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Why Is Pluto Not a Planet? What Is a Dwarf Planet?

By Shiwani PandeyOctober 30, 2022
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Pluto: Not a Planet but a Dwarf Planet

Growing up, we were told in our Science class that there are nine planets in the Solar System. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto constituted the planets of the Solar System and that is what we knew. In fact, we had even made different acronyms to remember the names of the planets. For a very long time, Pluto has been considered to be the youngest sibling amongst all the giant and big planets that are currently in our Solar System. But now, there are only 8 planets in the Solar System. So, why is Pluto not a planet? Read on ahead to find out more about it right now!

The Latest Photo of Pluto


The Latest Photo of Pluto

For those of you who don’t know, Pluto is now considered to be a dwarf planet. This planet is about 3.6 billion miles away from the sun and is silently revolving in the orbit that it has had for all these years. Of course, it is a completely lonely planet with no visitors and nothing to entertain. For sure, Pluto was once a part of the Solar System we have. It is etched in all the planetariums and science books for the students. However, this limelight for Pluto wasn’t for the long term. In just 76-80 years of gaining the reputation as a planet, this designation was taken away from Pluto. Read why Pluto is not a planet essay to get into more details.


A Little about the History of Planet Pluto

If you recall what you read about Pluto, it was discovered in the year 1930 and named ‘Planet X’. Clyde Tombaugh, an American astronomer is the person behind the discovery of Pluto. After its discovery, Pluto managed to gather a lot of popularity during that era. Not to mention Pluto also received more than 1000 different proposals for the nomenclature. However, in the end, the name Pluto was chosen after the Greek god in the Underworld. A schoolgirl living in England ended up naming the planet. After that, it was all sun and stars for Pluto as the planet managed to gather a lot of attention.


However, this planet was always under the scrutiny of different experts in terms of the mass that it had. After the initial calculations were made, the mass of Pluto was actually considered equivalent to the mass of Earth. However, following that in the year 1948, it was made aware that the mass of Pluto was equivalent to the mass of the Mars planet.


Finally, after the discovery of the largest Moon of Pluto, Charon, in the year 1978, the true mass of Pluto was known to people. It turns out that the mass of Pluto was actually just 0.2% of Earth’s mass. This is one of the top 10 reasons why Pluto is not a planet any longer. As soon as the astronomers heard the fact, they started building their doubts as well. 


Profile of Pluto 

Before jumping into the question of why is Pluto no longer a planet, let us learn a little bit more about Pluto and its profile. As we have mentioned before, the revelation of the mass of Pluto actually caused quite a stir in space studies. However, things still remained calm and composed. The situation was like that until the outbreak of other observatories and space-based technologies. In the year 1992, the Kuiper Belt was discovered. It is basically a collection of different celestial bodies that extend from Neptune’s orbit to 55 different astronomical units. So, Pluto was a part of that belt. Also, it was estimated that there are about 70000 different icy bodies that have the same composition that Pluto has.


In fact, the size of these objects turned out to be pretty close to that of Pluto. Hence, questions regarding the status of Pluto as a planet started coming up in discussions. Things finally exploded in the year 2005 with the discovery of Eris, a trans-Neptunian object. Eris was substantially larger than Pluto and the size of the object was a bit bigger as well. Also, the orbit of the object was pretty much the same size if not bigger than that of Pluto’s. 


Due to this controversy, the General Assembly of the International Astronomical Union was held in the year 2006. This union led to the establishment of ground rules for certain celestial objects to be classified as a particular planet. There were three conditions laid down for the objects to be considered planets. Firstly, the object should be in an orbit that is around the Sun. Secondly, the object is supposed to have sufficient gravity in order to pull itself into a spherical shape. The third condition was that the object should have ‘cleared the neighbourhood’ of the orbit that it has. 


Unfortunately for Pluto, the third condition wasn’t met. This condition basically meant that the object has to be properly and gravitationally dominant in the orbit. Either it should push or consume the other objects that are on the way. Unlike the other planets, the mass of Pluto was 0.7 times the mass of different objects that were in its orbit. Hence, Pluto wasn’t able to qualify in order to become a planet. However, the one good thing was that the objects that qualified the other 2 criteria mentioned in the rules would be qualified to be called a Dwarf Planet. Hence, our supposedly 9th planet of the Solar System earned the name tag of a Dwarf Planet. 



With time Eris was considered to be the largest of the dwarf planets due to the relative brightness that it has. However, after some calculations and studies, it was declared that the diameter of the object is smaller, making Pluto the largest dwarf planet in the Solar System. So, now you know why Pluto is no longer considered to be a planet. What do you think about the conditions? Do you think these are fair conditions and based on practical thinking and research? Or do you just miss calling Pluto the ninth planet of our Solar System? Think for yourself! Also, head over to our website for other interesting blogs and enhance your knowledge.