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Last Post 4/12/2010 9:12 PM by  Pat Reiff
pluto debate
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4/12/2010 7:07 AM

    Ashley Roberts (fx1)

    I seen a program on pbs the other night on pluto. Since pluto is known to have at least three moons now, how do you feel about its classification as a minro planet, and could it be reassigned to planet status?

    Tags: Pluto, Kuiper Belt, Eris, solar system, mnemonic, Mike Brown, classifying planets

    Kris Sigsbee

    Basic Member

    Basic Member

    4/12/2010 7:59 AM

    Hi Ashley,

    I don't think Pluto will be reinstated as a planet anytime soon. Having "moons" is not a sufficient condition for a solar system object to be classified as a planet under the current definition of a planet used by astronomers and space scientists. Many asteroids in our solar system may have other asteroids or objects orbiting around them like a moon. If having a moon was the only requirement, then we would have to reclassify every asteroid found with a "moon" to be a planet. Instead, we are now calling these objects binary or double- asteroids. Here is a link to some examples of asteroids that have "moons:"


    Pluto is considerably larger than these asteroids, but that also is not a sufficient condition for reinstating Pluto as a planet. Objects that are nearly as large, or possibly larger, than Pluto have recently been found beyond the orbit of Neptune. The largest of these objects, 2003 UB313, is now called Eris, after the Greek goddess of discord and strife. Eris appears to be larger than Pluto. If Pluto is reinstated as a planet because of its size, then we would also have to give Eris status as a planet. However, Pluto, Eris, and other similar objects are believed to have more in common with objects from the Kuiper Belt than they do with the terrestrial planets (Mercury, Venus, Earth, and Mars), so it seems unlikely that we will add these objects to the list of planets in our solar system. Here are some links where you can read more:



    KD Leka

    Basic Member

    Basic Member

    4/12/2010 3:46 PM

    hi Ashley,

    your question brings up a great point, which is that one of the things scientists do is to look at the many things in the universe and figure out which ones are like the others, and which ones are not. In many ways, that is the start to figuring out the underlying causes for the phenomenon that are observed. And what often happens is that the definitions used for the classifying can get modified along the way simply because we have learned more about the underlying physics. So, while it may be disappointing to see a planet demoted, it actually means that we are making progress in understanding the universe around us. and that's a good thing. :-)

    Pat Reiff

    New Member

    New Member

    4/12/2010 9:12 PM
    The good news about demoting Pluto is that I can now show all the planets to the students in my Astronomy classes on our 16 inch telescope. Pluto is hard to find and is hard to tell it's a planet in our scope. I have now rewritten the solar system mnemonic as "My Very Educated Mother Just Showed Us Neptune"

    We had a terrific speaker at Rice University March 30. It was Mike Brown, the Caltech researcher who discovered Eris and thus started the debate about demoting Pluto. The title of his talk was "How I killed Pluto and Why it had it coming". You can watch that seminar on our website...

    the "play" button is in the middle of the preview image... be sure your browser window is open wide. You'll need to have Quicktime to see the movie.

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