why is pluto not considered a planet?

Answer 1

http://en.wikipedia.org/wiki/Pluto
http://www.iau.org/fileadmin/content/pdfs/Resolution_GA26-5-6.pdf

on 24 august 2006, the international astronomical union reclassified pluto.

pluto does orbit the sun, is ball-shaped and is not a satellite, but it does not have an isolated orbit (a bunch of other similar bodies have similar orbits.) so it is not a planet.

i have been waiting for this since i was about ten when i learned that pluto didn't fit the pattern set by the major bodies in the solar system so it was an anomaly. it just felt "out of place". now that astronomers have found hundreds of other bodies with similar orbits, classifying "134340 pluto" as a planet is even more irrational. i feel somewhat satisfied, but i don't know how long this will drag on tho. many planetary astronomers are satisfied that the definition is rigorous enuf. i can accept that the definition is flawed, but i can not accept that "134340 pluto" is a planet.

this was the right thing to do, believe me. this does not change anything about pluto or the solar system. this just corrects the mistake of classifying pluto as a planet initially.

this same thing happened has happened before. in 1800, an astronomer found a body orbiting the sun between the orbits of mars and jupiter and thought it was a planet. astronomers finally stopped classifying them as planets after they found several other bodies with similar orbits, and no one thinks ceres, pallas, juno, and vesta are planets today.

many astronomers consider pluto and charon to be a binary system, but two small bodies orbit that system. they are called nix and hydra.

incidentally, "134340 pluto" was never a moon of neptune. neptune did capture triton. this is why triton has a retrograde orbit

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 and according to the new definition for a planet, Pluto should not be a planet.

Bye bye Pluto..

Answer 4

pluto is a considered a planet

Answer 5

Because its orbit more closely resembles a comet, regardless of what it's made of. Its orbit is tipped out of the plane that other planets orbit in, and crosses within another planet's orbit. It seems to be an object that was captured by the sun's gravity rather than something formed as part of the solar system.

Answer 6

first of all it only became a planet because a man decided to call it a planet, then some other man came around and said no its not a planet anymore because its to small. so because some other man decided it was to small it is now a dwarf plantet.

Answer 7

for a body to be a planet,
~It should be big(atleast bigger than pluto)
~It should have an elleptical orbit(pluto has one)
~It's orbit should not overlap any other planets orbit(unlike pluto whose orbit overlaps, neptune)

if all these conditions are satisfied then it is a planet

Answer 8

yeah, and who gets to decide what a planet is? i think if something has a moon its a planet, ipso facto pluto is a planet.

Answer 9

Too small

Answer 10

its TINY...