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Surprise planet discovered in twin star system

'This result has far-reaching implications,' astronomer says

By Richard Stenger (CNN)

Artist's interpretation of the Gamma Cephei stars and planet
Artist's interpretation of the Gamma Cephei stars and planet

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(CNN) -- The first planet found in a close-knit double star system suggests that the galaxy possesses many more planets than previously estimated.

Unlike our sun, a rare solitary specimen, the majority of Milky Way stars have companions. The discovery means that similar binary star systems could host planets as well, astronomers announced Wednesday.

The planet is more massive than Jupiter and orbits the primary star in the double system, slightly farther than the average distance between Mars and the sun, the scientists said. It completes one orbit every 2.5 years.

The larger star is about 1.6 times as massive as the sun. Like the found planet, the smaller companion star goes around the larger star, at about the same distance as Uranus does the sun.

"This is the first time that we find a planet in a relatively close binary system," said Michael Endl of the University of Texas at Austin, a member of the team studying the star system.

'This result has far-reaching implications,' astronomer says

"Since most stars in our galaxy are actually members of binary or even multiple systems, this result has far-reaching implications for how many planetary systems can be expected in our galaxy," Endle said.

A number of so-called extrasolar planets have been detected in other binary star systems. But the companion stars were hundreds or thousands of times farther away from the main star, compared with the secondary star in the Gamma Cephei system.

"The stars (in other systems) were far enough apart to be essentially acting totally independently," said Bill Cochran, one of the team's leaders and another University of Texas researcher.

In those systems, each star can be considered virtually solitary because it has little gravitational effect on the other, so finding planets there comes as little surprise, Endle said.

But planets would be expected to be much rarer in systems like Gamma Cephei that have close companion stars. With nearby stars tugging furiously at one another, they could easily disrupt the orbit of a neighboring planet, according to astronomers.

Cochran, Artie Hatzes of Germany and other scientists, including Canadian astronomers Gordon Walker and Bruce Campbell,have studied Gamma Cephei for decades, using a variety of telescopes.

A consistent, 2.5-year variation in the light output convinced Cochran and colleagues that the main star had a planet.

"The star itself would not be varying that nicely for eight cycles over 20 years. Our observing techniques include several good indicators of stellar variability and we see no variation that we can attribute to the star itself. The only logical thing that's left is a planet," Cochran said.

Gamma Cephei is about 45 light years away and appears as a single point of light near the Celestial North Pole. It marks the "tip" of the hat in the constellation Cepheus, or King.

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