What is this whole "Pluto is not a planet" thing about?

Answer 1

Pluto has been an oddity from the time it was discovered. Its orbit is way off the plane of the other planets' orbits, and highly elliptical; it is tiny, has a huge moon, and a few other peculiarities that escape me at the moment. The discovery of some other small and similarly peculier bodies re-ignited the controversy as to whether Pluto should be considered a planet, if so, the other bodies had at least as much claim as Pluto, but it wasn't a very good claim. So the International Astronomical Union, which has the say-so on such matters, sat down last summer to try to unscramble this mess. When the dust settled, they decided that neither Pluto nor any of the other oddities should be called planets, and laid down rules to deal with those and with future discoveries.

Answer 2

Pluto is not a classical planet, it is still a planet though, albeit a "dwarf planet"

A lot of people got upset when they found out that Pluto was going to "lose" it's planet status--which it really didn't, it was just reclassified. In science, things are constatnly being reclassified as they are studied and better understood. Failing to reclassify pluto on account of it being "cute" or some such thing is just not good science.

As one of the earlier posts pointed out, Pluto does a lot of things differently than the Classical planets, but it also does things the same. It orbits the sun, has three moons (though that definition is in question too, since one of the moons is so huge compared to Pluto) and is large enough that it's own weight has pulled it into a sphere. All the other planets do all that, too (except have moons, venus and mercury have none known). Pluto has a higher eccentricity and inclination, and orbits in a region known as the kuiper belt, which is a kind of asteroid belt made out of comets.

The other planets have cleared the area around them of debris, (there is not an asteroid belt around those planets) which turns out to be the single criteria that makes pluto not a classical planet. I think that this classification item is arbitrary, because for all we know, pluto could still be in the process of clearing it's area... And besides, we may venture out into space and find that sometimes planets do exist in what might be considered asteroid belts. Looking at a diagram of Jupiter and all the asteroids that swarm about in it's orbital vicinity, one wonders what "swept the area clean" means.

Personally, and I've read that this is not just me, there should be a mass and/or radius limit if you want to start calling some planets dwarf planets. This might seem arbitrary, but really is no more so than the current rules.

Planet: 1. Orbits the star (is not a moon). 2. Is big enough to be a sphere. 3. Has swept the area around it clear of debris.

Dwarf Planet 1. Orbits the star. 2. Is spherical.

Another thing--many people thought that "dwarf planet" just sounds dumb. The IAU should have used something more like "planetoid" as these bodies are sort of the transition between planets and asteroids. Oh well.

You can sort out the definition for yourself by looking at various websites online:

Answer 3

Because of the fact that Pluto is very far away from our home planet, and very little information that scientists got about this planet, most of them have doubts whether this chunk of rock can be considered a planet or just an asteroid floating out in space.

Answer 4

The International Astronomical Union decided that Pluto was no longer a planet. The reason is that while Pluto is round, orbits the sun, and has three moons, it has not cleared (via gravity) its own orbit of debris. Instead, they decided to classify it as a "dwarf planet".

See the details below.

RESOLUTION 5A
The IAU therefore resolves that "planets" and other bodies in our Solar System, except satellites, be defined into three distinct categories in the following way:

(1) A "planet" [footnote 1] is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

(2) A "dwarf planet" is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape [footnote 2] , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects [footnote 3] except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".


Footnote 1: The eight "planets" are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Footnote 2: An IAU process will be established to assign borderline objects into either dwarf planet and other categories.

Footnote 3: These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.

RESOLUTION 6A
The IAU further resolves:

Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.

Answer 5

The goverment is to poor to care about another planet jk. Because they have found asteroids bigger than pluto and charon in the kuiper belt and if pluto is a planet then they have to define the asteroids as planets. Another reason is because plutos course around the sun is "off" it crosses neptunes path every 300 years or so.

Answer 6

Pluto is a planet. Just not considered in the main group of them...have you heard about "Dwarf Planets"? Well, it is one of them...scientist belive Pluto came from the Kuiper belt. So..it is still a planet...

Answer 7

Scientist now say Pluto is to small and looks more like a piece broke off of another planet.

Answer 8

I'm not sure but talk about messin' people up! How are parents supposed to help their children with homework when they keep changing things on us!!

Answer 9

well...they think its jsut a star or smthing and same w. jupiter now..yea