t is not too hot and not too cold, and astronomers believe that a new planet detected outside our solar system may have a temperature that is just right to support life.
The planet orbits a red dwarf star called Gliese 581 and appears to be three times the mass of the Earth, the team at the University of California, Santa Cruz, and the Carnegie Institution of Washington said on Wednesday.
The team found it using indirect measurements from the Keck telescope in Hawaii, which has been used to scrutinize Gliese 581 for 11 years and has spotted other potential planets orbiting it.
"We had planets on both sides of the habitable zone -- one too hot and one too cold -- and now we have one in the middle that's just right," said Steven Vogt of 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," Vogt said in a statement.
The planet, called Gliese 581g, is 20 light-years away from Earth in the constellation Libra, according to the paper to be published in the Astrophysical Journal and available at .
A light-year is the distance light can travel in one year at a speed of 186,000 miles (300,000 km) a second, or about 6 trillion miles (10 trillion km).
The researchers use an indirect method radial velocity to detect planets. As a planet orbits, it makes the star wobble very slightly and this can be measured.
"There are now nearly 500 known extrasolar planets," Vogt's team wrote. "If the local stellar neighborhood is a representative sample of the galaxy as a whole, our Milky Way could be teeming with potentially habitable planets."
This planet, one of six whizzing around the little cool star, has a mass three to four times that of the Earth and orbits every 37 or so days, they calculated.
"Our findings offer a very compelling case for a potentially habitable planet," Vogt said.
They estimate temperatures on the planet average from -24 to 10 degrees Fahrenheit (-31 to -12 degrees C). The planet is locked facing its sun, like Mercury, so one side would be extremely hot and the other perpetually cold, with the livable range being at the edge where dawn and dusk would be on a spinning planet like Earth's.
If it was rocky, like Earth, it could have gravity similar to Earth's and it would be possible for liquid water to be on the surface, they said, although they have not detected water on Gliese 581g.
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