 | Planet Found Orbiting Puffed-Up Star By Jeanna Bryner Senior Writer posted: 01 December 2008 08:20 am ET |
The newly discovered exoplanet is nearly six times the mass of Jupiter and orbits the red giant star HD 102272, which is located 1,200 light-years away in the constellation Leo. To date, about 20 red giants are known to support planets. The researchers suspect another world is orbiting farther out in the system. If confirmed, the system would be the first red giant star known to support more than one planet.
Small and medium-sized stars like our sun become red giants when they exhaust all of their hydrogen fuel near the end of their lives. The stars' cores contract and begin to burn helium, while their outer shells balloon up to 100 times their original size. When our sun does that, Earth and other planets will be vaporized. The finding, which will be published in a forthcoming issue of the Astrophysical Journal, will shed light on how bloated stars interact with their resident planets.
The new planet orbits closer than any other world to its red giant parent, orbiting just 0.6 astronomical units (AU) from the star. The researchers suggest this distance could be the limit, with no planets venturing in closer to a red giant.
"When red-giant stars expand, they tend to eat up the nearby planets," said researcher Alexander Wolszczan, an astrophysicist at Penn State. "There appears to be a zone of avoidance around such stars of about 0.6 astronomical units."
One astronomical unit is equal to the average distance between Earth and the sun. The researchers detected the planet with the Hobby-Eberly Telescope of McDonald Observatory in Texas. They used the radial velocity method, which involves measuring the slight wobbles of a star caused by the tug of an orbiting planet. The host star is currently about 10 times the size of the sun, but it will eventually expand to up to 100 times the size of the sun. Since the star is a relatively young red giant, this mushrooming will probably not take place for another 100 million years, Wolszczan said. At that time, the star's outer shell will engulf this exoplanet.
"The planet finds itself orbiting, not in a vacuum anymore, but in gas that imposes a drag on the planet," Wolszczan told SPACE.com. "So its orbital energy gets lost to the surrounding atmosphere of the star through friction. And so [the planet] starts spiraling in."
While red giants vaporize those planets closest to them, they could thaw more distant worlds in their systems, creating new havens for life. This could happen in our own solar system when our sun begins its transition into a red giant in about 5 billion years, Wolszczan said. Earth will likely be destroyed, but more distant — and currently frozen — worlds such as Jupiter's frozen moon Europa will survive and perhaps be bathed in sunlight as our star rapidly expands.
Europa "may become a very pleasant, nice ocean world," Wolszczan said. "There would still be more than a billion years of time for life to develop again somewhere else in the solar system, even though at this point it is not quite possible."
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