"Unfair!" -Pluto.?

Question

Why is Pluto not considered a planet anymore?

Answer 1

Well, they no longer consider it becuase it doesn't meet this criteria:
it must orbit the Sun, it must be big enough for gravity to squash it into a round ball, and it must have cleared other things out of the way in its orbital neighborhood. The latter measure knocks out Pluto and 2003UB313 (Eris), which orbit among the icy wrecks of the Kuiper Belt, and Ceres, which is in the asteroid belt.

(1) A "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, and (c) has cleared the neighborhood 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, (c) has not cleared the neighborhood around its orbit, and (d) is not a satellite.

(3) All other objects except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".

another theory would be to blame Canada
enjoy

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

It is too small. When it was discovered there was no telescope good enough to accurately measure its size and it was estimated to be bigger than Mars just bases on its brightness and distance. Now we know for sure that it is smaller than the Moon, and that is just too small for a planet. It is more like a big asteroid. But lots of people, like you, objected to calling it an asteroid so they compromised and made up a new category: dwarf planet. They also reclassified the largest main belt asteroid, Ceres, as a dwarf planet as well as the newly discovered object once unofficially called Xena but now officially called Eris orbiting out even farther from the Sun than Pluto.

Answer 4

Astronomers have discovered a lot of icy bodies in the range of Pluto's size in the outer Solar System. Examples include Sedna, Quaoar, Varuna and Eris. Some of them are slightly bigger than Pluto. As more of these kind of objects were discovered, people started to wonder if they should be considered as planets since many of them are slightly bigger or smaller than Pluto. Because of this confusion, the International Astronomical Union (IAU) was called to examine the definition of a planet. If these objects (and Pluto) are to be accepted as planets, that will mean we will have as many as 10-12 new planets in the Solar System, making the total number of planets around 20+.
After much consideration the IAU decided to drop Pluto's planet status, making it easier for people since it is difficult to imagine our Solar System having a total of 20+ planets (many having weird, unusual names).

Answer 5

Pluto is no longer considered a major Planet now. It is known as a minor or dwarf planet together with Ceres and Eris.

Answer 6

Because it is not round,

The qualifications for a planet is that it has to be round, Pluto is not, That makes me wonder if we should consider Rosanne Barr a planet

Answer 7

I think that the scientists have found it not big enough to be called a planet. It's just an ice covered rock or so I've heard.