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Science  18 Apr 1997:
Vol. 276, Issue 5311, pp. 351

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  1. Bringing the Stars Down to Earth

    1. James Glanz

    With plasma discharges and giant lasers, physicists are creating miniature supernovae and solar eruptions in their laboratories, opening an era of hands-on astrophysics

    The resemblance immediately caught his eye, Bruce Remington recalls. Images in two different journals depicted daisylike patterns, formed when small ripples on a ball of plasma—or ionized gas—bloomed explosively into long, turbulent splashes. But the floral analogy wasn't what glued the Lawrence Livermore National Laboratory researcher to the pages; it was the gulf between what the look-alike images actually showed. One depicted the mixing of a speck of plasma less than a tenth of a millimeter across as a converging array of powerful laser beams at Livermore's Nova facility slammed into it. The other was a computer model—much simplified—of mixing in a supernova blast, millions of kilometers across.

    His first thought, Remington says, was: “’This must be a fluke.’” But when he worked out some of the numbers describing both systems, “it dawned on me that the physics was identical.” If so, the Nova laser, ordinarily used to compress dollops of plasma to the temperatures and pressures needed for fusion, might also be able to mimic the roiling, radiating, three-dimensional (3D) dynamics of exploding stars. Now, nearly 4 years later, Remington's hunch has borne fruit, as data begin pouring from a successful preliminary run of supernova experiments at Nova.

    The work has put him and his colleagues in the vanguard of a scientific movement that aims to bring astrophysics into the laboratory for study, rather than relying only on remote observations and computer simulations. With devices ranging from giant lasers to plasma-filled flasks, these experimenters are trying to mimic the huge solar eruptions called coronal mass ejections, the collision of material flung from supernovae with surrounding gases, and even some of the extreme conditions felt by particles near the boundaries of black holes. “There are very few contexts in which you can test the quite exotic physics you find in astrophysics,” says Adam Burrows, an astrophysicist at the University of Arizona. These high-energy plasma experiments, he says, “approach the conditions found in stars.”

    Already, the experiments have boosted astrophysicists' confidence in the computer codes they use to describe the heavens, while providing some uncanny miniatures of events that could only be seen from afar. But Burrows cautions that the current round of lab work should be considered “first generation,” and other astrophysicists are even warier. The scale differences between space and the lab “really clobber you” in mocking up some effects, says B. C. Low of the National Center for Atmospheric Research in Boulder, Colorado. Still, he says, the new work “can enrich your experience with astrophysical phenomena.”

    One spark for this burst of activity came just 10 years ago in February. The iron core of an old star in the Large Magellanic Cloud, just 170,000 light-years away, had grown so cool that it could no longer support the weight of the overlying layers. The core collapsed and then rebounded when it was compressed to the density of nuclear matter. The resulting shock wave, like a hellish version of the ripple created by dropping a rock into a pond, heaved all but the core of the star into space in a giant explosion. It also dealt a blow to prior understanding of how those explosions take place.

    In its old age, explains David Arnett of the University of Arizona, such a star has a layered structure, much like an onion. At the center is an iron core, which is enclosed in layers of successively lighter elements, topped off by helium and an outer envelope of hydrogen. Stellar modelers thought this onion structure would be preserved in the explosion, says Arnett, but their close look at supernova SN 1987A “provided evidence that the inside was drastically stirred up.”

    The first hint came just 3 weeks after the collapse, when the supernova starting glowing unexpectedly at certain wavelengths, suggesting that radioactive cobalt-56—generated deep in the star during the explosion—was already warming the expanding surface. In addition, Doppler shifts of the light showed that some of the debris was moving at thousands of kilometers per second, much faster than expected. It was as if “fingers” of fast-moving plasma were poking through the rest of the material. That interpretation seemed to be clinched when gamma rays from the cobalt-56 became directly visible 6 months earlier than expected. “It's a big turbulent mess, not at all like an onion skin,” says Jave Kane of the University of Arizona. “It would be nice if you could find a turbulent plasma at high pressure here on Earth” to study that mess up close.

    Scale models of stars

    At Livermore, says Kane, “we've created just such a plasma.” In the late 1980s, Barrett Ripin and his collaborators at the Naval Research Laboratory, and an independent Russian group, had proposed that laser implosions could mimic aspects of supernova explosions. Remington and his colleagues have now revived this analogy independently at Nova, the world's largest laser.

    Remington had realized that the turbulent fingers in the supernova probably result from the same sort of instability that causes a fuel pellet to resist uniform compression when Nova's beams converge on it. In the pellet, the instabilities develop as a compressed, fast-moving surface layer driven inward by the lasers runs into resistance from deeper, hotter, lower density material. In the supernova, the fingers grow as the fast-moving helium layer propelled outward by the explosion runs into the star's hydrogen envelope.

    The correspondence is close enough, says Remington, that “instead of thinking in kilometers, I change that to micrometers, seconds to nanoseconds—that's it, and the equations are the same.” The miniature supernovae, he thought, might be able to offer insights into questions that simulations in supercomputers can't answer. Among them: why the fingers of SN 1987A are moving so fast—much faster than they do in the best supercomputer simulations that try to mimic the instabilities.

    To produce its miniature supernovae, the Nova team, which includes Livermore's Gail Glendinning as the hands-on experimentalist, replaces the spherical pellet used for laser-fusion experiments with a target consisting of a sheet of copper, representing the supernova's helium layer, coated on one side with plastic, representing the hydrogen layer; the researchers mold minute ripples into the copper to “seed” the explosion with instabilities. They then install the target in a tiny window in the side of a millimeter-size, gold cylinder called a hohlraum, with openings at the ends through which the lasers fire. This heats the gold, producing a uniform background of x-rays that smack into the target from behind, on the copper side. In the subsequent explosion, the ripples in the target get amplified and are recorded by means of the shadows they cast against a separate x-ray source.

    In the first round of experiments—about 20 shots last year—long, two-dimensional ripples resembling the corrugations on a tin roof served as initial perturbations. The team showed that the instabilities spawned in the shots nicely match the instabilities predicted by the PROMETHEUS supernova computer model developed by Arnett and others, adding to their confidence in the approach. “I was surprised at how well it did,” Arnett says. “We certainly weren't tuning [the computer code] for those experiments.”

