why do we have 8 planets?

Answer 1

The international astronomical union voted on their definition of planet and only 8 of our "planets" qualified. Pluto was "demoted" to a dwarf planet. A few asteroids (like Ceres) were "promoted" to a dwarf planet.

FROM THE IAU WEBSITE:
"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"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) shape2 , (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

(3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as "Small Solar-System Bodies".

1The eight "planets" are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.
2An IAU process will be established to assign borderline objects into either dwarf planet and other categories.
3These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.


IAU Resolution: Pluto

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."

Both of these Resolutions passed on August 24, 2006

Answer 2

Because those who define what a planet is, decided that the objects going in orbit around our sun meet their definition of what a planet is, without that definition we could have hundreds maybe thousands of things called planets in our solar system, so in order to bring order, we must have labels for everything, how about this from dictionary.com,
Planet,
a. Also called major planet. any of the nine large heavenly bodies revolving about the sun and shining by reflected light: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, or Pluto in the order of their proximity to the sun.

they changed that definition just recently and now Pluto is no longer a planet, that's why we have 8.

Answer 3

We have eight planets because some 70 years ago someone discovered a celestial body and found that it fit the definition of a planet, which happened to include that a planet has its own satellite, orbited around a sun, and reflected the suns light, they called it Pluto. Two weeks ago, people who believed they were smarter than the scientists of 70 years ago, decided to change the definition of planet and Pluto suddenly didn't qualify. If that is the case can I change the definition of scientist?

Answer 4

We have 8 planets, 1 dwarf planet, and 2 planetoids. The two planetoids are Charon, and Xena.

Answer 5

Define Planet for me first

Answer 6

Because scientists are stupid and have nothing else better to do than to screw with our little heads.

P.S. I still think Pluto is a planet! So, hah! I win!

Answer 7

Because now i'm going through Post Traumatic Stress Syndrome. Also scientology(lol 5) wants to make money off of having to resupply every school with new books!

Answer 8

because we don't have more than 8 or less than 8

Answer 9

Cause thats how many planets that are out there that everybody is claiming.

Answer 10

Because Pluto sucks