Oldest known planet found
Envoi de ms le 06 Aout 2003 11:18:02:
http://www.theage.com.au/articles/2003/07/11/1057783355401.html
Oldest known planet found
July 12 2003
By Deborah Zabarenko, Kathy Sawyer
Washington
Astronomers have detected the Methuselah of planets, a world many times
older than any other known, a remarkable survivor formed in a violent,
primordial setting where planets were not thought to exist.
About 800 times bigger than Earth, the planet was born around a yellow,
sun-like star 13 billion years ago.
That is about 9 billion years earlier than any planet previously detected,
and a mere billion years after the Big Bang. It formed at a time when, most
astronomers believed, the universe had yet to create the raw materials
needed to make planets, scientists said this week as they revealed their
findings.
The discovery could change theories about how easily nature makes planets
from even the skimpiest of raw materials, and about the abundance of
planets - including some that might harbour life - thriving unexpectedly in
corners of the cosmos.
The oldest planet ever detected is more than twice the size of Jupiter,
locked in orbit around a whirling pulsar and a white dwarf - a small dying
star.
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Compared with the relative quiet of our own celestial neighbourhood, the
Milky Way, where Earth and the other planets orbit one 5-billion-year-old
star, the ancient group that holds the oldest planet has had a boisterous
past, the scientists said.
The old planet is located near the heart of a globular star cluster 5600
light years from Earth in the constellation Scorpius. A light year is about
10 trillion kilometres, 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
plentiful.
This finding, using data from the orbiting Hubble space telescope, indicated
that even globular clusters could produce planets despite the small amount
of heavy elements, said Steinn Sigurdsson, of Pennsylvania State University.
"What we think we've found is an example of the first generation of planets
formed in the universe," Dr 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, our solar system is third-generation, made from gas left by
the ashes of earlier generations of stars. And our sun is isolated, not
interacting directly with any other stars.
But, Dr Sigurdsson explains, globular clusters are like crowded
marketplaces, with stars so close together they have to interact.
That means the old planet, after forming around a sun-like star, was dragged
with that star towards the core of the globular cluster. Then the planet was
pulled towards a neutron star and its partner, locking 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. Changes in how it spun
helped the scientists to determine that one of the three objects was a
planet, said Harvey Richer, of the University of British Columbia.
The old planet is too far away to be seen, but because it exerts a slight
gravitational tug on the pulsar it orbits, scientists were able to figure
out its mass and position, Professor Richer said.
The old planet is among more than 100 planets detected outside our solar
system.
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