    The next step is to see whether the instabilities in these miniature supernovae can grow faster than those in the computer models. To find out, the team is already making laser targets that have more realistic, 3D perturbations, something like the bumps on an egg carton. The fingers that grow from such bumps may well shoot through the surrounding fluid faster, with less drag, than the 2D ripples, says Remington. After the first 3D shots late last year, an excited Remington would only say that “the experiment worked.” If it did succeed in reproducing the fast-moving instabilities, says Arnett, astrophysicists will feel more confident in their basic understanding of how SN 1987A exploded.

    A second set of Nova experiments focuses not on the observed part of the supernova explosion but on what is yet to come: the collision of the expanding debris with the strange, wispy set of rings surrounding it, which are thought to be gases blown out from the star for millions of years before it exploded. The collision should heat the rings, rebrightening the supernova as a whole by about a factor of 1000 over the next decade.

    Astrophysicists like Richard McCray of the University of Colorado, Boulder, hope those fireworks will reveal the rings' detailed structure, and perhaps their origin. In preparation, McCray and John Blondin of North Carolina State University are simulating the smashup in two dimensions on the computer, hoping to learn how to interpret the actual observations. As McCray explains, however, “The computer will never tell you what you've forgotten to include.” So, to make sure that their simulations are as realistic as possible, McCray, Paul Drake of the University of Michigan, and others are building and detonating plastic models of the supernova and its rings.

    In these experiments, the researchers spray x-rays from a Nova hohlraum onto a slice of plastic—playing the role of the exploding star—which then vaporizes and forms a shock. As the material expands, it plows through a tenuous foam called an aerogel, representing the wind of particles from the progenitor star. The team hopes to learn just how wrinkled the shock front between the “explosion” and the “wind” becomes, because such wrinkles should affect the display that results when the real supernova finally slams into the ring. “We'll get a lot more out of the real collision when it happens” after poring over data from the miniature system, says Drake, a veteran laser-fusion experimenter.

    Here comes the sun

    Less cataclysmic explosions are the subject of other miniaturization efforts, such as ones by Paul Bellan and Freddy Hansen of the California Institute of Technology. They are trying to mimic the turmoil in the atmosphere of the sun, where immense, plasma-laden arches of magnetic field may linger quiescently for days before suddenly rousing themselves—sometimes after merging—and erupting into space.

    One goal of the experiment is to explore a theory proposed by David Rust of Johns Hopkins University and his colleagues, which holds that the eruptions are triggered when the magnetic field becomes too tightly twisted, like a toy Slinky bent into an arch (Science, 15 September 1995, p. 1517). To produce twisted plasma arches, Bellan and Hansen started by placing a small horseshoe magnet against the side of a 1.4-meter vacuum chamber into which they could puff hydrogen gas. Then, they discharged a capacitor bank between the magnet's poles, turning the hydrogen into a plasma, which followed the arch of the field lines between the poles. Electric current running along the field lines added the twist, or helicity, that Rust's theory requires.

    The experiment promptly yielded support for a link between twist and instability. Two “satellite” arches formed spontaneously. “They started getting bigger, and they danced around,” says Bellan, “and they coalesced,” forming a new arch with a double dose of helicity. This new structure soon exploded. Richard Canfield of Montana State University, who is organizing an American Geophysical Union-sponsored conference on helicity in laboratory and space plasmas, says, “There is certainly a possibility that [the results] bear on the stability of natural phenomena like solar prominences.” But he cautions, “We'll just have to wait and see.”

    Instead of trying to bring entire astrophysical events into the lab, other researchers are trying to isolate and reproduce underlying processes—magnetic reconnection, for example, which is what allows magnetic arches to merge in the first place. Reconnection, in which the looping, arching, or spiraling field lines in two different blobs of plasma splice together, is also the driver for everything from solar flares to storms in the magnetosphere, the envelope of plasma trapped by Earth's magnetic field.

    Building on earlier work by Reiner Stenzel and Walter Gekelman at the University of California, Los Angeles, Masaaki Yamada and Hantao Ji of the Princeton Plasma Physics Laboratory are puffing out plasma “smoke rings” within a laboratory vessel by firing carefully controlled bursts of current through donut-shaped metal cores. They then allow the plasmas to merge. Because Yamada and Ji can control the angle at which magnetic field lines wind through these plasmas, called spheromaks, they can study how reconnection rates depend on the relative angles of the merging field lines. In this 3D geometry, they can also search for effects neglected in oversimplified, 2D theories, says Amitava Bhattacharjee, a theorist at the University of Iowa. “Real solar and magnetospheric configurations are three-dimensional,” says Bhattacharjee.

    So far, the team has shown that the reconnection rate is fastest when the merging field lines are nearly antiparallel. That matches a relationship seen in the “space weather” generated when magnetized plasma flies outward from the sun and strikes Earth's magnetosphere, notes James Drake, a plasma theorist at the University of Maryland, College Park. Storms are most likely, Drake notes, when the fields of the solar wind and the magnetosphere are antiparallel. The size of the reconnecting region also roughly matches the predictions of Drake's own computer model of reconnection. “This experiment is going to be a very nice place to test my theory,” he says.

    These laboratory flares and exploding stars mimic relatively familiar events. But researchers are considering other experiments that would probe far more exotic astrophysical environments. Toshiki Tajima of the University of Texas, Austin, and Pisin Chen of Stanford University have pointed out that the pressure of light from ultraintense, tabletop lasers (Science, 5 January 1996, p. 25) can shove electrons with a force equivalent to that of gravity's tug in the vicinity of a black hole with the mass of millions of suns.

    By colliding with the sea of “virtual” photons that, according to quantum mechanics, pop in and out of existence throughout space, such electrons might scoop an occasional photon out of the vacuum, causing empty space itself to glow. The process would mimic the so-called Hawking radiation that theorists predict is sparked by the powerful gravity of black holes. Tajima cautions that “the practical difficulties would be formidable”—especially picking the radiation out of a background of ordinary light.

