can anyone exsplain why pluto is nolonger a planet?

Answer 1

At the time Pluto was discovered, 1930, we knew relatively little about the solar sysytem, and absolutely nothing about the outer solar system, so there was no problem with calling Pluto a planet. As time went by, and our knowledge of the solar system and Pluto increased, it became increasingly clear that Pluto was very very different from the other eight planets in many ways, and it was inevitable that it would be reclassified. In 2006 the International Astronomical Union finally decided to make that change. It is too small (smaller than many of the moons of the inner planets), has a very eccentric orbit, has an orbit inclined very differently to the orbits of the other planets, and crosses the orbit of Neptune.

Answer 2

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) the neighborhood of its own orbit of debris. Instead, they decided to classify it as a "dwarf planet".

There is a precedent for this. When Ceres was first discovered in 1801, it was considered to be a planet. After astronomers discovered several other objects in the same orbit, it was reclassified as an asteroid. And, in 2006, it was again reclassified as "dwarf planet" just like Pluto.

Neither Ceres nor Pluto have enough mass (gravity) to accrete all the junk from their orbits. They will be "dwarf planets" until we humans decide otherwise.

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 3

Pluto is not a planet anymore because astronomers thought that it was to small to be a planet and because they kept finding other objects in space that were much bigger than Pluto. If the astronomers didn't take Pluto away we would have a lot of new planets. So Pluto is now a dwarf planet.

Answer 4

Yes, on August 24th, 2006 the International Astronomical Union defined the term "planet". (this is an international union that names stars planets asteroids etc.) Once they had a clear meaning of "planet" it was realized that Pluto was now in a new category called a "dwarf planet".

Answer 5

It was downgraded to a dwarf planet because it didn't meet the requirements for a Planet.

A Planet must meet these requirements:
1. The object must be in orbit around the Sun.
2. The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should pull it into a shape of hydrostatic equilibrium.
3. It must have cleared the neighborhood around its orbit.

Pluto hasn't cleared its neighborhood.

Links to follow:

The controversy
http://en.wikipedia.org/wiki/Pluto#Planetary_status_controversy

The IAU's redefinition of Planet
http://en.wikipedia.org/wiki/2006_redefinition_of_planet

Definition of Dwarf Planet
http://en.wikipedia.org/wiki/Dwarf_planet

hope this helps,

JT

Answer 6

I don't care what a bunch of arrogant scientists think, Pluto is still a planet. They say there may be millions of other plutos nearby. If so, make them all planets!

Answer 7

1. It's very small
2. It's orbit is dissimilar to the other planets, and infact more similar to the the orbits of the bodies in the kuiper belt

Answer 8

Because the interplanetary coalition of the United Nations didnt want a planet with the same name as a dog.

Answer 9

You could do a search online, as I just did, to find your answer. Here's one site I located because I wasn't sure if I remembered it's size was the reason it was demoted...

http://www.space.com/scienceastronomy/060824_planet_definition.html

Answer 10

Hi. They changed the rules.