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NS 3 nov 01

Lions in peril The future looks bleak for Africa's big cats

LIONS may soon become extinct in large parts of Africa. According to a comm4ssion set up under the auspices of the World Conservation Union (IUCN), there is not a single population of lions in West or Central Africa that is large enough to be viable.

Although there are thousands of lions in East Africa, little is known about the numbers in countries such as Cameroon, Mali and Senegal. In June, Hans Bauer of Leiden University in the Netherlands helped to organise a meeting of IUCN members working with lions in Cameroon to pool knowledge about how many there are. A report of the meeting will be published on the Internet at in two weeks' time.

There have been virtually no long-term studies of lions in the region. "The figures are estimates based on being in the field from time to time," says Bauer. But for a i population of lions to have enough genetic diversity to sustain itself without inbreeding, biologists estimate that it must contain around 100 breeding pairs, which means between 500 and 1000 animals in total.

But none of the populations in the region has anywhere near this number of animals. The two largest populations, in the Benoue area of Cameroon and on the Senegal-MaliGuinea border, have around 200 lions each. There are also about a dozen smaller populations, with around 50 lions each.

"It's a serious situation," says Bauer. "There's not one population that we can be sure will continue to be there.' And Will Travers of the Born Free Founda tion in I:ondon says, "It might seem Iike there are a lot of lions, but they have become a com pletely fragmented population."

Part of the problem is that lions are not generally thought of as being at risk. 'Nothing is being done in West and central Africa," says Bauer. 'There is no research and no specific conservation." A spokeswoman for the WWF says the conservation organisa tion does not work with lions "be cause they are not endangered".

One major reason for the lions' decline is that as agriculture spreads, they are squeezed into small and isolated tracts of land. Lions need huge areas to hunt between 20 and 200 square kilo metres for a single male-so even a national park of several hun dred square kilometres cannot support a large population, while lions that stray over the borders come up against local people and their livestock.

But Travers says it's vital not to give up hope. 'We shouldn't allow this depressing news to be a signal that it's all over for lions in these countries," he says. 'The lion is the symbol of Africa. If these countries can no longer say 'We've got lions', that will be a significant disincentive for wildlife tourists."

Bauer says that trouble for the lions could be a warning that the ecosystem as a whole is under threat. 'The lion is a keystone species," he says. 'It's a signal-the fact that lions are threatened now could mean that other species might be threatened in 20 to 30 years time." Joanna Marchant

Hot on the scent A quick sniff could do wonders for your sex life

AN APHRODISIAC nasal spray that is more potent than an oyster and faster-acting than Viagra has been developed by researchers in the US. If clinical trials are successful, this "desire aerosol" could provide th,e first effective treatment for women who suffer from a low libido. Tests on animals and people have shown that the experimental drug PT-141 made by Palatin Technologies in Edison, New jersey, can stimulate desire and sexually arouse both sexes. But unlike Viagra, the target of PT-14* is the brain rather than the sexual organs.

PT-141 is a synthetic copy of a naturally occurring neuropeptide called ct-melanocytestimulating hormone. MSH plays a role in stimulating sexual function and appetite. Within 10 to 15 minutes of squirting PT-141 up the nose, the drug activates melanocortin receptors in the hypothalamus region of the brain. This prompts the release of other sex hormones in a. domino-like effect, says neuroscientist Annette Shadiack, who directs the biological research at Palatin. "PT-141 triggers the centre [email protected] nature would normally start sexual behaviour," she says. Shadiack and her colleagues at Concordia University in Montreal tested PT-141 on female rats and found that those on the drug actively engaged in foreplay and solicited sex from their male partners seven to eight times as often as the rats in the control group.

The more PT-141 the female rats received, the greater the effect. During the 30-minute test period the insatiable rats copulated up to four times. "The females had a greater motivation for sex while on drugs," says Shadiack, who believes that PT-141 could be used to treat women who suffer from low libido. It could also help women with physical arousal problems, since the two are often linked.

Palatin recently completed a pre-clinical safety trial of the spray in men and found no changes in blood pressure, heart rate or respiration rate-adverse effects that are often associated with taking Viagra. Although the trial was not designed to test its effectiveness in arousing men, some of those who took PT-141 experienced spontaneous erections. So far, the only drug capable of increasing a woman's sex drive is Welibutrin. But this prescription drug is an antidepressant, and improved sex drive is only a side effect. There are other drugs that act on the brain's sexual centre, such as apomorphine and Melantan 11, which is also a synthetic form of MSH. But these drugs have the libido-dampening effects of inducing a feeling of nausea and vomiting. In the trials so tar, there has been no sign of these sickening side effects with PT-141.

