Is Pluto a planet?

Question

....or did it get decided that it isn't?

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

The international astronomic union has introduced a new class of object called "Dwarf Planets" to which Pluto belongs. So Pluto is no longer a planet. It has been degraded to "dwarf planet". The reason is that there are plenty of other rock pieces like Pluto flying around in the outer parts of our solar system (one of them called "Eris" is even bigger than Pluto) and also between Mars and Jupiter by the way (the asteroid belt). There is really no good reason why Pluto should have a special status over all the others just because it was discovered first so I think they have taken the right decision. The only logical alternative would be to call every piece of rock orbiting the Sun for a planet, but then the term would completely loose its meaning.
More info:
http://en.wikipedia.org/wiki/Dwarf_planet

Answer 3

It's a minor planet, or Kuiper belt object (KBO). They recently revised the definition of planets to a more strict definition because they began finding more and more objects in the outer reaches of the Solar System (the Kuiper belt) that were around the borderline between a large asteroid and a very small planet. So, instead of increasing the number of planets to 12 now and continually increasing in the future, they reduced it to eight which will likely not change.

Answer 4

They decided that Pluto is NOT a planet!!!

Answer 5

It was demoted, poor thing. It's now just a space rock. If you know a good planet therapist, Pluto probably could use one. :-(

Answer 6

Not anymore. Debate stemmed from their discovery of the tenth planet.

Answer 7

scientist are sayin that is not and that makes me mad cause i grow up thinkin that there's 9 planets in our solar system and now they tell me that there's only 8

Answer 8

Not a planet, I do think that they named it a moon.

Answer 9

they decided it wasn't but will always be a planet to me

Answer 10

no its not a planet anymore.