Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Pluto's planet status

  1. Not a planet

    5 vote(s)
  2. A single planet

    10 vote(s)
  3. A binary planet

    5 vote(s)
  4. Other (explain below)

    3 vote(s)
  1. Nov 28, 2004 #1
    Since I was a young Earthling, I had been told that Pluto was the ninth and outmost planet of our solar system.

    More recently, I have heard that Pluto did not form with the rest of our planets, had actually been captured late in the game, and therefore was not a planet at all.

    Today I ventured with my girlfriend (also an Earthling) to the National Air and Space Museum, where we were informed that Pluto is actually a binary planet, along with its "moon" Charon.
  2. jcsd
  3. Nov 28, 2004 #2


    User Avatar
    Gold Member

    I voted "other" because I don't care one way or the other. I will always remember Clyde Tombaugh because he was held up to us who grew up in the Cold War as an example of what a dedicated amateur could aspire to. When Sputnik was launched in 1957, suddenly US schools started taking sciences a bit more seriously, and Clyde was a handy role model. Yeah, Pluto is tiny and it has an inclined, elliptical orbit...it is least like the other planets in many respects, but who cares how it is classified? If it is classified as a "planetoid" or some such, teachers will have to spend time explaining its "demotion", and it will get more attention that way than it does currently.
  4. Nov 29, 2004 #3


    User Avatar
    Science Advisor
    Gold Member

    It really depends on your defintion of planet, some people like to thik of it as the smallest planet, this is mainly for historical reasons, others like to look on it as the largest object in a group of objects much more abundant than the planets - the planetoids. Arguably defining it as a planetoid is more objective than defining it as a planet, but then again the whole excerise as defining it as planet vs planetoid is fairly subjective.
  5. Nov 29, 2004 #4


    User Avatar
    Science Advisor

    If pluto-charon is considered a "binary" system, then certain earth-luna should be also!
  6. Nov 29, 2004 #5


    User Avatar
    Science Advisor
    Gold Member

    Mike Brown of Caltech [co-discover of Quaoar] made this comment. "If Pluto were discovered today, no one would even consider calling it a planet because it's clearly a Kuiper Belt object."
  7. Nov 29, 2004 #6


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member
    Dearly Missed

    A single planet!
    It's only charming that it is a bit weird..
  8. Nov 29, 2004 #7
    How many Kuiper belt objects are now considered to be in planetary orbit(?) around Sol and of sufficient mass(?) to be planetoids?
  9. Dec 2, 2004 #8


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    It's a member of the EKB, just like several thousand others. Its uniqueness is twofold - it's the largest (so far) and first to be discovered (being a binary is not unique - not only is Earth-Luna a binary, but there are at least 5 other EKB objects which are binary).

    As to Loren's question, it depends on your definitions. AFAIK, EKB objects aren't categorised by size (no more than asteriod belt ones are); and the MPC distinguishes between 'trans-Neptunian objects' (the classic EKB?), 'Centaurs' (orbit inside Neptune, e.g. Chiron), and 'scattered disk objects' (Sedna is listed as one such; it may, however, be the first discovered of a quite different kind of object).
  10. Dec 2, 2004 #9
    Seeing as there's no actual definition of what a planet is I'm going to vote it's a planet because it's a rather arbitrary definition anyway. Astronomy is filled with archaic things that would make more sense if we didn't use them the way they are (such as stellar magnitudes for example) so who really cares about one more?
    Plus if we demoted Pluto from planethood the mnemonic "My Very Educated Mother Just Served Us Nine Pizzas" wouldn't work anymore and then where would we be? :cry:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook