Cette découverte, réalisée grâce au télescope spatial américain Kepler, conforte la probabilité de trouver des planètes soeurs de la Terre dans notre galaxie, la Voie Lactée, estiment ces scientifiques dirigés par une astronome de la Nasa et dont les travaux sont publiés dans la revue américaine Science jeudi."C'est la première exoplanète de la taille de la Terre trouvée dans la zone habitable d'une autre étoile", souligne Elisa Quintana, une astronome du SETI Institute au centre de recherche Ames de la Nasa, qui a mené cette recherche.
"Ce qui rend cette découverte particulièrement intéressante c'est le fait que cette planète baptisée Kepler-186f est de taille terrestre en orbite autour d'une étoile dite naine, plus petite et moins chaude que le Soleil, dans la zone tempérée où l'eau peut être liquide", précise-t-elle.
Cette zone est dite habitable car la vie telle que nous la connaissons et qui dépend de la présence d'eau, a la plus grande probabilité de s'y développer, relèvent ces chercheurs.
Pour Fred Adams, professeur de physique et d'astronomie à l'Université du Michigan, "il s'agit d'un pas important dans la quête pour découvrir une exoplanète identique à la Terre", qui est l'objectif de la mission Kepler.
Sur les près de 1.800 exoplanètes détectées depuis les vingt dernières années, une vingtaine sont en orbite autour de leur étoile dans la zone habitable. Mais ces planètes sont nettement plus grandes que la Terre et de ce fait il est difficile, vu leur taille, de déterminer si elles sont gazeuses ou rocheuses, informe l'AFP.
[french.ruvr.ru]
17/4/14
New Earth-Size Planet Found ....
ReplyDeleteNot too big, not too small. Not too hot, not too cold. A newly discovered planet looks just right for life as we know it, according to an international group of astronomers.
Orbiting a star about 500 light-years away, the planet called Kepler-186f is about the same size as Earth. As this artist’s interpretation shows, it orbits its star at the right distance for liquid water on the surface. That is an essential condition for life as we know it.
But it is not exactly like Earth, NASA planetary scientist Elisa Quintana said via Skype.
“It’s more of an Earth’s cousin. It’s not an Earth’s twin. It shares the same characteristics as Earth, but their parent stars are very different," said Quintana.
Kepler-186f orbits a star that is smaller and cooler than our sun.
But, writing in the journal Science, the astronomers say the planet appears to be a closer relative than most of the hundreds of others discovered so far.
Some are massive gas-covered giants with thick, crushing atmospheres. Others orbit too closely to their stars and are too hot for life.
Two planets discovered last year are in the right orbit and might be good candidates for life, Quintana says, but they are a bit bigger than Earth.
“For the first time, we can actually say we now have a planet that is both Earth-sized and orbits in its star’s habitable zone," she said.
It may be the first time, but it probably is not the last, says Massachusetts Institute of Technology astrophysicist Sara Seager. She spoke to VOA via Skype.
“We’ve been waiting decades to understand how common habitable planets might be, and it’s looking like they’re really common. And this gives us excitement and motivation to take the next step," said Seager.
The next step would be to look for traces of life in the atmospheres of these distant worlds. That would take a more sophisticated space telescope. But budget cuts threaten that mission, says University of California at Los Angeles astrophysicist Ben in this Skype interview.
“In principle, we could do this in the next couple decades. But in practice, because there’s no money, it’s not gonna happen. It’s not gonna happen in my lifetime, for example," said Zuckerman.
Leaving earthbound concerns behind, NASA’s Elisa Quintana believes that when the next-generation space telescope is launched, it will find that we are not alone in the universe.
“I guess I’m an optimist. I think that life is definitely out there. Just looking at the abundance of stars. I mean, hundreds of billions of stars. The likelihood that one of them might have some form of life to me seems rather high. But everyone has their own opinion about that, I’m sure," she said.
In the meantime, the search continues for other worlds where life may find a home.
http://www.voanews.com/content/new-earth-size-planet-found/1895943.html
17/4/14