Why isn't Pluto considered 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

Is Pluto a planet???? Yes and no...

Well for starters, Pluto is just too small. In the neighborhood where Pluto lives? Planets are supposed to be huge. The Jovian planets, Jupiter, Saturn, Uranus and Neptune are 20 to 300 times the size of the Earth, and Pluto is really small compared to the Earth, smaller than our Moon. Kind of stands out.

And Pluto is not made out the same material as the Jovians. The large planets are mostly gigantic spheres of gas, mostly hydrogen and helium. Likely there are no solid surfaces, only denser and denser gas all the way in. Pluto is a small solid world of methane, water, carbon dioxide and ammonia ices, maybe a little rock and with a just hint of atmosphere (that freezes out and falls as snow in her "winter").

And third, Pluto's orbit is the most eccentric (oval shaped) and the most tilted to the plane that the rest of the planets orbit in. Also, Pluto is locked in a resonance with Neptune's orbit and comes closer to the sun than Neptune sometimes.

There were theories that Pluto was a lost moon of Neptune but that was before we discovered she a has one large moon (Charon) half her size (pretty much, this system is a double planet) and recently two other teeny-tiney moons (Nix and Hydra).

Pluto seems like she cant be an ejected moon-she must have formed on her own and seems to be part of an entire army of small icey-dwarf objects that circle just outside Neptune's orbit in what is known as the Kuiper belt. We have no idea of how many or how large these objects may be, hundreds???? NOT "planets" proper, hence the new term "dwarf planet" where Pluto is king.

But... I still think Pluto SHOULD be called a planet because of historical reasons (discovered by an American, financed by Percival Lowell, Tombaugh's life story, etc).

Answer 3

Because the International Astronomical Association voted last year to demote it. This was not the first time that this type of event has happened.

When Ceres was discovered in the early 19th Century it was initially classified as a planet. In the early 20th Century it was also demoted to what it was classified until last summer...an asteroid.

Now Ceres, along with Pluto, are classified as Minor planets.

The professionals need a classification system that is AGREED upon by all astronomers of all nations. So they do it democratically...they vote on it.

So, politically, it was demoted from its status as a Planet.

Answer 4

Because there are many differences between Pluto and the other planets, like the shape of it's orbit, the fact that it has a satellite, Charon, and it is almost as bid as it's satellite. To have an idea what I'm talking about, Charon's surface is as big as Europe, Asia and Australia put together

Answer 5

A plnaet has some defenite definitions.but some or many of these definitions dont define pluto.so pluto is not a planet.

Answer 6

It shrunk so they now think it is only an asteroid by size atleast.
Although they did discover a new planet made of dark matter they suspect they think it will help us in war harnessing the dark matter will be one of the greatest achievments of the world and we can use it for many things and that will probably make us able for access and we will eventually be abe to make new things if the scientists manage to harness it succesfully

Answer 7

A. It's too small.

B. It was not created from our planetary nebula, it was captured by the sun later.