Why was the planet Pluto no longer considered a planet in our solar system?

Question

and who determined this...and made it official ?

Answer 1

the international astronomical union voted on 24 august 2006 to adopt the following definitions of "planet", "dwarf planet", and "small solar system body" so pluto is not a planet. this does not change anything about the solar system or pluto. it just corrects the mistake of classifying pluto as a planet initially. some consider pluto and charon to be a binary system, but two small bodies orbit this system. they are called nix and hydra.

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

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

this same thing has happened before. beginning in 1800, astronomers found a few bodies orbiting between the orbits of mars and jupiter, and they finally stopped calling them planets after several discoveries. astronomers then added numerals to the names, and pluto recently got its numeral. 150 years from now, no one will think of "134340 pluto" as a planet. very few will even know we classified it as a planet. "1 ceres" and "136199 eris" are other dwarf planets.

i have been waiting for this since i was about twelve. i feel somewhat satisfied. i knew that pluto didn't fit the pattern set by the major bodies in the solar system so it was an anomaly. it just felt illogical and "out of place". this was the right thing to do, believe me. i don't understand why so many are having such a problem with this.

i don't know how long this will drag on tho. many planetary scientists are not satisfied that the definition is rigorous enough.

Answer 2

When Pluto was discovered it was called a planet because that's what they were looking for and there was no reason to call it anything else. Because of its wildly eccentric orbit most astronomers considered it an escaped moon of Neptune rather than a planet, but the distinction didn't matter and in popular parlance it was considered a planet. However, in the past few years a number of other bodies have been discovered in the outer reaches of the Solar System, some as large as Pluto. With many more expected to be discovered. So astronomers had a problem, were these all planets? Did we want a Solar System with dozens of planets, all but the inner eight frozen lumps orbiting in the outer reaches of the Solar System? So they decided to come up with an actual scientific definition of planet to distinguish the eight main planets from all the other stuff orbiting out beyond Pluto. And since Pluto clearly had more in common with all these outer bodies, it as classified along with them as dwarf planet. Basically astronomers were just correcting an old mistake, Pluto should never have been considered a planet in the first place. It's not the first time this has happened, for many decades in the nineteenth century several asteroids were called planets. Eventually astronomers realized they were too small to be considered planets and classified them as asteroids. This is how science works, old mistakes are corrected as our knowledge increases. The reclassification of Pluto is a good example of how that happens.

Answer 3

International Astronomical Union are the people who make these decisions and pluto was declared a dwarf planet

The 2006 redefinition of "planet" by the International Astronomical Union (IAU) states that, in the solar system, a planet is a celestial body that:

is in orbit around the Sun,

has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape,
and
has "cleared the neighborhood" around its orbit.

A non-satellite body fulfilling only the first two of these criteria is classified as a "dwarf planet",

Answer 4

There are three main conditions for an object to be called a 'planet', according to the International Astronomical Union (IAU) resolution passed August 24, 2006.

The object must be in orbit around the Sun.
The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should pull it into a shape of hydrostatic equilibrium.
It must have cleared the neighborhood around its orbit.

Pluto fails to meet the third condition and was demoted.

Answer 5

I'm guessing you were too lazy to look it up and read the answers to the other 100 people who already asked this question in the last 2 months? Use the search feature, it's handy!

It's a dwarf planet now. It's still out there. Along with 100's of similar sized objects past the orbit of Neptune.

Astronomers, they voted on it after much debate and it's still under review.

Answer 6

According to the scientsts, they think that Pluto is too small to be a planet. They think that Pluto is a moon itself with few moons at its side.

Answer 7

it is too small as compared to other 8 planets so it is no more considered as a planet

Answer 8

Because it does not clear the neighbourhood around its orbit.

Answer 9

It's too small.