Note in Science page
Created Oct 01 10, Updated Jul 28 11 03:01
Gliese 581g: the first ~habitable exoplanet? go to comments

11 years of radial velocity observations of the nearby red dwarf star Gliese 581 by a team of planet hunters from the University of California Santa Cruz, and the Carnegie Institution of Washington led to the discovery a new planet named Gliese 581g.

The newly discovered planet Gliese 581g (not shown) lies in the middle of the habitable zone! © ESO/Franck Selsis, University of Bordeaux taken from

This earth like planet – 3.1 to 4.3 times the mass of the Earth and a radius of 1.3 to 2.0 times that of Earth – is revolving tidally locked with a period of 36.6 days around the red dwarf star Gliese 581, 20.5 light years away from earth (in the constellation Libra). It is believed to be the first discovered planet that falls within a star’s habitable zone (Goldilocks, where the existence of liquid water is considered a strong possibility) ever found, the most Earth-like planet, and the best exoplanet candidate with the potential for harboring life found to date!

Its mass indicates that it is probably a rocky planet with a definite surface and that it has enough gravity to hold on to an atmosphere, likely one that is denser than Earth’s.
With one side of the planet always facing the star (tidal lock), temperatures could range from blazing hot in the light side to freezing cold in the dark side, with continuous Earth-like temperatures imaginable along the area between the bright and the dark side (where the sun would always be near the horizon). n.b. What a strange (for us) world!

Personally, given the ubiquity and propensity of life to flourish wherever it can, I would say that, my own personal feeling is that the chances of life on this planet are 100% [polemic]. I have almost no doubt about it… Life on other planets doesn’t mean E.T. Even a simple single-cell bacteria or the equivalent of shower mold would shake perceptions about the uniqueness of life on Earth.
(Steven Vogt, first author)

The fact that we were able to detect this planet so quickly and so nearby tells us that planets like this must be really common.
(Steven Vogt)

Gliese 581g wikipedia article
National Science Foundation News article
The Astrophysical Journal article

Oct 22, 2010:


First Goldilocks Exoplanet May Not Exist

Since publishing the data set the American group had used, the Swiss had extended their record to 6.5 years, including a total of 180 measurements. “We do not see any evidence for a fifth planet … as announced by Vogt et al.,” Pepe wrote to Science in an e-mail from the meeting. On the other hand, he added, “we can’t prove there is no fifth planet.”

If those orbits are in fact circular, as the American group believes, the supposed elongation could mask the presence of a smaller fifth planet. But even if data-analysis issues are not ironed out, all agree, a few more years of observation should do the trick.

Feb 2011:

not about Gliese but exoplanet hunt:

NASA spots 54 potentially life-friendly planets

In just a year of peering out at a small slice of the galaxy, the Kepler telescope has spotted 1,235 possible planets outside our solar system. Amazingly, 54 of them are seemingly in the zone that could be hospitable to life

NASA Finds Earth-Size Planet Candidates in Habitable Zone, Six Planet System

Of the 54 new planet candidates found in the habitable zone, five are near Earth-sized. The remaining 49 habitable zone candidates range from super-Earth size – up to twice the size of Earth – to larger than Jupiter.

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