SVTR

http://www.nature.com/news/2007/070423/full/070423-5.html / Published online: 25 April 2007; | doi:10.1038/news070423-5

The most Earth-like planet yet

Extrasolar planet grabs attention of astronomers and alien-hunters.

Katharine Sanderson

As this artist's impression shows, we now know of three planets orbiting the red star Gliese 581. ESO

Astronomers have found an Earth-like planet circling a dim red star not far, in galactic terms, from our Solar System. The planet, just five times the mass of our own, might be the best hope yet of a world that can support life.

The extrasolar planet, or exoplanet, is orbiting one of our closest stellar neighbours, the red dwarf star Gliese 581, just 20.5 light years away. Stéphane Udry of the Geneva Observatory in Switzerland and his colleagues spotted the planet by detecting wobbles in the parent star, caused by the orbiting planet's gravity.

The planet is much closer to its star than we are to the Sun - orbiting at one-fourteenth of the Earth-Sun distance. But because Gliese 581 is a red dwarf, which emits less light and heat than the Sun, the planet is in the so-called 'habitable zone' for its star. The researchers' calculations suggest that the planet's average temperature is between 0 and 40 °C - perfect for liquid water, and perhaps even life, to exist.

But this is a very crude temperature estimate, says Udry's colleague Michel Mayor, principal investigator for HARPS (High Accuracy Radial velocity Planetary Searcher), the instrument that made the observations in La Silla, Chile. To get a better idea, more information about the nature of the planet would be needed - for example, whether it has an atmosphere. "For the time being, it is difficult to know more," he says.

In with a chance

The new planet is the closest in mass to Earth ever discovered outside our Solar System -the previous nearest match was roughly 5.5 times the mass of Earth and in a much more distant orbit from its star. The technique used by Udry's team can only put a lower limit on the planet's likely mass, and its size can therefore only be guessed at: if the planet is rocky and Earth-like, its radius should be around 1.5 that of Earth. If the planet is ocean-like, it will be slightly bigger. The researchers have submitted their results to the journal Astronomy & Astrophysics.

Information about the planet's composition can only be gleaned if the planet is passing in front of, or transiting, its star, and the chances of seeing that happen with any one planet is about 2%, says Mayor. But this doesn't mean that they will stop looking. "We have good reason to believe that this kind of planet exists around other stars," he says. And if there are a lot of planets whizzing around their stars, at some point a transiting planet will be seen.

The latest discovery follows news two years ago of two other planets orbiting Gliese 581, one roughly eight times the Earth's mass, and the other around 15 times Earth mass.

If Udry's models are correct, the new planet would be a so-called 'super-Earth' - a very exciting prospect, says exoplanet expert David Charbonneau at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. "If the planet is a rocky super-Earth, then perhaps it has a surface with liquid water and life," he suggests.

There is another, less exciting option, however, which would make the planet slightly less homely, Charbonneau adds: "If instead the planet is a 'sub-Neptune', then it would have a large gas envelope that buries the surface below, making it inhospitable for life."

References : Udry U., et al. Astron. Astrophys. (submitted) .

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http://www.futura-sciences.com/news-gliese-581c-premiere-planete-extraterrestre-compatible-avec-vie_10726.php
La découverte autour de l'étoile Gliese 581 (Gl 581) d'une planète extraterrestre marque une étape importante car, pour la première fois, celle-ci réunit toutes les caractéristiques considérées comme indispensables à l'apparition éventuelle d'une forme de vie.

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http://www.la-croix.com/photo2/index.jsp?docId=2301300&rubId=4085

La première planète potentiellement habitable

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http://www.techno-science.net/?onglet=news&news=3999

Une planète "habitable" à vingt années-lumière de la Terre

Vue d'artiste du système planétaire autour de la naine rouge Gliese 581. 

http://www.futura-sciences.com/news-champignons-9-metres-haut_10731.php Par Jean Etienne, Futura-Sciences, le 26/04/2007 à 17h03
Depuis leur première description en 1959, ces curieux troncs fossiles qui peuvent atteindre 6 à 9 mètres de haut, intriguent et divisent les spécialistes. On en sait aujourd'hui un peu plus. Ce seraient des champignons. [...] Ces fossiles, qui remontent au Dévonien (350 - 400 millions d'années), ont été découverts un peu partout sur la planète, et constituaient donc une espèce particulièrement répandue. Ils se présentent sous la forme de grands troncs cylindriques de dimensions impressionnantes, au point que les scientifiques les ont longtemps pris pour des conifères.

