EMBARGOED FOR RELEASE: 23 JUNE 1999 AT 14:00:00 ET US
Contact:
Claire Bowles
claire.bowles@rbi.co.uk44-171-331-2751
US Contact: New Scientist Washington office
newscidc@idt.net202-452-1178
*New
Scientist
If the Sun is exceptional, alien life may be hard to find
What a star!
**
Don't believe everything you read
in books-our Sun is no ordinary star. And
its very uniqueness has
implications for SETI, the search for
extraterrestrial life, claims Guillermo
Gonzalez of the University of
Washington in Seattle: "Unless astronomers
narrow down their search to
stars as exceptional as the Sun, they are wasting
much of their time."
The Sun is a single star whereas most stars are in
multiple systems. But
that apart, textbooks say the Sun is pretty average.
However, after
trawling through the data on the Sun, Gonzalez has found
many
idiosyncrasies. It is among the most massive 10 per cent of stars in
its
neighbourhood. It also has 50 per cent more heavy elements than other
stars
of its age and type, and about a third of the variation in brightness.
The most unusual aspects of the Sun concern its orbit around the centre
of
the Galaxy, says Gonzalez. Its orbit is significantly less elliptical
than
that of other stars of its age and type, and hardly inclined at all to
the
Galactic plane. What's more, the Sun is orbiting very close to
the
"corotation radius" for the Galaxy-the place at which the angular speed
of
the spiral pattern matches that of the stars.
Gonzalez argues that
these exceptional characteristics made it possible for
intelligent life to
emerge on Earth. He points out that stable planetary
orbits such as the
Earth's are much more likely around single stars like
the Sun. For a massive
star with inhabitable planets that are relatively
far away, stellar flare-ups
would be little threat to the planets. Heavy
elements are essential to make
planets like Earth, and a star with a stable
light output is essential for
life.
As for the orbit of the Sun, its circularity prevents it plunging
into the
inner Galaxy where life-threatening supernovae are more common. And
its
small inclination to the Galactic plane prevents abrupt crossings of
the
plane that would stir up the Sun's Oort Cloud and bombard the Earth
with
comets. By being near the Galaxy's corotation radius, the Sun
avoids
crossing the spiral arms too often, an event that would expose it
to
supernovae, which are more common there.
Because life-bearing
stars have to be close to the corotation radius, that
rules out more than 95
per cent of stars in the Galaxy in one fell swoop.
"There are fewer stars
suitable for intelligent life than people realise,"
says Gonzalez, who has
submitted his findings to Astronomy & Geophysics.
"I'm amazed at how
little thought the SETI people put into selecting their
stars."
Seth
Shostak of the SETI Institute in Mountain View, California, disagrees.
"Our
targets are all very close to the Sun. They share our Galactic
neighbourhood
and motions. If the Sun is the most suitable type of star to
be scrutinised,
then we are, indeed, looking in all the best places."
"Most astronomers
disagree with Gonzalez," adds SETI researcher Dan
Werthimer of the University
of California at Berkeley. "Our Sun is pretty
average. In any case, you don't
need a star exactly like our Sun for life."
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