    Such challenges, together with the vast gulfs in scale between the cosmos and the lab bench, mean that these astrophysical microcosms won't be putting telescopes and supercomputers out of business anytime soon. But there is no question that a new player has arrived on the scene, says Bhattacharjee: “There is, in the final analysis, no substitute for comparison with experiment.”

    Additional Reading

  2. Taking the Measure of Life in the Ice

    1. Kathryn S. Brown
    1. Kathryn S. Brown is a science writer in Columbia, Missouri.

    At first glance, the seventh continent's pack ice seems like an eerie wasteland. But looks can be deceiving. Hidden inside the meter-thick slabs of ice that form each year across 20 million square kilometers of the Southern Ocean, a diverse ecosystem is thriving. The interior of an ice floe is much like a frozen honeycomb, laced with channels of slushy brine. These waterways teem with algae, which capture light filtering through the ice and help form the basis of a frosty food web that cycles carbon and other nutrients up through krill and fish to penguins, seals, and whales.

    Scientists have long known that this “crop” of algae grows each year in the ice. But they have had difficulty quantifying it because the ice—and its suitability as algae habitat—varies enormously across the ocean. Now, on page 394, ecologist Kevin Arrigo of NASA's Goddard Space Flight Center in Greenbelt, Maryland, and colleagues unveil a mathematical model that uses data and equations derived from remote-sensing satellites and laboratory and field studies to put real numbers on the total primary production, or plant life produced through photosynthesis, in pack ice. Among other findings, the model reveals that this ice yields fully one-quarter of the primary production in the part of the Southern Ocean that is covered with ice.

    Bumper crop.

    The most productive (red) ice surrounding Antarctica forms annually.


    With the model, researchers say they will finally be able to begin unraveling the Southern Ocean's complex food web and better understand the role these tiny organisms play in cycling carbon through the biosphere. “It's great progress for the field,” says Cornelius Sullivan, director of the Office of Polar Programs at the U.S. National Science Foundation, who adds that the study is one of the first to look at the overall contribution of algae in pack ice to the ocean ecosystem.

    More than 150 years have passed since British botanist Sir Joseph Dalton Hooker first described “microscopic vegetables,” or brown algae, in Antarctic sea ice. Since then, researchers have learned that sea-ice populations of algae are determined by basically two resources: sunlight and nutrients—the phosphates, nitrates, and silicates in seawater. But getting a fix on the total algal production in pack ice has proved difficult. The ice is vast, cold, and unstable, making it a dangerous place for fieldwork. “Scientists have not been able to carry out large-scale synopses or studies on sea-ice ecology,” says study co-author Gerhard Dieckmann of the Alfred Wegener Institute for Polar Marine Research in Bremerhaven, Germany.

    What's more, says Arrigo, “the ice isn't a single slab. It's dynamic and heterogeneous.” As a result, the amount of algae can vary considerably even within the layers of a single floe. In the deeper layers, for instance, algal growth may be stifled by lack of light, while populations near the top may not get the nutrients that flood into the base of the ice from the seawater below.

    So, Arrigo and his colleagues set out to estimate primary production by simulating this icy habitat in a computer. They turned to satellite images of the region for basic information about cloud cover and snow cover. From field studies, they incorporated information about the pack ice's porosity and other physical characteristics. Then they worked in equations describing how algal growth responds to changes in light, temperature, and nutrient supply.

    According to the model, even during the gloomy Antarctic winter, an average of 50 micrograms of algae grow in each square meter of ice every day. The total production each year turned out to be about 35 billion kilograms of carbon, or about one-fourth of the total primary production in the ice-covered Southern Ocean, say the researchers.

    According to the model, the most important factor in algae production was snow cover. In general, regions that got a lot of snow produced the most algae per square meter of ice, says Arrigo. The snowy Weddell Sea, for instance, just one-quarter of the ice-covered waters around Antarctica, produced half the algae in pack ice. While a light dusting of snow can limit algal growth by blocking out sunlight, a heavy snow can dunk an ice floe, flooding it with fresh nutrients from deeper seawater. Algae in the ice then feast on the sudden, free lunch. The other crucial determinant of algal growth turned out to be ice porosity. As the ice became more porous, usually as a result of warming weather, nutrient-rich brine flushed through the ice, spurring algal blooms.

    Scientists are still uncertain how sea-ice algae affects the Southern Ocean food web. Overwintering crustaceans—like copepods and juvenile krill—feed on algae living on the bottom of ice floes, says Robin Ross, a biologist at the Marine Science Institute at the University of California, Santa Barbara. And each spring, a variety of organisms—including larval fish and ocean-floor sponges and sea stars—get fat grazing on algae and other plankton poured into the ocean as pack ice melts. But it is not yet clear how much these events affect other animals, such as whales and other marine mammals, further up the food web. Says Ross, “We're still working out the details of sea-ice dynamics.”

  3. Researchers Make Slick and Sticky Films

    1. Robert F. Service

    Living cells are masters of hierarchical building. For much of their molecular architecture, they first string together amino acids into proteins, then assemble proteins into more complex structures. Chemists have been working to imitate this skill, in the hope of making new materials tailored right down to the arrangement of molecules. Researchers have logged some initial successes, designing molecules that take a first step toward hierarchy by linking together into aggregates resembling tiny balls, sheets, and webs.

    Now, on page 384, researchers at the University of Illinois (UI), Urbana-Champaign, report taking this assembly process to a new level of sophistication, creating molecules that assemble themselves over several size scales, first forming clusters, then sheets, and, ultimately, thick films. Because the building-block molecules are all oriented in the same direction, the films' properties mirror those of the individual molecules, yielding a bottom surface that's sticky and a top that's slick. This property could make the films useful for everything from anti-icing coatings on airplane wings to anti-blood-clot linings for artificial blood vessels, says Samuel Stupp, who led the UI effort. “It's a tour de force of chemistry,” says Edwin Thomas, a materials scientist at the Massachusetts Institute of Technology in Cambridge.

