SETI bioastro: Finding more Jupiter-type worlds in the galaxy

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Date: Sun Feb 10 2002 - 22:35:32 PST


>From The Age, 7 February 2002


The possibility that alien life thrives in our galaxy has been boosted by
Sydney physicists who say planets such as Jupiter, which protects the Earth
from rogue asteroids, are more common than previously thought.

Through some mathematical wizardry, the professor of astrophysics at the
University of New South Wales, Charley Lineweaver, concluded that there were
50 per cent more Jupiter-like planets among the Milky Way's 300 billion
stars than previously thought.

This means there may be 30 billion star systems capable of supporting life.

Scientists have found 74 planets outside the solar system by observing stars
"wobbling" - a gravitational effect caused by orbiting planets.

They are all many times the size of Jupiter and are close to their host
stars, which is a poor condition for a star system to support life.

Professor Lineweaver said that because of technical limitations, we could
not see smaller planets. This had created the false statistical assumption
that most planets were very hot giants.

"It's a bit like lining up everybody in the world and only looking at people
above six foot eight and then you say, 'Wow, people are tall!"' he said.

With a colleague, Daniel Grether, Professor Lineweaver rejigged the maths
with what he calls "an unbiased sample".

Jupiter's massive gravity acts as a shield, sucking in most rock debris left
over from the formation of the sun and the solar system before it can
threaten Earth through a catastrophic asteroid collision such as the one
that wiped out the dinosaurs.

It is believed life on Earth did not begin to develop beyond single-cell
organisms until the heaviest cosmic bombardment of ceased about 3.8 billion
years ago.

"It tells us that life may have formed on Earth as soon as it possibly could
have," Professor Lineweaver said.

As recently as 1994, Jupiter's immense gravity pulled comet Shoemaker-Levy
into a death plunge. Had it hit Earth, the comet would have wiped out life.

In a separate development, more than 80 leading international scientists
have written to the Federal Government asking it to restart Australia's
contribution to the Spaceguard program, a United States-led project to spot
dangerous asteroids.

Professor Lineweaver's research will be published in the journal
Astrobiology and has impressed some Australian scientists.

Vince Ford from the Australian National University's Mount Stromlo
Observatory, described the research as "pretty damned exciting".

"It's another little step along the way to saying there are more Earth-like
planets," he said. "Ten years back, the chances seemed to be pretty slim.
Now it's starting to look as though there are planets all over the place."

Scientists will soon be able to see clearly enough into space to test
Professor Lineweaver's calculations. "At the moment, it's like having a boat
with a radar and the radar just cannot see something over the horizon," he
said. "In the next few years, this will change. We will start to see
Jupiters. We're just on the verge of being able to get these numbers."

Copyright The Age Company Ltd 2002.

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