Why is pluto considared by some not to be a real planet?

Question

Short ansers please!

Answer 1

The International Astronomical Union determines what the definitions are officially. In the latest 'reform', the definition of the word planet does not fit the case of Pluto.
They have created a new class called 'dwarf planets' which includes Pluto and a few more similar objects.
We now have planets, dwarf planets and minor planets.

Answer 2

Because it is so small. There are a number of dwarf planets (which is what Pluto is now considered to be) in the Oort Cloud some of which are actually larger than Pluto is. The Oort cloud is like the asteroid belt except that it is about 1 AU (Astronomical Unit- distance from Sun to the Earth) past Pluto at Pluto's farthest point from the Sun (more info on the Oort cloud here... http://en.wikipedia.org/wiki/Oort_cloud ). Since there are a number of larger bodies in the Oort cloud that aren't considered planets it was decided to demote Pluto to a dwarf planet classification.

Answer 3

This is a real debate. The reason it was "kicked out" is because they found another object (Xena) that was larger than it. This started a large debate whether to include this "tenth" planet. Pluto is now known as a Dwarf Planet, which is somewhat misleading because it is implying that it is still a planet, which it is not. Pluto and Xena are part of the Kuiper Belt, which is like the Asteroid Belt but beyond the PLanet Neptune, and with generally larger objects than asteroids...so large that they are gravitationally pulled to become a sphere. Pluto is now a Kuiper Belt object, like Xena and other objects in that belt.

Answer 4

Pluto is nothing to sneeze at . Its been there for years among the large planets of the solar system. Its a Dwarf, but because its little , it should have never been discrimnated against. There should have been some laws about that,
PLuto even has moons. It takes Pluto 241 years to orbit the solar system.
Pluto fits into Bode,s law of planet radius vector.

Answer 5

It is not a debate.

It is not considered by some.

The International Astronomical Union convenes every three years to discuss such matters. In 2006, Pluto was demoted to dwarf planet under the revised definitions of 'planet'.

If you continue to use the term planet when referring to the dwarf planet Pluto, you are incorrect.

There are those who choose to have a difficult time letting go of the past. Just like there are those who still believe that the world is flat. Do not be one of those people.

Nobody is 'discriminating' against Pluto.

oaklord-- I truly feel sorry for your astronomy students who are fed disinformation from a teacher who refuses to teach them facts because he is afraid to give up his past ideas. You are not a scientist and should not be teaching. The IAU definition of planet was not 'forced through' by anyone. It was discussed and voted on. Other definitions were discussed and tossed out. The definition vote was passed unanimously! Your charges that it 'will not hold up' stem from your own refusal to allow anything that doesn't meet your personal approval to change.

mayor-- In order for hypotheses to be accepted, they need to be based upon reasoning. Your suggestion that Pluto is some gas ghost from another solar system stems from watching too much television. Try picking up a book sometime. Your dreamworld even extends so far as to call yourself a 'realist'.

Answer 6

I'm Old School so to me Pluto will always be a planet as long as it's there out in space.

I obviously don't know as much about this as most of you, if not all of you here, but after reading all of the posts in this section, I have to point something out to you that you may not have considered...

Ever wondered what kind of intelligent life forms could exist out in the vast amounts of galaxies, because everyone else seems to explain and display alien life as humanoids or something from our beloved Earth like a virus or harmful fungi etc.

My point is (without offending anyone) what if there was an intelligent life-form, for mere hypothesis, which was made entirely of different gases with no solid foundations, it would seem like some sort of gas ghost to most, but imagine a whole existence of these beings in another galaxy they wouldn't eat instead they would absorb nutrients they needed straight from their own birth Planet by touch alone.

(sure so hypothetically as mankind gets smarter and more creative we can think and understand this kind of ideology and then the media will take it to humorous and extreme levels and the idea gets scewed.)

But consider that possibility, maybe that is what Pluto is...an entire existence of nothing solid just gas and vapour...frozen in time and maybe even lost from it's original solar system.

Although Hypothesis is probably highly unlikely, I would hope, for those that didn't see it like that before, that I've opened your mind to a new thought or passage of thinking.

Thanks for letting me get that off my chest
The Realist Spiritualist

Answer 7

Pluto is considered a "dwarf planet" which is not the same definition of "planet". Dwarf planets have not "cleared their neighborhood" of it's own orbit, meaning they are not gravitationally dominant. Pluto meets the criteria for being a planet except for this detail.

Answer 8

It is true that there are three criteria put in place by the IAU for labeling something a "planet": orbiting a star, large enough for gravitation to force it into a spherical shape, and "clearing out it's orbit". It is this last which has caused all the havoc. If you consider that Hadal planets (those beyond 30 AU from their star) both have a much greater volume of space to "clear" and that, according to Kepler's law, travel much more slowly than their nearer neighbors - this requirement makes it impossible to have a "planet" beyond 30 AU or so from a star.
Pluto would have to clear a volume of space thousands of times larger than an inner planet like Jupiter, and because it orbits much more slowly, the time and number of orbits needed to clear an orbit quickly becomes ridiculous. Pluto would need to be orbiting for many times longer than the current age of the Universe to have swept through its orbit as many times as Jupiter has. Oh, Jupiter hasn't "cleared" its own orbit either - there are thousands of Trojan asteroids in its own orbit right now.
The 'planetary dynamics' faction which forced this definition through at the last IAU meeting won't be able to hold this ground.
By the way, my astronomy students learn about all currently discovered planets in our system - all 16 of 'em... and about the appx. 240 extra-solar planets we know about as well. And I teach about Pluto-Charon as a binary planet.

Cheers from a friend of Clyde Tombaugh

Answer 9

The International Astronomical Union decided that to be considered a planet it has be a celestial body that:
1. Is in orbit around the Sun
2. Has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape
3. Has cleared the neighborhood around its orbit.

Pluto misses out on the last point.

I still think it should be a planet.

Answer 10

It hasn't cleared its orbit of debris.
The IAU decided that was one of the criteria for planethood, and Pluto doesn't meet that criteria.