    At the heart of the new films is a pencil-shaped organic molecule that Stupp and his colleagues call a “rodcoil,” because one half of the molecule is rigid and the other half is flexible. The rigid end is composed of compounds called biphenyl esters that lock stiffly together. The floppy end is made up of compounds called isoprenes, which, in turn, are connected to other flexible groups called styrenes. Finally, an ultrasticky phenolic group sits on the end of the rod portion, while a slippery methyl group caps the flexible coil end.

    Rodcoils aren't brand-new. Stupp and his UI colleagues first constructed the molecules 2 years ago. Their hope was that the rodcoils would assemble themselves into a continuous thin sheet in which all the molecules would point the same way. They found instead that the molecules formed thick films (Science, 28 April 1995, p. 500). At the time, they assumed that the rodcoils simply lined up, regiment style, to form sheets that then became layered into films. But in the current paper, the UI team reports that the film is, in fact, the product of a more involved, three-step hierarchical process.

    At the smallest scale, groups of about 100 rodcoils aggregate into mushroom-shaped clusters, with the rodcoils' rigid ends forming the stems and the flexible coils forming the caps. The mushroom shape, says Stupp, is the result of two opposing forces. An attractive intermolecular force among biphenyl esters on neighboring rods draws this portion of the molecules tightly together, while a repulsive force pushes the floppy coils apart. Once the mushrooms have grown to about 5 nanometers in diameter, “the repulsive force of the coils overcomes the attractive force of the rods, and they stop growing,” says Stupp. The result is the creation of thousands of nearly identically sized mushrooms.

    Tight fit.

    Mushroom-shaped molecules pack together into a layered film.


    In the next level of organization, the mushrooms pack side by side, same side up, to form sheets. And finally, in the last level of the hierarchy, the sheets stack in layers—again, same side up—to form a thick film. Just why the sheets stack up this way “is a bit mysterious,” says Stupp. The arrangement requires the water-loving, or hydrophilic, sticky phenolic groups on the tip of the stems to sit next to the water-fearing, or hydrophobic, methyl groups on the top of the caps. And hydrophilic and hydrophobic molecules typically want little to do with one another.

    But after running a series of computer models, Stupp and his colleagues now believe that what forces the hydrophilic and hydrophobic groups together is nature's even greater abhorrence of a vacuum: The stacked arrangement may be the most space-saving way to pack together the mushroom-shaped clusters. The rigid stems in one layer of mushrooms press down into the flexible caps in the layer below. But rather than crushing the caps, the stems nestle down into them, pushing aside the floppy molecules so that they fill in some of the space around the stems. As a result, despite the natural repulsion between caps and stems, the film ends up having a “polar” order, with all the caps facing up and all the stems facing down.

    This polar stacking is likely to make the UI films a hit production, as it endows the top and bottom surfaces with very different properties. Already, the films have sparked the interest of researchers at Foster-Miller Inc., a technology-development company in Waltham, Massachusetts, who are investigating them for use as anti-icing coatings for airplane wings. The most common of the deicing treatments now used—spraying an antifreeze compound on airplane wings just prior to takeoff—isn't foolproof because rain and wind can quickly remove the antifreeze. By contrast, the sticky side of the UI films adheres so “tenaciously” to metal and other surfaces, says Stupp, that one day, a coating made of the films might be able to prevent ice buildup for months or years at a time.

    Down the road, Stupp and his colleagues also hope to create films with other properties, by replacing the sticky and slippery groups capping the rodcoils with compounds that perform other functions, such as conducting electricity or changing their size in response to an electric jolt. If successful, these sequels might even upstage the originals.

  4. An Ocean Emerges on Europa

    1. Richard A. Kerr

    Hints of ancient life on Mars have captivated planetary scientists since last summer, but last week their attention jumped to Jupiter's moon, Europa, when researchers announced what they consider persuasive evidence of a deep ocean below Europa's icy surface. Images newly returned by the Galileo spacecraft show a complex, shattered terrain that bears an eerie resemblance to the ice cover of the Arctic Ocean, researchers said at a NASA press conference in Pasadena, California. If Europa does harbor an ocean, the planet would have an abundance of liquid water—a key prerequisite for life. Some members of the Galileo team, however, aren't ready to take the plunge.

    When Galileo began returning images of Europa late last year, planetary scientists realized that something has been disrupting much of the moon's surface by squeezing up ridges and crumpling some areas into thoroughly chaotic terrain. Last month, at the Lunar and Planetary Science Conference in Houston, team member Clark Chapman of the Southwest Research Institute in Boulder, Colorado, argued that the striking dearth of meteorite craters on some parts of Europa implies that the surface is still being reshaped.

    Now, the latest Galileo images have convinced some researchers that a thin layer of ice floating on liquid water is the most reasonable way to explain this turmoil. Europan geology “does look a lot like the ice cover of the Arctic Ocean,” said arctic researcher Max Coon of NorthWest Research Associates Inc., in Bellevue, Washington. Kilometers-long slabs of ice appear to have broken off and drifted in a “sea” of what looks like refrozen water. “These are icebergs,” said Galileo team member Paul Geissler, of the University of Arizona. He and fellow team member Michael Carr of the U.S. Geological Survey in Menlo Park, California, argued that only the circulation of a warm ocean could have partially melted the ice crust and dragged the “icebergs” around.

    But not everyone is convinced. “It's a bold hypothesis that probably has some staying power,” said team member Robert Sullivan of Arizona State University, “but there is room for some surprises.” Indeed, each time Galileo has swung by Europa and gathered more images, geologists have had to toss out previous ideas about the moon's geology. In January, for example, the team suggested that “ice volcanoes” have flooded the surface with icy lavas, but Sullivan has now backed away from that idea. Team member Robert Pappalardo of Brown University remains cautious too: “I don't think we have proof of an ocean,” he says. “I would argue for keeping open the option that this stuff has moved around on top of ductile ice instead of an ocean. We have a good suggestion of an ocean, but it needs testing.”

