Scientific American (ISSN ), Volume , Number 3, September , published monthly by Scientific American, a division of Nature. 36 SCIENTIFIC AMERICAN MIND. NovEMbER/DECEMbER 36 SCIENTIFIC AMERICAN MIND. July/AuguST SOUNDSURGERY. [. 36 SCIENTIFIC. Scientific American (December ), , Published online: 17 November | doi/scientificamerican
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Scientific American is the essential guide to the most awe-inspiring advances in science and technology, explaining how they change our understanding of the. BEHAVIOR •BRAIN SCIENCE •INSIGHTS. November/December Mind. lesforgesdessalles.info POLICE VIOLENCE: WHY COPS LOSE CONTROL page . November , lesforgesdessalles.info Illustration by Marcos Chin medıtator of. Contemplative practices that extend back thousands of years.
Cover titled. Discovery of Five Irregular Moons of Neptune. Because these players were older than their teammates when they joined the leagues, they would have enjoyed advantages in size and strength, allowing them to handle the ball and score more often. Even J. This southward extruding zone is thought to represent the ductile lower crustal channel of Tibet as it grinds its way to the surface. Connect, Inspire, Empower.
The John J. For a more in-depth explabeen shown to be highly effective in Madison, Wis. This force also produces drag. The neutrino has been found. Frederick Reines and Clyde L. Cowan, Jr. The discovery of Neptune was a crowning achievement of classical physics: The neutrino is a similar achievement of modern physics, and its discovery is a vindication of the law of the conservation of energy. As regards the new aeroplane which Messrs.
Thus may be explained the persistency with which mythology and folk lore allude to pygmy people. At his own expense he sent out three expeditions. Two of them came to grief on the coast of South America, and the third was abandoned after cruising along the coast of Chile and Peru for several years in search of the treasure.
Within the case is a bell and spring hammer, the latter connected with a fob chain. The supposition is, that the thief will pull the chain in order to obtain the prize. But instead of getting the watch, the watch gets him.
The pull sounds the alarm bell, the owner of the watch grabs the rogue, and the policeman conducts him to limbo.
But all that bon-offset programs are the latest rage. At partying had a downside — pollution. One least a dozen companies offer the promise to million soccer tourists consumed a lot of en- mitigate greenhouse gas emissions from acergy.
A consortium Voluntary offset programs, however, are not including FIFA, the international soccer fed- regulated, so consumers cannot be sure that eration, and the German football associa- they are investing in environmentally sound tion DFB donated 1. But governments are starting to pay heed to offsets. Europe established a cap-and-trade system last year that limits carbon dioxide emissions from about 50 percent of industry to reach its emissions goals as dictated by the Kyoto Protocol.
As the trading market evolves, some environmentalists think that voluntary offset programs could join existing cap-and-trade market schemes to cut emissions even more substantially. That system suffered a setback in May after governments realized that they had set emissions limits too high. The European Union is discussing how to tighten the scheme. Under the Regional Greenhouse Gas Initiative, Northeast and mid-Atlantic states plan to implement a market-based cap-and-trade program for all greenhouse gases emitted from power plants in the area.
In California, a pending bill would cap greenhouse gas emissions from all industries in the state. The fermenting mass generates gas, which fuels stoves and replaces kerosene. Two other sustainable energy projects will take place in South Africa. One will capture off-gas at a sewage treatment facility and burn it to supply electricity to Sebokeng, a township near Johannesburg. World Cup organizers could have planted trees — as has been done by previous sporting events, such as the Super Bowl— or invested in other projects on home turf.
But planting has been criticized because trees take years of growth to suck up an equivalent amount of released carbon. Currently, voluntary activities do not generate tradable emission credits.
But imagine if they did. Next year, however, the high-energy frontier will move to Europe, where the even more powerful Large Hadron Collider will begin operations near Geneva. Fermilab intends to shut down the Tevatron by The high-energy protons crash into beryllium targets, producing pions that spit out neutrinos as they decay. Astrophysicists speculate that an unknown substance called dark energy has sped up the expansion over the past few billion years.
Interestingly, the energy density needed to drive the current acceleration is roughly comparable to the estimated energy density of neutrinos.
Rob Fardon, Ann E. Fortunately, similar inters to a massive detector in the abandoned vestigations in Japan may complement the Soudan Iron Mine in northern Minnesota. To increase their chances of The long journey gives the particles more success, Fermilab engineers are tweaking time to oscillate. This past March, MINOS their accelerators to maximize the power of scientists announced that only about half of the MINOS beam, which in turn raises the the expected muon neutrinos arrived at the number of neutrino interactions in the deSoudan detector, suggesting that the remain- tector.
The warranty did not cover oceanographic expeditions. Even J. Craig Venter, famous for his role in decoding the human genome, had frozen his microbial samples from the Sargasso Sea for sequencing back on shore. His results showed that the surface water in the balmy sea around Bermuda teems with genetic material. The biologists from Connecticut wanted to go deeper into the ocean— and go beyond microbes — to test for diversity among the animals at the base of the food web.
Working with a sequencer at sea would give them the best results. The researchers are part of the Census of Marine Life, an international network of marine scientists that began a mission in to identify every living creature in the ocean by Brown, Wiebe, the chief scientist, and his team used the net device to scour the Sargasso Sea. Lashed down with a bungee cord in an air-conditioned room sat a brand-new, kilogram DNA sequencer. Zooplankton are w w w. Some individuals attract and sting prey; others propel the colony.
