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why does pluto not considered as a planet recently?

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  • 1 decade ago
    Favorite Answer

    The easy answer: there is a new definition for the word "planet" (as of August 2006) and Pluto does not meet the definition.

    PS: There is lots of discussion on whether people are happy with the new definition. So I suspect that, after a few years, it may get discussed again. However, it is not the first time that "planets" get demoted. The first few asteroids that were discovered (e.g., Ceres) were called planets at first. They were later demoted to "minor planets" -- also known as "asteroids" because they looked like points, instead of disks, in 19th century telescopes (asteroid = star-like, stars look like points, planets look like disks).

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  • 1 decade ago

    According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit.

    Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.

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  • Otis F
    Lv 7
    1 decade ago

    The International Astronomical Union decided that Pluto was no longer a planet. The reason is that while Pluto is round, orbits the sun, and has three moons, it has not cleared (via gravity) its own orbit of debris. Instead, they decided to classify it as a "dwarf planet".

    See the details below.

    RESOLUTION 5A

    The IAU therefore resolves that "planets" and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:

    (1) A "planet" [footnote 1] is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

    (2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape [footnote 2] , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

    (3) All other objects [footnote 3] except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".

    Footnote 1: The eight "planets" are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

    Footnote 2: An IAU process will be established to assign borderline objects into either dwarf planet and other categories.

    Footnote 3: These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

    RESOLUTION 6A

    The IAU further resolves:

    Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

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  • Anonymous
    1 decade ago

    Scientists redid the defination of a planet. Since other Kuipler belt objects have been found that met the old defination, it was decided instead of naming new planets to the solar system, they would drop Pluto to the new Dwarf planet defination and go on from there.

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  • 4 years ago

    the three products (no longer 2) that have been those days seen for planetary status have been got here across a while in the past, Ceres in 1801, Charon in 1978 and Xena in 2003. The international Astronomical Union created a clean class of Dwarf Planets for all 3, Pluto and a selection of of different different Trans-Neptunian products and 3 different asteroids,

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  • 1 decade ago

    BEcause the IAU determined this new definition of planet. Pluto however will always in my mind be teh 9th planet. Here's the definition.

    is in orbit around the Sun,

    has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape, and

    has "cleared the neighborhood" around its orbit.

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  • 1 decade ago

    because recently scientists found lots of other planet in the milky way galaxy that are bigger than Pluto. so they consider Pluto as a small planet / asteroid.

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  • 1 decade ago

    And Pluto is pissed over it and is going to turn into the Meteor that is going to wipe us out!!!! Like I said before if Uranus can be a planet Pluto can too.

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  • 1 decade ago

    it's too small, there are other plutos around the actual opne so then our solar system would have like 20-30 planets

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  • 1 decade ago

    pluto is too small and its orbit around the sun is so far off the orbit of neptunes scientists believe it is part of the kuiper belt, made up of frozen rocks.

    Source(s): SPACE.com
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