Why is Pluto no longer a planet?

Answer 1

2177

http://answers.yahoo.com/search/search_result;_ylt=AoZkyAHG.80Ctr_JGw1YT_AazKIX;_ylv=3?p=is+pluto+a+planet

http://en.wikipedia.org/wiki/2006_redefinition_of_planet

Answer 2

Pluto was once called a planet because it was a solid body, thought to be bigger than Mercury, orbiting the sun. Recent decades brought the discovery that it was smaller than Mercury, but it kept its designation as a planet.

In the last few years, a number of bodies, some slightly smaller and some larger than Pluto, have been found not much further from the sun, in similar orbits (inclined, and possible coming inside Neptune's orbit). There is reason to believe that there may be hundreds of them.

If Pluto was to be considered a planet, then the new discoveries would have to be also. This would mean that there could be several hundred "planets".

Men with beards decided that this was too untidy, so they changed the definition of the word "planet" to exclude Pluto and others like it. Thus, we have 8 planets.

It's not the first time it happened. After its discovery, the asteroid Ceres was considered a planet, until more of the same type were found. The 19th Century folks weren't so insecure in their daily lives that they had to form a "Save Ceres Club" or anything like that. And people on this forum say how sophisticated we are these days . . .

It's an arbitrary definition set by people. Pluto is the same as it always was, it's where it's always been, and its feelings aren't hurt by what we call it.

Answer 3

Pluto is no longer a planet because the IAU (International Astronomical Union), in an August 24th, 2006 meeting, redefined what constitutes a planet. In light of new scientific data, and the discovery of many more objects in our solar system, clearer definitions were needed. (Remember, back in 1930 when Pluto was discovered, all we really knew was that it was a point of light that moved.)

Pluto is now classified as a "dwarf planet". There are three currently recognized dwarf planet's in our solar system; Ceres (in the asteroid belt which lies between the orbits of Mars and Jupiter), Pluto, and Eris (which lies further out than Pluto).

To be specific, Pluto was reclassified as a dwarf planet because it fails to meet the planetary criteria of "clearing the neighborhood of its orit".

Resolution 5A(1) defines a planet.
Resolution 5A(2) defines a dwarf planet.

(these are both near the bottom of the page in the link provided)

For a transcript of the session, including what defines a planet and what defines a dwarf planet, see the link provided below.

Answer 4

Planet is an object category. Just like we classify some organisms to be bacteria or Virus' if we learn something new about an object and need to move it into a more appropriate classification the we re-classify it.

The re-classification has not changed Pluto in any way, it just places it into the same category as other similar objects. It was done because Pluto has less in common with the Terrestrial, Gas and Ice planets as it has for Comets and Asteroid. But since it fits somewhere between, they gave it, Ceres and Eris a new category all of there own - Dwarf Planet. (Note that the IAU was very specific in stating that a Dwarf Planet is NOT a subset or type of planet)

Answer 5

Hi,
The short answer is that Pluto is not a planet because it does not follow the definition of a planet.

The long is answer is as follows:
Planets: The eight worlds starting with Mercury and moving out to Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Dwarf planets: Pluto and any other round object that "has not cleared the neighborhood around its orbit, and is not a satellite."
Small solar system bodies: All other objects orbiting the sun.

Pluto and its moon Charon, which would both have been planets under the initial definition proposed Aug. 16, now get demoted because they are part of a sea of other objects that occupy the same region of space. Earth and the other eight large planets have, on the other hand, cleared broad swaths of space of any other large objects.

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

Dwarf planets are not planets under the definition, however.

Furthermore, there will be hundereds of dwarf planets up and coming. They can't all be classified as planets.

Answer 6

Pluto is still a planet, but no longer part of the Solar System.

This is because Pluto's orbit grew slightly wider, causing it to move away from the sun. It's distance from the sun is to far away to be part of the solar system, so in late 2006, scientists excluded Pluto from our Solar System.

But don't worry, there's another planet waiting to be discovered within the solar system. Scientist are yet to decide if it is capable to be part of the solar system.

Answer 7

Because scientists with their big egos decided kick pluto in the nads and demote it to a dwarf planet. This is because it is smaller than what they say is the smaller for a planet (smallest is mercury size).

Answer 8

It is still a planet ...it even has a moon ....
You can't change reality by VOTING against it.

If it acts like a duck and quacks like a duck....it IS a duck...

Who cares what a bunch of loons have voted ....Pluto is and always will be a PLANET.

Answer 9

Because it got in my way.

Answer 10

dint, pay there Taxes,