The genes of this and all marine creatures may be sequenced by Whatever happens to zooplankton in the ocean has an immediate impact on the rest of the marine food web. Change in pressure is not a problem for most of these grazers, which can descend hundreds of meters deep during the day. At night they rise back up near the surface to feed, treading carefully near the thermocline, the distinct boundary between the deeper, colder water and the warmer surface water.
A change in temperature from near freezing to bathtub-water warm can kill the temperature-sensitive creatures. But just how much of an impact it will have is unknown. This expedition changed and DNA break down. Most zooplank- that. By the time they returned to port on started at the surface and continued collecting throughout the water col- April 30, the scientists had catalogued animals and genetically bar-coded umn at every 1, meters of depth.
The expedition was unique in hav- of them. By the Census of ing taxonomists working over the mi- Marine Life scientists expect to have croscopes side by side with the molecu- bar-coded all 6, known species of lar biologists preparing the species for zooplankton and potentially that many sequencing.
Maybe in spurts or maybe all at once, a fury of volcanism paved over nearly the entire surface. To fathom why a planet would have done such a thing to itself, researchers need to know its inner torment. On Earth, such waves make themselves felt in various ways, ranging from radio interference created as they ripple through the ionosphere to the infrasound that some scientists think animals perceive during quakes.
It goes the other way, too: The dense Venusian atmosphere, usually a hindrance for observers, is a boon for aeroseismology. At a given altitude, the acoustic amplitude of a venusquake is times that of a comparable earthquake.
Garcia says quakes might also generate the equivalent of tsunamis which are buoyancy-driven rather than pressure-driven waves. His team estimates that a magnitude 6 quake, occurring at a depth of 30 kilometers, should cause the air pressure and density to oscillate by as much as 10 percent.
It would raise the temperature at an altitude of kilometers by 10 degrees Celsius over an area kilometers across. The heat pulse, lasting several minutes, is well within the means of the Venus Express spectrometer to detect— if it can be teased out from other atmospheric processes. Even the mere detection of a quake would be a breakthrough.
To be sure, probing internal structure with the resolution of Earth seismology would require multiple seismometers on the ground, each refrigerated to survive the degree C temperature. The detection of quakes by VEx might shake loose support for a proposal by Stofan and her colleagues in the early s to do just that. Only then might scientists come to learn why Venus is the goddess not of love but of tragedy. In May the Environmental Protection Agency proposed its continued sale, despite considerable evidence suggesting it is carcinogenic and harmful to the brain and nervous system, especially in children.
On several occasions, the agency has come close to banning the pesticide — used in no-pest strips as well as in agriculture — but has always backed away. They are to nerve agents than the human nervous sysnot entirely safe, either. One better alternative is boric acid, tem. The idea was that small amounts of especially when used in bait traps, these agents would be lethal to insects and which draw bugs and keep the harmless to people. Fortunately, Questions about their safety arose in the the best ways to control insects s.
The EPA considered a ban on 13 pesin the home do not require any pesticides, just good ticides in , including DDVP, but took housekeeping: The EPA missed that deadline. The EPA again failed to act. The EPA has acted on many of them, but it is unlikely to meet its deadline for completing the pesticide review. But that is unlikely to limit human exposure, insists David E.
The dispute is most likely headed to court. Paul Raeburn writes about science, policy and the environment from New York City. He some scholars, this ancient art represents compared these data with measurements the handiwork of shamans; others detect taken from children, teenagers and traces of initiation rites or trancelike states.
The groups A new interpretation offers a more prosaic are comparable, he reasoned, because both explanation for cave art: Statistically, the cave handprints match ing and sex.
During the late Paleolithic era, 10, to up with modern children aged 10 to 16, 50, years ago, humans roamed a vast Guthrie reports in his book, The Nature of steppe covering modern Europe, Asia and Paleolithic Art, published earlier this year. North America. Guthrie estimates the sex ratio of the handprints as largely male, by three or four to one.
He argues that the subject matter of much Paleolithic art is consistent with its being created by adolescent boys, who would have been preoccupied with hunting and mating.
As magical totems, perhaps part of hunting or evidence of its down-to-earth origins, he fertility rituals performed by shamans. Dale Guthrie, a paleobiologist emeritus at could still have played a role in some images, the University of Alaska—Fairbanks. Dale Guthrie of the University of Alaska—Fairbanks. But that is not to say that they had a monopoly on artistic expression.
The constant environment of a cave tends to preserve its contents, Guthrie notes, so those who ventured inside are disproportionately represented. Jewelry, pottery, clothing and soft artifacts would have degraded more readily.
It can be injected, snorted and eaten, but smoking is the most popular method. Smoking and injection provide the most stimulation. In the U. In , 1. Methamphetamine Use, Abuse, and Dependence: By the Northeast, the upper South, Texas, and comparison, cocaine binges rarely last more East Central states.
The meth problem grew out of addiction tin follows the epidemic closely. She believes to over-the-counter remedies available since that larger quantities of the drug are becomthe s for the treatment of asthma, nar- ing available in the East as organized gangs colepsy and other ailments. Furthermore, amine, could also be used for staying awake she notes that these gangs are now selling and suppressing appetite, a boon to truck a purer and hence more potent form of drivers, students and people wanting to the drug.
