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Science - Reuters

NASA: Oldest Planet Formed 13 Billion Years Ago
Thu Jul 10, 5:20 PM ET Add Science - Reuters to My Yahoo!


By Deborah Zabarenko

WASHINGTON (Reuters) - The oldest planet ever detected is nearly 13 billion years old and more than twice the size of Jupiter, locked in orbit around a whirling pulsar and a white dwarf, astronomers said on Thursday.


Reuters Photo



Compared with the relative youth and stability of our own celestial neighborhood, where Earth and the other planets orbit a single 5-billion-year-old star in a quiet neighborhood of the Milky Way, the ancient group that holds the oldest planet has had a boisterous past, scientists said at a NASA (news - web sites) briefing.


The old planet is located near the heart of a globular star cluster some 5,600 light-years from Earth in the constellation Scorpius. A light-year is about 6 trillion miles, about the distance light travels in a year.


Globular clusters were generally thought to be lousy environments for forming planets, because the clusters coalesced so early in the universe's development that the heavier elements needed to make planets were not yet present in abundance.


This finding, made with data from the orbiting Hubble Space Telescope (news - web sites), indicates that even globular clusters can produce planets despite the small amount of heavy elements, said Steinn Sigurdsson of Pennsylvania State University.


FIRST GENERATION PLANET


"What we think we've found is an example of the first generation of planets formed in the universe," Sigurdsson said. "We think this planet formed with its star, 12.713 billion years ago when the (Milky Way) galaxy was very young, just in the process of forming."


By comparison, Earth and the rest of our solar system is a third-generation affair, made from gas that was polluted by the ashes of earlier generations of stars. And the sun is off by itself, not interacting directly with any other stars.


But globular clusters are like crowded marketplaces, with stars so close together they are forced to interact. That meant that the old planet went along for the ride, Sigurdsson said.


After forming around a sun-like star, the old planet was dragged with the star toward the core of the globular cluster. Then the planet was pulled toward a neutron star and its companion, enmeshing all four bodies into a tangle of orbits.


The neutron star grabbed the sun-like star and the old planet and booted its original companion into space. In time, the planet's star aged into a red giant and then into a white dwarf, a dying star that can only shine with stored heat.


The neutron star evolved into a fast-whirling pulsar and changes in how it spun helped scientists determine that one of the three cosmic objects dancing in space was a planet, said Harvey Richer of the University of British Columbia.


The old planet is too far away to be directly observed, but because it exerts a slight gravitational tug on the pulsar it orbits, scientists figured out its mass and position based on its pull on the pulsar, Richer said.


The old planet is among more than 100 planets detected outside our solar system.