Why Pluto is not a planet again?

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

"Planet" can really be defined however you want. There are some definitions that have as few as 4 planets, some that have 11, some that have 13, hell, even some that have over 30 planets. In the opinions of many astronomers, Pluto, among other bodies like Ceres or Eris, all deserve to be called planets. You can do so too if you wish, they are all gravitationally rounded and directly orbit the Sun. Also, that article is terribly inaccurate. Pluto will not have a clear neighborhood any time soon. Also, at LEAST 4 planets are known to have rings, not just Saturn.

Answer 3

Several good reasons why pluto is not a planet:
- Pluto has a highly eliptical orbit compared to the orbits of the 8 real planets
- Pluto's orbital plane is much different from the other planets
- Pluto is tiny... about the size of earth's moon
- Pluto and it's "moon" Cheron actually orbit each other, so it's more like a 2 planet system than a planet with a moon
- Pluto isn't round like the other plantes - it is lumpy.
- There are objects further out from Pluto that are actually larger than Pluto, yet are not considered planets either

Those are just the big reasons why Pluto got kicked out of the group of planets. Although I feel kind of bad about it, it really makes sense. Pluto is far too different from the 8 real planets to belong in the group.

Answer 4

Pluto (39 AU average), is the largest known object in the Kuiper belt and was previously accepted as the smallest planet in the Solar System. In 2006, it was reclassified as a dwarf planet by the Astronomers Congress organized by the International Astronomers Union (IAU).

Answer 5

Because Pluto is too small, it has a very elliptical orbit, and it does not have any of the same properties of all other known planets.

Answer 6

Some people got together and decieded it was to small and down graded it to a darwf planet

There has been resistance amongst the astronomical community towards the reclassification, dubbed the "Great Pluto War" by some astronomers

Read more on the link

Answer 7

a planet isn't necessarily defined by size. it has to do with the body clearing it's orbit of other objects. since pluto regularly crosses neptune's orbit and is small they call it a dwarf planet now.
a dwarf planet is defined as:
(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;
(c) has not cleared the neighbourhood around its orbit; and
(d) is not a satellite

Answer 8

well its too small...and its too distant