Palatin will begin clinical trials next year to test their bottled aphrodisiac in both men and women. And who knows, if all goes well nostrils could one day become an erogenous zone. Diane Martindate, New York

Lighthouses that never dim Miraculous beacons illuminate the dawn of time

WHAT if a lighthouse looked as bright from 100 kilometres as it did from 100 metres? Strange as it may sound, an astrophysicist is claiming beacons like this exist in the Universe in the form of X-ray-emitting jets emerging from quasars. Common sense says that galaxies and stars should appear fainter the farther away they are, which is why astronomers build ever more powerful telescopes.

But Dan Schwartz of the Harvard-Smithsonian Center for Astrophysics believes X-ray jets from quasars look just as bright no matter how far away they are. This makes them unique cosmic probes which may allow astronomers to see right back to the edge of the "cosmic dark age" approximately 14 billion years ago, when the Universe lit up like a Christmas tree as stars switched on for the first time. Astronomers believe that the X-ray jets are created by high-energy electrons streaming from the vicinity of supermassive black holes within distant quasars, though nobody knows exactly how they do this. Now Schwartz is proposing that the electrons boost the photons in the cosmic background radiation-the "afterglow" of the big banggiving them X-ray energies. This process would have been more efficient in the past, when the Universe was smaller and more cosmic background photons were squeezed into a given volume. So older, more distant quasars appear just as bright as younger, closer ones.

Schwartz says the effect is the result of an extraordinary combination of factors. 'The increase in efficiency exactly compensates for the dimming effect of distance,' he says. "So, unlike all other astronomical objects, or anything in the familiar world, X-ray jets are beacons which never dim.' But not all astronomers agree. Some believe that the X-rays are created when powerful magnetic fields decelerate the high-energy electrons, forcing them to give up energy in the form of X-rays. "However, in many cases this assumption leads to a total energy a thousand times less than is needed to create the observed X-ray luminosity," says Schwartz. If Schwartz's model is right, scientists may be able to use these X-ray beacons to observe the first stars switching on at the end of the cosmic dark age, and also to probe the cosmic background radiation itself at early times. These are important tasks for astronomers attempting to understand how the Universe evolved. "This is an absolutely mind-blowing possibility," says quasar expert David Hough of Trinity University in San Antonio, Texas. "Who'd have thought we'd discover a beacon that could illuminate the beginning of time?" Marcus Chown More at: hftp:Hxxx.lant.govlabs/astro-ph/OiiO434

Liquid Space
IS SPACE just space? Or is it filled with some sort of mysterious, intangible substance? The ancient Greeks believed so, and so did scientists in the 19th century. Yet by the early part of the 20th century, the idea had been discredited and seemed to have gone for good. Now, however, quantum physics is casting new light I on this murky subject. Some of the ideas that fell from favour are creeping back into modern thought, giving rise to the notion of a quantum ether. This surprising revival is affording new insights into the nature of motion through space, the deep interconnectedness of the Universe, and the possibility of time travel. Ingenious new experiments may even allow us to detect the quantum ether in the lab, or harness it for technological purposes.

If so, we'll have answered a question that has troubled philosophers and scientists for millennia. In the Sth century BC, Leucippus and Democritus concluded that the physical universe was made of tiny particles-atoms-moving in a void. Impossible, countered the followers of Parmenides. A void implies nothingness, and if two atoms were separated by nothing, then they would not be separated at all, they would be touching. So space cannot exist unless it is filled with something, a substance they called the plenum. If the plenum exists, it must be quite unlike normal matter. For example, Isaac Newton's laws of motion state that a body moving through empty space with no forces acting on it will go on moving in the same way. So the plenum cannot exert a frictional drag-indeed, if it did, the Earth would slow down in its orbit and spiral in towards the Sun. Nevertheless, Newton himself was convinced that space was some kind of substance. He noted that any body rotating in a vacuum-a planet spinning in space, for example - experiences a centrifugal force. The Earth bulges slightly at the equator as a result. But truly empty space has no landmarks against which to gauge rotation. So, thought Newton, there must be something invisible lurking there to provide a frame of reference. This something, reacting back on the rotating body, creates the centrifugal force. The 17th century German philosopher Gottftied Leibniz disagreed. He believed that all motion is relative, so rotation can only be gauged by reference to distant matter in the Universe. We know the Earth is spinning because we see the stars go round. Take away the rest of the Universe, Leibniz said, and there would be no way to tell if the Earth was rotating, and hence no centrifugal force. The belief that space is filled with some strange, tenuous stuff was bolstered in the 19th century. Michael Faraday and James Clerk Maxwell considered electric and magnetic fields to be stresses in some invisible material medium, which became known as the luminiferous ether. Maxwell believed electromagnetic waves such as light to be vibrations in the ether. And the idea that we are surrounded and interpenetrated by a sort of ghostly jelly appealed to the spiritualists of the day, who concocted the notion that we each have an etheric body as well as a material one.