  5. Miocene Primates Go Ape

    1. Ann Gibbons,
    2. Elizabeth Culotta

    Wind back the clock 5 million to 23 million years to the Miocene, and parts of Eurasia and Africa would seem like the planet of the apes. “If you could have walked from Spain to China 10 million years ago, you'd have seen an amazing diversity of apes,” says University of Texas paleoanthropologist John Kappelman, who estimates that no less than 30 different types of early apes lived during the Miocene. But after this spectacular flowering, nearly all these apes became extinct, with only one lineage surviving to give rise to modern apes and humans. Although there have been plenty of candidates for this distinction, including chimpanzee-sized apes from Europe called Oreopithecus and Dryopithecus, anthropologists have had only fragmentary fossils to tell them which one.

    Now, thanks to new fossil finds, two African species are seeking prime ancestral spots on the modern ape family tree. New “apelike” arm and ankle bones from one candidate, Kenyapithecus, indicate that this 14-million-year-old primate was “the best, most likely ancestor of humans, chimps, and gorillas,” say paleoanthropologists Monte McCrossin and Brenda Benefit of Southern Illinois University. And another team has proposed a larger tree dweller called Morotopithecus as an even earlier ancestor. In a report on page 401, Northern Illinois University anthropologist Daniel Gebo and his colleagues identify modern features of this ape's back and shoulder, and date the fossils at 20.6 million years old. That would push the emergence of a modern ape-like body plan back by 5 million years and force researchers to “rethink all of the relationships of apes in the Miocene,” says University of Missouri paleoanthropologist Carol Ward.

    Kenyapithecus has been a contender for human ancestry ever since the 1960s, thanks to face bones and teeth that set it apart from other Miocene apes. But other parts of Kenyapithecus's skeleton turned out to look more primitive, and it was pushed to an outlying branch of the ape family tree—outside the African ape group, which includes modern gorillas, chimps, and humans (see diagram). Now, however, McCrossin and Benefit claim that new fossils found last summer on Maboko Island in Kenya's Lake Victoria bring Kenyapithecus back in the African ape family.

    Miocene muddle.

    New fossil specimens raise questions about relationships on the ape family tree.

    Working with 135 excavators, they unearthed several new Kenyapithecus bones that they say resemble those of modern apes, including a straight upper arm bone and an ankle bone shaped to allow Kenyapithecus to rotate its foot sideways—a feature of living chimps that allows them to cling to trees with their feet and also walk flat-footed on the ground. Together with modern features of its jaw, teeth, and face, Kenyapithecus is the closest ancestor of African apes, McCrossin and Benefit proposed last week at the annual meeting of the American Association of Physical Anthropologists in St. Louis.

    A different set of traits has convinced Gebo, Laura MacLatchy of the State University of New York, Stony Brook, and their colleagues that Morotopithecus is an even older ancestor. Vertebrae from this ape, found in Moroto, Uganda, in the early 1960s, had long tantalized researchers because they suggest that Morotopithecus had a stiff back—a feature critical for the occasional upright posture adopted by modern apes. But other traits in Morotopithecus's teeth and face were primitive.

    In 1994 and 1995, however, Gebo and MacLatchy's team found a partial shoulder bone and parts of two leg bones or femurs at Moroto. Not only did argon-argon dating show these fossils to be at least 20.6 million years old—5 million years older than had been thought—but they were unexpectedly modern. The shoulder socket, or glenoid, was round, suggesting that Morotopithecus's shoulder joints were mobile, allowing this ape to hang by its arms in trees, as do living apes such as chimps and orangutans. And the lower part of the femur has modern features, says MacLatchy. “Given these traits, we think it was a sister species to living apes,” she says.

    The new data will likely lead to a rearrangement of where different Miocene apes sit in the primate family tree and may also change researchers' views on which traits are most reliable for determining ancestry. For example, if the large-bodied Morotopithecus is our close relative, then large body size is a primitive trait for all apes, contrary to existing models. What's more, some molecular clocks assume that great apes—orangs, chimps, gorillas, and humans—split off 13 million years ago, using the date from a Pakistani ape called Sivapithecus. The new date for Morotopithecus could alter those calculations, says Kappelman.

    Others caution that it is too early to be redrawing family trees, noting that both claims rely mainly on skeletal traits rather than on the teeth or skull features usually used for classification. University of Toronto paleoanthropologist David Begun, for example, notes that the classification of Morotopithecus as a sister group to living apes depends primarily on just two skeletal bones, one of which is very fragmentary. Nor are Begun, Ward, and others convinced that the new arm bone of Kenyapithecus is apelike; they are waiting for a published description of the fossils. “I think we can expect continuing clouds of discomfort as to how to handle all this new material,” says Kappelman. “But it's the beginning of a great research enterprise.”

  6. Growing Crystals With a Twist

    1. Robert F. Service

    Researchers who make semiconductor crystals for computer chips and other electronics applications are notorious perfectionists—and for good reason. To give the best performance, a chip has to be nearly defect free. But growing perfect crystals is difficult because of mismatches between the atomic lattice pattern of the semiconductor and the substrate, a supporting surface that provides a template for the crystal being deposited on top. As a result, strain builds up in the growing lattice, triggering cracks in the crystal. Now, however, researchers have found a simple way to ease the strain.

    At the semiannual Materials Science Research meeting in San Francisco 2 weeks ago, a team of researchers from Cornell University in Ithaca, New York, and Sandia National Laboratory in Albuquerque, New Mexico, reported that a thin, flexible film sandwiched between the substrate and the crystal can act as a buffer. By absorbing the strain, it allows a wide variety of crystalline materials to be grown on the same substrate material virtually defect free, even when the distance between atoms in the two lattices differs by as much as 15%—a considerable mismatch by industry standards.

    According to David Jesson, a semiconductor growth expert at Oak Ridge National Laboratory in Tennessee, the team's findings are “very interesting” because they may allow scientists to create high-quality crystals of new semiconductors. And that, says Cornell team leader Yu-Hwa Lo, could open the door to higher performance computer chips as well as new optoelectronic devices, such as more sensitive infrared detectors and chip-based lasers that beam out colors across the rainbow.

    Up to now, crystal growers have been in a bind. They need substrates to organize the growth of semiconductor crystals, but standard substrates do this a little too well. Their atoms are locked into such a strong, rigid lattice that when strain builds up between the two layers, it's inevitably the more fragile, still-forming crystal that fractures. So, Lo and his colleagues decided to see if they could create a sacrificial layer that would absorb the building strain and fracture, thus sparing the growing crystal.

