First “potentially habitable” exoplanet discovered


September 30, 2010

Artist's conception showing the inner four planets of the Gliese 581 system and their host star (Image: Lynette Cook)

Artist's conception showing the inner four planets of the Gliese 581 system and their host star (Image: Lynette Cook)

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If you’re looking to get away from it all then Gliese 581g might just fit the bill. But be prepared to pack enough for the trip that, even on a rocket traveling 30,000 km per second (18,640 miles per second), would take 200 years. Gliese 581g is the first exoplanet discovered that sits in an area where water could exist on the planet’s surface. If confirmed, this would make it the most Earth-like exoplanet yet discovered and the first strong case for a “potentially habitable” one.

Gliese 581g is located 20 light years from Earth, orbiting the nearby (in astronomical terms) red dwarf star Gliese 581. It, along with the discovery of another new planet, brings the total number of known planets around this star to six – the most yet discovered in a planetary system outside our own. Like our solar system, the planets around Gliese 581 have a nearly-circular orbit.

Full of potential

But perhaps put off packing your bags just yet. To astronomers, a “potentially habitable” planet isn’t necessarily one where humans would thrive. Rather, it refers to a planet that could sustain life. Actual habitability depends on many factors, but having liquid water and an atmosphere are among the most important.

With a mass three to four times that of Earth, Gliese 581g orbits its star in just under 37 days. Its mass indicates that it is probably a rocky planet with a definite surface and enough gravity to hold onto an atmosphere.

However, the planet is tidally locked to the star, meaning that one side is always facing the star, while the other side is in perpetual darkness. This means that the most habitable zone on the planet’s surface would be the line between shadow and light known as “the terminator”.

A long time coming

Gliese 581g’s discovery by a team of planet hunters from the University of California (UC) Santa Cruz and the Carnegie Institution of Washington was the result of more than a decade of observations using the W. M. Keck Observatory in Hawaii, one of the world’s largest optical telescopes.

Using the HIRES spectrometer on the Keck I Telescope, the team was able to precisely measure the star’s motion along the line of sight from Earth, and detect the new planet using the radial velocity method. This is when the gravitational tug of an orbiting planet causes periodic changes in the radial velocity of the host star.

"Our findings offer a very compelling case for a potentially habitable planet," said Steven Vogt, professor of astronomy and astrophysics at UC Santa Cruz. "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."

Two previously detected planets orbiting Gliese 581 lie at the edges of the habitable zone. One, Gliese 581c, is on the hot side and the other, Gliese 581d, is on the cold side. While some astronomers still think that planet d may be habitable if it has a thick atmosphere with a strong greenhouse effect to warm it up, others are skeptical. The newly discovered planet g, however, lies right in the middle of the habitable zone.

Sponsored by NASA and the National Science Foundation (NSF), the team’s new findings are reported in a paper published in the Astrophysical Journal.

About the Author
Darren Quick Darren's love of technology started in primary school with a Nintendo Game & Watch Donkey Kong (still functioning) and a Commodore VIC 20 computer (not still functioning). In high school he upgraded to a 286 PC, and he's been following Moore's law ever since. This love of technology continued through a number of university courses and crappy jobs until 2008, when his interests found a home at Gizmag. All articles by Darren Quick

I fail how they can tell if it is tidally locked since they cannot see it directly and the spinning of a planet has no known effect on it\'s own how in blazes can they tell if it is spinning at all?

Ronald Cooper

Well let\'s get right over there so we can ruin another planet before someone else beats us to it!


Tidally locked? Forget it. It\'s long been known that such planets would have a blazing hot perpetually bright side and a freezing perpetually dark side, with incredibly fierce winds between the zones as cold air rushes along the surface to the hot side, where it gets heated, rises up and blasts back to the cold side, cools and is falls down to the surface again.


Well, since Gadgeteer knows every conceivable life form in the universe, we can go ahead and close the books on Gliese. There apparently is no way life could survive in extreme heat (which it isn\'t specified if the distance from the sun provides a survivable temperature regardless of tidal lock). I guess Titan is a bust too, since it\'s frozen. I wonder why scientist believe there could possibly be life under the ice? Must be all that fancy education, filling their heads with ignorance...

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