Why u believe that Pluto is not a planet ??

Question

Why u believe that Pluto is not a planet ?? and if it is due to annoucement of some community of scientist on what basis they have removed the honour of Pluto of being a planet.

Answer 1

It is not a question of believing, but just to adhere to the rules of the International Astronomical Union. It happens that the center of masses of Pluto and Caronte, its moon, is outside of the Pluto sphere.
I think it has been an unfair decision whith respect to USA people, for Pluto was the only planet discovered by US astronomers. But sometimes science needs to be hard, in order to clarify concepts.

Pluto is no more a planet, but a 'dwarf planet', as stated by a recent astronomers agreement (Praga IAU meeting, august 2006) to precisely define the terms of solar system bodies, now that a lot of are known and will be known thank to probes, telescopes, etc. Here down are the specs:

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.

RESOLUTION 5B
Insert the word "classical" before the word "planet" in Resolution 5A, Section (1), and footnote 1. Thus reading:

(1) A classical "planet"1 is a celestial body . . .

and
1The eight classical planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Answer 2

I've been an astronomy teacher for 20+ years, and I've always listed Pluto in the list of planets with a question mark next to it.
(Long before this recent IAU debacle which also decided to call asteroid Ceres a planet).

Why?
Because it had too many anomalies.

The inner planets are rocky
The outer planets are gas giants.
Pluto? An ice ball.

Planets have almost circular orbits near the ecliptic plane.
Pluto? Eccentric and inclined.

Planets' moons are small compared to the planet, or absent for the smallest.
Pluto? A small double planet.

Pluto's fate was sealed when the Kuiper Belt was found to have thousands of other ice balls out there, many bigger than Pluto.
(The Oort cloud theory of comets may be next to fall).

Pluto will always be an 'honorary planet' because it has a cool name and an interesting story behind it. It is still a planetary BODY, because it orbits the sun. But if we were totally impartial, the reasoning would be...

.. if we just arrived from another star system to map this Sol solar system, what would we report as planets?

The four inner rockies? - Yes
The four gas giants? - Definitely
The thousands of outer ice balls? - No
The thousands of planetary asteroids in the middle? - No

Not that difficult is it?
So why did the the IAU take so long arguing about it and why did they STILL get it wrong??

Answer 3

Currently, the definition of a planet (as opposed to an asteriod or a TNO) is rather arbitrary. If astronomers reach a consensus on what the defintion of a planet should be, then IAU may reclassify some Solar System objects. However, in the absense of such a consensus, the definition is historical and arbitrary; moreover, many people outside the professional astronomy community have an interest in this issue, as the media attention attests. "Until there is a consensus that one of the physical definitions is clearly the most useful approach in thinking about the solar system, the IAU will not 'demote' Pluto or 'promote' Ceres," says the IAU.


thats why

Answer 4

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 5

The community which honoured Pluto as planet dishonoured Pluto later.

Answer 6

The main reason is that Pluto do not revolve in orbit like other planets it cuts through the orbit of Neptune may be it is a moon of planet Neptune.It is also smaller in size than other planets.But this is not a concrete reason.

Answer 7

Pluto is not a planet because it is too small, it has a very elliptical orbit, and there are objects bigger than it beyond its orbit. Pluto was never a planet. People called it a planet because they did not know about the Kuiper Belt.

Answer 8

It's not just because Pluto is small. They removed Pluto as a planet because it's orbit is irregular. When it gets too close to neptune, it gets sucked in and its orbit changes. It revolves around neptune instead.

Don't worry though, because it is now honoured as a moon.

Answer 9

The distant, ice-covered world is no longer a true planet, according to a new definition of the term voted on by scientists today.


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Virtual Solar System
Pluto's New Moons Named Nix, Hydra (June 23, 2006)
Pluto to Get Partners? New Definition of "Planet" Proposed (August 16, 2006)

"Whoa! Pluto's dead," said astronomer Mike Brown, of the California Institute of Technology in Pasadena, as he watched a Webcast of the vote. "There are finally, officially, eight planets in the solar system."

In a move that's already generating controversy and will force textbooks to be rewritten, Pluto will now be dubbed a dwarf planet.

