3 reasons why Pluto is not a planet

The reason why Pluto is not considered a planet anymore is because it does not satisfy the third requirement of being a planet, which is that it must have “cleared the neighborhood” of its orbit. This means that a planet must be the basic dominant gravitational body in its orbit, and Pluto is not. There are many objects similar to Pluto in and around its orbit, and Pluto is only about 0.07 times the mass of other objects in its orbit. In comparison, Earth has 1.7 million times the mass of other objects in its orbit.

A planet has to be the basic dominant gravitational body in its orbit, Pluto fails to meet this criteria, as there are many objects similar to Pluto in and around its orbit. Pluto is only about 0.07 times the mass of other objects in its orbit.

My (Mercury) Very (Venus) Educated (Earth) Mother (Mars) Just (Jupiter) Showed (Saturn) Us (Uranus) Nine (Neptune) Planets (Pluto). This rhyme helped countless middle school kids, including me, learn the names of the nine planets in our solar system, as well as their order in our solar system!

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However, that all changed in the year 2006, when the International Astronomical Union took away our beloved Pluto’s status as a planet. All the rhymes we had learnt were suddenly useless. Pluto, named after the God of the Underworld, was suddenly not a planet anymore.

Let us look at Pluto’s Journey, how Pluto ‘the planet’ was born, and how its planetary status was eventually taken away from it.

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Pluto: The Journey

Pluto was discovered by Clyde W. Tombaugh on February 18, 1930. At that time, Pluto was the smallest planet yet discovered, and it was also the farthest planet from the Sun. Pluto’s mass is 1.31×1022 kg. While this may seem large, it’s only about 1/500th of Earth’s mass. Pluto is also mostly made of ice and rocks. Pluto takes about 248 earth years to complete one revolution around the Sun.

Compared to other planets, Pluto’s orbit is highly eccentric, so for a period of 20 years, out of its 248-year orbit, it is closer to the Sun than Neptune. This last happened in January 1979, when Pluto crossed Neptune’s orbit. It remained within Neptune’s orbit until February 1999. This will not happen again before the year 2226!

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Pluto was comfortably rotating and revolving around its orbit as the tiniest and farthest planet from the Sun, and everything was going pretty good for Pluto. However, with more recent advancements in Science and Technology, scientists were able to find other celestial objects similar to Pluto that were also made up of ice and rocks.

This spelled trouble for Pluto, as this made it just just another member of the collection of large objects in the Kuiper Belt. The Kuiper Belt extends from the orbit of Neptune for roughly 55 astronomical units (55 times the distance of the Earth to the Sun). Astronomers estimate that there are about 70,000 objects similar to Pluto in the Kuiper Belt.

Astronomers continued discovering objects similar to Pluto in the Kuiper Belt, and while they were all smaller than Pluto, astronomers knew that it was only a matter of time before they found an object larger than Pluto.

This discovery happened in the year 2005, when Mike Brown and his team discovered an object named Eris, whose mass was larger than Pluto’s. At that point, Pluto’s status as a planet came under serious threat.

Year 2006: Pluto is Not a Planet Anymore

On August 24, 2006, the International Astronomical Union (IAU) passed two resolutions that revoked Pluto’s planetary status.

The IAU defined three requirements for an object to be considered a planet:

1) A planet should orbit around the Sun

2) It should be spherical or round in shape

3) A planet must have “cleared the neighborhood” of its orbit.

While Pluto satisfies the first two conditions, it does not satisfy the third condition.

Why Pluto is not a planet?

A planet has to be the basic dominant gravitational body in its orbit, Pluto fails to meet this criteria, as there are many objects similar to Pluto in and around its orbit. Pluto is only about 0.07 times the mass of other objects in its orbit. In comparison, Earth has 1.7 million times the mass of other objects in its orbit.

So, my friends, that was how Pluto’s planetary status came to an end after 76 years.