'The slopping of your drink in a lurching aeroplane is attributable to the influence of all the matter in the Universe'

But when Albert Michelson and Edward Morley tried to measure how fast the Earth is moving through the ether, by comparing the speed of light signals going in different directions, the answer they got was zero. An explanation came from Albert Einstein: the ether simply doesn't exist, and Earth's motion can be considered only relative to other material bodies, not to space itself. In fact, no experiment can determine a body's speed through space, since uniform motion is purely relative, he said. Sounds OK so far, but there was one complication: acceleration. If you are in an aeroplane flying steadily, you can't tell that you're moving relative to the ground unless you look out of the window, just as Einstein asserted. You can pour a drink and sip it as comfortably as if you were at rest in your living room. But if the plane surges ahead or slows suddenly, you notice at once because your drink slops about. So although uniform motion is relative, acceleration appears to be absolute: you can detect it without reference to other bodies. Einstein wanted to explain this inertial effect-what we might commonly call g-forces-using the ideas of the Austrian philosopher Ernst Mach. Like Leibniz, Mach believed that all motion is relative, incluidng, the gravitation of all the matter in the Universe-an idea that became known as Mach's principle. Einstein warmed to the idea that the gravitational field of the rest of the Universe might explain centrifugal and other inertial forces resulting from acceleration. However, when in 1915 Einstein finished formulating his general theory of relativity -a theory of space, time and gravitationhe was disappointed to find that it did not incorporate Mach's principle. Indeed, mathematician Kurt G6del showed in 1948 that one solution to Einstein's equations describes a universe in a state of absolute rotation-something that is impossible if rotation can only be relative to distant matter. So if acceleration is not defined as relative to distant matter, what is it relative to? Some new version of the ether? In 1976 1 began investigating what quantum mechanics might have to say. According to quantum field theory, the vacuum has some strange properties. Heisenberg's uncertainty principle implies that even in empty space, subatomic particles such as electrons and photons are constantly popping into being from nowhere, then fading away again almost immediately. This means that the quantum vacuum is a seething frolic of evanescent 'virtual particles'.

Although these particles lack the permanence of normal matter, they can still have a physical influence. For example, a pair of mirrors arranged facing one another extremely close together will feel a tiny force of attraction, even in a perfect vacuum, because of the way the set-up affects the behaviour of the virtual photons. This has been confirmed in many experiments. So clearly the quantum vacuum resembles the ether, in the sense that there's more there than just nothing. But what exactly is the new version of the ether like? You might think that a real particle such as an electron moving in this sea of virtual particles would havf to batter its way through, losing energy Ind slowing down as it goes. Not so. Like the ether of old, the quantum vacuum exerts no frictional drag on a particle witg constant velocity. But it's a different story with acceleration. The quantum vacuum does affect accelerating particles. For example, an electron circling an atom is jostled by virtual photons from the vacuum, leading to a slight but measurable shift in its energy. And according to my 1976 calculations, an observer accelerating through empty space should see themselves surrounded by electromagnetic radiation, like that from a hot object. The stronger the acceleration, the hotter the radiation. Later that year, William Unruh at the University of British Columbia reached a similar conclusion by considering how the quantum vacuum might affect an accelerating particle detector. Unruh's method was readily adaptable to rotational acceleration, and calculations revealed that a rotating detector in a vacuum would also see radiation. Could this heat radiation be the ether glowing? To find out for sure, we would have to actually observe the radiation. However, the effect is tiny: to register a temperature of just 1 kelvin requires an acceleration of about 10^21g. Accelerating a physicist so severely is hardly a practical proposition. But maybe we could subject a subatomic particle to such violence. Last month, Daniel Vanzella and George Matsas of the State University in Sao Paulo, caused a stir by pointing out that if the radiation effect exists, it could cause a proton to do something that would never happen otherwise. A rapidly accelerated proton would absorb energy from the surrounding radiation and turn into a neutron, creating a positron neutrino in the process. But achieving such enormous accelerations is extremely difficult, even with a proton. So is there a gentler way? In the 1970s, Stephen Fulling and 1, then working at King's College London, investigated how the quantum vacuum would be disturbed by a moving mirror. We found that, as with a moving particle, there was no effect if the mirror moves at a constant velocity. Somewhat to our puzzlement, the same turned out to be true for a uniformly accelerating mirror. However, a mirror that changes its acceleration-by wiggling back and forth, say-excites the quantum vacuum and creates real photons. It might be possible to amplify this moving-mirror radiation by using a resonant cavity with vibrating walls. Marc-Thierry jaekel, Astrid Lambrecht and Serge Reynaud of the University of Paris, jussieu, described such an experiment earlier this year. They showed that the resonant oscillations not only amplify the radiation, they mean that it is emitted in sharply peaked bursts, helping to make it distinctive. The unsolved problem is how to shake the cavity violently enough while keeping it very cold, so that heat radiation doesn't swamp the still faint signal. There could be a way to feel the ether more directly. Theory predicts that the quantum vacuum behaves in some ways like a viscous fluid. According to general relativity, a gravitational field is just a distortion of the geometry of space-time. And it turns out that bending space puts a strain on the quantum ether. If this strain changes with time, you get friction. Leonard Parker discovered in the late 1960s that an expanding or contracting Universe would create particles out of a pure vacuum. In effect, the stretching of space jiggles up some of the virtual particles and turns them into real particles. At about the same time, Unruh and Alexei Starobinskii of Moscow University predicted a similar effect near black holes. They showed that if a black hole (which is actually just highly warped empty space) rotates, it emits quantum particles and glows. The quantum ether provides a neat way to explain this. As the hole rotates, it drags the ether around with it. The dragging effect is fiercer closer to the hole, so the ether is sheared, which heats it and makes it glow. Unfortunately the glow is so faint that no readily foreseeable telescope will be able to capture it.

