Many of you have seen the Drake Equation, a function of seven variable
that can predict the likelyhood of finding extra-terrestrial
civilizations. (see http://www.seti-inst.edu/science/drake-bg.html for
details.)
One of the problems with the Drake Equation is that many of the factors
are unknown. However, a group of Australian researchers believe they
have found the limits of the "habitable ring" around our galaxy. Such a
find narrows the range of factors, making the Equation more accurate.
It also will help SETI researchers direct their searching resources to
likely areas of the sky.
From The Age,
http://www.theage.com.au/articles/2004/01/01/1072908849778.html
Galaxy's life zone pinpointed
By Stephen Cauchi
Science Reporter
January 3, 2004
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."
--
Gregory Gadow
techbear@serv.net
http://www.serv.net/~techbear
"If you make yourself a sheep, the wolves will eat you."
-- Benjamin Franklin
.
|