    Their strategy was to top the substrate material with a few weakly bound layers of atoms that could move around and absorb the strain. But because any atoms deposited directly onto the substrate would be locked into the same rigid lattice, creating this weak layer required a little ingenuity. The team started with a slab of gallium arsenide (GaAs), a standard substrate crystal, coated with a layer of indium arsenide. Then, they added a film of GaAs as little as five atomic layers thick, which ultimately would serve as the flexible film. Finally, they took a second slab of GaAs and bonded it on top—but with a twist.

    Instead of stacking the two slabs neatly, like playing cards in a deck, the scientists rotated the top GaAs slab so that its lattice was at a 45° angle relative to that of the substrate slab and the GaAs film, below. The researchers then used two conventional etching solutions to eat away the bottom two layers until only the ultrathin GaAs film was left attached to the second GaAs substrate. This served as the new substrate and starting material for growing high-quality crystals.

    When the researchers tested their new substrate by growing new semiconductor compounds on top, such as one made from indium antimonide (InSb), the difference was readily apparent. InSb films grown on conventional substrates are normally riddled with as many as 10 billion defects per square centimeter. But on the flexible substrate, the defects were reduced over 1 millionfold to an undetectable level.

    Lo explains that bonding the GaAs slab and ultrathin film together at an angle “dramatically changes the property of the [film]” by preventing the thin film's atoms from forming rigid covalent bonds with the bulk GaAs substrate. “That allows the atoms [in the thin layer] to move,” absorbing strain, he says.

    This ability to turn out relatively defect-free semiconducting crystals could speed up the commercialization of blue lasers using semiconductor chips made from gallium nitride (GaN), says Lo. Because there is no cheap substrate with a lattice closely matched to GaN, lasermakers end up with GaN films containing billions of defects, which can trap heat and cause the devices to burn out rapidly. The Cornell researchers have yet to show that their technique can be used to build better GaN lasers or other working devices, but Lo says they are already gearing up to do just that. If the technique works, it will undoubtedly inspire other semiconductor researchers to search for a little more perfection of their own.

  7. Herbert Benson: Mind-Body Maverick Pushes the Envelope

    1. Wade Roush

    BOSTON–In 1972, leading cardiovascular researcher Lewis K. Dahl of Brookhaven National Laboratory on Long Island gave a prestigious lecture to members of the High Blood Pressure Council, gathered that year in Cleveland, on the causes of hypertension. Dahl had bred a strain of laboratory rats, called S, whose blood pressure soared fatally high if they ate too much salt; the rats also seemed susceptible to several other suspected causes of hypertension. But there was one factor, Dahl said, that could be ruled out: psychological stress. He had harried S rats with random electric shocks, a classic stressor, and found no rise in blood pressure.

    It was an uncontroversial point. Amid the polite applause, however, a lone challenger at the back of the auditorium rose to speak. “With all due respect,” he said, “it's not that stress isn't important—you just did the experiment the wrong way.” Dahl glared at his young questioner and waved off the comment. But the criticism so irritated him that upon returning to Brookhaven he got the best grad student he could find, an experimental psychology student named Richard Friedman, to—as Dahl put it to him—“design a psychology experiment where even fanatics like this guy can see that stress isn't important.” In a study that grew into his Ph.D. thesis, Friedman designed an alternate stress experiment, shocking the S rats on a random schedule after they pressed a lever to obtain a food pellet. They promptly developed much higher blood pressure—proving, as Friedman reported in Science in 1976, that Dahl's critic had been right: Stress does have profound physical consequences.

    Years later, Friedman joined the lab of cardiologist Herbert Benson at Beth Israel Hospital in Boston and joked to his new mentor about how the provocation of a nameless “fanatic” at the back of the hall in Cleveland had helped launch his career. Benson laughed: That fanatic, he said, was me.

    Today, the once-heretical notion that mental state can influence blood pressure is part of mainstream medical thinking, and Friedman is Benson's right-hand man at the Mind/Body Medical Institute (MBMI), a nonprofit research and education center they founded in Boston in 1988. And Benson, with appointments at Beth Israel Deaconess Medical Center and Harvard Medical School, has made a career out of provoking the biomedical research community to accept ideas once considered fringe. He's famous coast to coast for his work on the “relaxation response”—a term he coined to describe physiological changes, including a decrease in stress hormones and heart rate, seen during states of relaxation. He has promoted meditation to help treat everything from hypertension to headaches, and he has at least partially succeeded: Today, relaxation therapies are taught in 60% of U.S. medical schools and offered by many major hospitals.

    Stepping too far?

    Harvard cardiologist Herbert Benson has made a career out of pushing science to its limits.


    In the research world, Benson still faces many critics who charge that his science is skimpy. Recent studies have even raised questions about his best known work on the effectiveness of the relaxation response. Yet, Benson is a well-established researcher, with an endowed chair in his name at Harvard and a string of grant awards from the National Institutes of Health (NIH)—from the medical institutes, not from the Office of Alternative Medicine. Just last month, NIH's National Heart, Lung, and Blood Institute awarded MBMI nearly $500,000 to study relaxation as a treatment for insomnia. He's also a wildly successful popularizer—with millions of copies of his books in print—who distances himself from pop gurus like Deepak Chopra by claiming scientific evidence for all his ideas. “Benson is to be congratulated for opening the door” to the links between mind and body, says former Surgeon General C. Everett Koop. “Good doctors have always used anything available to them in the healing of their patients. I would caution against the skepticism that [says] this is all bunk.”

    But now, even some of the 61-year-old Benson's supporters wonder if he's gone off the deep end. His latest forays have been in an even more provocative realm: religion. In his 1996 book Timeless Healing: The Power and Biology of Belief, he contends that humans are “wired for God”—that believing in God can improve your health and is in fact an evolutionarily adaptive trait. “Perhaps instinctively, human beings [have] always known that worshipping a higher power was good for them,” Benson writes. In the book and in a Harvard Medical School continuing education course run by MBMI, Benson argues that the calm instilled by faith itself can be a powerful force for healing.

