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Thursday, May 12, 2005

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International

X-rays reveal origins of Earth

Tim Radford

Scientists peer across 1,500 light years of space Telescope Chandra studies 1,400 young stars A unique look at stars

LONDON: Scientists who peered for 13 days across 1,500 light years of space believe they may have the answer to one of creation's great puzzles: the formation and survival of rocky planets such as Earth.

They used a sophisticated orbiting x-ray telescope called Chandra to study 1,400 young stars in the Orion Nebula and identify 27 that behave very much as the sun must once have done 4.6 billion years ago.

These very young stars, surrounded by discs from which planets could condense, tend to erupt in vast flares far greater than anything now observed from the mature sun. These flares could be evidence of a process that would clear the way for small rocky planets to form.

By looking at a place far away and long ago in the galaxy the scientists peer back to a time when Venus, Earth and Mars might have first formed from stony cinders whirling around a violent young star. ``We don't have a time machine to see how the young sun behaved, but the next best thing is to observe the sun-like stars in Orion,'' said Scott Wolk of the Harvard Smithsonian centre for astrophysics in Cambridge, Massachusetts, on Tuesday night. ``We are getting a unique look at stars between 1 million and 10 million years old — a time when planets form.'' Until 1995 the nine planets around the sun were the only planets known in the whole universe. Then, using sophisticated gravitational observations, astronomers began to infer the existence of huge, Jupiter-like objects orbiting stars up to 100 light years away. The catch was that — in the 120 planetary systems so far observed — there would be no room for bodies capable of nurturing life.

Earth is sometimes called the Goldilocks planet: it is not too warm, not too cold, not too big and not too small for life to survive on it. Some scientists have argued that planets such as Earth might be very rare. But research with Chandra began to expose the machinery that makes another Earth or Mars. Astronomers trained their instrument on a tiny smudge of light in Orion, a nursery of stars an enormous distance from Earth.

Stars form from clouds of gas and dust: planets condense from the leftovers, whirling around in a disc around the young star. A Jupiter-sized planet orbiting close to its parent star would dislodge or destroy any potential Earth or Venus-sized bodies. Huge x-ray flares, of the kind observed again and again in the Orion 27, would in effect keep the big brothers at a safe distance.

``It acts like a planetary protection service. Even though the x-ray flare may be bad for whatever is going on on the surface of the Earth, at that instant we don't care. It makes the disc very turbulent, and keeps Jupiter where it is,'' said Dr. Wolk. The research was a stunning demonstration of the power of Chandra to count the individual stars that form a tiny speck of distant light.

``We see Orion in the winter sky, brilliantly glowing. We see the belt, and the four stars around it. And then there is this little fuzzy thing: that's it, not much bigger than a star,'' Dr. Wolk said.

Earth-like planets may be rare: but at last researchers have found a mechanism that permits their existence, and some of the conditions under which life might emerge.

- Guardian Newspapers Limited 2005

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