Meth users are probably getting sicker. In their wake, found that the number of meth users during many others followed: SAMHSA found, howephedrine or pseudoephedrine; the last are ever, that the proportion of these users medications available without prescription. That translates into , peomethamphetamine; Mexican gangs bring ple who are at particular risk of violence into the country most of the remainder.
They fabricated a touch sensitivity. Future touch sensors for robots based on this work will most likely rely not on light signals but rather on electrical impulses, researcher Ravi Saraf explains. For a few million years, the North Pole felt downright Floridian thanks to the presence of greenhouse gases released by some unknown geologic process. The warmth as recorded by the core data is 10 degrees Celsius higher than climate models had predicted.
Virtually all these chestnuts were killed within 50 years by a fungus introduced to the U. He notes that the chestnut-killing fungus may not have thrived on the dry, rocky mountaintop where this stand dwells. The American Chestnut Foundation announced May 19 it would breed the trees with blight-resistant Chinese chestnuts in the hopes of eventually developing a hardier, mostly American hybrid. Marine biologists had noticed that in this typically social crustacean, sickly looking lobsters, infected with a lethal and contagious virus called PaV1, usually become isolated from the pack.
To determine if the avoidance is purposeful, scientists set up two adjacent dens in a tank of seawater, tied either a sick or healthy lobster in one den and then introduced a second lobster. If the second creature was already infected, it bunked with its sick or healthy tank-mate equally often. But healthy lobsters were one fourth as likely to share dens with infected lobsters than with healthy ones — even before the sickies became contagious — probably because of chemical signals.
A double-blind study, however, shows that a three-day treatment is just as effective. Though abundant in the centrosomes, few to no copies of these RNAs were found elsewhere in the cell, and their sequences were not seen in any genome database. Relatively little is known about the inner workings of centrosomes even after a century of study, and the investigators suggest their discovery could explain centrosome evolution and function. One device consists of layers of gallium arsenide and aluminum arsenide that emit and partially trap sound vibrations in the solid phonons oscillating in the terahertz range.
Physicists describe this so-called saser, for sound laser, in the June 2 Physical Review Letters. The system generates multidirectional ultrasound and might aid in studying so-called random lasers that likewise produce scattered, coherent light, co-designer Richard Weaver of the University of Illinois informed the Acoustical Society of America on June 8.
Fig trees may have marked the beginning of agriculture 11, years ago. Now, in a step toward using stem cells in cardiac repair, they have found where they lurk, based on mouse studies: Storms are similar bucket.
As they dialed up the speed to a few in principle to a semistationary bucket, spins per second, the vortex adopted a trefoil which may explain structured hurricane shape, then became square, pentagonal and eyes, and the underlying principle might aphexagonal. The sluggish outer layer of water ply to bathtub drains, too, Bohr says. Water adopts trefoil, square and pentagonal shapes depending on the rotational speed.
But much of physics is counterintuitive, as is the case in many other disciplines, and before the rise of modern science we had only our folk intuitions to guide us.
Folk psychology compelled us to search for the homunculus in the brain— a ghost in the machine — a mind somehow disconnected from the brain. Folk economics caused us to disdain excessive wealth, label usury a sin and mistrust the invisible hand of the market. The reason folk science so often gets it wrong is that we evolved in an environment radically different from the one in which we now live.
Our senses are geared for perceiving objects of middling size — between, say, ants and mountains — not bacteria, molecules and atoms on one end of the scale and stars and galaxies on the other end. We live a scant three score and 10 years, far too short a time to witness evolution, continental drift or long-term environmental changes.
Causal inference in folk science is equally untrustworthy. We correctly surmise designed objects, such as stone tools, to be the product of an intelligent designer and thus naturally assume that all functional objects, such as eyes, must have also been intelligently designed.
We lived in small bands of roaming hunter-gatherers that accumulated little wealth and had no experience of free markets and economic growth. Folk science leads us to trust anecdotes as data, such as illnesses being cured by assorted nostrums based solely on single-case examples.
Equally powerful are anecdotes involving preternatural beings, compelling us to make causal inferences linking these nonmaterial entities to all manner of material events, illness being the most personal. Because people often recover from sickness naturally, whatever was done just before recovery receives the credit, prayer being the most common. The April issue of the American Heart Journal published a comprehensive study directed by Harvard Medical School cardiologist Herbert Benson on the effects of intercessory prayer on the health and recovery of patients undergoing coronary bypass surgery.
The 1, patients were divided into three groups, two of which were prayed for by members of three religious congregations. Prayers began the night before the surgery and continued daily for two weeks after.
Half the prayer recipients were told that they were being prayed for, whereas the other half were told that they might or might not receive prayers. Case closed. But for us to discriminate true causal inferences from false, real science trumps folk science.
Although the administration of George W. Bush has often stated its commitment to the spread of democracy, partly to combat the risks of terror, it relies excessively on military approaches and threats rather than strategic aid. Consider Liberia, just emerging from a prolonged civil war, and Haiti, which has suffered decades of intense political instability.
Both nations have recently elected new democratic governments, but both face continuing possibilities of internal violence and disorder. When the public thinks that a newly elected national government will succeed, local leaders throw their support behind it.
Individuals and companies become much more likely to pay their taxes, because they assume that the government will have the police power to enforce the tax laws. A virtuous circle is created.
Rising tax revenues strengthen not only the budget but also political authority and enable key investments — in police, teachers, roads, electricity— that promote public order and economic development.