    If that suggestion were not provocative enough, Benson now plans to test the power of prayer. Using funds donated by a private foundation, MBMI is planning a study of whether “intercessory” prayer—prayer for someone else's recovery—works. Certainly, the U.S. public thinks it does: A recent Newsweek survey found that 87% of adults believe God sometimes answers their prayers—and a Nature poll found that 40% of all biologists, physicists, and mathematicians believe in a God who answers prayers.

    Not surprisingly, the notion of putting prayer under a scientific lens strikes many scientists as quixotic, embarrassing, or worse. New York University rheumatologist Gerald Weissman, who has described meditation as akin to “magic potions,” says Benson and other mind-body practitioners such as Chopra “are all mesmerians, shills of the worst sort preying on the sick.” Even if the study found a significant effect from prayer, adds Dan Blazer, an epidemiologist and psychiatrist at Duke University, “clinical studies like this necessitate taking the next step and asking what is the mechanism by which that effect works. [With prayer], we can't even begin to know how to ask that.”

    Those who have raised questions about Benson's past work say that's just the problem—that he avoids or skips over the questions nearest and dearest to most researchers' hearts: the mechanisms behind the effects he studies. Even some of those who study mind-body effects are wary. “The person in me says ‘Of course, I believe emotions have something to do with disease,’ but the scientist in me says ‘Prove it to me,’ “says Esther Sternberg, a rheumatologist at the National Institute of Mental Health, who is part of a network of mind-body researchers organized by the John D. and Catherine T. MacArthur Foundation. Benson, she says, has served mainly as a champion of popular beliefs, and it has taken a second wave of hard-nosed researchers to explore the mechanisms of the mind-body link.

    Benson—who recently began taking his own medicine by meditating 10 minutes each day—remains unflustered and unfailingly cordial in the face of such criticism. Now nearing the end of his career, the silver-haired, suavely dressed scientist asks calmly: Who better to examine the possible effects of prayer than representatives of the biomedical establishment?

    Tension over hypertension

    Benson's calmness in the face of criticism today isn't surprising, given that he's been in the firing line for more than a quarter of a century. Benson, who got his M.D. from Harvard Medical School in 1961, was among the first to explore the idea that combating stress through mindful relaxation might lower blood pressure, and he has published a string of studies in peer-reviewed journals showing that this is so; one of his first was a study published in Science in 1971. But in spite of such papers, the idea that hypertension could be counteracted by calming the mind was considered bunk back then. Colleagues giggled when he spoke about relaxation during medical rounds, Benson recalls. “‘It's all the placebo effect,’ they'd say. ‘Psychological processes simply don't exert that powerful an influence.’ ‘Do you know what you're doing? Throwing away your career.’”

    But as things turned out, few medical careers have been more publicly successful. Benson's book The Relaxation Response has sold 4 million copies worldwide, and physicians and other caregivers flock to his courses. (Nearly 3000 attended recent offerings on “Spirituality & Healing in Medicine.”) Biomedical researchers were slower to take interest, but many now take the mind-body link seriously; a 1993 meta-analysis, for example, found 857 studies in the medical literature between 1970 and 1991 on the treatment of hypertension using cognitive or behavioral techniques such as relaxation.

    Pop star.

    Over 4 million copies of Benson's popular books are in print.


    Many physicians and researchers agree that Benson has helped kick off what is now a legitimate field of research, albeit an offbeat one; indeed, there are now scores of studies on the biochemistry of the links between the nervous and immune systems, a field called psychoneuroimmunology (Science, 14 February 1997, p. 930). “I admire somebody like Dr. Benson who has the guts to tackle tough issues and to bring good, hard-core science to bear on them,” says David Felten, a leading psychoneuroimmunologist at the University of Rochester in New York. “He is the pioneer who pointed the way.”

    One measure of the sway Benson's ideas acquired over the years is the success of MBMI, which earns income from grants from NIH and private foundations—and also makes a tidy sum from corporate programs in relaxation and medical continuing-education courses. All told, the 30-person institute, which has six affiliated centers in other cities, had total revenues of $2.6 million in 1996.

    Along the way, however, there have been critics who call Benson a better showman than a scientist. In the early 1980s, when Benson requested more space for his research at Boston's Beth Israel Hospital, the chief of medicine assembled an outside committee to evaluate his work. Psychoendocrinologist Bob Rose, himself a former editorial board member of the journal Psychosomatic Medicine, led the review panel—and emerged skeptical of Benson's science. He remains so today, as director of health programs at the MacArthur Foundation and chair of its mind-body research network. “Herb has claimed to do the very basic kinds of biological research that document the psychobiological mechanisms underlying the relaxation response, but it turns out when you look very carefully that he hasn't done that,” says Rose, who was also Benson's classmate at Harvard Medical School. Indeed, a detailed critique of Timeless Healing finds many scientific holes (see Book Review, p. 369).

    Benson insists that his interest in mechanism “goes back to my very roots” as a physiology fellow and instructor at Harvard. He says he and his collaborators have always tried to define the relaxation response in state-of-the-art terms, using the latest measuring devices, including electroencephalograms (EEGs). “We are vitally interested in mechanism. But there is another fundamental issue here. … Mind may never be defined in reductionistic terms, because of its very nature.” In other words, if researchers can't say how the brain gives rise to consciousness, they can't ascertain exactly how mental states initiate changes in the body. “Therefore, to be criticized for studying only the effects of psychological states is an absurdity.”

    And Benson's science does have its supporters: Felten says Benson's data correlating relaxation and physiological change “are as solid as any measurements of physiological systems can be” and that Benson's critics sometimes ask too much. “We still want to study the underpinnings, the mechanisms, but the fact that we can't give you all of them right now, today, doesn't mean the connection doesn't exist.”

    Still, recent studies have raised questions about whether the relaxation response does indeed lower blood pressure and suggest that the effects may be restricted to certain populations. For example, in 1992 a major NIH-coordinated study of 2100 subjects on the verge of hypertension found that weight loss and sodium reduction significantly decreased blood pressure—but relaxation did not. On that basis, researchers contributing to this “Trials of Hypertension Prevention” study decided not to test relaxation in a larger Phase II study, which is still under way. Other studies, including the 1993 meta-analysis, find that relaxation is better than no therapy at all in lowering blood pressure, but it isn't much better than a placebo.

