Explain why pluto has been demoted (no longer a planet)?

Answer 1

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 2

"IAU Decision

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

There are three main conditions for an object to be called a 'planet', according to the IAU resolution passed August 24, 2006.

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 fails to meet the third condition.

The IAU further resolved that Pluto be classified in the simultaneously created dwarf planet category, and that it act as prototype for a yet-to-be-named category of trans-Neptunian objects, in which it would be separately, but concurrently, classified.

Prior to this decision several other definitions had been proposed, some of which might have ruled out planetary status for Earth or Mercury or may have classified several of the asteroids as planets. This version was democratically chosen in a successful attempt at avoiding these non-traditional results."

This, and more, from Wikipedia, the free, online encyclopedia at:
http://en.wikipedia.org/wiki/Pluto

Hope this helps!

Answer 3

Good question. It cannot be done using the reasons officially given, because that would also mean Earth had to be demoted.

(earth has not cleared its orbit, or if it has then so has pluto)

What remains is a complete arbitrary process, perhaps even a manipulated voting. I'm afraid we'll never know.

Answer 4

basically what is the definition of a planet

figure that out and you will find the reason why pluto has been demoted

Answer 5

Cos he kept on canoodling with all the stars, rarely came to the planet meetings, and we he did, he turned up drunk as a skunk

Answer 6

Because nobody spoke up for the Plutonians at the conference table...we always pick on the little guys.

Answer 7

I heard that it is too small to be called as one of the major planets in our solar system.

Answer 8

it is too small to be a planet. it is also considered a moon of uranus. it is even smaller than our own moon

Answer 9

It's too small, it's like a twins with its moon.