Luckily, you don't need a black hole to observe ether.

In 1997, John Pendry of Imperial College, London, showed that a mirror sliding sideways parallel to another mirror facing it should experience friction even in a vacuum, because the virtual photons sandwiched between the parallel plates would heat up the mirror surfaces. This heat energy can come only from the kinetic energy of the plates, which would therefore be slowed down.

The same would apply to a single atom moving near a metal surface. So in theory, an atom dropped down the exact centre of a vertical metal pipe should reach a terminal velocity as it ploughs through the viscous quantum vacuum, just like a ball bearing dropped into oil. With advances in cold-atom optics, such an experiment might be feasible in the near future.

Yet even if we could detect the quantum ether as dramatically as this, all the effects I have described so far are weak. None of them has a powerful influence on the Universe, so you might think the quantum ether is just a minor curiosity. But some physicists think the very opposite is true.

Bernard Haisch of the California Institute for Physics and Astrophysics in Palo Alto and his colleagues have calculated the effect of the quantum vacuum on an accelerating charged particle, and claim that it mimics the effect of mass (New Scientist, 3 February, p 22). This, says Haisch, is the true origin of inertia, and solves the old conundrum about acceleration and relative motion. Put bluntly, your drink slops when an aircraft lurches because the quantum vacuum pushes against the accelerating atoms. Although few scientists have so far accepted this claim, the possibility is tantalising.

And there is a curious pointer to something deeper. Quantum physics is famed for its 'non-locality": the fact that it is not possible to characterise the physical situation at a point in space without reference to the state of the system in the wider surroundings. The quantum vacuum is no exception, since its state is defined across all of space. This enables it to "feel' the structure of the entire Universe, and thereby to link the global and the local in precisely the manner that Mach had in mind. This nonlocality hints at a possible connection between local physics and distant matter in the Universe -a connection that could be mediated by the quantum ether. Among other things, it could explain why we share an absolute frame of acceleration with the distant stars.

This is not the ether of Maxwell. Rather than being the medium that transmits light, it is made of light-virtual photons-and other virtual particles. Nor is it the plenum. The Greek philosophers' original argument against the void has lost much of its force, because physicists today have little difficulty imagining the concept of empty space. But now they question whether space itself is truly fundamental. Perhaps space as we know it is a special configuration of a deeper quantum entity, the properties of which we can only guess at. Far from abhorring a vacuum, nature may have worked very hard to create one. El

Paul Davies is a physicist and writer based at Macquarie University, Sydney, and the University of Queenstand. His latest book How to Build a rime Machine will be published this month by Allen Lane, The Penguin Press

NS 12 jan 2002

This little piggy had none Even knocking out a gene might not be enough to prevent pig organs being rejected by the humans.

TWO separate teams have taken a key step towards creating pigs whose organs won't be instantly rejected by our imipune system. But there is still a lot of work to do before pig organs could permanently replace failing human ones. At any time, more than 60,000 people are waiting for transplants in the US alone. Thousands die each year because not enough organs are available. Some doctors think pig organs could fill the gap. Though primates are a closer immunological match, pigs are easier to breed and raise.

But the human body doesn't take kindly to pig parts. Pig cells have a sugary chemical on their surface that antibodies in our blood immediately latch onto, causing an immune system attack so severe it merits its own name-hyperacute rejection. This can disrupt the blood supply of a healthy organ and destroy it within hours.