Mais Francis Hueber, un chercheur au Muséum national d'histoire naturelle de Washington, a émis dès 2001 une thèse selon laquelle il s'agirait bien de champignons. Lui-même et son équipe se sont appuyés sur une étude isotopique de Prototaxites de diverses provenances, notamment le Canada, l'Australie et l'Arabie Saoudite. Ils ont pour cela examiné et mis en rapport les ratios des isotopes 12 et 13 du carbone. Ceux-ci sont répartis régulièrement dans les plantes, qui produisent cet élément à partir du CO2 présent dans l'air, et varient peu d'une espèce à l'autre. Par contre, chez les champignons, qui ne réalisent pas la photosynthèse, le carbone provient de la nourriture, comme pour les animaux et présentent des ratios variables.

Selon Francis Hueber, les variations des ratios observés entre les valeurs isotopiques du carbone sont trop différentes pour qu'il puisse s'agir de plantes. Une dernière observation manque encore cependant pour valider définitivement la thèse des chercheurs: la découverte de spores fossiles, dont l'existence est liée à toutes les espèces de champignons et qui en constituent le seul moyen de reproduction.

Sections fossiles de Prototaxites (Crédits : Muséum national d'histoire naturelle de Washington)

http://www.nature.com/news/2007/070423/full/070423-6.html Published online: 24 April 2007; | doi:10.1038/news070423-6

Every cloud has an invisible halo

Unseen particles may confuse climate models.

Philip Ball

Clouds are bigger than they look, according to new measurements by atmospheric scientists in Israel and the United States. They say that clouds are surrounded by a 'twilight zone' of diffuse particles, invisible to the naked eye, extending for tens of kilometres around the cloud's visible portion.

These vast, sparse haloes of droplets may have been overlooked in atmospheric studies, the researchers say. And they think that this could have skewed attempts to understand how clouds influence climate.

Clouds are one of the biggest sources of uncertainty in efforts to measure and predict global warming. They have two opposite effects: increasing warming by absorbing heat radiated from the planet's surface (which is why cloudy nights are warmer), while offsetting this by reflecting sunlight back into space from cloud tops.

Most atmospheric scientists now think that clouds have an overall global cooling effect. Measurements of warming trends therefore have to take into account whether the skies are cloudy or not, and model forecasts of future warming may hinge on whether they predict more or less cloudiness...

 References : Koren I., et al. Geophys. Res. Lett., 34. L08805 (2007).

http://www.nature.com/news/2007/070423/full/070423-3.html / Published online: 23 April 2007; | doi:10.1038/news070423-3

Migraines may slow memory loss

Sufferers show less cognitive decline as they age.

Heidi Ledford

A migraine is not just a headache, it is an über-headache - a pounding, queasy, searing pain that can incapacitate its victims for hours on end. And as if the pain weren't bad enough, sufferers were also thought to show diminished memory and verbal skills.

But new research now suggests that although migraines are sometimes associated with diminished cognitive skills, sufferers may in fact show less memory loss as they age than those who are migraine-free.

The results are puzzling, admits Amanda Kalaydjian of the National Institute of Mental Health in Bethesda, Maryland, who led the study. "We originally hypothesized that migraineurs would be doing worse," she says, "so I was really surprised."

Slower decline

More than 28 million people in the United States suffer from migraines, and women are three times more likely than men to have the condition. The cause is still unknown, and different theories have blamed nervous-system malfunctions, chemical imbalances, over-reactive blood vessels, or a combination of factors.

