[naturenews] from [nature.com]
[naturenews]
Published online 8 December 2009 | Nature | doi:10.1038/462705a
News
Exoplanet claim bites the dust
Ground-based astrometry dealt a blow as planet found not to exist.
Katharine Sanderson
Is there really a planet orbiting VB10 (red star)?NASA/JPL-CaltechStrike one planet from the list of 400-odd found around stars in other solar systems: a proposed planet near a star some 6 parsecs from Earth may not exist after all.
The finding is also a strike against a planet-seeking strategy called astrometry, which measures the side-to-side motion of a star on the sky to see whether any unseen bodies might be orbiting it. Ground-based astrometry has been used for more than a century, but none of the extrasolar planets it has detected has been verified in subsequent studies.
In May, Steven Pravdo of the Jet Propulsion Laboratory in Pasadena, California, and his colleagues raised fresh hopes for the technique when they announced an exoplanet, six times more massive than Jupiter, orbiting VB10, a star about one-thirteenth the mass of the Sun, using a telescope at the Palomar Observatory in southern California (S. Pravdo and S. Shaklan Astrophys. J. 700, 623–632; 2009). But now a group led by Jacob Bean at the Georg-August University in Gottingen, Germany, has used a different approach, and found nothing. "The planet is not there," says Bean.
Bean and his colleagues used a well-honed technique called radial velocity, which has found most of the extrasolar planets detected so far. The method looks for shifts in the lines of a star's absorption spectrum to track its motion towards and away from Earth, which would be caused by the influence of a planet.
Radial-velocity measurements typically exploit the visible bands of the electromagnetic spectrum. But VB10 is a very dim star and gives off most of its light as infrared radiation. At the Very Large Telescope in Chile, Bean placed a gas cell filled with ammonia in the path of the starlight, enabling him to calibrate the instrument for the infrared.
"We would definitely have seen a significant amount of variation in our data if [the planet] was there," says Bean, who has submitted the work to the Astrophysical Journal (J. L. Bean et al. Astrophys. J. preprint at http://fr.arxiv.org/abs/0912.0003; 2009).
Pravdo says that Bean and his colleagues "may be correct, but there is hyperbole in their rejection of our candidate planet". Bean's paper, for instance, only rules out the presence of any planet that is at least three times more massive than Jupiter, says Pravdo, adding that the work "limits certain orbits for possible planets but not all planets".
"Unfortunately, astrometry is a very difficult business," counters Bean, explaining that Earth's atmosphere can introduce distortions that affect the measurements. Astrometrists rely on watching a field of stars about the same distance away as the target star to calibrate their measurements, and that can be tricky, says Alessandro Sozzetti, an astrometry expert at the Turin Observatory in Italy. "Even if we think we have selected a good set of reference stars," he says, "we may still be limited by atmospheric effects that cause an extra jitter" in the motion of those stars.
Alan Boss, an exoplanet expert at the Carnegie Institution of Washington, agrees. He points to the well-known 'detection' of 1963, when Dutch astronomer Piet van de Kamp used astrometry to claim that two planets were orbiting Barnard's Star — a finding disproved a decade later. The dispute over the VB10 planet, says Boss, "is another example of how hard it is to detect extrasolar planets using astrometry from the ground".
Astronomers expect astrometry to work much better above the distorting effects of the atmosphere. Two space missions in the works — the European Space Agency's GAIA, due to launch in 2012, and NASA's Space Interferometry Mission, the launch date for which is yet to be set — will use the technique to search for planets as small as Earth around Sun-like stars, says Sozzetti. More significantly, astrometry can yield the mass of a planet, whereas radial velocity only puts a lower limit on it.
Bean admits that astronomers might one day find a planet around VB10 if they scrutinize the star long and hard enough. "The main lesson from VB10," says Boss, is that a lot of high-quality data are needed to be sure that an exoplanet is present.
[naturenews]
Published online 8 December 2009 | Nature | doi:10.1038/news.2009.1131
News
Testosterone link to aggression may be all in the mind
A dose of the hormone makes human game-players behave more fairly.
Alison Abbott
{Higher levels of testosterone do not necessarily lead to more aggressive behaviour.}
The popular idea that testosterone always makes people more aggressive has been debunked by researchers. A team based in Switzerland has shown that the hormone can make people behave more fairly in an effort to defend their social status.
Ernst Fehr, an experimental economist at the University of Zurich, and his colleagues used the 'ultimatum bargaining' game to test how testosterone would affect behaviour in a group of 121 women. Counter-intuitively, women who were given testosterone bargained more fairly.
But the idea that testosterone causes aggression in humans, as it clearly does in rodents, is so firmly ingrained in the human psyche that women who believed they had been given testosterone — whether or not they had — bargained much less fairly.
Women, not men, were tested because they have less variable 'baseline' blood testosterone levels.
The study is published in Nature1. "It is a folk hypothesis that testosterone causes aggression," says Fehr. "But human society is more complex than this."
Fair play
Several studies in humans have shown positive correlations between high blood testosterone levels and confrontational behaviour. But it has been hard to determine experimentally whether the aggression is caused by testosterone or is instead a consequence of a challenge to a person's social status.
