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  Keck consists of two identical telescopes. Both have 10-meter mirrors made of thirty-six segments; with its support structure, each segment weighs close to a thousand pounds, costs close to a million dollars, and would suffice to create a fine, university-grade telescope on its own. The telescopes' "tubes" are spindly steel skeletons that look as delicate as spiders' webs but are more precisely configured than a racing sloop's rigging. "We use the telescope's mission to motivate ourselves," one Keck astronomer told me. "If a little wire or something is found intruding into the optical path, we think, If the light has been traveling through space for 90 percent of the history of the universe, and it got this close to the telescope, we'd better make sure it gets the rest of the way."

  Few of the astronomers awarded time on the big telescopes actually go there to observe anymore. Most submit their requests electronically—on a recent night at Gemini, the scheduled projects ranged from "Primordial Solar System Masses" to "Magnetic Activity in Ultracool Dwarfs"—and the results are sent back to them. Geoff Marcy, a modern-day Prince Henry the Navigator, whose team has discovered more than 150 planets orbiting stars other than our sun, gets more observing time than most at Keck but has not been there for years. Instead, his extrasolar-planet team observes from a remote operating facility at UC Berkeley. During observing runs, Marcy reports, "we settle into a routine of working all night. We have all our books and other resources here at hand, plus enough normal life so our spouses don't forget us."

  In addition to their unprecedented light-gathering power, today's big telescopes benefit from their adaptive optics (AO) systems, which compensate for atmospheric turbulence. The turbulence is what makes stars glitter; telescopes magnify every twinkle. A typical AO system fires a laser beam into a thin layer of sodium atoms 56 miles high in the atmosphere, causing them to glow. By monitoring this artificial star, the system determines how the air is churning and adjusts the telescope's optics more than a thousand times each second to compensate. Gemini pays a pair of students ten dollars an hour to sit outside the dome all night, walkie-talkies in hand, ready to warn the astronomers to turn off the laser should an airplane approach. "It's incredible to see in practice," says Scott Fisher. "When the AO system is off, you see a nice, pretty star that looks a little fuzzy. Turn the AO on, and the star just goes phonk! and collapses to a tiny point."

  Objects in the night sky are measured in degrees, the full moon spanning about one half of a degree. Without AO, a powerful telescope on a fine night can perceive objects separated from each other by as little as one 3,600th of a degree, or one arc second. Thanks to Keck's AO system, UCLA astronomer Andrea Ghez was able to make a motion picture of seven bright stars whirling around the invisible black hole at the center of our galaxy over a period of fourteen years: the entire movie takes place inside a box measuring only one arc second on a side. Based on the frenzy of the stars in the grip of the black hole, Ghez calculated that it has the mass of 4 million suns, generating enough gravitational force to slingshot some stars that pass too close right out of our galaxy. Several such hypervelocity stars have been located, speeding off toward the depths of intergalactic space like party crashers ejected from an exclusive nightclub.

  What's next? Even bigger telescopes, of course, with the capability to shoot cosmic pictures faster, wider, and in even greater detail. Among the behemoths due to come on line within a decade are the Giant Magellan Telescope, the Thirty Meter Telescope, and the 42-meter European Extremely Large Telescope—a scaled-down version of the 100-meter Overwhelmingly Large Telescope, which was tabled at the planning stage when its projected budget turned out to be overwhelming too.

  Particularly innovative is the Large Synoptic Survey Telescope, or LSST, whose 8.4-meter primary mirror was cast last August in a spinning furnace under the stands of the University of Arizona Wildcats' football stadium in Tucson. (The rotation technique produces a mirror blank that is already concave, reducing the amount of glass that must be ground away to bring the mirror to a proper figure.) Conventional telescopes have narrow fields of view, typically spanning no more than half a degree on a side—much too narrow to take in the enormous patterns that grew out of the big bang. The LSST will have a field of view covering 10 square degrees, the area of fifty full moons. From its site in the Chilean Andes, it will be able to image galaxies far across the universe in exposures of just 15 seconds each, capturing fleeting events to distances of over 10 billion light-years, 70 percent of the way across the observable universe. "Since we'll have a big field of view, we can take a whole lot of short exposures and— bang, bang, bang, bang—cover the entire visible sky every several nights, and then repeat," says LSST Director Tony Tyson. "If you keep doing that for ten years, you have a movie—the first movie of the universe."

  The LSST's fast, wide-angle imaging could help answer two of the biggest questions confronting astronomers today: the nature of dark matter and the nature of dark energy. Dark matter makes its presence known by its gravitational attraction—it explains the rotation speed of galaxies—but it emits no light, and its constitution is unknown. Dark energy is the name given to the mysterious phenomenon that for the past 5 billion years has been accelerating the rate at which the universe expands. "It's a little bit scary," says Tyson, "as if you were flying an airplane and suddenly something unknown took over the controls."

