Why is there only 8 planets now

  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. chroot

    chroot 10,351
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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. Last edited: Aug 31, 2006
  5. EL

    EL 780
    Science Advisor

    The alternatives were (basically) to include three new planets, or take away Pluto, and the later was chosen...
  6. LURCH

    LURCH 2,507
    Science Advisor

    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. SpaceTiger

    SpaceTiger 2,969
    Staff Emeritus
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    Last edited: Aug 31, 2006
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