning the desert into deepening shades of pink, he reflects on the marvel of his radio telescope on the mountain behind us. “It's just a big garbage-can lid,” he confides to me. “With it, we can detect molecules light-years away. It's lousy with them out there.” Fifty years ago, astronomers believed that it was impossible that even the simplest molecules could form around a star or in interstellar space. For these astronomers, the Earth was more than just the only planet with life; it was also the only known place in the cosmos with complex organic, or carbon-based, chemistry—the foundational molecules of life. But radio telescopes have revealed an otherwise invisible universe.

  Radio astronomers haven't discovered alien life, but perhaps they have discovered something more profound. “Our observations suggest a universal prebiotic chemistry,” says Jan Hollis, a veteran American radio astronomer who has discovered more than a dozen complex carbon molecules, including the first sugar found in interstellar space. Wherever astronomers look, from around dying stars to the depths of interstellar space—the cold, dense clouds from which stars emerge—they now see that the universe abounds with molecules. Far from being alien, most of these molecules look very familiar: they are the building blocks of life. Astronomers don't see other life, but they see life's precursor molecules, like footprints in the sand leading up to its doorway.

  RADIO WHISPERS FROM THE UNIVERSE

  The first person to actually hear cosmic radio signals thought he somehow had his wires crossed. It was a serendipitous discovery and without doubt the greatest scientific offshoot of the ongoing effort to avoid dropped phone calls. In 1927, the Bell Telephone Company in the United States introduced the first transatlantic call service. Seventy-five dollars bought callers three minutes of air time from New York to London via radiotelephone, which converted their voices into radio waves that were bounced from the ocean surface to the ionosphere, or upper atmosphere, across the Atlantic Ocean. But there was a problem: many calls were disrupted by electrical static.

  Karl Jansky, a young engineer at Bell's Holmdel, New Jersey, laboratories, was asked to figure out what was causing the interference. Jansky embraced the project with gusto. He built a large antenna mounted on a turntable so that he could track the source of the interference and then doggedly began searching for it. By 1932, he'd figured out that thunderstorms were partly to blame. But there was something else that was producing a very steady hiss-type static. Jansky continued to track this hiss, turning his antenna this way and that, until he realized that the sound wasn't coming from anything on Earth; it came from above his head. He'd tuned into the Milky Way. His report, “Electrical Disturbances Apparently of Extraterrestrial Origin,” marked the birth of radio astronomy.

  For astronomers, the fact that the universe was sending out radio waves was greeted with head scratching and dismissal as a cosmic novelty rather than a serious topic. Astronomers had no experience with radio technology. Radio itself was new; radio broadcasts having begun only in the early 1920s. People felt awed by the ability to tune in to a new radio station across town; the idea of tuning in to the cosmos was just too far-out. Dutch American radio astronomy pioneer Grote Reber summed up most astronomers' responses to the discovery of stellar radio waves when he observed that they “could not dream up any rational way by which radio waves could be generated, and since they didn't know of a process, the whole affair was [considered by them] at best a mistake and at worst a hoax.”

  World War II changed that. The war transformed the way a generation of physicists and engineers, and some astronomers, thought about electromagnetic radiation. They received training in thinking not about waves of visible light but rather about microwaves and radio waves. During the war, legions of Allied and Nazi physicists and engineers raced to develop new and improved forms of radar, which gave them the ability to use radio waves and shorter microwaves to detect otherwise invisible objects that were obscured by distance and darkness. There was soon a clear hint that tracking enemy movements overlapped with astronomy. The most notable crossover occurred on the morning of February 12, 1942, when two German battleships passed through the English Channel undetected by British naval radar. The British were terrified. Had the Nazis developed a new radar-jamming technology? J. S. Hey, the British physicist assigned to troubleshoot the situation, discovered an unexpected, politically neutral source of the radio interference: the rising Sun. Somehow, the Sun's intense sunspot activity was producing a river of interfering radio waves.

  After the war, astronomers at observatories across Europe, in Britain, and, to a lesser extent, in the United States scrounged up war-surplus radar materials. The most sought-after were the 7.5-meter Würzburg Riese antennae used in the German air defense radar system. Antennae that had been turned skyward to watch for Allied bombers were now turned to look deeper into the night sky, all the way to the stars. With all these antennae turned to the heavens, a new view—a radio view—of the cosmos began to take shape. It wasn't just the Milky Way's stars or the Sun that were communicating in radio waves, the universe was abuzz with them. In 1948, Cambridge astronomers using two Würzburg Riese antennae tuned in to an intense radio signal in the constellation Cassiopeia. They'd stumbled on the remains of a supernova, a stellar explosion still sizzling in radio waves. In 1955, two American astronomers trying to figure out what was causing interference with their radio telescope realized they were tuning in to Jupiter. By 1959, another pair of American scientists tweaked the idea that if you could tune in to stars and planets, you might also be able to pick up alien radio broadcasts from across the Milky Way. Within a year, American astronomer Frank Drake began the first radio-telescope search for interstellar communication, using the US National Radio Astronomy Observatory in Greenbank, West Virginia, setting the stage for today's SETI projects. By 1964, back at the Bell labs in New Jersey, Arno Penzias and Robert Wilson were trying to figure out what was causing the steady radio static on their twenty-foot radio telescope. At one point, they climbed up the antenna to clean it, thinking the static might be caused by encrusted pigeon poop. It wasn't the bird crap; it was the cosmos talking to them. At the same site where Jansky had been surprised by the song of the Milky Way, Penzias and Wilson had serendipitously tuned in to the cosmic microwave background, the attenuated birthing sounds of the big bang, a radio astronomy fluke that earned them the 1978 Nobel Prize in Physics.

  For all this growing buzz
over the sounds of the big bang or dying stars, it was on a much smaller level that a handful of astronomers believed their radio telescopes could make a huge difference. They didn't want to search for big objects but tiny ones: atoms and molecules. This molecular radio dreaming started in Nazi-occupied Holland during a gathering of Dutch astronomers in mid-1944, at the largely empty Leiden University where PhD student Hendrik van de Hulst shared a remarkable insight. He imagined that just as atoms and molecules in stars have distinct visible light fingerprints, they also emit distinct signatures at radio wavelengths—each molecule is its own tiny radio station, broadcasting at a particular frequency. So, van de Hulst suggested, if you knew a molecule's frequency, you could tune in and see if it was in outer space, as if tuning in to your favorite radio station.

  Van de Hulst's quantum calculations indicated that every neutral hydrogen atom should emit an atomically faint radio signal, and since hydrogen is the cosmos' most abundant atom, this signal might turn into a hydrogen radio roar. And, van de Hulst said, he'd calculated the channel: look for it at a wavelength of twenty-one centimeters. By 1951, three research groups, using surplus war equipment, tuned in to interstellar hydrogen, soon revealing the Milky Way to be full of vast, diffuse clouds of it. This discovery of galactic clouds of hydrogen didn't, however, spark a radio search for other atoms or molecules. Hydrogen, astronomers believed, was in a class of its own—it was the abundant, simplest building block of the cosmos. Hydrogen could survive, but there was no point in searching for scant amounts of other atoms, let alone molecules—the marriage of two or more atoms. The cosmos was simply too harsh a place—too hot or too energetic—for molecules either to form, or, in the off chance they did form, to avoid being immediately ripped asunder. The cosmos, they believed, was elemental.