When the public believes that a government will fail, the same process runs in reverse. Pessimism splinters political forces.
Tax payments and budget revenues wane. The currency weakens. Banks face a withdrawal of deposits and the risk of banking panics. Disaster feeds more pessimism. By attending to the most urgent needs of these fragile states, U. To an informed and empathetic observer, the necessary actions will usually be clear. Both Liberia and Haiti lack electricity service, even in their capital cities. Both suffer from pervasive infectious diseases that are controllable but largely uncontrolled.
But if each impoverished farm family is given a bag of fertilizer and a tin of high-yield seeds, a good harvest with ample food output can be promoted within a single growing season.
Electric power can be restored quickly in key regions. And safe water outlets, including boreholes and protected natural springs, can be constructed by the thousands within a year. Far too often, however, the U. Rather than giving practical help, the rich countries and international agencies send an endless stream of consultants to design projects that arrive too late, if ever. They ignore emergency appeals for food aid. Pessimism breeds pessimism. Eventually the government falls, and the nascent democracy is often extinguished.
By thinking through the underlying ecological challenges facing a country— drought, poor crops, disease, physical isolation— and raising the lot of the average household through quick-disbursing and well-targeted assistance, U.
Like many physicists, Connes hopes that the Higgs particle will show up in detectors. The Higgs is the still missing crowning piece of the so-called Standard Model— the theoretical framework that describes subatomic particles and their interactions. In commutative algebra, the product is independent of the order of the factors: But some operations are noncommutative.
Take, for example, a stunt plane that can aggressively roll rotate over the longitudinal axis and pitch rotate over an axis parallel to the wings. Assume a pilot receives radio instructions to roll over 90 degrees and then to pitch over 90 degrees toward the underside of the plane. But if the order is inverted, the plane will take a nosedive. Operations with Cartesian coordinates in space are commutative, but rotations over three dimensions are not.
Because of the Heisenberg uncertainty principle, one cannot measure both quantities simultaneously. As a consequence, position times momentum does not equal momentum times position. Hence, the quantum phase space is noncommutative. Moreover, introducing such noncommutativity into an ordinary space — say, by making the x and the y coordinates noncommutative — produces a space that has noncommutative geometry. Through such analyses, Connes discovered the peculiar properties of his new geometry, properties that corresponded to the principles of quantum theory.
On a day plagued by introducing a mathematical technique called renormalization. Like a caged lion, the year-old Connes walks corresponded to reality. Outside, police sirens scream amid student protes- portunity to explore the space in which physics lives.
The linkage gave renormalization a mathematically rigel. The relation between renormalization and noncommutaBut the spacetime used in general relativity, also based on tive geometry serves as a starting point to unite relativity and electrodynamics, was left unchanged. Connes proposed some- quantum mechanics and thereby fully describe gravity. He has already shown, with physicist Carlo Rovelli is that of spacetime as a noncommutative space that can be of the University of Marseille, that time can emerge naturally viewed as consisting of two layers of a continuum, like the from the noncommutativity of the observable quantities of two sides of a piece of paper.
The space between the two sides gravity. Time can be compared with a property such as temof the paper is an extra discrete noncontinuous , noncom- perature, which needs atoms to exist, Rovelli explains.
What about string theory? The discrete part creates the Higgs, whereas the continuum parts generate the gauge bosons, such as the W and the quantum world? Connes contends that his approach, looking for the mathematics behind the physical phenomena, and Z particles, which mediate the weak force. Connes has become convinced that physics calculations is fundamentally different from that of string theorists. Although the Standard Model which still is a long way to go to reach the Planck scale, which proved phenomenally successful, it quickly hit an obstacle: That is not quite halfway.
Physicists, in- But to Connes, the glass undoubtedly appears half full. Starting around , workers will cultivate expertise technology in the s. Yet it is maturing rapidly. By , nents into three-dimensional circuits and whole devices. Descriptions of nanotech typically characterclude molecular nanosystems — heterogeneous ize it purely in terms of the minute size of the physnetworks in which molecules and supramolecular structures serve as distinct devices.
The proteins ical features with which it is concerned — assemblies between the size of an atom and about molecular inside cells work together this way, but whereas biological diameters. But at this scale, rearranging the atoms wider range of environments and should be much faster.
Comand molecules leads to new properties. Medical applications might be as ambitious as new and the adjustable behavior of collectives. Thus, nanotechnol- types of genetic therapies and antiaging treatments. Nanotech does, however, , involves the development of passive nanostructures: Helping the public to perceive nanobers in new composites or carbon nanotube wires in ultra- tech soberly in a big picture that retains human values and quality of life will also be essential for this powerful new disminiaturized electronics.
The second stage, which began in , focuses on active cipline to live up to its astonishing potential. New drug-delivery particles Mihail C.
Roco is senior adviser for nanotechnology to could release therapeutic molecules in the body only after they the National Science Foundation and a key architect reached their targeted diseased tissues. Electronic compo- of the National Nanotechnology Initiative. ROCO Rearranging atoms leads to new properties. The craters are named after the Argonauts of Greek mythology: After all, he reasoned, in the entire 20th century, astronomers had come across only a few. Sheppard more optimistically predicted twice as many, given the increased sensitivity of modern astronomical facilities.
Sheppard is now a richer man. Since that night, our team has discovered 62 moons around the giant planets, with more in the pipeline.
