Why is Pluto not considered to be a planet?

Answer 1

Its not that Pluto isn't considered a planet anymore. Pluto is just considered a dwarf planet.

Answer 2

Its not that Pluto isn't considered a planet anymore. Pluto is just considered a dwarf planet.

Answer 3

Pluto is not a planet because it doesn't meet the necessary requirements needed to be a planet. It is now called a Dwarf Planet: A body in space, not an asteroid nor a comet.

The requirements to be a regular planet are:

1. It needs to be in orbit around the sun--Yes, Pluto does orbit the sun.

2. It needs to have enough gravity to pull itself into a spherical shape -- Pluto has sufficient gravity to have become spherical. (This is called hydrostatic equilibrium, by the way.)

3. It needs to have "cleared the neighborhood" of its orbit -- Uh oh. Here's the "problem" with Pluto. According to this IAU rule, Pluto is not a planet. Clearing the neighbourhood means that a planet needs to have enough gravity to pull or push object away from or towards it.

We see the "rule violation" that has arisen, but what does "cleared its neighborhood" mean? As planets form, they become the dominant gravitational body in their orbit in the Solar System. As they interact with other, smaller objects along their orbital path, they either consume them or sling them away with their gravity. Pluto is only 0.07 times the mass of the other objects in its orbit. The Earth, in comparison, has 1.7 million times the mass of the other objects in its orbit.

Any object that doesn't meet this 3rd criterion is considered a dwarf planet. And that makes Pluto a dwarf planet. There are still many objects with similar size and mass to Pluto jostling around in its orbit. And until Pluto crashes into many of them and gains mass, it will remain a dwarf planet. Eris suffers from the same problem.

It's not impossible to imagine a future, though, where astronomers discover a large enough object in the distant Solar System that could qualify for planet-hood status. Then our Solar System would have 9 planets again.

Even though Pluto is a dwarf planet, and no longer officially a planet, it'll still be a fascinating target for study. And that's why NASA has sent their New Horizons spacecraft off to visit it. New Horizons went past Pluto in July 2015, and it captured the first closeup images of the (dwarf) planet's surface.

Space enthusiasts will marvel at the beauty and remoteness of Pluto, and the painful deplaneting memories will fade. We'll just be able to appreciate it as Pluto, and not worry how to categorize it. At least now you know why Pluto was demoted.

Pluto is not considered a planet because it shares its orbital neighbourhood with many other icy debris called the Kulper Belt Objects (KBOs) , so it fails to comply with one of the criteria for a planet to be a planet thatb was established in 2006.

Answer 4

Pluto is not a planet because it doesn't meet the necessary requirements needed to be a planet.

The requirements are:

1. It needs to be in orbit around the sun--Yes, Pluto does orbit the sun.
2. It needs to have enough gravity to pull itself into a spherical shape -- Pluto has sufficient gravity to have become spherical. (This is called hydrostatic equilibrium, by the way.)
3. It needs to have "cleared the neighborhood" of its orbit -- Uh oh. Here's the "problem" with Pluto. According to this IAU rule, Pluto is not a planet.

We see the "rule violation" that has arisen, but what does "cleared its neighborhood" mean? As planets form, they become the dominant gravitational body in their orbit in the Solar System. As they interact with other, smaller objects along their orbital path, they either consume them or sling them away with their gravity. Pluto is only 0.07 times the mass of the other objects in its orbit. The Earth, in comparison, has 1.7 million times the mass of the other objects in its orbit.

Any object that doesn't meet this 3rd criterion is considered a dwarf planet. And that makes Pluto a dwarf planet. There are still many objects with similar size and mass to Pluto jostling around in its orbit. And until Pluto crashes into many of them and gains mass, it will remain a dwarf planet. Eris suffers from the same problem.

It's not impossible to imagine a future, though, where astronomers discover a large enough object in the distant Solar System that could qualify for planet-hood status. Then our Solar System would have 9 planets again.

Even though Pluto is a dwarf planet, and no longer officially a planet, it'll still be a fascinating target for study. And that's why NASA has sent their New Horizons spacecraft off to visit it. New Horizons will reach Pluto in July 2015, and it will capture the first closeup images of the (dwarf) planet's surface.

Space enthusiasts will marvel at the beauty and remoteness of Pluto, and the painful deplaneting memories will fade. We'll just be able to appreciate it as Pluto, and not worry how to categorize it. At least now you know why Pluto was demoted.

Pluto is not considered a planet because it shares its orbital neighbourhood with many other objects, so it fails one of the criteria for a planet established in 2006.

Answer 5

Pluto is not considered a planet because it has not cleared its orbit of other debris, which is one of the criteria for being classified as a planet. Additionally, its small size and composition more closely resemble that of other dwarf planets in the Kuiper Belt rather than the eight planets in our solar system.

Answer 6

It doesn't meet the established criteria for a planet.