But it's no longer part of an exclusive club, since there are more than 40 of these dwarfs, including the large asteroid Ceres and 2003 UB313, nicknamed Xena—a distant object slightly larger than Pluto discovered by Brown last year.

"We know of 44" dwarf planets so far, Brown said. "We will find hundreds. It's a very huge category."

A clear majority of researchers voted for the new definition at a meeting of the International Astronomical Union (IAU) in Prague, in the Czech Republic. The IAU decides the official names of all celestial bodies.

The tough decision comes after a multiyear search for a scientific definition of the word "planet." The term never had an official meaning before.

What Is a Planet Today?

According to the new definition, a full-fledged planet is an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, a planet has to dominate the neighborhood around its orbit.

Pluto has been demoted because it does not dominate its neighborhood. Charon, its large "moon," is only about half the size of Pluto, while all the true planets are far larger than their moons.

In addition, bodies that dominate their neighborhoods, "sweep up" asteroids, comets, and other debris, clearing a path along their orbits. By contrast, Pluto's orbit is somewhat untidy.

The new definition of "planet" retains the sense that a true planet is something special.



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Virtual Solar System
Pluto's New Moons Named Nix, Hydra (June 23, 2006)
Pluto to Get Partners? New Definition of "Planet" Proposed (August 16, 2006)

"It's going to be hard to find a new planet," Brown said. "You'd have to find something the size of Mars. Finding a new planet will really mean something."

Raising the Bar

A previous proposal, unveiled last week, would have set the bar for planethood considerably lower.

The earlier proposal also required planets to be round as a result of their own gravitational force. But it did not specify that a planet has to dominate its region, and that omission would have granted planet status to a lot of bodies.

Last week's proposal would have kept Pluto as a planet. But it also would have upgraded Charon to a planet in its own right. The proposal would have made full-fledged planets of 50 or more additional objects, including Ceres and 2003 UB313.

"Astronomers, who are normally mild-mannered types, are revolting against the IAU proposal," Brown wrote on his Web site last week, soon after the initial unveiling.

In response, the IAU committee charged with composing the definition "reversed course completely, and offered up a definition that's much more scientifically palatable," said astrophysicist Alan Boss of the Carnegie Institution in Washington, D.C., today.

"They reworked it and it has become a much superior definition. I think this will stand the test of time," Boss said.

Disgruntled

But for now the vote is drawing some opposition. Planetary scientist Andy Cheng said the definition is ambiguous, because it hasn't answered the question "how round is round?"

"This will be an issue in the future," Cheng said. "Dozens of objects are going to be straddling this line. The new definition is not going to help us with this."

"I'll still continue to maintain that Pluto is a planet," he said.

Owen Gingerich is an astronomer and historian at Harvard University in Cambridge, Massachusetts, and head of the IAU committee proposing the definition. He favored a special distinction for Pluto.

Gingerich supported a proposal to call the big eight planets classical planets—as opposed to just plain "planets"—and Pluto and the others dwarf planets, so there would be two classes of planets.

"This would have been much more sensible," Gingerich said.

The IAU members overwhelmingly rejected this idea.

"I think they voted primarily on scientific grounds and were not sensitive to the historical and cultural role that Pluto has played," Gingerich said.

The definition that won the vote is "a bit of a semantic atrocity," he added.

The definition was bound to be messy. It had to be palatable to many researchers and to address the plethora of celestial objects.

But most IAU members agreed that a line should be drawn somewhere to separate the largest bodies from what might be called the riffraff of our solar system.


Not Universal

Last week's proposed definition was meant to apply to all planets in the universe. But, faced with the difficulty of arriving at a consensus on universe-spanning criteria, the IAU committee narrowed the definition to apply only to our solar system.

Richard Conn Henry is an astrophysicist at Johns Hopkins University in Baltimore, Maryland. He says he never considered whether Pluto should be a planet until a few years ago.

But when the planetarium at New York City's American Museum of Natural History removed Pluto from the ranks of the planets, it got him thinking.

"This tiny thing in this oddball orbit—a planet? Give me a break!" Henry said.

"I think that, when the dust settles, people will recognize that there really are just eight planets."

Answer 10

Pluto is a cartoon dog created by Walt Disney it's
Master is Mickey Mouse.