Why is Pluto Not a Planet?

pluto.jpgIn August of 2006 Pluto was declared to no longer be a planet. This was due to a rewriting of the definition of “planet”.

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.

Pluto is now officially a “dwarf planet”. But it’s no longer part of an exclusive club, since there are more than 40 of these dwarfs, including the large asteroid Ceres and 2003 UB313, nicknamed Xena—a distant object slightly larger than Pluto discovered by Brown last year.


Update Feb 2009: You can talk about this topic in the discussion forum at (and play video games too!):

Update May 2009: Here is information about the “Planet X” theory and information on why Pluto was initially considered a planet: http://en.wikipedia.org/wiki/Planet_x

Update August 25 2009:
The debate rages on. Did you know that 90% of the critical letters complaining about Pluto’s demotion come from North America? Food for thought, here’s the article:

132 thoughts on “Why is Pluto Not a Planet?

  1. i think pluto isnt a planet coz it haz ice and stuff on it. does any one here like chocolate coz i do……….

  2. i like chocolate 2 and pluto isn’t a planet cos there are at least 70 000 other planets the same size as pluto in the kuiper belt so really its just another kuiper belt object

  3. i like chocolate 2 and pluto isn’t a planet cos there are at least 70 000 other planets the same size as pluto in the kuiper belt so really its just another kuiper belt object

  4. Hey this is Rosalia and whated to say that pluto isn’t a planet bcause it is covered with ice and otherthings i don’t know so this is what i just wanted to say this becaues i think i am really smart but in my family evreyone thinks i’m STUIP which i am not so this is what i wanted to say about pluto that it is covered with lots of ice and it is not considered a plante anymore so there you have it!!!


  6. PLUTO is not a planet,but its far better to be a Dwarf PLANET,and there are hundreds of Dwarf PLANETS in the solar system which does not resemble PLANETS.Therefore PLUTO has no question of becoming a PLANET.

  7. i think Pluto is nOt bEcAUsE it iS the FARtHEsT plANeT In thE SOLar SysTEM aH bzta pra saken d Xa plANeT i h8 nThaT PlANet so MuCh!!!

  8. PLOUTO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    I LOVE YOU PLOUTO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!CHOCOLATE


  9. hi!i say that pluto is no more a planet coz there is no life in pluto and if scientist will agree that pluto is a planet they will have to allow the asteriods which are as same size as pluto which is impossible because they are more than 40 asteriods so if they allow pluto to be a planet they will have to allow 40 asreriods to be a planet and pluto has no life coz it’s too cold there that if someone wiil go in that planet he/she will freeze that is what i wanted to say tanxs

  10. hi! pluto is ma best planet and wen i heard dat pluto is not a planet i was so dissapointed i luvvvv pluto it is da besttttt!!!!!!!!!!!!

  11. hi! i say that pluto is no more a planet coz it is a big ball of ice and it was the ninth planet of solar system and it does not fit in with the pattern of the other planets

  12. Pluto can’t be a planet…. it’s a dog!!!!!!!!!!!!!!Forget chocolate, how about Nutella 🙂

  13. i am researching why pluto is not a planet… well, first, it has not “cleared its neighborhood” of its orbit…but,those other laws, pluto did pass it… i think pluto should be a planet… i guess we will have to settle it as a dwarf planet…:(

  14. i think pluto shoulf be a planet because its been one for the longest and it shouldnt matter wat the definition sats cuz to me pluto is a still a planet no matter wat no one says

  15. no 1 cares wether or not pluto is a planet!!!!!!!!!!!!!!!!!! and only cool kids can like chocolate and u guys r not cool!!!!!!! ur nerds:(

  16. i am very sad that pluto is not a planet and what is up with the chocolate bussines

  17. pluto is a grrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrreat planet although it is not anymore

  18. i hate science and i love chocolate like helllllllllllll

    y r we sopposed to go to skool if we dont attend claasses that wat i do

    see ya every1:)

  19. I think PLUTO is a planet because its in the solar system and I LOVE SNOW .I think all the people who said and made PLUTO not a planet to retern our pluto a planet even if it is different from the others .We are different too!

  20. Ok Pluto will always be a planet in my books. But techniqelly with all the scientist facts about what defines a planet Pluto misses out on one of these. And if scientiest did decide to let Pluto be a planet they would have to let approx 40 ‘planets’ into our solar system which would totally suck. With PLutos compositions and everything Pluto is just another object in the Kuiper Belt. But for many years before PLuto was discovered, scientist believed that there would be a ninth planet in the solar system, so what changed their mind to not let Pluto be one? ARRR it anoys me but im sorry to say Pluto is not a PLanet but a dwarf planet, but PLuto will always be a planet to me.

    And guys seriously chocolate? how the hell do you get from space to chocolate? i know it is awesomely awesome, but seriously?

  21. Pluto is smaller than any other planet, even smaller than Eath’s moon. Its dense and rocky. Pluto’s orbit is erratic. One of its moons, Charon, is about half Pluto’s size! Its now officially a “dwarf planet” and officially not considered a planet.