Other groups have found an additional But even astronomers generally adopt the popular usage. Adding to the challenge, they are distributed over a much larger region of space. Scanning such a vast area for moons demands the newest, largest digital detectors and the analysis of up to gigabytes of data a night [see box on page 46]. Our own Hawaii Moon Survey focused initially on Jupiter, whose proximity allows us to probe small moons that would be too faint to detect around the other, more distant giant planets.
Their long, looping, slanted orbits indicate that they did not form in situ but instead in paths encircling the sun. In essence, they are asteroids or comets that the planets somehow captured. The moons might have come from the Kuiper belt beyond Neptune or from regions closer in. Their capture may have involved collisions or other interactions in a younger, more densely populated solar system. All four giant planets, irrespective of mass, turn out to have similar irregular moon systems.
The bodies occupy a wide range of sizes, with smaller ones being much more abundant. The orbits of these moons are some of the most complicated in the solar system. Because they roam so far from their host planet, they are tugged by both planetary and solar gravity, and their orbits precess rapidly— that is, the long axis of the ellipse representing the orbit rotates. Odder still, most of the irregulars have retrograde orbits, which means they each trundle around their host planet in a direction opposite to the sense of the rotation of the planet.
In contrast, regular moons have prograde orbits. Regular moons share this motion because, astronomers think, they coalesced from disks around their respective planets. So the contrary behavior of the irregular moons is a sign of a different origin. These bodies are not well explained by standard models, and a wave of fresh theoretical work is under way.
It seems that they are products of a long-gone epoch when the gravitational tug of the newly formed planets scattered — or snatched— small bodies from their original orbits.
Studying them promises to illuminate the early stages in the development of the solar system. The full extent of the system of moons around Saturn was barely known until recent years.
The satellites fall into two broad categories: Some revolve in the same direction as Saturn rotates red ; others go the opposite way green. Similar systems surround the other giant planets far left. These diagrams show a sampling of the total number of moons. The otherwise modest effects of solar gravity accumulate over time, destabilizing the orbit; the ellipse elongates to such an extent that the moon either collides with the planet or one of its larger moons or breaks out of the Hill sphere and falls into the gravitational clutches of the w w w.
Prograde orbits are more vulnerable than retrograde ones. If irregular moons were originally equally likely to be either prograde or retrograde, this resonance could explain why most moons are now retrograde. Another resonance, known as the Kozai resonance, couples the tilt and shape of the orbit.
Moons that are hauled into inclined orbits wind up on highly stretched ellipses, again leading potentially to their ejection or destruction. That may be why observers have found no moons with inclinations between 50 and degrees.
In short, the irregular moons we see today appear to be the survivors of gravitational interactions that cleared out many of their brethren. Still other features of the orbits require processes beyond those of gravity. If so, many of the irregular moons we see today are the second generation — one step removed from the original population.
Beyond learning something about the orbits of irregular moons, astronomers have made some progress in discerning other properties.
Most of the moons are so faint that they have been able to uncover very little about their composition. Color is a proxy for composition, so this discovery implies a likeness in makeup — further supporting the idea that group members are fragments of a larger, bygone parent body.
The two irregular moons of Neptune seen by the Voyager 2 space probe, Nereid and Triton, also have icy surfaces. The ices hint that these objects formed relatively far from the sun, like comets. The irregular moons of Jupiter are pitchblack and appear to be devoid of ice, probably because they are closer to the sun and too warm for ice to be stable. Astronomers have proposed three capture mechanisms.
For all three, the initial stage is the formation of asteroid-size bodies called planetesimals. Many agglomerate to form the rocky cores of the giant planets. The leftovers are vulnerable to being captured. Understanding how that happened is not easy. In the complex interplay of solar and planetary gravity, asteroids and comets are routinely pulled into shortlived orbits around the giant planets.
Jewitt traces his interest in astronomy to age seven, when he was astonished by a spectacular meteor shower visible against the sodium-lit night skies of industrial north London. Sheppard, his former graduate student, recently became a Hubble postdoctoral fellow in the department of terrestrial magnetism at the Carnegie Institution of Washington.
Kleyna grew up on a farm in Maine, enjoys incomprehensible art-house cinema and is now a Parrent postdoctoral fellow at the University of Hawaii, where he mainly studies dark matter in dwarf galaxies.
The leaves enter the vortex, swirl around for perhaps a few dozen times and then are blown out in an unpredictable way.
Had it not met an untimely death, the comet would have been ejected back into heliocentric orbit within a few hundred years. Astronomers know of several objects that survived temporary capture by Jupiter and returned to orbiting the sun. Planetesimals passing through this atmosphere lose energy to friction and can be captured. Its gravity rapidly strengthens, snatching nearby planetesimals that happen to fall within its expanded gravitational domain, or Hill sphere.
Two planetesimals passing near the planet almost collide. One loses energy and falls into orbit white. The other gains energy and escapes red. But for a body to be permanently captured from heliocentric orbit into a bound, stable orbit around a planet, it must lose some of its initial energy. Essentially the body has to be slowed down to prevent it from escaping again.
Moon capture, then, must have occurred long ago, at a time when the solar system had different properties. In the s theorists proposed three possible mechanisms, all functioning during or soon after the epoch of planet formation.
Pollack and Joseph A. Tauber of Cornell University, w w w. Jupiter and Saturn, quite unlike Earth and other terrestrial planets, are composed primarily of hydrogen and helium. Most probably, they formed when a core of rock and ice, of roughly 10 Earth-masses, pulled in vast quantities of gas from the primordial disk surrounding the young sun.