  The LSST could help solve these immense riddles thanks in part, oddly enough, to the science of acoustics. The big bang was noisy. Although sound cannot propagate through the vacuum of today's space—as pedants are fond of reminding the directors of science-fiction films—the early universe was a thick plasma and as alive with sound as a drummers' convention. Certain tones resonated in the primordial plasma like the tones of struck wineglasses, and these harmonies, etched into sheets of galaxies that today shamble across billions of light-years, contain precise information about the nature of dark matter and dark energy. If astronomers can map these large-scale structures accurately, they should be able to identify the signatures of dark matter and dark energy in the big bang's harmonics. The Sloan Digital Sky Survey, a pioneering wide-angle study, captured some of this information when it mapped the sky from 1999 through 2008. The LSST is designed to go much deeper into cosmic space. It may not resolve the mysteries, but, predicts Tyson, "it will go a long way toward showing what dark energy and dark matter aren't."

  The LSST's photographic "speed" will also give astronomers a better look at events too short-lived to be readily studied today. Most astronomers, even amateurs using backyard telescopes and off-the-shelf digital cameras, regularly record fleeting events of unknown origin. You take a series of digital exposures, and in one of them a spot of light appears where none was before or after. It may have been a cosmic ray hitting the light-detection chip, a high-velocity asteroid hurtling through the field of view, or a blue flare on the surface of a dim red star. You just don't know, so you shrug and move on. Because the LSST will take so many repeat exposures of the entire sky, it could resolve many such riddles.

  Tomorrow's enormous telescopes will do as much in one night as today's do in a year, but that will not necessarily render the older telescopes obsolete. When the giants come on line, says Scott Fisher, "the Geminis of today will become the telescopes that get to go out and do the surveys," finding interesting phenomena for the largest scopes to investigate in detail. "It's like a pyramid, and it feeds both ways: when a really big telescope finds something exciting that we can't spend every night observing, the astronomers can apply for time on a smaller telescope to, say, check it out every clear night for a year and see how it changes over time."

  Orbiting space telescopes are opening up another dimension. NASA's Kepler satellite, which launched in March 2009, is methodically imaging the constellation Cygnus, looking for the slight dimming of light caused when planets—some perhaps Earthlike—transit in front of their stars; Geoff Marcy's team will then use Keck to scrutinize stars flagged by Kepler to confirm that they have planets. In the
future, pairs of mirrors deployed in orbit and linked by laser-ranging systems could attain the resolving power of telescopes measuring thousands of meters across. One day, observatories sitting in craters on the far side of the moon may probe the universe from surroundings ideally quiet, dark, and cold. The coming combination of smart satellites talking to big, increasingly automated ground telescopes, themselves linked together by fiber-optic networks and employing artificial intelligence systems to search out patterns in the torrents of data, suggests a process as much biological as mechanical, akin to the evolution of global eyes, optic nerves, and brains.

  Film directors like to say that each movie is really two movies—the one you make and the one you say you're going to make while raising the money. The point is that nobody can accurately predict the outcome of any genuinely creative venture. The same is true of scientific discovery: scientists can explain what they expect to accomplish with bigger and better telescopes, but such predictions are mostly just extrapolations from the past. "If you're going to Washington to seek funding for a new telescope and you make a list of what you'll see through this new window on the universe, you know that the most interesting thing it will discover is probably not on your list," says Tyson. "It's likely to be something totally new, some out-of-the-box physics that's going to blow our minds."

  The marvelous model of the big-bang universe pieced together in the twentieth century arose largely from just such unanticipated discoveries. Edwin Hubble discovered the expansion of the universe accidentally, at the telescope: cosmic expansion had been implied by Einstein's general theory of relativity, but Hubble knew nothing of the prediction, and not even Einstein had taken it seriously. Dark matter was discovered accidentally; so was dark energy. A telescope doesn't just show you what's out there; it impresses upon you how little you know, opening your imagination to wonders as big as all outdoors. "The spyglass is very truthful," said Galileo.

  TIMOTHY FERRIS Seeking New Earths

  FROM National Geographic

  IT TOOK HUMANS thousands of years to explore our own planet and centuries to comprehend our neighboring planets, but nowadays new worlds are being discovered every week. To date, astronomers have identified more than 370 "exoplanets," worlds orbiting stars other than the sun. Many are so strange as to confirm the biologist J. B. S. Haldane's famous remark that "the universe is not only queerer than we suppose, but queerer than we can suppose." There's an Icarus-like "hot Saturn" 260 light-years from Earth, whirling around its parent star so rapidly that a year there lasts less than three days. Circling another star 150 light-years out is a scorched "hot Jupiter," whose upper atmosphere is being blasted off to form a gigantic, cometlike tail. Three benighted planets have been found orbiting a pulsar—the remains of a once mighty star shrunk to a spinning atomic nucleus the size of a city—while untold numbers of worlds have evidently fallen into their suns or been flung out of their systems to become "floaters" that wander in eternal darkness.

  Amid such exotica, scientists are eager for a hint of the familiar: planets resembling Earth, orbiting their stars at just the right distance—neither too hot nor too cold—to support life as we know it. No planets quite like our own have yet been found, presumably because they're inconspicuous. To see a planet as small and dim as ours amid the glare of its star is like trying to see a firefly in a fireworks display; to detect its gravitational influence on the star is like listening for a cricket in a tornado. Yet by pushing technology to the limits, astronomers are rapidly approaching the day when they can find another Earth and interrogate it for signs of life.

