A team of planet hunters led by astronomers at the University of California (UC), Santa Cruz and the Carnegie Institution of Washington has announced the discovery of a planet orbiting a nearby star, Gliese 581, at a distance that places it squarely in the middle of the star’s “habitable zone.” This would be the most Earth-like exoplanet and the first truly habitable one yet discovered. The research was supported by grants from NASA and the National Science Foundation. “Goldilocks” refers to an exoplanet whose temperatures are “not too cold, not too hot, but just right” to maintain water and support Earth-like life.
Alan Boyle writes:Astronomers say they’ve found the first planet beyond our solar system that could have the right size and setting to sustain life as we know it, only 20 light-years from Earth.
“My own personal feeling is that the chances of life on this planet are 100 percent,” Steven Vogt, an astrophysicist at the University of California at Santa Cruz, told reporters today. “I have almost no doubt about it.”
The discovery, published online in The Astrophysical Journal, is the result of 11 years of observations at the Keck Observatory in Hawaii. Astronomers participating in the Lick-Carnegie Exoplanet Survey detected the planet by tracking the faint gravitational wobbles it produced in its parent star. Now they say there may well be many more planets out there like this one.
“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,” Vogt said in a news release.
One of Vogt’s co-authors, Paul Butler of the Carnegie Institution, reminded reporters during a teleconference today that the first exoplanet orbiting a normal star was detected 15 years ago. Since then, almost 500 other alien planets have been found. “We’re at exactly that threshold now with finding habitable planets,” Butler said.
The newfound planet, known as Gliese 581g, is estimated to be 3.1 to 4.3 times as massive as Earth, and makes a complete circuit around its sun in just under 37 days. If the planet has a rocky composition like Earth’s, it would be 1.2 to 1.4 times as wide as our own planet, qualifying it as a “super-Earth.”
Even more intriguingly, the red dwarf star’s dimness and the planet’s orbital distance (0.146 AU, less than half the distance between Mercury and our sun) suggest that the planet’s average surface temperature is not that far below water’s freezing point (somewhere between 10 and -24 degrees Fahrenheit, or -12 and -31 degrees Celsius).
Although that average may sound chilly, the astronomers say Gliese 581g appears to be tidally locked to its star, with one side perpetually in the sun and the other side perpetually dark. That means the highs on the day side would be hellishly hot. The lows on the night side would be unendurably cold. But there would be a livable zone along the line between shadow and light.
“Any emerging life forms would have a wide range of stable climates to choose from and to evolve around, depending on their longitude,” Vogt said.
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