The best way to prevent hyperacute rejection is to "knock out' the gene for alpha-1,3-galactosyltransferase (GGTAl), the enzyme that makes the sugary coating of pig cells. Two groups have now accomplished this goal, one at the biotech company PPL Therapeutics and another led by Randall Prather of the University of Missouri Columbia. His piglets were born months before PPI!S, but PPL last week announced the birth of its piglets the day before Prather's work was published online by Science.

Both teams began by disabling the GGTA 1 gene in skin cells from pig fetuses. Thanks to the advent of cloning, they were then able to create embryos that had the altered DNA from these cells. The world's first cloned pigs were only born in March last year.

In total, there are now nine female cloned piglets all lacking one copy of GGTA 1. Normal breeding or another round of cloning will be necessary to knock out both copies of the gene. The researchers are confident that organs from animals lacking both copies won't provoke hyperacute rejection.

But there are other, slower forms of rejection that can destroy xenotransplants. Immune cells called natural killer cells attack the tissue. Mismatches between the pig and human blood-clotting system can cause massive clots to form in the transplanted organ and beyond. And work by Hugh Auchincloss at Massachusetts General Hospital in Boston suggests that T-cell mediated rejection, the major cause of rejection in human-to-human transplants, is more severe-and harder to control with conventional immunosuppressive drugs.

Julia Greenstein of Immerge BioTherapeutics in Charlestown, Massachusetts, which has been working with Prather, says that many of these responses may be triggered or exacerbated by the same sugar that causes hyperacute rejection. "We're hopeful that eliminating the sugar gets us past a number of obstacles,' she says.

Not everyone is so confident. 'We don't know yet whether this is a major breakthrough clinically, or just another layer on a dense onion of xenotransplant issues," says Auchincloss, also an adviser to Immerge BioTherapeutics. "I suspect the second." Only now that the GGTA 1 knockout pigs exist, he points out, will it be possible to assess the severity of other forms of rejection.

Greenstein expects that xenotransplantation will still require the help of so-called tolerance thera pies that make recipients' immune systems more receptive to foreign organs. For its part, PPL plans to make at least three more genetic changes to the knockout pigs to try to prevent other forms of immune rejection.

Even if rejection can be overcome, would-be xeno transplanters will still have to convince regulators that viruses lurking in the DNA of pigs don't pose a threat (New Scientist, 26 August 2000, p 7). Some of these porcine endogenous retro viruses (PERVS) can infect human cells. But the breed of pig Prather used doesn't appear to have such PERVS, -and PPL says it may try to knock out active PERVS in its animals. Philip Cohen

Moral outrage Bizarre as it seems, indignation makes the world go round

IT'S not love, affection or even blatant self-interest that binds human societies together. It's anger. Swiss researchersmade the unsettling discovery while trying to fathom what makes people cooperate.

Traditional explanations, such as kinship and reciprocal altruism, rely on genetic relationships or self-interest. These work for animals, but fail for humans because people cooperate with strangers they may never meet again, and when the pay-off is not obvious.

Such cooperation can be explained if punishment of freeloaders or "free-riders"those who do not contribute to a group but benefit from it-is taken into account. HoWeWr, irweal life, punishment is rarely without cost to the punisher. So why should someone punish a free-rider? Because of emotionally driven altruism, says Ernst Fehr, an economist at the University of Zurich in Switzerland.

To test this "altruistic punishment" hypothesis, Fehr and his colleagues played an experimental game with six groups of four students each, in which real money was at stake. Each member was given 20 monetary units (MUs) to keep or invest in a group project. For every MU invested, the return for the group was 1.6 MUs, which was divided equally among the four. members. So if only one person chose to invest, putting in I MU, she got back only 0.4 MU. But if everyone invested the full 20 MUs, they each ended up with 32 MUs, making total cooperation worthwhile.

Investment, therefore, was always in the interests of the group, but never in the interest of the individual doing the investing. A free-rider would benefit from not investing. She could just gain from the money invested by others. After a series of six games, in which members'investments were anonymous and everyone invested simultaneously, Fehr found that members contributed an average of 10 MUs in the first game. But cooperation quickly unravelled, says Fehr. Contributions dropped to 4 MUs by the sixth game. So Fehr decided to allow members to punish free-riders in their group, but at a cost. If a member punished another, it cost the punisher 1 MU and the punished 3 MUs. In six such games the average investment was always higher than in those without punishment, increasing to over 16 MUs. The threat of punishment sustained cooperation.

