Why Pluto is no longer a planet?

Answer 1

Since the discovery of Pluto in 1930 astronomers had considered the solar system to have nine planets and assorted other bodies. However, since 2000 the discovery of at least three bodies (Quaoar, Sedna and Eris), all comparable to Pluto in terms of size and orbit, had led to a situation where either these minor bodies would have to be added to the list of officially recognized planets or older ones would need to be removed in order to ensure consistency in definition.

In 2006 the matter came to a head with the need to categorize and name the recently-discovered trans-Neptunian object Eris, which, being larger than Pluto, was thought to be at least equally deserving of the status of 'planet'. The IAU decided that the term planet would be redefined. According to the new definition there are currently eight planets and three dwarf planets known in the solar system.

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) 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 3

In many ways, Pluto does not ressemble other planets in our Solar system. It is too small, and its orbit it different from that of the other planets. Since the discovery of Pluto, there have been many other Pluto-like "planets" discovered out there. These objects out there are too small to be considered planets. They are actually Kuiper Belt objects. The Kuiper belt is believed to be debris left over from the formation of the Solar system.

Answer 4

Because it's moon, Charon, is almost as big as it. It has a rocky surface and it's just a big icy asteriod in most astronomers minds. But in MY mind, Pluto is still a planet!!!

Answer 5

That is the new opinion. but in MY mind.. in MY opinion., Pluto is STILL a planet

Answer 6

I heard that it is like one of the asteriods in the asteriod belt. so there are hundreds of millions of plutos out there. I forgot where I heard it from

Answer 7

im sick of answering question like this. im not saying no more.

Answer 8

it is too "small" in diameter