Meanwhile, attempts to catalogue the damage wrought by a lifetime of migraine attacks have met with conflicting results. Some studies suggest that migraineurs have poorer memories and less verbal ability than those without the condition, whereas other studies show no difference at all between sufferers and non-sufferers. Most of these studies were small and relied on patients in headache clinics, meaning that the study population can be skewed towards those with more severe cases of the condition, Kalaydjian points out.

Kalaydjian decided to test how cognitive function in migraineurs changes over time. She and her colleagues tested word recall and overall cognitive function in 1,448 people, including 204 migraine sufferers selected from a broad epidemiological study and not from headache clinics.

The results, published today in Neurology, show that sufferers do perform worse on memory tests than non-sufferers, both during the initial screens performed from 1993 to 1996 and in follow-up interviews in 2005. But although both groups tended to show signs of cognitive decline in the roughly 12 years between the two tests, many migraineurs did not decline as rapidly. In particular, the ability to remember specific words did not weaken as much in migraineurs who suffer from migraines with 'aura', the flashing lights, squiggly lines and other visual interruptions that accompany some migraines. And in other tests of cognitive function, migraineurs who were older than 50 did not weaken as quickly as people in the same age group who do not suffer from migraines.

Exactly why the migraineurs would be more protected from cognitive decline remains a mystery. "Since no one really knows what causes migraines, it's really difficult to say what about them may or may not decrease the cognitive decline," says Kalaydjian.

Brains trained?

One possibility is that lifestyle differences in those with migraines could have a protective effect. Migraineurs may take non-steroidal anti-inflammatory medications such as ibuprofen to relieve their pain, and some studies have suggested that these drugs may help to protect against cognitive decline. People with migraines may also be better stewards of their own health. A lifestyle designed to stave off migraines would include regular exercise, attention to diet and adequate sleep, all of which could boost overall health and cognitive function.

It will take more targeted studies to untangle all of these contributing factors, says Kalaydjian. When she factored information about sleeping habits, exercise and medication into analyses of her current data, the difference was still there, suggesting that these theories may not represent the whole answer.

It is also possible that migraines may genuinely deliver fundamental cognitive benefits in addition to these lifestyle factors, says Karen Waldie, a neuroscientist at the University of Auckland in New Zealand. Waldie speculates that decades of cerebral insult could train a migraineur's brain to better protect itself on a cellular level, and that sufferers' brains are "used to problems that the non-migraineur might not have experienced".

References : Kalaydjian A., Zandi P. P., Swartz K. L., Eaton W.W. & Lyketsos C. Neurology, 68. 1417 - 1424 (2007).

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http://www.futura-sciences.com/news-migraines-ameliorent-elles-memoire_10728.php
Par Jean Etienne, Futura-Sciences, le 26/04/2007 à 11h03

C'est ce qu'on pourrait penser, si l'on en croit les résultats obtenus par une équipe de scientifiques américains, en se basant sur des tests passés auprès de sujets migraineux à partir de 1993, et dont les résultats ne manquent pas de surprendre.

Amanda Kalaydjian et ses collègues de l'Ecole de Santé Publique Johns Hopkins Bloomberg, à Baltimore, a évalué sur le long terme l'évolution des facultés de mémorisation, entre autres, de 1448 femmes volontaires, membres de la Baltimore Epidemiologic Catchment Area Study. Parmi elles, 204 migraineuses chroniques.

Deux séries de tests ont été pratiquées, d'abord entre 1993 et 1996, puis entre 2004 et 2005. Ceux-ci consistaient essentiellement en des exercices de mémorisation, ce que l'on appelle communément un "Mini-Mental State Examination".

Sans surprise, les chercheurs ont d'abord constaté que les femmes migraineuses obtenaient de moins bons scores en comparaison aux sujets ne souffrant pas de cette affection. Mais la mise en corrélation des résultats des deux séries de tests a surpris toute l'équipe, car il apparaissait nettement que si les facultés cognitives diminuent avec l'âge, celles des migraineuses se réduisent nettement moins vite.

