Fwd = Odds of Earth being hit by big asteroid lowered
- Forwarded by: fwestra@... (Frits Westra)
Original Date: Fri, 9 Nov 2001 11:09:00 -0800
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Odds of Earth being hit by big asteroid lowered
Reuters News Service
WASHINGTON -- Astronomers delivered good news Wednesday -- we are much
less likely to get wiped out by a big asteroid than previously
The odds are only about 1 in 5,000 that an asteroid big enough to wipe
out civilization will hit the Earth in the next 100 years, a team at
Princeton University reported -- far lower than previous estimates of
1 in 1,500.
Research on ones that have hit the Earth -- like the one that wiped
out the dinosaurs 65 million years ago -- shows that a collision with
a large asteroid half a mile in diameter could kill a quarter of the
Research has also shown that such enormous asteroids strike the planet
regularly -- every 100 million years or so.
Astronomers have been looking around to see how many of those
asteroids might be out there.
Using data from the Sloan Digital Sky Survey, the Princeton team,
headed by Zeljko Ivezic, estimated the solar system contained about
700,000 asteroids that size -- about one-third the number in earlier
That suggested there was a 1-in-1,500 chance one would hit Earth in
the next century.
"Our estimate for the chance of a big impact contains some of the same
uncertainties as previous estimates, but it is clear that we should
feel somewhat safer than we did before we had the Sloan survey data,"
The Sloan survey is mapping one-quarter of the sky using the telescope
at Apache Point Observatory in New Mexico.
Writing in the November issue of the Astronomical Journal, Ivezic said
they were able to assess more accurately the size of known asteroids.
Asteroids with a surface of carbon are dark, like lumps of coal, while
rocky asteroids are much brighter. To a casual observer, a small,
rocky asteroid looks as bright and as big as a larger, rocky one.
"You don't know precisely the size of an object you are looking at
unless you know what type it is," Ivezic said. He said the Sloan
survey looks at the color, so astronomers can distinguish between
carbon and rock.
They looked at 10,000 asteroids were able estimate that the asteroid
belt contained about 700,000 that were bigger than half a mile in
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