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To: T L Comiskey who wrote (1403)1/12/2000 6:24:00 PM
From: T L Comiskey  Read Replies (1) | Respond to of 12254
 
Scientists Revise Near Earth Asteroid Count

By Rick Callahan
The Associated Press
Jan. 12 ? Earth may be threatened by fewer
killer asteroids than astronomers thought.
Scientists had estimated
that 1,000 to 2,000
mountain-sized asteroids
periodically cross Earth?s
orbit. That translated into
about a 1 percent chance in
the next 1,000 years of one
of those asteroids
slamming into Earth with
catastrophic consequences.
But new research
suggests that Earth shares
the inner solar system with
only half as many of these
large, ?near-Earth?
asteroids ? about 700.

Don?t Get Complacent
Though the new findings cut in half the chances
of a giant asteroid collision in the thousand-year
time-frame, that doesn?t mean humans can let
their guard down when it comes to watching the
skies for potentially life-snuffing asteroids, said
David Rabinowitz of Yale University, the study?s
co-author.
?I?m not getting any more sleep knowing this.
I?m just happy that we?re well on our way to
finding most of these asteroids,? he said.
The asteroids being counted have diameters
between two-thirds of a mile to six miles, or big
enough to wreak global disaster if they smacked
into the planet.
Rabinowitz and colleagues at NASA?s Jet
Propulsion Laboratory reported their findings in
Thursday?s issue of the journal Nature.

Computers Vs. People
They used a one-meter telescope in Hawaii that is
equipped with a highly sensitive device that
captures digital images of the night sky.
Photos snapped of the same section of the
sky on different nights were scrutinized by
computer software that quickly spots tiny blips of
light from asteroids on the move. A few years
ago, astronomers had to perform that task
themselves by laboriously comparing photos ? a
time-consuming chore prone to error.
Rabinowitz said the new technology should
allow astronomers to find 90 percent of large
near-Earth asteroids within the next 20 years.
That?s good news for anyone worried about a
cataclysm like the one believed to have wiped out
the dinosaurs 65 million years ago, said Scott
Hudson, a professor of electrical engineering at
Washington State University.

Know How Big a Task
?It?s a first step toward really knowing the
magnitude of the task that lies ahead,? said
Hudson, who is involved in radar imaging of
near-Earth asteroids. ?Now the task is to go out
and find all of these objects.?
At the same time, there are still plenty of
smaller asteroids out there that, while not posing
a global threat to Earth, could still lay waste to
entire cities, said Brian G. Marsden, director of
the International Astronomical Union.
?I wouldn?t want to say we?re safe. I wouldn?t
be as rash as that because we?ve got all sizes of
these things to watch out for,? he said.
Asteroids are large lumps of rock, iron and
other material believed left over from the
formation of the solar system.
NASA has launched sky-watch programs
aimed at finding most large near-Earth asteroids.
Other countries also are keeping watch. Two
weeks ago, Britain created a committee to assess
the risk of asteroids or comets smashing into the
Earth.