23 décembre 2005

Life's ingredients circle Sun-like star

NewScientist.com news service
David L Chandler

The first evidence that some of the basic organic building blocks of life can exist in an Earth-like orbit around a young Sun-like star has been provided by NASA's Spitzer Space Telescope.
Spitzer took infrared spectrograms of 100 very young stars in a nearby stellar nursery, a huge cloud of dust and gas 375 light years away in the constellation Ophiuchus. And one of those stars showed signs of the organic molecules, acetylene and hydrogen cyanide.
These gases, when combined with water, can form several different amino acids. These are needed to form proteins, as well as one of the four chemical letters, or bases, in DNA, called adenine.
The organic molecules were detected in a ring of dust and gas circling a young star called IRS 46. Such dust rings, found around all of the young stars that were examined by the Spitzer telescope, are believed to be the raw material for planetary systems.
The spectrographic data showed that the gases were so hot that they must be orbiting close to the star, approximately in its "habitable zone", the region where Earth orbits the Sun and where water is just at the borderline between liquid and gaseous states.
The detection supports the widely held theory that many of the molecular building blocks of life were present in the solar system even before planets formed, thus assisting the initial formation of complex organic molecules and the start of life itself.
Planet forming
Observations earlier in 2005 by a different team using Spitzer showed that simpler organic molecules, called polycyclic aromatic hydrocarbons, were present in galaxies as much as 10 billion years ago.
The star IRS 46 and its emerging planetary system "might look a lot like ours did billions of years ago, before life arose on Earth", said Fred Lahuis of Leiden Observatory in the Netherlands, who led the research team.
Acetylene and hydrogen cyanide have been detected before in places closer to home, such as the atmospheres of the giant planets Jupiter and Saturn, and in comets. Observations by the European Infrared Space Observatory have also shown the compounds to exist around massive stars.
But the new findings are the first to show they can occur around other Sun-like stars, and in a region where planets are likely to form. Follow-up observations with the Keck Observatory in Hawaii suggest that a stellar wind is beginning to blow away the dust surrounding IRS 46. This may be the start of what is thought to be a final stage in the formation of planets.
The research will be published in the Astrophysical Journal in January 2006.

Contrairement aux affirmations des tenants du soi-disant "dessein intelligent" (qui viennent de subir une cuisante défaite judiciaire au procès de Dover aux USA), les conditions de la formation de vie organique planétaire n'ont pas l'air d'avoir de difficultés pour s'établir dans des environnements semblables à celui de la Terre et du Soleil. La "complexité irréductible du vivant" en apparaît brusquement moins irréductible que prévu par ces adeptes du créationnisme déguisé.

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