May 16, 2011
Potential Earth-Like Planet Outside Our Solar System
Scientists said on Monday that a rocky planet outside our solar system is the first to meet key requirements for sustaining life.
Modeling of planet Gliese 581d shows that it has the potential to be warm and wet enough to nurture Earth-like life.
The planet orbits on the outer fringes of the star's "Goldilocks zone," where it is not so hot that water boils away, nor so cold that water is perpetually frozen.
"With a dense carbon dioxide atmosphere -- a likely scenario on such a large planet -- the climate of Gliese 581d is not only stable against collapse but warm enough to have oceans, clouds and rainfall," researchers with France's National Centre for Scientific Research (CNRS) said in a press release.
Over 500 planets orbiting other stars have been recorded since 1995, detected mostly by a tiny wobble in stellar light.
The new study shows that Gliese 581d has a mass seven times that of Earth and is about twice our planet's size.
It had initially been dismissed as a candidate in the hunt for life when it was originally spotted in 2007.
It receives less than a third of the solar radiation Earth gets, and may be "tidally locked," which means one side always faces the sun while the other is dark.
The scientists' new model of the planet shows that its atmosphere would store heat well, thanks to is dense CO2. The red light from the star would also penetrate the atmosphere and warm the surface.
The researchers said that "in all cases, the temperatures allow for the presence of liquid water on the surface."
CNRS said for budding space travelers, Gliese 581d would "still be a pretty strange place to visit."
"The denser air and thick clouds would keep the surface in a perpetual murky red twilight, and its large mass means that surface gravity would be around double that on Earth."
A spaceship traveling close to the speed of light would take over 20 years to reach the planet, while our present rocket technology would take 300,000 years.
Reference: Gliese 581d is the first discovered terrestrial-mass exoplanet in the habitable zone". R.D. Wordsworth, F. Forget, F. Selsis, E. Millour, B. Charnay, J-B. Madeleine. The Astrophysical Journal Letters, May 12, 2011
Image Caption: After more than four years of observations using the most successful low-mass-exoplanet hunter in the world, the HARPS spectrograph attached to the 3.6-meter ESO telescope at La Silla, Chile, astronomers have discovered in this system the lightest exoplanet found so far: Gliese 581 e (foreground) is only about twice the mass of our Earth. The Gliese 581 planetary system now has four known planets, with masses of about 1.9 (planet e, left in the foreground), 16 (planet b, nearest to the star), 5 (planet c, center), and 7 Earth-masses (planet d, with the bluish color). The planet furthest out, Gliese 581 d, orbits its host star in 66.8 days, while Gliese 581 e completes its orbit in 3.15 days. Credit: ESO
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