Crucially, the punishment was an altruistic act, as the punisher would never encounter the same free-rider again. To understand the motive behind altruistic punishment, the researchers questioned the students about their emotions. They found that anger appeared to be the cause. "At the end of the experiment, people told us that they were very angry about the free-riders," says Fehr. "Our hypothesis is that negative emotions are the driving force behind the punishment."

"It's a great experiment," says Herb Gintis, an expert on human cooperative behaviour at the University of Massachusetts in Amherst. Social policies which do not provide an outlet for stich emotions will fail, he says. In the 1980s, for instance, people revolted against the welfare state in the US because they felt that perceived freeloaders were not being taken to task. Anit Ananthaswamy More at: Nature (vot 415, p 137)

Thanks for all the fish Europe is plundering poor countries' food stocks

POOR coastal nations are sacrificing their long-term prosperity by allowing European fishing fleets to catch their fish at iockbottom prices. The warning comes from the UN, which has just completed a study into the impact of free trade on the environment. It says poor countries are forfeiting the future health of fish stocks worth billions of dollars and the incomes of their own fishers in return for paltry short-term financial gains. One such na,,tion is Argentina, whose exchequer is carrently bankrupt. After the country opened up its fisheries to European [email protected], exports of fish leapt by almost 500 per cent%etween 1985 and 1995. But in the past few years catches have dropped by a quarter as a result of overfishing. According to the report, which was prepared for ongoing talks on trade and the environment at the World Trade Organization, the unsustainable fishing of one species-hakehas cost Argentina $500 million. It says a better managed fishery could benefit the economy by as much as $5 billion. Several other countries face a similar problem. Fish stocks all over the world are suffering as too many, often heavily subsidised vessels chase a dwindling number of fish, warns Klaus Tbpfer, director of the UN Environment Programme. Rich nations send their surplus fleets to foreign waters, where they drive local fishing communities "into ever greater poverty, as well as robbing the marine environment", he says. One of the nations most at risk is Senegal in West Africa, which is currently deadlocked in talks with the EU over the price of access to its fisheries. The report concludes that EU fishing of Senegalese waters over the past decade has had a devastating effect on some key fish stocks and resulted in 'a serious impact on local food supplies". Many EU vessels, once laid up by restrictions designed to protect European fish stocks, now head south to plunder West African waters. Two-thirds of Senegal's export revenues come ftom fish "exports" to Europe.

Last spring, the EU sought a new deal with Senegal that would increase its take of shrimp, hake, octopus, grouper and other species by up to 60 per cent (New Scientist, 31 March 2001, p 19). Talks on how high a price Senegalls government might charge stalled just before Christmas, when Senegalese negotiators banned further visits by EU vessels until the dispute was resolved. Now, in a comment that is bound to anger EU negotiators, the UNEP report says Senegal should charge more for access to its fish and "suspend fishing in cases where a stock is seriously depleted".

The EU is under growing pressure from scientists and environmentalists to apply the same conservation rules to fish stocks abroad that it increasingly applies at home. Later this month, the European Commission is expected to release a report outlining how this might be done. "But right now the EU is still trying to export its excess fishing capacity to countries like Senegal," says Julie Cator, European fisheries coordinator for the World Wide Fund for Nature. Fred Pearce

Other Earths

VETERAN planet hunter Geoff Marcy has a wide grin on his face. He's found another planet, and one that's more significant than any he has spotted so far. "Every new planetary system reveals some new quirk that we didn't expect. We've found planets in small orbits and wacky eccentric orbits." But no one had found anything that looked remotely like our own Solar System. Now that has changed. Last August, Marcy's colleague Debra Fischer announced that a second planet has been discovered orbiting the star 47 Ursae Majoris. What makes this system so special is that both planets have almost circular orbits-like those of the planets in our own Solar System. If these planets were orbiting our Sun, they would be somewhere in the asteroid belt. They are not too dissimilar in mass to our giant worlds Jupiter and Saturn, giving this planetary system an uncanny resemblance to our own. Even the parent star is Sun-like.