The ultimatum game makes it possible to distinguish between these possibilities.
{{“It is a folk hypothesis that testosterone causes aggression. But human society is more complex than this.”}
Ernst Fehr
University of Zurich}
In the game, two individuals must agree on the division of a sum of money. The proposer suggests a particular splitting of the sum and the responder must accept or reject the offer. The proposal is an ultimatum — the responder may not make a counter-offer. If the responder accepts the proposal, the money is duly allocated. If the responder rejects the proposal, neither the proposer nor the responder gets any money.
Responders normally reject very low offers as unfair — they would rather receive no money than see their partner carry off a disproportionate amount of cash.
Some proposers offer a 50-50 split because they are motivated by fairness, although most push to keep a bit more for themselves — but not so much more that they risk rejection and ending up with nothing.
Fehr's team reasoned that if testosterone caused aggression, it would cause proposers to make low offers. If, however, it promoted social-status-seeking behaviour, proposers would make higher offers to avoid the social affront of having their offers rejected.
Beggaring belief
The women were given either 0.5 mg testosterone or a placebo four hours before playing the ultimatum game for the sum of 10 money units. Before they played, they were asked to say whether they believed they had been given testosterone or placebo.
Women who received testosterone made significantly higher offers than those who received placebo — an average of 3.9 money units compared with the placebo group's average offer of 3.4 money units.
"In the socially complex human environment, pro-social behaviour, not aggression, secures status," says Michael Naef, an experimental economist at the Royal Holloway, University of London, who is a co-author on the paper.
The study has an additional, equally important message: those who believed they received testosterone, whether they had or not, made much lower offers — as low as 2 money units in some cases, or even nothing. "We think their belief that they had received testosterone, and that testosterone promotes aggression, gave them an up-front excuse to act more aggressively," says Fehr.
Responders remained as likely to reject a shabby offer when they were treated with testosterone as when they received placebo, showing that the hormone was not promoting altruistic behaviour.
Adam Goodie, a psychologist at the University of Georgia in Athens who works on decision-making, says: "The paper is a major blow to the popular wisdom that testosterone simply makes you more aggressive and less cooperative — the true picture is not nearly as negative."
"And it takes the field of neuroeconomics an important step further by showing that not only does biology affect economic behaviour — but so does belief," he adds.
The powerful impact of belief is a good lesson for neuroeconomists, adds Fehr: "Belief should always be controlled for in neuroeconomics studies, but often it is not."
References
1. Eisenegger, C. et al. Nature doi:10.1038/nature08711 (2009).
[naturenews]
Published online 8 December 2009 | Nature | doi:10.1038/462705a
News
Exoplanet claim bites the dust
Ground-based astrometry dealt a blow as planet found not to exist.
Katharine Sanderson
Is there really a planet orbiting VB10 (red star)?NASA/JPL-CaltechStrike one planet from the list of 400-odd found around stars in other solar systems: a proposed planet near a star some 6 parsecs from Earth may not exist after all.
The finding is also a strike against a planet-seeking strategy called astrometry, which measures the side-to-side motion of a star on the sky to see whether any unseen bodies might be orbiting it. Ground-based astrometry has been used for more than a century, but none of the extrasolar planets it has detected has been verified in subsequent studies.
In May, Steven Pravdo of the Jet Propulsion Laboratory in Pasadena, California, and his colleagues raised fresh hopes for the technique when they announced an exoplanet, six times more massive than Jupiter, orbiting VB10, a star about one-thirteenth the mass of the Sun, using a telescope at the Palomar Observatory in southern California (S. Pravdo and S. Shaklan Astrophys. J. 700, 623–632; 2009). But now a group led by Jacob Bean at the Georg-August University in Gottingen, Germany, has used a different approach, and found nothing. "The planet is not there," says Bean.
Bean and his colleagues used a well-honed technique called radial velocity, which has found most of the extrasolar planets detected so far. The method looks for shifts in the lines of a star's absorption spectrum to track its motion towards and away from Earth, which would be caused by the influence of a planet.
Radial-velocity measurements typically exploit the visible bands of the electromagnetic spectrum. But VB10 is a very dim star and gives off most of its light as infrared radiation. At the Very Large Telescope in Chile, Bean placed a gas cell filled with ammonia in the path of the starlight, enabling him to calibrate the instrument for the infrared.
"We would definitely have seen a significant amount of variation in our data if [the planet] was there," says Bean, who has submitted the work to the Astrophysical Journal (J. L. Bean et al. Astrophys. J. preprint at http://fr.arxiv.org/abs/0912.0003; 2009).
Pravdo says that Bean and his colleagues "may be correct, but there is hyperbole in their rejection of our candidate planet". Bean's paper, for instance, only rules out the presence of any planet that is at least three times more massive than Jupiter, says Pravdo, adding that the work "limits certain orbits for possible planets but not all planets".