Before settling into their modern, relatively compact forms, the planets may have passed through a transient, distended phase, during which their atmospheres extended hundreds of times farther than they do now.
In true Goldilocks style, a passing asteroid or comet would have met one of three distinct fates, depending on its size. If it was too small, it burned up in the bloated atmosphere, like a meteor. If it was too large, it plowed through unimpeded and continued in orbit about the sun. If it was just right, it slowed down and was captured. This process is a natural version of the aerobraking procedure that many planetary probes have used to enter orbit.
One problem with the gas-drag model is that it does not explain the presence of irregular satellites around Uranus and Neptune. They are equipped with digital detectors of more than million pixels each. The central problem is to distinguish objects in the solar system from more distant stars and galaxies. Observers use two methods. We compare three images of the same area, spaced some time apart.
During that time, Earth moves partway around the sun, changing our vantage point and causing bodies to appear to shift position; the closer the body, the more it appears to move. The second method involves a velocity measurement. In the summed image, background stars appear as streaks and the irregular moons as bright dots.
This mechanism of capture was first expounded by Thomas A. Like gas drag, however, this mechanism has trouble accounting for the moons around Uranus and Neptune, neither of which underwent a runaway growth in mass. Most models indicate that these planets grew slowly by accumulating asteroid- and comet-size bodies, perhaps taking tens or hundreds of millions of years to reach their presentday masses.
The other objects here are background stars. Thought to be about two kilometers across, the moon has an orbit that stretches 31 million kilometers away from the giant planet. An alternative model for forming Uranus and Neptune, proposed by Alan Boss of the Carnegie Institution of Washington, is that they started out as massive as Jupiter and Saturn and were whittled down by ionizing radiation from nearby massive stars.
The irregular moons are even harder to understand in this model, because a shrinking planet would tend to lose moons rather than grabbing them. In both the gas-drag and pull-down models, the irregular moons were acquired early in solar system history, probably before Earth had reached a recognizable state.
Because of their greater distance from the sun and the consequently lower density of material in the outer regions of the circumsolar disk, their cores took a longer time to reach the critical mass needed to precipitate gaseous collapse. Before that happened, the solar nebula had largely dissipated, and so Uranus and Neptune never had extended atmospheres, like those of Jupiter and Saturn. How can gas drag operate when there is not much gas?
They suggested that collisions between two bodies in the Hill sphere of a planet could dissipate enough energy to allow one of them to be captured.
This idea, called three-body capture, received relatively little attention in the 35 intervening years, perhaps because such collisions are exceedingly rare now.
Yet newer work shows that no collision is needed. The three bodies need only interact gravitationally. If they exchange energy, one can gain energy at the expense of the others.
The process is a scaled-up version of the gravitational slingshot effect that space mission planners use to boost deep space probes. This past May, Craig Agnor of the University of California, Santa Cruz, and Doug Hamilton of the University of Maryland suggested another form of three-body capture in which a binary object is sheared apart by the gravity of a planet, leading one component to be ejected and the other pulled into orbit.
The process works for both gas giants and ice giants. These types of interactions would have been most probable near the end of the planet formation epoch, after the Hill spheres had grown to their present proportions but before the leftover debris of planet formation had been cleared out.
Threebody capture might be able to account for why each planet has roughly the same number of irregular moons: Even if three-body interactions explain how the irregular moons were captured, where did they come from to begin with? Researchers have suggested two distinct possibilities.
The moons could be asteroids and comets that had w w w. Most of their cohorts were incorporated into the bodies of the planets or catapulted out of the solar system. Another possibility emerges from a recent model in which the solar system remained choked with debris until some million years after the planets formed.
Strong gravitational interactions between Jupiter and Saturn then set up oscillations that shook the entire system. Billions of asteroids and comets were scattered as the major planets lurched into their present, more stable orbits.
A tiny fraction of the scattered bodies could have been captured. In this scenario, proposed last year by K. Luu and David C. Spectral measurements should one day be able to test these two hypotheses. If they have similar compositions, that would argue for the second hypothesis, in which the moons all formed together and then dispersed. Recent work suggests that it and a partner orbited the sun in mutual embrace, until Neptune sundered them and claimed Triton as its own.
Exploration of the irregular moon systems is ongoing. Two things are already evident: The modern solar system simply offers no suitable mechanism through which moons could be captured. Second, the similarities among the irregular moon populations of all four outer planets suggest that they arose by three-body interactions, the only known mechanism that is about as effective for Neptune as it is for Jupiter.
Like skid marks on a road after a car crash, the irregular moons swooping around the giant planets provide us with tantalizing clues about past events that we could never have witnessed directly.
Kavelaars et al. Discovery of Five Irregular Moons of Neptune. Matthew J. Holman et al. Photometry of Irregular Satellites of Uranus and Neptune. Tommy Grav, Matthew J. Holman and Wesley C. Fraser in Astrophysical Journal, Vol.
Available online at arxiv. Cassini Imaging Science: Initial Results on Phoebe and Iapetus. Porco et al. Craig B. Agnor and Douglas P. Hamilton in Nature, Vol. Hawaii Irregular Satellite Survey Web site: AUGUS T Disabled genes, molecular relics scattered across the human genomic landscape, have a story of their own to tell. The bones of long-dead genes — known as pseudogenes— litter our chromosomes. It is already clear that a whole genome is less like a static library of information than an active computer operating system for a living thing.