Comment expliquer ces résultats ? A cette question, Amanda Kalaydjian ne peut qu'émettre des hypothèses. Même si les causes de la migraine paraissent essentiellement liées à des anomalies vasculaires entraînant vasodilatation et augmentation de la perméabilité vasculaire, elles restent incomplètement élucidées, et difficiles à identifier. Actuellement, les chercheurs ignorent par quel mécanisme cette pathologie pourrait freiner la perte de facultés liée au vieillissement.

L'équipe ne pense pas que cet effet bénéfique soit lié à la prise de médicaments anti-inflammatoires. Cependant, elle n'exclut pas que le mode de vie des migraineux, rendu plus sain par suite de périodes de repos plus longues, de séances de relaxation anti-stress, et surtout de la volonté de réduire la consommation d'alcool, source de déclenchement de cette pathologie, pourrait expliquer en partie ces résultats.

Mais Amanda Kalaydjian estime qu'il existe vraisemblablement un facteur biologique à la base de cette différence, basé sur l'activité neuronale et la vasodilatation, qui jouerait un rôle de protection chez les migraineux.

http://www.nature.com/news/2007/070423/full/070423-1.html / Published online: 23 April 2007; | doi:10.1038/news070423-1

Ancient fossil forest found by accident

Treasure trove of extinct species discovered in old coal mine.

Katharine Sanderson

Geologists have found the remains of a huge underground rainforest hidden in a coal mine in Illinois. The fossil forest, buried by an earthquake 300 million years ago, contains giant versions of several plant types alive today.

Experts say the forest was growing on top of peaty soil when an ancient tremor plunged it about 5 metres down, allowing it to be buried and fossilized beneath further layers of more recent rock. It dates from a time when North America and Europe were joined together, at the Equator - similar forests went on to be transformed into the rich coal seams of the two continents.

The forest was discovered in 2005 by John Nelson of the Illinois State Geological Survey, who was making routine measurements in a mine in Vermilion County. He called in a team of palaeontologists to investigate the forest. As they drove down to 100 metres below ground, they saw the forest's remains in the glare from their miners' lamps as they looked up at the ceiling. "You actually see roots coming down; you see tree trunks lying in the ceiling," says Howard Falcon-Lang of the University of Bristol, UK, a member of the research team.

The forest is not the oldest to be discovered - others are known that are up to 370 million years old - it is the sheer size of the forest that is significant. It has allowed Falcon-Lang and his colleagues to show that the distribution of plant species that made up the forests in the Carboniferous era differed from region to region, rather than being randomly mixed.

"Forests closer to the coast differed from forests slightly further inland," says Falcon-Lang. "It is a subtle point but one that could not have been made without the great size of the sampled area," says Kirk Johnson, chief curator at the Denver Museum of Nature and Science, Colorado. "Without a large area to sample, there was really no way to know."

The ancient forest bears little resemblance to modern equivalents. "The diversity of the first rainforests was bizarre," says Falcon-Lang. He and his team found the remains of tree-sized clubmosses, horsetails and ferns - plants that today grow 2 or 3 metres tall, but in the ancient forest reached heights of up to 40 metres. Also surprising is the presence of remains from mangrove-like plants. "It was always assumed that mangrove plants had evolved fairly recently," says Falcon-Lang.

The forest probably had about 50 different plant species, although Falcon-Lang says that this is a conservative estimate. We probably lumped several similar species together as one," he explains. Modern rainforests are more diverse, containing as many as 500 plant species per hectare.

This discovery also shows that the fundamental processes that guide the complexity and evolution of forests has been around for hundreds of millions of years, says Scott Hocknull, a curator at the Queensland Museum in Brisbane, Australia. "Knowing this and how it has played out so many times in history will allow ecologists to better understand the complexity of modern forest systems," he adds.

The forest's long life will now be cut short - the mine is likely to collapse in the next few years and there are no plans to preserve it for the sake of the fossils. But Falcon-Lang is philosophical about losing the forest, pointing out that if it weren't for mining, the forest would never have been discovered in the first place.

References : DiMichele W. A., et al. Geology, 35. 415 - 418 (2007).