"Unfortunately, astrometry is a very difficult business," counters Bean, explaining that Earth's atmosphere can introduce distortions that affect the measurements. Astrometrists rely on watching a field of stars about the same distance away as the target star to calibrate their measurements, and that can be tricky, says Alessandro Sozzetti, an astrometry expert at the Turin Observatory in Italy. "Even if we think we have selected a good set of reference stars," he says, "we may still be limited by atmospheric effects that cause an extra jitter" in the motion of those stars.
Alan Boss, an exoplanet expert at the Carnegie Institution of Washington, agrees. He points to the well-known 'detection' of 1963, when Dutch astronomer Piet van de Kamp used astrometry to claim that two planets were orbiting Barnard's Star — a finding disproved a decade later. The dispute over the VB10 planet, says Boss, "is another example of how hard it is to detect extrasolar planets using astrometry from the ground".
Astronomers expect astrometry to work much better above the distorting effects of the atmosphere. Two space missions in the works — the European Space Agency's GAIA, due to launch in 2012, and NASA's Space Interferometry Mission, the launch date for which is yet to be set — will use the technique to search for planets as small as Earth around Sun-like stars, says Sozzetti. More significantly, astrometry can yield the mass of a planet, whereas radial velocity only puts a lower limit on it.
Bean admits that astronomers might one day find a planet around VB10 if they scrutinize the star long and hard enough. "The main lesson from VB10," says Boss, is that a lot of high-quality data are needed to be sure that an exoplanet is present.
[naturenews]
Published online 8 December 2009 | Nature | doi:10.1038/news.2009.1131
News
Testosterone link to aggression may be all in the mind
A dose of the hormone makes human game-players behave more fairly.
Alison Abbott
{Higher levels of testosterone do not necessarily lead to more aggressive behaviour.}
The popular idea that testosterone always makes people more aggressive has been debunked by researchers. A team based in Switzerland has shown that the hormone can make people behave more fairly in an effort to defend their social status.
Ernst Fehr, an experimental economist at the University of Zurich, and his colleagues used the 'ultimatum bargaining' game to test how testosterone would affect behaviour in a group of 121 women. Counter-intuitively, women who were given testosterone bargained more fairly.
But the idea that testosterone causes aggression in humans, as it clearly does in rodents, is so firmly ingrained in the human psyche that women who believed they had been given testosterone — whether or not they had — bargained much less fairly.
Women, not men, were tested because they have less variable 'baseline' blood testosterone levels.
The study is published in Nature1. "It is a folk hypothesis that testosterone causes aggression," says Fehr. "But human society is more complex than this."
Fair play
Several studies in humans have shown positive correlations between high blood testosterone levels and confrontational behaviour. But it has been hard to determine experimentally whether the aggression is caused by testosterone or is instead a consequence of a challenge to a person's social status.
The ultimatum game makes it possible to distinguish between these possibilities.
{{“It is a folk hypothesis that testosterone causes aggression. But human society is more complex than this.”}
Ernst Fehr
University of Zurich}
In the game, two individuals must agree on the division of a sum of money. The proposer suggests a particular splitting of the sum and the responder must accept or reject the offer. The proposal is an ultimatum — the responder may not make a counter-offer. If the responder accepts the proposal, the money is duly allocated. If the responder rejects the proposal, neither the proposer nor the responder gets any money.
Responders normally reject very low offers as unfair — they would rather receive no money than see their partner carry off a disproportionate amount of cash.
Some proposers offer a 50-50 split because they are motivated by fairness, although most push to keep a bit more for themselves — but not so much more that they risk rejection and ending up with nothing.
Fehr's team reasoned that if testosterone caused aggression, it would cause proposers to make low offers. If, however, it promoted social-status-seeking behaviour, proposers would make higher offers to avoid the social affront of having their offers rejected.
Beggaring belief
The women were given either 0.5 mg testosterone or a placebo four hours before playing the ultimatum game for the sum of 10 money units. Before they played, they were asked to say whether they believed they had been given testosterone or placebo.
Women who received testosterone made significantly higher offers than those who received placebo — an average of 3.9 money units compared with the placebo group's average offer of 3.4 money units.
"In the socially complex human environment, pro-social behaviour, not aggression, secures status," says Michael Naef, an experimental economist at the Royal Holloway, University of London, who is a co-author on the paper.
The study has an additional, equally important message: those who believed they received testosterone, whether they had or not, made much lower offers — as low as 2 money units in some cases, or even nothing. "We think their belief that they had received testosterone, and that testosterone promotes aggression, gave them an up-front excuse to act more aggressively," says Fehr.
Responders remained as likely to reject a shabby offer when they were treated with testosterone as when they received placebo, showing that the hormone was not promoting altruistic behaviour.
Adam Goodie, a psychologist at the University of Georgia in Athens who works on decision-making, says: "The paper is a major blow to the popular wisdom that testosterone simply makes you more aggressive and less cooperative — the true picture is not nearly as negative."
"And it takes the field of neuroeconomics an important step further by showing that not only does biology affect economic behaviour — but so does belief," he adds.
The powerful impact of belief is a good lesson for neuroeconomists, adds Fehr: "Belief should always be controlled for in neuroeconomics studies, but often it is not."
References
1. Eisenegger, C. et al. Nature doi:10.1038/nature08711 (2009).
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