The definition of "planet" set in 2006 by the International Astronomical Union (IAU) states that in the Solar System a planet is a celestial body that:

1. is in orbit around the Sun,
2. has sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and
3. has "cleared the neighborhood" around its orbit.

Answer 7

Just a few years ago, in 2005, the celestial body slighly more massive than Pluto, now called Eris, was discovered with a mean distance from the sun of about 9 billion miles, or roughly three times that of Pluto which up to that time was considered the ninth and most distant planet. Originally designated by NASA as the tenth planet, this designation was troublesome to many astronomers, considering that two other similar bodies also more distant than Pluto and only slightly less massive were discovered about the same time: Makemake and Haumea. Concerned about the possible proliferation of "cheap planets", it was quickly decided that these new trans-Neptunian bodies, along with Pluto, would not be considered "planets", but rather a new category was devised for such objects: "dwarf planet", which would include the inner solar system asteroid Ceres (located between Mars and Jupiter) and maybe a small handfull of other similarly located asteroids. To distingusih these trans-Neptunian dwarf planets from large inner solar system asteroids, the Trans-neptunian dwarfs were further given the nomenclature of "plutoid". Operating under the logic of "If it's good enough for Eris, it's good enough for Pluto", Pluto was thus demoted to being a "plutoid" rather than a true "planet".

The definition of something large enough to be considered a "dwarf planet" is that it must not orbit another planet (which would make it a moon), but it also must be massive enough so that it assumes a roughly spherical shape. To be considered to be a true planet, the body must not only be roughly spherical, but also of sufficient mass to have cleared out its orbit of other debris, which the asteroid Ceres and the four known "plutoids" have not.

Answer 8

Pluto is way to small to be a planet.Now we have 8 planets in our solar system not 9.Pluto is much smaller then earths moon!If Pluto was just a little bit smaller then Mercury, it would be a planet, but Pluto is TINY compared to mercury.

Answer 9

Short Answer:

Pluto was reclassified in 2006 by the International Astronomical Union. It is now called a minor planet or dwarf planet because we now know much more about our solar system and Pluto's character and make up than we did when it was discovered in 1930. It turns out there are many of these small icy objects like Pluto out there, some larger than Pluto, and if one did not have a good definition of the term "planet" then one would have thousands of "planets" that consist of objects in the Kuiper Belt. (The Kuiper Belt is like the asteroid belt but further out and mostly icy objects further away than Neptune.) Ultimately, this is a matter of classification, not basic science, so the validity of the classification can be a matter of debate.

Longer Answer:

Pluto is a minor planet; it's just no longer considered a major planet. It orbits a star, and its gravity has formed it into spheroid shape. These are requirements that major planets must meet. However, it has not cleared its neighborhood of debris. During the formation of the planets, the materials in the original accretion disk began to clump and clot, eventually leaving one very big clump within an orbital region. Earth is the big clump in our orbit, and there are no other large bits of debris left around us. Adjacent planets are not debris; they have stable orbits far enough away that do not allow for the planets to collide.

Pluto is odd in several ways. It spends most of its time far out in the Kuiper Belt, a region of objects similar to asteroids, but that are "volatiles" rather than rocky. They are made of ices of methane, ammonia and water. Pluto is there now. Since the vast majority of its time is spent in the Kuiper Belt, it hasn't really cleared its neighborhood of debris. The Kuiper Belt probably contains more than 70,000 objects. Many are obscured from view by the disk of the Milky Way. Pluto is sometimes called a Kuiper Object. Pluto's orbit also brings it within the orbit of Neptune for 15-17 years of its 248 year orbit. There is no pair of major planets in our system that has that configuration. So one might argue: If there is a piece of debris near Neptune's orbit, namely Pluto, doesn't this disqualify Neptune from being a planet? It hasn't cleared its neighborhood of debris. The answer is that Pluto and Neptune have a precise harmonic relationship; two orbits by Pluto equal 3 orbits by Neptune. And the orbit of Pluto is such that it can never collide with Neptune. So Pluto is not an object that can ever be cleared by Neptune. Because of the harmonic relationship, some suggest that Pluto is really a moon of Neptune.

Here is some trivia: Pluto is not the only Kuiper Object that orbits within Neptune's orbit-- there are others, and they have the same harmonic relationship with Neptune! Also, no one alive today will be around the next time Pluto is closer to us than Neptune. That won't happen until the year 2231.

So Neptune is a major planet, and Pluto, the Kuiper Object, is a minor or dwarf planet. Pluto is still there; it hasn't been banished from the solar system. We can still explore it and learn from it. We can enjoy the thought of it, and let it fire up our imaginations. It's just not a major planet.

Answer 10

1) 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.

2) 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.

3) Pluto is also on the borderline of a region in our Solar System known as the Kuiper Belt where many icy bodies (both big and small) orbit the Sun at a very large distance.