As products of the processes by which genomes remodel and update themselves, pseudogenes are providing new insights into those dynamics, as well as hints about their own, possibly ongoing, role in our genome. If errors in a copy destroy its ability to function as a gene, dogenes during the late s, when however, it becomes a pseudogene instead right.
The alignment shown here of incapable of giving rise to a protein. Cellular sequence that looked like a globin gene machinery reads the DNA alphabet of nucleotide a partial sequence for a human gene RPL21 but could not possibly give rise to a proagainst one of its pseudogene copies bases abbreviated A, C, G, T in three-base tein.
Even single-base mutations in codons in pseudogenes. The human genome is made up Nonsynonymous mutation of more than three billion pairs of nucleotides, the building blocks of DNA molecules. Yet less than 2 percent of our genomic DNA directly encodes proteins. With ongoing annotation of the hu- many of them and why, if they are really Perhaps a third is noncoding sequences man genome sequence, our research useless, they have been retained in our within genes, called introns.
The re- group, along with others in Europe and genome for so long. A small much of it is effectively genomic dark discovered. Humans have only an esti- fraction of pseudogenes are believed to matter whose function is still largely a mated 21, protein-coding genes, so have once been functional genes that mystery.
But most randomly scattered like rusted car parts parts. Their sheer prevalence has raised pseudogenes are disabled duplicates of on the landscape — and in surprising many questions, including how they working genes. They may have been came into existence, why there are so dead on arrival, having suffered lethal numbers. Normally, the mRNA is destined for translation into a protein — but sometimes it can instead be reverse-transcribed back into DNA form and inserted in the genome. A splicing process next cuts introns out of the raw transcript and joins exonic sequences to produce an edited messenger RNA mRNA version of the gene.
Pseudogenes can be born in two ways, each of which yields a distinctive facsimile of the original parent gene. Just before dividing, a cell duplicates its entire genome, and during that process, an extra copy of a gene can be inserted into the chromosomes in a new location. Alternatively, a new version of a gene can also be created through reverse transcription: Known as retrotransposition, this phenomenon can occur because of the activity of another type of transposable genetic actor, known as a long interspersed nuclear element, or LINE, that behaves like a genomic virus.
These two processes, duplication and retrotransposition, are major forces that remodel genomes over the course of evolutionary time, generating new variation in organisms. They are the means by which genomes grow and diversify, because many replicated genes remain active. But if the gene copy contains disabling typos or is missing pieces of the original, such as the promoter, it will become a pseudogene.
Pseudo genes made from mRNA lack introns and are described as processed pseudogenes. Although the overall distribution of most pseudogenes across human chromosomes seems completely random, certain kinds of genes are more likely to give rise to pseudogenes. Geneticists organize functional genes into families based on their similarity to one another in both sequence and purpose.
Only about a quarter of these family groups are associated with a pseudogene, and some families have spun off an inordinate number of copies. In one extreme case, a single ribosomal protein gene known as RPL21 has spawned more than pseudogene copies. Those responsible for basic cellular housekeeping functions, such as the genes in the ribosomal protein family, are abundantly expressed, providing more opportunities to create processed pseudogenes.
Because pseudogenes have been accreting this way in our genomes for so long, some are relics of genes eliminated during the course of evolution, and no functional version exists today.
Consequently, intergenic regions can be seen as vast molecular fossil beds offering a silent record of events in our evolutionary past. Family Histories t h e p r i nc i pl e s of natural selection appear to extend to individual genes, strongly constraining mutations in the sequences of functional genes.
Gulo makes an enzyme that is the last element in a biochemical pathway for synthesizing vitamin C. Most mammals possess the active gene, but the primate lineage seems to have lost it more than 40 million years ago. When the Gulo gene became a pseudogene, primates became dependent on food sources of vitamin C to avoid scurvy. Scientists can use this tendency to derive a kind of molecular clock from the nucleotide changes in pseudogenes and use it to study the overall dynamics and evolution of the genome.
Tracking the evolutionary path of genes and pseudogenes helps molecular biologists to uncover instances of gene birth and death just as the study of mineral fossils tells paleontologists about the creation and extinction of species. About 8, of our pseudogenes are processed; the rest include duplicated pseudogenes and other nonprocessed subcategories. RPL21 orange are scattered across the human chromosomal landscape.
Overall distribution of pseudogenes in the human genome appears to be completely random, although some local genome regions tend to contain more pseudogenes. Those DNA regions may be analogous to certain geochemical environments that better Differences in pseudogenes offer hints about diverse life histories. Lancet and his colleagues found in Analysis of the mouse genome, for studies of apes, monkeys and other dis- example, has shown that 99 percent of tant primate cousins that the greatest human genes have a corresponding verloss of olfactory receptor genes — that is, sion in the mouse.
Although the human the greatest increase in OR pseudo- and mouse lineages diverged some 75 genes — occurred in ape and monkey lin- million years ago, nearly all of the human eages that evolved the ability to see color genome can be lined up against equivain three wavelengths of visible light.
The lent regions, known as syntenic blocks, link may suggest that a sensory trade-off in the mouse genome. Yet despite this took place over time in the primate lin- similarity in functional genes and overeage when better eyesight made an acute all genome structure, just a small fraction sense of smell less critical.
