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Astrophysics

Earth 2.0 : The Search Continues

earth 2.0

© ESO

Artist rendering of the three planets orbiting Gliese 581 (in red). The farthest one (forefront) is telluric, 5 times the mass of Earth, and could have liquid water on its surface.


 

Located 20.5 light years away from Earth, two potentially habitable planets are capturing the public's imagination. After the initial discovery of a gas planet in 2005, researchers from three French labs associated with CNRS,1 the Geneva Observatory, and the Astronomy Center in Lisbon, spotted two new telluric (hard surface) exoplanets orbiting the Red Dwarf star Gliese 581, last April.

At the time, the team only focused on the planet closest to the star because, according to their temperature estimates, it was between 0° and 40°C. That meant that any water on it would be liquid, and that it could sustain life. Today, however, researchers are saying that the second planet could be the one “warm enough” to accommodate life, were it surrounded by an atmosphere.

Indeed, if an atmosphere surrounds a planet, the resulting greenhouse effect significantly hikes up the temperature on the ground. This is known as the “Venus effect,” so called because thick CO2-rich clouds send Venus' temperature soaring to over 400°C.

“Early theoretical models suggest that the presence of an atmosphere would make the first planet too warm to be habitable,” says Xavier Delfosse, researcher at France's LAOG. On the other hand, Delfosse says this Venus effect would be quite welcome on the second telluric planet orbiting Gliese 581. With a mass eight times larger than Earth, it could potentially be habitable if a protective layer of gas warmed it enough to compensate for its greater distance from the star. “Unfortunately, we do not yet have the technology to either confirm or reject these predictions,” adds Delfosse. Indeed, HARPS, the spectrograph of the European Space Observatory in Chile, lets researchers detect, but not actually see, these exoplanets. “Planets exert a slight pull on the stars around which they rotate,” explains Delfosse. “If we notice that the speed of the star changes at regular intervals over several years, then we know there's a planet orbiting around it.”

The researcher predicts new technology will soon surpass this lengthy “radial speed” detection method, but not for another 15 years or so. That's when the European mission DARWIN2 should be ready to detect telluric planets and analyze the composition of their atmosphere.

 

Lucille Hagège

Notes :

1. Laboratoire d'AstrOphysique de Grenoble (LAOG) (CNRS / Université Joseph Fourier); Institut d'Astrophysique de Paris (CNRS / Université Paris-VI); Service d'aéronomie du CNRS, Verrières le Buisson (CNRS / Université Paris-VI / Université Saint-Quentin).
2. www.darwin.rl.ac.uk


Contacts :

Xavier Delfosse
LAOG, Grenoble.
xavier.delfosse@obs.ujf-grenoble.fr


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