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Scientists Estimate 30 billion Earths

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    NHNE News List Current Members: 676 Subscribe/unsubscribe/archive info at the bottom of this message. ... SCIENTISTS ESTIMATE 30 BILLION EARTHS By Dr David
    Message 1 of 1 , Jul 1, 2002
      NHNE News List
      Current Members: 676
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      By Dr David Whitehouse
      BBC News
      Monday, 1 July, 2002


      Astronomers say there could be billions of Earths in our galaxy, the Milky

      Their assessment comes after the discovery of the 100th exoplanet -- a
      planet that circles a star other than our own.

      The latest find is a gas giant, just like all the other exoplanets so far
      detected, and orbits a Sun-like star 293 light-years away.

      Scientists say they are now in a position to try to estimate how many
      planets may exist in the galaxy and speculate on just how many could be like
      the Earth. The answer in both cases is billions.

      Virtually all the stars out to about 100 light-years distant have been
      surveyed. Of these 1,000 or so stars, about 10% have been found to possess
      planetary systems.

      So, with about 300 billion stars in our galaxy, there could be about 30
      billion planetary systems in the Milky Way alone; and a great many of these
      systems are very likely to include Earth-like worlds, say researchers.

      Better grasp

      The 100th new planet circles the star HD 2039. It was found by astronomers
      using the Anglo-Australian Telescope as part of the Carnegie Institution
      Planet Search Program.

      The Jupiter-sized world circles its star every 1,210 days at a distance of
      about 320 million kilometres (200 million miles).

      Astronomer Dr Jean Schneider, who compiles the Extrasolar Planets Catalogue,
      told BBC News Online: "The 100th planet is symbolic and important.

      "The first discoveries concentrated on short orbital periods because of the
      limited timebase of observations. Now, we are learning more about the
      statistics of long orbital periods and know to what extent our own Jupiter
      is exceptional or not."

      New telescopes

      With the new world, astronomers say that they have just about finished
      surveying all the Sun-like stars out to a distance of 100 light-years from

      Current planet detection technology -- based on the "wobble" induced in the
      parent star by the gravitational pull of the orbiting planet -- can only
      detect worlds about the mass of Saturn or larger. Earth-sized worlds are too
      small to be seen.

      But even in this "biased" survey of giants, the smaller worlds predominate
      -- which makes astronomers think that Earth-like worlds do exist. They may
      even be as common a Jupiter-sized exoplanets.

      And if stellar statistics gathered in our local region of space are applied
      to our galaxy of 300 billion stars, then there may be 30 billion
      Jupiter-like worlds and perhaps as many Earth-like worlds as well.

      Astronomers will have to wait for a new generation of space-based telescopes
      incorporating advanced detectors before they can detect Earth-sized worlds
      orbiting other stars.


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