  Only eleven exoplanets, all of them big and bright and conveniently far away from their stars, have as yet had their pictures taken. Most of the others have been detected by using the spectroscopic Doppler technique, in which starlight is analyzed for evidence that the star is being tugged ever so slightly back and forth by the gravitational pull of its planets. In recent years astronomers have refined the Doppler technique so exquisitely that they can now tell when a star is pulled from its appointed rounds by only one meter a second—about human walking speed. That's sufficient to detect a giant planet in a big orbit or a small one if it's very close to its star, but not an Earth at anything like our Earth's 93-million-mile distance from its star. Earth tugs the sun around at only one-tenth walking speed, or about the rate that an infant can crawl; astronomers cannot yet prize out so tiny a signal from the light of a distant star.

  Another approach is to watch a star for the slight periodic dip in its brightness that will occur should an orbiting planet circle in front of it and block a fraction of its light. At most a tenth of all planetary systems are likely to be oriented so that these mini-eclipses, called transits, are visible from Earth, which means that astronomers may have to monitor many stars patiently to capture just a few transits. The French COROT satellite, now in the third and final year of its prime mission, has discovered seven transiting exoplanets, one of which is only 70 percent larger than Earth.

  The United States' Kepler satellite is COROT's more ambitious successor. Launched from Cape Canaveral last March, Kepler is essentially just a big digital camera with a .95-meter aperture and a 95-megapixel detector. It makes wide-field pictures every thirty minutes, capturing the light of more than 100,000 stars in a single patch of sky between the bright stars Deneb and Vega. Computers on Earth monitor the brightness of all those stars over time, alerting humans when they detect the slight dimming that could signal the transit of a planet.

  Because that dimming can be mimicked by other phenomena, such as the pulsations of a variable star or a large sunspot moving across a star's surface, the Kepler scientists won't announce the presence of a planet until they have seen it transit at least three times—a wait that may be only a few days or weeks for a planet rapidly circling close to its star but years for a terrestrial twin. By combining Kepler results with Doppler observations, astronomers expect to determine the diameters and masses of transiting planets. If they manage to discover a rocky planet roughly the size of Earth orbiting in the habitable zone—not so close to the star that the planet's water has been baked away nor so far out that it has frozen into ice—they will have found what biologists believe could be a promising abode for life.

  The best hunting grounds may be dwarf stars, smaller than the sun. Such stars are plentiful (seven of the ten stars nearest to Earth are M dwarfs), and they enjoy long, stable careers, providing a steady supply of sunlight to any life-bearing planets that might occupy their habitable zones. Most important for planet hunters, the dimmer the star, the closer in its habitable zone it lies—dim dwarf stars are like small campfires, where campers must sit close to be comfortable—so transit observations will pay off more quickly. A close-in planet also exerts a stronger pull on its star, making its presence easier to confirm with the Doppler method. Indeed, the most promising planet yet found—the "super Earth" Gliese 581 d, seven times Earth's mass—orbits in the habitable zone of a red dwarf star only a third the mass of the sun.

  Should Earthlike planets be found within the habitable zones of other stars, a dedicated space telescope designed to look for signs of life there might one day take a spectrum of the light coming from each planet and examine it for possible biosignatures such as atmospheric methane, ozone, and oxygen, or for the "red edge" produced when chlorophyll-containing photosynthetic plants reflect red light. Directly detecting and analyzing the planet's own light, which might be one ten-billionth as bright as the star's, would be a tall order. But when a planet transits, starlight shining through the atmosphere could reveal clues to its composition that a space telescope might be able to detect.

  While grappling with the daunting technological challenge of performing a chemical analysis of planets they cannot even see, scientists searching for extraterrestrial life must keep in mind that it may be very different from life here at home. The lack of the red edge, for instance, might not mean a terrestrial exoplanet is lifeless: life thrived on Earth for billions of years
before land plants appeared and populated the continents. Biological evolution is so inherently unpredictable that even if life originated on a planet identical to Earth at the same time it did here, life on that planet today would almost certainly be very different from terrestrial life.

  As the biologist Jacques Monod once put it, life evolves not only through necessity—the universal workings of natural law—but also through chance, the unpredictable intervention of countless accidents. Chance has reared its head many times in our planet's history, dramatically so in the many mass extinctions that wiped out millions of species and, in doing so, created room for new life forms to evolve. Some of these baleful accidents appear to have been caused by comets or asteroids colliding with Earth—most recently the impact, 65 million years ago, that killed off the dinosaurs and opened up opportunities for the distant ancestors of human beings. Therefore scientists look not just for exoplanets identical to the modern Earth but for planets resembling Earth as it used to be or might have been. "The modern Earth may be the worst template we could use in searching for life elsewhere," notes Caleb Scharf, head of Columbia University's Astrobiology Center.