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Scientists Pinpoint Milky
Way's 'ET Zones'

By Stephen Cauchi
Science Reporter
The Age - Australia
1-2-4



Australian scientists have helped narrow the search for extraterrestrial life.
 
Researchers from Melbourne's Swinburne University of Technology have identified the part of our galaxy where Earth-like planets capable of harbouring life are likely to flourish.
 
It is called the Galactic Habitable Zone - an area where rocky planets not only form easily, but can safely harbour life away from deadly hazards such as exploding stars.
 
The ring-shaped region contains about 10 per cent of the galaxy's 200 billion or so stars and, aptly, includes our own sun.
 
Scientists from Swinburne University of Technology and the University of New South Wales wrote the research paper, which was published in the journal Science.
 
The three researchers used a model that examined whether stars were likely to have life-bearing planets.
 
Such stars need to be old, so their planets have time to develop life.
 
They need to contain metal, essential for the formation of rocky planets.
 
And they need to be away from supernovas, or exploding stars, which can be fatal to life in neighbouring solar systems.
 
Such stars, the team found, were concentrated in the part of the galaxy they dubbed the Galactic Habitable Zone, between 23,000 and 30,000 light years away from the centre of the galaxy (which is about 100,000 light years wide).
 
"Not surprisingly, Earth's solar system falls within the zone, although it's younger and further from the galactic centre than the average complex life-bearing planet," said a co-author of the paper, Yeshe Fenner, from Swinburne's Centre for Astrophysics and Supercomputing.
 
Stars that contain metals are most likely to harbour rocky planets, although those with too much metal could be dangerous, the researchers said.
 
Stars that were too rich in metal spawned giant planets with orbits dangerous to smaller, Earth-like planets.
 
"There is a goldilocks zone of metallicity: with too little metallicity, Earth-mass planets are unable to form, or with too much metallicity, giant planets destroy Earth-mass planets," the paper said.
 
Another of the researchers, Professor Brad Gibson of Swinburne, said the discovery of the GHZ did not mean advanced life necessarily existed beyond Earth, "but if there is life, we've determined where you are most likely to find it".
 
"Our Milky Way galaxy is home to hundreds of billions of stars but until recently astronomers could only guess as to how many are hospitable for the development of complex life," said co-author Dr Charles Lineweaver from the University of NSW. "What we have done for the first time is to quantify carefully where complex (animal) life is likely to exist."
 
Copyright © 2004 The Age Company Ltd.
 
http://www.theage.com.au/articles/2004/01/01/1072908849778.html?from=storyrhs


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