At last we know there are some planetary systems where a comfortable twin to Earth might exist. And for astronomers trying to understand how planetary systems are born, it's a welcome respite from a period of feverish work, trying to revise their theories to fit all those weird planets. The discovery of the Solar Solar's near-twin is now providing some reassurance that their revamped theories of planet formation are at last on the right lines. It has all taken some time to achieve, because it starts with one of the most difficult tasks for ari, observational astronomer: to track down extrasolar planets. You can't do this just by pointing a telescope. "Right now, it's impossible even with our most powerful telescopes to see a planet," explains Debra Fischer, who works with Marcy and Paul Butler at the Lick Observatory in California. "The planet reflects such a tiny amount of starlight. It's like a little firefly buzzing around in the headlights of an oncoming car." But astronomers knew that a star with planets in tow would 'wobble" by a very small amount, just a few metres per second, as the planets tug the star back and forth as they orbit. Several teams were on the case. First past the post were the Swiss astronomers Didier Queloz and Michel Mayor, who in 1995 discovered a planet half the mass of Jupiter orbiting the star 51 Pegasi. Soon the planets began to roll in. In just six years, astronomers have turned up 66 systems containing 74 planets. But even as the tally of extrasolar planets began to mount, the planet hunters became increasingly uncomfortable. They had confirmed, to everyone's satisfaction, that stars have planets in tow. But these were not like the obedient worlds of our Solar System, with nice near-circular orbits and gas giants located a decent distance from their parent star. These were planets from hell-and they were breaking all the rules. Queloz realised that all was not well right from the start when he discovered the planet orbiting 5 1 Pegasi. The star wobbled with a period of just over four days-indicating that the planet circled its star absurdly close in. Even Mercury, the closest planet to the Sun, takes 88 days to orbit. Queloz's world is so close that it is blowtorched by the star's heat. The planet's temperature must be higher than that of a blast furnace, and its atmosphere swollen to grotesque proportions.

It turned out to be the first of many-a world similar in mass and make-up to our Jupiter, but 20 times closer to its parent star than the Earth is to the Sun. The rogue worlds rapidly acquired the nickname 'hot Jupiters". It certainly wasn't what the planet hunters had been expecting. They were looking for a system much like our own, with massive Jupiter-like planets in stable, near-circular orbits far from their star. This wasn't just a result of conservative thinking; astro nomers simply thought they knew enough about the basic recipe for making new worlds.

A circular disc of gas and dust surrounds a newly born star. Within the disc, the matter clumps together to make rocky or icy lumps about a hundred kilometres across. These, in turn, build up to become planets. The puzzle of the hot Jupiters was that only out at a much greater distance should you get enough material to build a giant planet.

But one theorist was unfazed by the hot jupiters. Sipce the 1980s, Doug Lin, of the University of California, Santa Cruz, had been calculating how the gravity of the massive disc around a star would affect an embryonic planet growing within. He found that the disc is very good at robbing energy from the planet. As a result, the planet naturally spirals in towards its parent star. "It wasn't surprising to me when the observa-tion showed that a planet had formed and migrated inwards-that in fact caused me a great deal of joy," Lin recalls. "What surprised me was how it could migrate all the way in and then stop almost next to the surface of the star." Lin suspects the answer lies in the central star. If it is spinning rapidly, tidal forces can transfer energy to the planet: the star slows down, while the energy pumped into the planet's orbit stops it from shrinking any more. A similar thing is happening with the Earth-Moon system; the Earth's spin is gradually slowing down as it gives energy to the Moon, which is being pushed away from us.

Pawel Artymowicz at the University of Stockholm in Sweden has a different idea. He thinks there's something about discs we don't understand yet, which makes them stabilise when two bodies are orbiting with very short periods. It's based on the fact that many young stars also live together in very close pairs, when theory says they too should have spiralled together and coalesced. But Artymowicz admits that this is one idea among many: "This is still a hardhat construction area for theories," he says.

In any case, a runaway giant would have dire consequences for any Earth-like planet. Gravitational drag from the wayward hot Jupiter would sap orbital energy from a smaller world and push it into the star. Theory says giant planets should spiral inwards very quickly, in a matter of a few million years-yet in our Solar System we seem to have had a lucky escape as Jupiter has stayed out at a safe distance. But Lin thinks there may be more to it than luck. He believes our Solar System could have had previous generations of planets that ended up incinerated within the Sun. "What we see in our Solar System may be the survivors of repeated generations of protoplanets that underwent infant mortality," Lin explains. "The planets we see today may be the last of the Mohicans."

As if hot Jupiters were not enough, the planet hunters also began to turn up other bizarre objects: wayward worlds in wildly eccentric orbits. 'We found a planet around 70 Virginis that was a real weirdo," recalls Marcy. "The orbit was so elongated that people thought to themselves, is this a planet or is it some other kind of beast? But sure enough, it turns out it's a planet, and we've found some 30 or 40 more of these planets in elongated orbits. And we now realise that most extrasolar planets are not in circular orbits, but in these elliptical ones."

