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Why is there only 8 planets now

  1. Aug 30, 2006 #1
    Please explain why there is no pluto any more:surprised :surprised :surprised :surprised :surprised :surprised :surprised :surprised :surprised :surprised :surprised :surprised :surprised :surprised :surprised :surprised
  2. jcsd
  3. Aug 30, 2006 #2


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    The International Astronomical Union recently changed the official definition of "planet." Pluto does not meet this new definition. Pluto still exists, but it is no longer considered a planet.

    - Warren
  4. Aug 31, 2006 #3


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    I thought that 12 planets met the new criterion - including Ceres and the one which orbits around a mutual point with Pluto...

    <read it in the Guardian the other week>

    Can't find the link to my story yet. Here's an official 8 planet one: http://www.planetary.org/home/

    Ahhh... the 12 planet thing seems older: http://www.space.com/scienceastronomy/planet_denitions_030227.html

    or not: http://news.bbc.co.uk/1/hi/sci/tech/4795755.stm

    :confused: :confused: :confused:
    Last edited: Aug 31, 2006
  5. Aug 31, 2006 #4


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    The alternatives were (basically) to include three new planets, or take away Pluto, and the later was chosen...
  6. Aug 31, 2006 #5


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    I doubt it will last for long, though. The new definition is very sketchy, and depends upon a body having "cleared out" the immediate vicinity of its orbit. Pluto was not disqualified because of its size, or the eccentricity of its ellipse, or its inclination to the orbital plane, but because it crosses Neptune's orbital radius. By this definition, Neptune (having failed to "clear out" Pluto from its orbit) should also be disqualified.

    In fact, because there are still thousands of NEO's whizzing about the inner solar system, many of them crossing inside the orbit of Venus, the new definition may reduce the entire solar system to only one planet: Mercury!
  7. Aug 31, 2006 #6


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    Last edited by a moderator: Apr 22, 2017
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