American Association: Starlight 'reveals billions of Earths'
telegraph.co.uk
Wednesday 21 February 2001
American Association: Starlight 'reveals billions of Earths'
By David Derbyshire, Science Correspondent, in San Francisco
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THE Galaxy is teeming with billions of Earth-like planets, some capable of supporting life, according to a study.
An analysis of light from hundreds of nearby stars suggests that at least half contain iron left after collisions with asteroids. And the astronomers behind the study believe that where there are asteroids with unstable orbits, there are rocky planets like Mars, Venus and Earth.
Only a few years ago, astronomers were unable to say whether planetary systems like our solar system were rare or common. But studies of the "wobble" of stars, caused by the gravitational tugs of large planets, has provided evidence of 55 giant planets outside the solar system.
Researchers also believe that they have seen such a giant planet passing in front of a star, reducing its brightness temporarily. The search for iron that might have been devoured by stars in collisions with metal-rich asteroids offers a third technique for spotting possible solar systems.
Dr Norman Murray, of the University of Toronto, examined the light signature from 466 Sun-like stars and another 20 that were entering old age within 325 light years of the Sun. "What I found is evidence that there is terrestrial type material orbiting most of the stars in the solar neighbourhood," he told the American Association for the Advancement of Science meeting in San Francisco.
"The implication, if this result holds up, is that there are Earth-like bodies in orbit around most of the stars in the galaxy." Because stars naturally contain iron, just looking for evidence of the metal is not enough to prove the existence of rocky asteroids. Instead, he looked for clues that the iron had been added to the stars long after they were formed.
A small star will devour iron deposited on its surface, mixing it in thoroughly with stellar gas. But the largest stars have more stable outer layers and will retain higher levels of accreted iron away from their interiors. Dr Murray found that iron concentrations jumped when stars reached a certain size, suggesting that their iron could have been deposited by rocky asteroids. Other means of adding iron to stars were unlikely or impossible.
He also found that iron levels in the stars known to have orbiting planets were much higher than average. If rocky material was orbiting stars, then over time it would clump together to form rocky planets. And if asteroids were flying into the suns, it is likely that the gravitational pull of planets was sending them into their chaotic orbits.
Dr Murray, who is keen to repeat the study, said: "If there are terrestrial bodies around these stars, then at least the probability that there is life that is similar to what we consider to be life has to be more likely.
"If there weren't any terrestrial planets, there wouldn't be terrestrial-based life. So it is one more indication that life might be common in the galaxy, but we don't know that."
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