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Last Post 10/19/2011 11:15 AM by  Terry Kucera
other Pluto
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10/19/2011 4:51 AM

    Sarah S

    Now that Pluto is known to have as many as three moons, whats your thoughts on it being classified as a minor planet, and could it be brought bacl to planet status?

    Tags: Pluto, dwarf planet

    Kris Sigsbee

    Basic Member

    Basic Member

    10/19/2011 8:23 AM

    Hi Sarah,

    The number of moons that a planet has does not affect whether or not it is classified as a major or minor/dwarf planet, according to the current definitions. If the number of moons that planet has was the only factor in deciding which planets were major or minor, then tiny Pluto would be a major planet, and much larger Mercury and Venus would have be be demoted to dwarf planets because they do not have any moons. If this were the case, then we should probably demote Earth to dwarf planet status too, since our planet only has one moon, and Pluto has more. However, the number of moons is not the main factor used to determine whether an object is a major or minor planet. Basically, to be considered a major planet, an object must have cleared the vicinity of its orbit of all other large objects or debris and be the dominant object in its orbit. This is pretty much the case for the major planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. There are large asteroids that have smaller asteroids orbiting around them like moons, which are not classified as major planets, because there are too many other asteroids in nearly the same orbit. Pluto's orbit crosses the orbit of Neptune and Pluto does not appear to have cleared its orbit of other objects, so it is a dwarf planet. Other factors that also need to be considered when classifying solar system objects are their shape (is it spherical under its own gravity?) and the nature of its orbit around the Sun (does it orbit in the same direction as the other planets?).


    Terry Kucera

    Basic Member

    Basic Member

    10/19/2011 11:15 AM

    Hi Sarah,

    Those moon's of Plutos have been known for a while - since before the IAU decided to start calling Pluto a dwarf planet rather than a planet, so I don't think it is going to make a difference. There are a number of astroids that also have moons - see http://solarsystem.nasa.g...ds&Display=Moons .


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