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Fwd = Odds of Earth being hit by big asteroid lowered

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  • Frits Westra
    Forwarded by: fwestra@hetnet.nl (Frits Westra) URL: http://www.chron.com/cs/CDA/story.hts/space/1124076 Original Date: Fri, 9 Nov 2001
    Message 1 of 1 , Nov 9, 2001
      Forwarded by: fwestra@... (Frits Westra)
      URL: http://www.chron.com/cs/CDA/story.hts/space/1124076
      Original Date: Fri, 9 Nov 2001 11:09:00 -0800

      ========================== Forwarded message begins ======================


      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
      thought.

      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
      world's population.

      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
      estimates.

      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,"
      Ivezic said.

      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
      diameter.

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