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updated 12/21/2011 2:18:33 PM ET 2011-12-21T19:18:33

Scientists have found a system of planets that appears to have survived being engulfed by their dying parent star.

The discovery raises questions about the ultimate fate of our solar system when the sun runs out of hydrogen gas in about 5 billion years and violently transform into an expanding red giant star.

Scientists believe all the planets from Earth inward will be destroyed when the sun expands, but new research suggests that if planets are large enough, they may outlast their parent star's death, even if they are engulfed.

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Astronomers using NASA's Kepler telescope have found two planets orbiting very close to a star that is past the red-giant phase. The pair circle less than 1 percent of the distance that Earth orbits the sun.

From that position, the planets would have been deeply engulfed by the star when it expanded in its senior years. So how did they survive?


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Lead researcher Stephane Charpinet, with the University of Toulouse in France, suggests the planets might not have started out where they are now and that they were most likely a lot bigger than Earth, with more material to weather the searing heat from their expanding star.

"The system was probably more like the many stellar systems that have been discovered so far, with giant planets orbiting relatively close to their parent star," Charpinet wrote in an email to Discovery News.

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Another possibility is that the two planets found circling the evolved star aren't original members, points out astronomer Eliza Kempton, with the University of Southern California at Santa Cruz.

The planets could have formed anew from material that was left behind when the star blew off its outer layers after its red-giant phase, Kempton said.

"The expansion of the sun will surely kill off all life on Earth," she said. "However, the existence of planets orbiting an evolved star points to an interesting possibility that" all close-in planets are not entirely destroyed during stellar evolution."

The research also sheds light on a long-standing mystery of how red giant stars shed their outer layers if they don't have a binary star companion to gravitationally sheer it off. The tug may come from the star's planets.

"We may have found the smoking gun," astronomer Elizabeth Green with the University of Arizona's Steward Observatory, told Discovery News.

The former red giant star is known as KIC 05807616. The research on its remnant planets appears in this week's Nature.

© 2012 Discovery Channel

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