Sat, Jul 12, 2003 - Page 6 News List

Astronomers find oldest known, gaseous planet


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."

Astronomers in recent years have found 107 other extra-solar planets -- planets outside of the solar system -- but all of those are about the same age or just slightly older than the sun, 4.5 billion years.

It was thought that planets could not form until there had been at least one generation of stars after the Big Bang because the 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.

The sun is a third-generation star, but the M4 stars are believed to be in the first generation after the Big Bang, some 14 billion years ago.

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