    Benson says the problem is simply that these studies lump subjects together. Those whose initial blood pressure is highest, or whose hypertension was clearly linked to mental stress, do benefit, he insists. Indeed, when psychologist Wolfgang Linden of the University of British Columbia controlled for differences in pretreatment blood pressure in his own 1994 meta-analysis, he found that psychologically based therapies, including relaxation, did lower blood pressure significantly.

    And Benson points to dozens of studies that underscore other health benefits of relaxation. A 12-member Technology Assessment Panel convened last year by the Office of Medical Applications of Research at NIH, for example, found “strong evidence” that relaxation techniques are an important weapon against chronic pain.

    The faith factor

    Yet, even as his message spread, Benson found himself thinking seriously about some of his critics' charges. From the outset, skeptics had derided the physiological changes Benson observed in his meditating subjects as “nothing but the placebo effect,” that mysterious but undeniable pattern in which a certain fraction of patients in clinical trials—about 35%—get better even if given a sugar pill or other dummy treatment. Most scientists have attributed this to some sort of shadowy mind-body interaction: Believing in a treatment may help it work. And Benson decided that there was some truth to the idea that patients' belief in the relaxation response was enhancing its benefits.

    But rather than discount the placebo effect, Benson wondered if he could make use of it. That's where his recent interest in religion and health comes in. “The most profound belief people can have” is belief in a higher power, he says. Benson, himself a believer in God, also noted that most of the world's major religions feature prayer rituals resembling meditation.

    Many epidemiological studies have shown that churchgoers have better clinical outcomes than do atheists—but that finding is often attributed to the extra social and community support people gain from belonging to a church. Benson is proposing something far more radical: that belief itself could affect health. “I was coming closer to defining a biological role of belief in God, a line of inquiry I wasn't sure either scientists or theologians would appreciate,” Benson writes in Timeless Healing.

    That didn't stop him. Eager to test the link between religiosity and health, he and colleagues developed an index that roughly quantifies the depth of subjects' spiritual feelings. In a study reported in 1991 in the Journal for the Scientific Study of Religion, the group taught the relaxation response to adult outpatients with a variety of disorders; they found that subjects who scored high on their spirituality index—those who, in Benson's words, “felt the presence of a power, a force, an energy close to them” during meditation—seemed to benefit more.

    Of course, it's not necessarily surprising that “spiritual” people gain more from meditation than do skeptics. And it's conceivable that belief in a higher power might help some people deal with stress. But Benson's latest studies focus on a proposition that is hard to rationalize: whether praying for someone's else's health actually helps those being prayed for to get well. Benson's interest was piqued by a controversial study reported in the Southern Medical Journal in July 1988, indicating that 192 coronary intensive-care patients who were prayed for by born-again Christians had better clinical outcomes than did 201 controls, although no one but the Christian “intercessors” knew who was prayed for. Many researchers, including Benson, found flaws in the study's design, including an imprecise definition of a “good” clinical course. But Benson and Friedman are interested. “Why not have a look at this in a scientific fashion?” asks Benson.

    Champion of the spirit.

    Benson says spirituality and healing deserve scientific study.


    So, he, Friedman, and colleagues have designed a controlled, randomized, double-blind study of intercessory prayer, funded by the John Templeton Foundation, a private foundation that aims to “use scientific evidence to reveal knowledge about God.” The MBMI team is wary about revealing details of their study: If well-wishing such as prayer can exert action at a distance, Friedman explains, then negative thoughts from skeptics could just as easily skew the results. They did disclose, however, that intercessors in the study will pray for two of three groups of coronary bypass patients. One group will know that it is being prayed for, while the other two will know that one of them is being prayed for, but not which one. The study thus aims to probe two different questions: whether there is a health benefit from knowing that others are praying for you, and whether intercessors can affect the world through pure thought. “Somebody needs to replicate the [1988] study, if only because it's so widely quoted,” says Friedman.

    Right-hand man.

    Benson's provocations inadvertently launched Richard Friedman's career.


    The research world is skeptical, to say the least, that such a study can produce any sort of useful result. Without the standard tools of clinical and epidemiological investigators, it simply isn't science, scoffs the MacArthur Foundation's Rose. “For example, is there a dose-response curve—is there a difference between 1 hour of praying for someone else and 3 hours? Otherwise, we're just going back to voodoo, orgone energy, karma, and vibes.” Epidemiologist Blazer of Duke adds that “It would be very difficult to convince most people that you really had valid controls”—a point that is even echoed by some religious scholars. “There can be no such thing as a controlled study of prayer,” says Hector Avalos, a former child faith healer who is now a professor of religious studies at Iowa State University and director of the Committee for the Scientific Evaluation of Religion, a group of skeptical scholars who investigate paranormal religious claims. “You can never confirm that someone was not prayed for. There might be one person praying for all the sick people in the world. How could you possibly control for something like that?” Others question whether medical science should intrude in matters of the spirit. “Religion is there to provide faith, not to heal,” says David Spiegel, a research psychiatrist at Stanford University School of Medicine who did a pioneering study showing that group therapy boosts the survival of women with breast cancer. “I worry about doctors treading in a domain they don't know much about.”

    Other researchers, however, say they at least admire Benson's courage. “He's pointing out something that the public is talking about,” says Margaret Chesney, a research psychiatrist at the University of California, San Francisco. “Science has been fairly devoid of spirituality, and Herb is putting it out on the table,” she says. “We need that, but it's a tough position to be in—you open yourself up to criticism.” And Blazer, even though he says “I don't think [the study] is going to inform us in the long run about whether prayer works,” adds that he's pleased that Benson is carrying it out, as it “will stimulate a conversation about whether science can actually help us study this area.”

    Whether the research world is interested or not, Benson is continuing with his plans. He says his greatest hope is that his career has helped to “lessen the medical suffering of humans,” by using science to narrow the gap between mind and body. He still has a long way to go, jokes one leading mind-body researcher: “Tell him I'm praying for him.”

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