Dan Vergano, USA TODAY
Our nearest stellar neighbor possesses an Earth-sized planet, report European astronomers. But nobody likely lives on its furnace-hot surface.
Alpha Centauri, a triple-star system, resides some 4.3 four light-years away, about 25.4 trillion miles. In a study led by Xavier Dumusque of Switzerland's Geneva Observatory and released Tuesday by the journal Nature, astronomers have announced the discovery of the first planet detected orbiting one of the stars in this system.
Dubbed Alpha Centauri Bb, the planet orbits the sun-like star Alpha Centauri B, circling so closely -- once every 3.2 days -- that its surface likely roasts at temperatures above 2,200 degrees Fahrenheit, Dumusque says.
The observation is based on four years of telescope observations of wobbles in the star induced by its close-orbiting companion. The chance of a false-detection of the planet in the data is 1-in-1,000, the researchers suggest.
Astronomers estimate that about 30% of stars possess Earth-like rocky planets, based on the roughly 800 planets detected orbiting nearby stars in the last two decades. The new planet is the closest yet found to our solar system, if confirmed, and orbits a star visible to the naked eye.
"That is a real wow factor," says planetary theorist Alan Boss, author of The Crowded Universe: The Search for Living Planets, who was not on the discovery team. "Humans have been staring at this stellar system for many thousands of years without knowing that there was another Earth-mass planet there all the time."
However, astronomer Artie Hatzes of Germany's Thuringian State Observatory is more cautious about the planet detection claim in a commentary accompanying the study. "It is a weak signal in the presence of a larger, more complicated signal," Hatzes says. "In my opinion, the matter is still open to debate."
Dumusque says that more looks at the star should strengthen the finding and notes that there is a possibility that the planet may slightly eclipse, or transit, in front of the star, another tell-tale sign of its existence measurable by astronomers. He adds that more planets may await discovery at Alpha Centauri, including ones at habitable distances from the stars there.