How come Pluto is no longer labeled as a planet?

Question

I understand that it is "too small" but it still orbits our sun, it's still a part of our solar system. What is it labeled now? And who decides what's a planet or not? Who else was heartbroken when they announced Pluto of not being a planet?

Answer 1

I was sad too...but this is the reason.

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.

There are actually 40 other dwarf planets like Pluto in our solar system. If Pluto were to stay a planet, then we would have a whole bunch.


http://news.nationalgeographic.com/news/2006/08/060824-pluto-planet.html

Answer 2

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].

Answer 3

I believe it's now classified as a dwarf planet which, as far as I understand, is something that is between a planet and an asteroid.

Just because it orbits the sun doesn't meant something is a planet. There are thousands of asteroids in the asteroid belt that do the same thing. There are also rogue asteroids that aren't part of the belt that orbit the sun. Even Helley's Comet "orbit's" the sun.

The people who decide what is and isn't a planet are the astronomers at the International Astronomical Union who meet to decide such things and to standardize astronomical terms and such. They deemed Pluto to be a dwarf planet because, up until that point, the definition of "planet" was a bit iffy. Nearly anything that orbited the sun and was reasonably round could be defined as a planet and, since we keep finding things like that, we'd end up with hundreds, if not thousands, of "planets" so a firm definition had to be created. When it was, Pluto didn't meet the requirements.

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) the neighborhood of its own orbit of debris. Instead, they decided to classify it as a "dwarf planet".

There is a precedent for this. When Ceres was first discovered in 1801, it was considered to be a planet. After astronomers discovered several other objects in the same orbit, it was reclassified as an asteroid. And, in 2006, it was again reclassified as "dwarf planet" just like Pluto.

Neither Ceres nor Pluto have enough mass (gravity) to accrete all the junk from their orbits. They will be "dwarf planets" until we humans decide otherwise.

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

It is now a dwarf planet, based on a new definition created by the Internation Astronomical Union (IAU). The definition of planet now requires that an object not only orbit the Sun and have sufficient mass for gravity to pull it into a spheroidal shape, as Pluto does, but also that it must have "cleared the neighborhood of its orbit," which Pluto has not. Pluto shares its orbital space with a multitude of similarly sized objects. Pluto and many similar objects actually have orbital resonances with Neptune, which governs these cycles because it has cleared its neighborhood.

Answer 6

It is ridiculous what the IAU did just because they didn't want to categorize another planet. I was very sad when they announced Pluto as a dwarf, but now I reject their decision, because NASA, many people, and even the government of New Mexico refuse to take this seriously. Here is the proof:
1)Pluto is rounded by it's own gravity
2)It orbits the sun
3)It has an atmosphere
4)It has three moons of it's own
5)The IAU says pluto hasn't "cleared it's orbit", but neither has Jupiter, because it is surrounded by Trojan asteroids, what will they do next, call Jupiter a dwarf planet????

Eventually pluto's status will be restored!!

Answer 7

thers a new definition of a planet According to the new definition of a planet, 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.

Answer 8

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.

Answer 9

If pluto were as close to the sun as the earth is then it would grow a tail, that is why pluto is no longer labeled as a planet. Planets do not have tails, comets do!

As much as we like to keep traditions (like we have 9 planets in the solar system) science does not work that way! As our knowledge increases, new definitions are created, and according to the new definition pluto is no longer considered a planet, but is now considered a "dwarf planet"

Answer 10

There are three main conditions for an object to be considered a 'planet':

1. The object must be in orbit around the Sun.
2. The object must be massive enough to be a sphere by its own gravitational force. More specifically, its own gravity should pull it into a shape of hydrostatic equilibrium.
3. It must have cleared the neighbourhood around its orbit.

Pluto fails to meet the third condition