These planets too pose a deadly threat to worlds like the Earth. Their gravity tends to sling smaller worlds away into the distant cosmos. Again, most theorists were caught on the hop. They had assumed the regular disc surrounding a young star should spawn a planetary system with circular orbits. The answer, according to Artymowicz, can be found by looking more closely at the original disc. His computer simulations of the protoplanetary disc reveal beautiful swirling "arms", like a spiral galaxy. If the disc is massive enough, the gravity of these arms can divert a young planet into an eccentric path. Lin instead blames the highly eccentric orbits on other planets orbiting the star. "As in a family, the siblings tend to perturb each other, and sometimes this interaction becomes so strong it can break up the family." He has applied this theory to Upsilon Andromedae, a system that includes a hot Jupiter and two eccentric planets. But this answer doesn't satisfy Alan Boss from the Carnegie Institution of Washington. For him, the eccentric solar systems are forcing us to find a new theory for making the heaviest planets. Boss's calculations show that the gradual assembly of small chunks of rock and ice can't build anything much bigger than Jupiter. Instead, he envisages the primeval disc spontaneously breaking up into several large lumps of gas, each of which becomes a giant planet. This theory has the advantage that the unstable lumps of gas won't generally be following circular paths around the star. Amid this welter of new theories explaining why other planetary systems should be different from ours, Fischer's announcement of a Solar System "twin' brought people up sharply. The star 47 Ursae Majoris had been on Marcy's hit list from the very beginning, and its bigger planet was one of the earliest to be discovered. This planet circles its star in just under three years. Fischer kept on returning to the star, however, concerned with niggling discrepancies between the prediction and the star's actual wobble. Once she'd taken away the effect of the first planet, she realised there was a much smaller wobble, with a period of seven years.

Whereas the first planet was 2.5 times heavier than Jupiter, the second weighed in at about three-quarters of Jupiter. Intriguingly, their masses are in the same ratio as the masses of Jupiter and Saturn in our system. And their distances from the suns are in roughly the same ratio, too, though the 47 Ursae Majoris planets are less than half the distance out. So this has proved that our Solar System is not unique, but it begs the question of why our Solar System and the planets of 47 Ursae Majoris are so unusual. Lin puts it down to weight and age. The more massive the planets are, the more intensely they interact with each other and the more quickly they will disrupt each other's orbit. 'Our own Solar System is atypical,' he says, "because we are relatively low in mass." Given enough time, though, even the orbits of our lightweight planets will become unstable. Fortunately for us that's many billions of years in the future. On the theoretical side, then, astronomers have worked out why many planetary systems are so different from our Solar System. Indeed, they now think that massive discs around young stars would naturally turn into something very different-systems of hot Jupiters and wayward planets. We live in a different kind of place because both the original spiral-armed disc and the subsequent planets are relatively lightweight.

Even the system around 47 Ursae Majores isn't exactly like our5. Identical twins will be harder to find-and will require a longer vigil. Jupiter takes about 12 years to circle the Sun, and Saturn takes 30. The present planet search has only been going for a dozen years, so it would only now be turning up cousins of our giant worlds, those with orbits of less than a dozen years or so. To find a true twin of our Solar System, we may need another 10 years of data or more.

So it's early days yet, but Butler is prepared to speculate on the number of Solar System lookalikes. "We can make a preliminary guess that about 5 per cent of planetary systems are in circular orbits," he ventures. Artymowicz tends to agree: "I think it's less than 10 per cent." These observations need a telescope dedicated to planet searches. Fischer looks forward to the day when she can monitor stars every night and detect distant planetary companions. "We hope to raise $5 million to purchase a dedicated 2-metre telescope." The telescope would be located at the Lick Observatory on Mount Hamilton, above Silicon Valley. But the dream of every planet hunter is not to find more jupiters and Saturns-it is to find another Earth. And the only way to do that is from the cold, clear vantage of space. Queloz is thrilled at the prospect, especially a mission now being planned by the European Space Agency. "There's this ultimate European mission called Darwin,' he explains. "The big goal is to see an Earthlike planet and analyse its light. We want to see if we can detect oxygen or wateryou know, the kind of holy elements that are linked to life." The American counterpart to Darwin is the Terrestrial Planet Finder-an ambitious mission that involves a whole fleet of telescopes sailing together in space. Like Darwin, TPF will use destructive interference to cancel out light from the star, making the planets visible. These spacecraft-or, more likely, a combined mission-may fly within 15 or 20 years. Then we should learn whether our Solar System is one of a kind or not. Artymowicz predicts that only a few per cent of systems with a giant planet will have an Earth-like world: in most cases, the Jupiter will have gone off on a rampage. But he also thinks there may be many planetary systems which started off with even less matter than the Solar System. In that case, there'd be no disruptive giant planets at all. "Who knows," he muses, "maybe 50 per cent of stars have big chunks of rockmaybe Earths-circling around them." El

Heather Couper and Nigel Henbest are the authors of Extreme Universe (Channel 4 Books), accompanying the Channel 4 TV series Edge of the Universe, 14 and 21 January at 9 pm