However, it’s not all bad news for Pluto, as astronomers have not forgotten Pluto. They have actually given it a new name – a “dwarf planet”. Dwarf planets are the objects that satisfy the first two conditions required to be a planet. At present, there are five dwarf planets, namely Pluto, Ceres, Haumea, Makemake and Eris.

While Pluto may not be a planet anymore, its discovery has helped astronomers know more about our solar system and the region outside it. Therefore, it’s unlikely that our beloved Pluto will be forgotten anytime soon. In fact, NASA has launched a space craft named “New Horizions” that will study the dwarf planet Pluto. It was launched on January 19, 2006, and is expected to fly by Pluto on July 14, 2015.

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References

  1. NASA
  2. University of California, Santa Barbara Science Line

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Isn’t that just terrible? One of our precious 9 planets is no longer considered a planet! When did that happen you ask? Way back in 2006. Since then, time and gain, there have been rumors regarding the restoration of its planetary status. But none of them are true. Pluto will never be a planet again. Why not, you ask?

In order to be classified as a Planet, the body must

  1. Orbit around the sun.
  2. Have enough mass so that its own gravity overcomes the rigid body forces and it assumes a spherical shape.
  3. Have a clear neighborhood, in its orbit around the sun,

Pluto is not a Planet because

  1. Pluto is a relatively round body, and also orbits the sun, but crossing Neptune’s orbit! Not very planet friendly!
  2. Being so small, it cannot clear its path and hence has a very busy neighborhood, thereby violating the definition of a planet.

According to the new definition of a planet which was coined in 2006, Pluto was demoted to the status of a dwarf planet!

Planet or not, we still love you Pluto!

3 Pluto Fun Facts

  1. Recent discoveries show that Pluto is the biggest of the dwarf planets.
  2. It is also called the “King of the Kuiper Belt”
  3. It is also one half of the first “Binary Planetary Sytem’, the other half being its biggest moon, Charon.

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Today’s Wonder of the Day was inspired by Allison from AL. Allison Wonders, “Why is Pluto not a planet?” Thanks for WONDERing with us, Allison!

By now you have probably heard that Pluto is no longer a planet. But why is that? What did it do to lose its status as the tiniest planet in our solar system?

American astronomer Clyde Tombaugh discovered Pluto in 1930. From 1930 until 2006, Pluto sat comfortably beyond Neptune as the ninth planet in our solar system.

In 2006, however, changes were made. The truth is, nothing about Pluto changed, but the definition of a planet did. Once these changes became official, Pluto no longer fit the definition of a planet.

According to new rules adopted by the International Astronomical Union, a celestial body must meet the following criteria in order to qualify as a planet:

  • A planet must be round.
  • A planet must orbit the sun.
  • A planet must have “cleared the neighborhood" of its orbit. This means that as a planet travels, its gravity sweeps and clears the space around it of other objects. Some of the objects may crash into the planet, others may become moons.

Pluto follows the first two rules: It is round, and it orbits the sun. It does not, however, follow the third rule. It has not yet cleared the neighborhood of its orbit in space. Because it does not follow this rule, Pluto is no longer considered a planet.

Don't feel too sad for Pluto, though. It has a new title — “dwarf planet." Dwarf planets are celestial bodies that only meet the first two criteria in the new definition of a planet.

Dwarf planets, like Pluto, have not yet cleared the neighborhoods of their orbits — and still have some cleaning to do if they will ever become "true" planets.

Pluto is in good company. There are currently five dwarf planets, but scientists expect more will be discovered over time.

Four of the dwarf planets — Pluto, Makemake, Haumea and Eris — are located beyond Neptune. The fifth dwarf planet, Ceres, lives in an asteroid belt between Mars and Jupiter.

Facts about Pluto:

  • Pluto is about the size of the moon.
  • It takes approximately 248 Earth years for Pluto to make one trip around the sun. Since astronomers discovered Pluto in 1930, it has not completed one trip around the sun. It still has more than 150 Earth years to go!
  • Pluto is so far away that it takes more than five hours for light from the sun to reach it. The sun's light reaches Earth in only eight minutes!