Why is Pluto no longer consider as a planet ?

Answer 1

Essentially, because its orbit crosses with that of Neptune.

Answer 2

"On August 24, 2006 the IAU defined the term "planet" for the first time. This definition excluded Pluto, which was then reclassified under the new category of dwarf planet"

in other words:

an international group of scientists has decided that Pluto does not have some of the characteristics required for an object to be called a planet. this is a just a rule for classification purposes. Pluto is still Pluto. these scientists have just decided that Pluto must now be classified as a "dwarf planet".

Answer 3

Technically it was never a planet just an asteroid, in the Kuiper Belt. But in 2003 they discovered and asteroid bigger than Pluto in that Belt, and temporarily named it 2003ub313 so now Pluto is just a minor planet, just like the 4 unknown ones around the middle of our solar system. I know I'm sad Pluto is only a rock now but oh well. Hey, I know what the official name should be for 2003ub313, "The evil sucky rock that wiped out our favorite planet!" Also Pluto is smaller than the U.S.

Answer 4

Although Answer Champion's answer was comprehensive, it wasn't entirely correct. Few scientists argue that Pluto originated elsewhere than the Solar System. Rather, they mostly agree that it formed in the same way as other Kuiper Belt objects -- it is merely one of the largest (and by a long way the earliest discovered) of them. To answer the original question, the discovery of the full range of Kuiper Belt objects, including at least one object, Eris, larger than Pluto, was the actual stimulus for reclassifying Pluto.

[Also a physics PhD, who attended the IAU meeting at which the resolution was passed.]

Answer 5

Says who... pluto is considered as a planet. Apart from pluto ther a 2 more bodies revolving aroud the sun which are also considered as planets.

Answer 6

hy is Pluto no longer consider as a planet ?
Since its discovery in 1930, Pluto has been a bit of a puzzle:
It's smaller than any other planet – even smaller than the Earth's moon.
It's dense and rocky, like the terrestrial planets (Mercury, Venus, Earth and Mars). However, its nearest neighbors are the gaseous Jovian planets (Jupiter, Saturn, Uranus and Neptune). For this reason, many scientists believe that Pluto originated elsewhere in space and got caught in the Sun's gravity. Some astronomers once theorized that Pluto used to be one of Neptune's moons.
Pluto's orbit is erratic. The planets in our solar system all orbit the Sun in a relatively flat plane. Pluto, however, orbits the sun at a 17-degree angle to this plane. In addition, its orbit is exceptionally elliptical and crosses Neptune's orbit.
One of its moons, Charon, is about half Pluto's size. Some astronomers have recommended that the two objects be treated as a binary system rather than a planet and satellite.
These facts have contributed to the long-running debate over whether to consider Pluto a planet. On August 24, 2006, the International Astronomical Union (IAU), an organization of professional astronomers, passed two resolutions that collectively revoked Pluto's planetary status. The first of these resolutions is Resolution 5A, which defines the word "planet." Although many people take the definition of "planet" for granted, the field of astronomy had never clearly defined what is and is not a planet.

Here's how Resolution 5A defines a planet:

A 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, and (c) has cleared the neighbourhood [sic] around its orbit [ref].
Pluto is relatively round and orbits the Sun, but it does not meet the criteria because its orbit crosses Neptune's orbit. Critics of the resolution argue that other planets in the solar system, including the Earth, have not cleared the neighborhood around their orbits. The Earth, for example, regularly encounters asteroids in and near its orbit. Resolution 5A also establishes two new categories of objects in orbit around the sun: dwarf planets and small solar-system bodies. According to the resolution, 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, (c) has not cleared the neighbourhood [sic] around its orbit, and (d) is not a satellite [ref].
Small solar-system bodies are objects that orbit the Sun but are neither planets nor dwarf planets. Another resolution, Resolution 6A, also specifically addresses Pluto, naming it as a dwarf planet.
Not all astronomers support Resolutions 5A and 6A. Critics have pointed out that using the term "dwarf planet" to describe objects that are by definition not planets is confusing and even misleading. Some astronomers have also questioned the resolutions' validity, since relatively few professional astronomers had the ability or opportunity to vote.

Here's how the two resolutions classify the objects in orbit around our sun:

Planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
Dwarf planets: Pluto, Ceres (an object in the asteroid belt between Mars and Jupiter), 2003 UB313 (an object farther from the Sun than Pluto)
Small solar-system bodies: Everything else, including asteroids and comets

Answer 7

Because it is too small. In 1930 we though it was bigger than Mars. New measurements show it to be smaller than the Moon. Also, lots of other small objects have been recently discovered orbiting way out past Neptune. At least one of these objects is bigger than Pluto! Pluto rightly belongs in this newly discovered outer asteroid belt (called the Kuiper belt or just "Trans Neptunian Objects") than it does in the family of planets.

Answer 8

Scientists have recently changed the definition of a planet.

The heavenly body must be relatively spherical in shape, and it must be the largest body in "its neighborhood".

Pluto, a large ice chunk, is decidedly NOT spherical, but more potato shaped, and its supposed moon Charon (pronounced Kar-RONE) is larger.

Charon is now considered the planet, and Pluto is Charon's satellite, or moon.

Answer 9

Because the lazy, overpaid scientists of the world were sitting around one day, sucking on their 40th coffee of the day, when their wired, little cerebellums said to them,"HEY! I know what I can do to try to convince the peasantry of the earth that we're worth our hyperextended salaries that we're paid to make futile attempts to save the planet! We'll tell them that Pluto is no longer a planet and watch as the Plutonians of the earth fall into massive depressive states so we can conjure up a new idea to bilk more cash out of the pockets of the idiots who pay us now to incite them that we can find a new drug to treat Plutonian Depressive Syndrome! That's at least 10 years work and and a whole lot more starving people who could have benefitted from all that floating money! Quickly now, call CNN, this is NEWS!"

Or something like that...

Answer 10

The answer by "answer champion" is by far the best answer; and I am speaking as a Physicist (PhD in atomic and molecular Spectroscopy). His answer provides clear definitions and because of that should be voted the best answer. I know that when it comes to voting I will cast my vote for him.

Answer 11

Commies