what are the reasons why pluto not considered as planet anymore?

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

Well for starters, Pluto is just too small. In the neighborhood where Pluto lives? Planets are supposed to be huge. The Jovian planets, Jupiter, Saturn, Uranus and Neptune are 20 to 300 times the size of the Earth, and Pluto is really small compared to the Earth, smaller than our Moon. Kind of stands out.

And Pluto is not made out the same material as the Jovians. The large planets are mostly gigantic spheres of gas, mostly hydrogen and helium. Likely there are no solid surfaces, only denser and denser gas all the way in. Pluto is a small solid world of methane, water, carbon dioxide and ammonia ices, maybe a little rock and with a just hint of atmosphere (that freezes out and falls as snow in her "winter").

And third, Pluto's orbit is the most eccentric (oval shaped) and the most tilted to the plane that the rest of the planets orbit in. Also, Pluto is locked in a resonance with Neptune's orbit and comes closer to the sun than Neptune sometimes.

There were theories that Pluto was a lost moon of Neptune but that was before we discovered she a has one large moon (Charon) half her size (pretty much, this system is a double planet) and recently two other teeny-tiney moons.

Pluto seems like she cant be an ejected moon-she must have formed on her own and seems to be part of an entire army of small icey-dwarf objects that circle just outside Neptune's orbit in what is known as the Kuiper belt. We have no idea of how many or how large these objects may be. NOT "planets" proper, hence the new term "dwarf planet" where Pluto is king.

BUT I still think Pluto should be called a planet because of historical reasons (discovered by an American, financed by Percival Lowell, Tombaugh's life story, etc).

Answer 3

The new rules for being a planet:

(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 (near spherical) shape; and
->(c) has cleared the neighborhood around its orbit;

There are many objects in the neighborhood of Pluto's orbit. These objects lie in The Kuiper belt which is basically a belt of comets and icy planets like Pluto -- Some are even bigger then Pluto!

P.S. It has nothing to do with size since Pluto is round ( the Moon could be a planet if it didn't orbit Earth), rather it's because Pluto belongs to an entire class of objects so that if Pluto was a planet so would many Kuiper belt objects.

Here's a transcript of NOVA Science NOW that discuses it with a video:

Answer 4

Recently astronomers have actually came up with a definition or a planet, or rather refined the privious definition. Before we thought that anything sperical in an orbit around the Sun was a planet. But now we know a bit more about the solar system and how its formed.

The orbits of planets lie in the plane of the solar system. Plane of a solar system is shaped like a frizbee, flat and circular. The direction perpendicular to it, is the axis around which the Sun spins.

Most planets orbits lie in that plane to within some degree. Pluto's orbit is tilted by 17.15 degrees to that plane. Compare that to other planets Mercury 7 degrees, Venus 3.39, Earth 0.00, Mars 1.85, Jupiter 1.30, Saturn 2.49, Uranus 0.77, Neptune 1.77. So the tilt or inclination of Pluto is more then twice as large as that of Mercury.

The orbits of most planets are nearly circular. However Pluto's orbit is elliptical to the point that it actually crosses inside the orbit of Neptune.

Pluto is small, with a diameter of 1,400 miles, Pluto is, by far, the smallest planet. Seven moons in the solar system are larger: Io, Europa, Ganymede, Callisto, Titan, Triton, and of course, Earth’s Moon. This leads us to believe that Pluto will eventually be swept up by Neptune.

We're also finding similar icy bodies beyond the planet of Pluto. It may be that Pluto is just largest of all those bodies.

Answer 5

Since its discovery in 1930, Pluto has been a bit of a puzzle:

# t'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.
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.

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.

Answer 6

Well, the main reason that Pluto was denoted from a planet to a minor planet was its size, orbit, and moon.

A. Size
- Pluto is 1/8 the mass of our Earth and smaller than our moon.

B. Orbit
- Its orbit takes it 248 years to rotate the sun.
- Its orbit is elliptical and comet shaped.

C. Moon - Charon
- Charon is almost 90% Pluto's size.
- Charon and Pluto rotate around each other (binary system).
- Not common in regular planets.

Answer 7

what's a Planet immediately? in accordance to the hot definition, an entire-fledged planet is an merchandise that orbits the sunlight and is sufficiently huge to are starting to be around by using strain of its very own gravity. as nicely, a planet has to dominate the community around its orbit. Pluto has been demoted by using fact it does not dominate its community. Charon, its large "moon," is in simple terms approximately 0.5 the dimensions of Pluto, on an identical time as each and every of the actual planets are some distance bigger than their moons. as nicely, bodies that dominate their neighborhoods, "sweep up" asteroids, comets, and different debris, clearing a course alongside their orbits. by contrast, Pluto's orbit is particularly untidy.

Answer 8

It's too small. It's smaller than other objects out there that aren't planets. But Pluto will always be a planet to me.

Answer 9

Poor Pluto =(

Answer 10

It is too small to be classified as a planet under the new rules.