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It’s not just the number or size of planets, but where they are found. Scientists once thought systems with two stars were just too chaotic to have planets nearby. But so far, astronomers have found three different systems where planets have two suns, something that a few years ago seemed like purely “Star Wars” movie magic.

“Nature must like to form planets because it’s forming them in places that are kind of difficult to do,” said San Diego State University astronomy professor William Welsh, who wrote a study about planets with two stars that’s also published in the journal Nature.

The gravity of two stars makes the area near them unstable, Welsh said. So astronomers thought that if a planet formed in that area, it would be torn apart.

Late last year, Kepler telescope found one system with two stars. It was considered a freak. Then Welsh used Kepler to find two more. Now Welsh figures such planetary systems, while not common, are not rare either.

“It just feels like it’s inevitable that Kepler is going to come up with a habitable Earth-sized planet in the next couple of years,” Caltech’s Johnson said.

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Online:

Nature: http://www.nature.com/nature

American Astronomical Society: http://www.aas.org