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WASHINGTON - Astronomers said Thursday the oldest and most distant planet yet found is a huge, gaseous sphere 13-billion years old and 5,600 light years away, a discovery that could change theories about when planets formed and when life could have evolved.
The planet, more than twice the size of Jupiter, orbits two stars, a pulsar and a white dwarf that linked together about a billion years ago. The system is in the constellation Scorpius within a globular cluster called M4 that contains stars that formed billions of years before the sun and its planets.
"All of the stars in this cluster are about the same age, so the presumption is that the planet is that age also," Harvey Richer, an astronomer at the University of British Columbia in Vancouver, Canada, said Thursday at a NASA news conference.
The pulsar, a rapidly spinning star, was discovered in M4 about 15 years ago. Astronomers shortly afterward found that it was gravitationally bound to a white dwarf, the remnants of an ancient, sunlike star that had exhausted its hydrogen and helium fuel. There was suspicion that yet another body was orbiting nearby, but the planet was not discovered until astronomers studied data from the Hubble Space Telescope.
Alan Boss, an astronomer at the Carnegie Institution in Washington, said finding such an ancient planet is a "startling revelation" because it means that planets could have formed within a billion years after the big bang, far earlier than most theories have stated.
"This means that 13-billion years ago, life could have arisen and then died out," said Boss. "This has immense implications."
It was thought that planets could not form until there had been at least one generation of stars after the big bang because planet building requires heavier elements, such as carbon, silicate and iron. These elements, called "metals" by astronomers, are thought to have formed during the life cycle of the early stars, when hydrogen and helium were burned in fusion fires.
Steinn Sigurdsson, a professor of astronomy at Pennsylvania State University, said there were enough heavy elements in the M4 complex to have formed some terrestrial planets, like Earth and Mars, in orbit of the sunlike star. He said it is theoretically possible that life could have formed on those planets some 12.5-billion years ago.