Using the rate of sequence decay ceptor repertoire. Many dead-on-arrival relative to the parent genes to determine pseudogene copies are an immediate by- their age, it is also clear that many pseuproduct of this process. But the subse- dogenes in the human and mouse gequent death of additional duplicates, nomes have arisen at different times. Consequently, differences pseudogenes in each of the lineages. The number of pseudogenes in different genomes varies greatly, more so than genes, and it is not readily predictable, because it is neither strictly proportional to the size of a genome nor to the total number of genes.
One of the largest known gene families in mammals, for example, consists of more than 1, different genes encoding olfactory receptors, the cell-surface proteins that confer our sense of smell. Detailed analyses of olfactory receptor OR genes and pseudogenes by Doron Lancet and Yoav Gilad of the Weizmann Institute of Science in Rehovot, Israel, show that humans have lost a large number of functional olfactory receptor genes during evolution, and we now have fewer than of them in our genome.
For comparison, versions of about human olfactory receptor pseudogenes are still functional genes in the genomes of rats and mice. This difference is not surprising given that most animals depend more for their survival on the sense of smell than humans do. In fact, humans have considerably more olfactory receptor pseudogenes than chimpanzees do, indicating that we lost many of those functional genes after our split from the ape lineage.
Zheng, after completing his Ph. But Gerstein and Zheng were intrigued by the enormous data analysis challenges posed by the sequencing of the human genome and chose to start scanning and sifting the regions of DNA between genes.
These disablements cannot be tolerated by true genes and are thus typical manifestations of pseudogenes. More subtly, the theory of neutral evolution introduced by mathematical biologist Motoo Kimura in the s holds that nonfunctional DNA sequences can change freely, without the constraint of natural selection. Thus, individual nucleotide mutations can be divided into two types: Large-scale pseudogenization is most often seen among genes that, like the olfactory receptor family, are responsible for responses to the environment.
Such pseudogenes may therefore be under evolutionary constraint, which implies that they might have some function after all. One way to try to ascertain whether pseudogenes are functioning is to see whether they are transcribed into RNA.
In their studies, in fact, more than half the heavily transcribed sequences map to regions outside of known genes. What is more, a number of those transcriptionally active intergenic areas overlap with pseudogenes, suggesting that some pseudogenes may have life left in them.
Our research group is part of a consortium of laboratories working to understand what is going on in the dark matter of the genome.
Previous studies as well as preliminary ENCODE data indicate that at least one tenth of the pseudogenes in the human genome are transcriptionally active. Knowing that so many pseudogenes are transcribed does not tell us their function, but together with evidence that certain pseudogenes are better preserved than background intergenic sequences, it certainly challenges the classical view of pseudogenes as dead.
One possibility is that pseudogenes play some ongoing part in regulating the activity of functional genes. Early efforts to catalogue pseudogenes were largely driven by the need to distinguish them from true genes when annotating genome sequences. Identifying pseudogenes is not as straightforward as recognizing genes, however.
Based on characteristic elements, pattern-seeking computer algorithms can scan DNA sequences and identify genes with moderate success.
Recognition of pseudogenes, in contrast, relies primarily on their similarity to genes and their lack of function. Computers can detect similarity by exhaustively aligning chunks of intergenic DNA against all possible parent genes.
Just as a living organism can die of many different causes, a variety of deleterious mutations affecting any step in the process of making a protein can disable a copied gene, turning it into a pseudogene. And at least two examples of pseudogenes behaving in a similar manner have been documented so far. The investigators found that in the neurons of a common pond snail, both the gene for nitric oxide synthase NOS and its related pseudogene are transcribed into RNA but that the RNA transcript of the NOS pseudogene inhibits protein production from the transcript of the normal NOS gene.
Then, in , Shinji Hirotsune of the Saitama Medical School in Japan traced deformities in a group of experimental baby mice to the alteration of a pseudogene. The inactivity of an important regulatory gene called Makorin1 had derailed the development of the mice, but Hirotsune had not done anything to Makorin1. He had accidentally disrupted the Makorin1 pseudogene, which affected the function of its counterpart, the Makorin1 gene. Because many pseudogenes have sequences highly similar to those of their parent genes, it is very tempting to speculate that the NOS and Makorin1 pseudogenes are not just isolated cases.
Instead their activity may be the result of selection w w w. Protogenes a n e xc i t i ng e r a of molecular paleontology is just beginning.
Current techniques rely heavily on sequence comparison to wellcharacterized genes, and although they can readily identify recently generated pseudogenes, very ancient and decayed sequences are probably escaping detection. Recent hints that not all pseudogenes are entirely dead have been intriguing, and some evidence also exists for the possibility of pseudogene resurrection— a dead gene turning back into a living one that makes a functional protein product.
Careful sequence comparisons have shown that one cow gene for a ri- bonuclease enzyme was a pseudogene for much of its history but appears to have been reactivated during recent evolutionary time. Slight differences in the pseudogene complements of individual people have also been found— for example, a few olfactory receptor pseudogenes straddle the fence: These anomalies could arise if random mutation reversed the disablement that originally produced the pseudogene.
Our studies have suggested, however, that in yeast, certain cell-surface protein pseudogenes are reactivated when the organism is challenged by a stressful new environment. RSVP 's are appreciated. Scientific American special issue: Our Story GWEN came about as we began to realize how poorly female graduate are connected and noticed the lack of support structure at the graduate level.
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