  22. Pluto should be considered a planet because it has been a planet since 1930 and just because so scientist wants to change the definition its a dwarf now. You guys are racist

  23. How is it that you can just change a definition to define what is considered a planet and what isn’t?

  24. Because under the old definition of a “planet” – and the discovery of new objects – we would end up with many many nearby “planets” – which is just confusing for everyone. So they redid the definition of a planet to keep the local number manageable. That’s a simplified explanation.

  25. pluto is i snt a planent coz its a silly fakin planet ok any one like ice lollyes coz i do….

  26. Why in the world cant pluto be a planet????? im doing a project on pluto and just because it is covered in ice doesnt mean that pluto isnt a “planet”. it has a moons just like the other “planets”. it even orbits the sun! but now scientists say that pluto came from another galaxy and that it just got stuck in orbit around the sun. poor pluto is now a “dwarf” planet…. ~niki b.~



    Pluto Isnt a planet Because its moon Charon is Half the size of pluto. so it is not a planet..


  29. I dont think that pluto is a planet cuz it is to far away from the sun and it is WWWWAAAAAYYYY TO small!!!!!-But i like its name

  30. Pluto is 2 small and itz got ice and is 2 far from da sun itz sum tiny planet innit who lykz fifa o9 bang bang

  31. alright guys, Pluto is no longer a planet because the IAU changed the definition of “planet”. A planet is the following:
    1. An object that orbits the sun. It can not be orbiting any other object.
    2. Be a sphere- must have enough gravity to smooth itself out (major bumps and ridges)
    3. Clears its orbital neighborhood- No other bodies in its orbit. Should sweep up all debris in its orbit (except for moons, since they are gravitationally caught).

    The IAU did NOT look out to simply stripe Pluto of its planetary status, they simply redefined “planet”, and Pluto just so happen to fail at the third requirement as listed above. It is not because it is too small, it just needs to meet requirements, none of which specify a certain size a planet must be. If it were categorized as such, it would simply be science by convenience.

    I hope this cleared some things up.

    I love chocolate too XP

  32. WHY DOES EVERYONE CARE SO MUCH ABOUT THIS GIANT SNOWBALL IF SCIENTISTS SAY ITS NOT A PLANET THEN ITS NOT A PLANET now if it was a giant chocolate ball or something then it should be considered a planet but it isn’t so it’s not.


  33. pluto is not a planet, i think cuz it’s a dwarf……????i think…????im confused….:{….?????

  34. im hot ur not lolx……dnt u wish ur girlfren was hott lyke meh….lmao…:)……..

    oh yea were suppose to be talk’n bout dhat planet…..its a dwarf rite….??????


  36. you guys are rong pluto is not aplanet for some stupid reason but i am ten years old and i am studing in school about this so i think i was made to not be a planet makayla

  37. and jayzee i wouldnt use words like that around kids because i now what that says because my dad does it all the time makayla to Jayzee

  38. can you just tell me if pluto is a planet or not.
    and all these lil kids leavin stupid comments,
    your really immature and you needa get a lifee if you
    dont care about this then dont go on this website and read all the stufff. ohhkk.
    -bee breeezzyyy ;]

  39. guys Pluto is a planet.
    just because Pluto doesn’t have a clear neighborhood shouldn’t classify it as a planet. i think if that’s the case than Neptune should not be classified as a planet either. because Pluto orbits overlaps Neptune orbits making Neptune not have a clear neighborhood. so if that’s really the case then Neptune should not be a planet either. therefore Pluto should be considered a planet as well. lastly i don’t think that it is right to classify a planet with such little qualification when talking about something this major. so we wont have to second guess and regulate the rules in order for something to be or not to be a planet. also for it would not cost so much to buy new text books!!! but then again I’m no scientist
    [a 9th graders opinion]

  40. Pluto should be considered a planet. It has always been considered a planet, until 2006. Nothing has drastically changed about Pluto and it does cross orbit Neptune. The only thing that has changes is the homosapian definition of what makes a planet.

    People can never leave anything alone, but constantly change what works to fit their discoveries. I hope they made great $ to change the definition and finally make a new discovery that Pluto is actually classified as a dwarf planet…. WTF is a dwarf planet. A planet is a planet is a planet. Dwarf… BULLSHIT that’s what it is. So now this PLANET is considered to be part of the Kuiper belt… a belt/home of comets. Redunkulous!!!!!!!!

  41. Science will always be changing when new evidence presents itself. The discoveries of space are continuing. If Pluto were defined as a planet – then there are also hundreds of others that would now have to be called planets. So the choice was to either include those hundreds of others as planets, or redefine Pluto as not being a planet.

    Adding hundreds of planets to the records overnight was a little much to handle, so they chose to redefine Pluto.

  42. im sooooooooooooooooooooo sad tht pluto isnt a planet anymore because its interesting to learn about the plant pluto…
    it has alot of memmories tht are not goin 2 be left behind!!!!!!!!!