Why is pluto not regarded as an actual planet?

Question

I just recently heard that pluto isn't a planet. Any suggestions as to why that is?

I would realy love to find out this answer. It would enhance my own understanding of the solar system I live in. Thanks for your help.

Answer 1

The International Astronomical Union decided that Pluto was no longer a planet. Instead, they decided to classify it as a "dwarf planet" because it has not cleared its orbit of debris.

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

Something less than 400 members of the 10,000 member IAU voted under a veil of assumed authority to downgrade Pluto's status as a planet after they rewrote the rule book. Most of the new criteria they established that must be met in order for an object to be considered a planet is met by Pluto. It orbits a star, it has a moon, and it is generally spherical in shape. The disqualifying new rule was that Pluto has not cleared its orbital path around the sun and there are other objects sharing the same orbit. This would mean that if another object enters or is found to exist in the same orbital path of the Earth, the Earth would not be a planet. The IAU also failed to take into consideration as to whether or not Pluto is in the process of clearing its orbital path and just needs a few billion more years.

Answer 3

http://en.wikipedia.org/wiki/Pluto

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

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 4

Until fairly recenty there was no objective definition of the word 'planet'. Basically it was just all the things that people had called planets, so this included Pluto.

But with additional planets being found outside our own solar system, and objects within our solar system larger than Pluto in solar orbit but not called planets, the astronomical community decided it was time to come up with an objective definition of the word (ie one based on the physical characteristics of the body in question, rather than historical usage).

What they found was that if you constructed a definition that included Pluto, it also had to include a lot of other rocks and we would probably end up with 50 or more planets.

This didn't seem very satisfactory and didn't seem to separate the major bodies in solar orbit from the many lesser bodies in a satisfactory way. So the compromise was to create a class of 'dwarf planets' (including Pluto and two others, but with lots of candidates waiting to be included) and keep the word planet for the eight major bodies.

('Minor planet' is something different again - this is the host of smaller chunks of rock bigger than 10m across. Anything smaller than that gets called a meteroid.)

Answer 5

It's far too small. technically it should never have been classed as a planet in the first place, but as it is the only one americans have ever discovered, they wanted it as a planet. Well now it's a dwarf planet, along with a few others that are out there.

Really, i think it was get rid of one 'planet' or classefy 2/3 more dwarf planets a proper planets, as the one after pluto is, I believe, larger.

Answer 6

Pluto was officially labeled the ninth planet of the Solar system by the ISU (International Astronomical Union) in 1930 but it was downgraded to a dwarf planet by in 2006 because it does not meet certain characteristics required to be a planet.

For more details visit the following site

http://www.solarviews.com/eng/pluto.htm

Answer 7

hi!
Pluto is now demoted as one of the planet or the ninth planet because of it's characteristics that inaccurate to a real planets characteristics. the first characteristic that a real planet should obtain is it's size and Pluto is just about a size of a moon. the other one is that a Pluto is too far to be recognize by it's neighborhood, and lastly, Pluto has no permanent orbits around the sun.

Answer 8

The planet Pluto is now considered a Minor planet because its not big enough to be officailly classed as a planet, the ateroids are considered minor planets too for some reason. and Pluto is just a barren rock too.

Answer 9

It was on tv this week in the uk.... its because of its size and they have found other things bigger in the same area and even our moon is bigger than pluto. If they did call it a planet still then all of saturns moons etc would have to be called planets.... hope that helps

Answer 10

It is still a "dwarf planet".

It now fails the new definition of a "classical planet", because it doesn't have sufficient mass to "clear the neighbourhood around its orbit".

However, some argue that the Earth, whilst massive, doesn't do this either ...