A planet
outside of the solar system has been discovered orbiting a dying, puffed-up
star called a red giant.
The finding
could help astronomers learn more about the fate of our solar system.
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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