The Fate of Pluto

Hi friends... I have finally started a blog as requested by my friends. Since this is my first topic I have decided to share my knowledge on my favorite topic Astronomy, and in astronomy this is the topic which is discussed most in recent times.


As soon as you read the word 'Pluto' the questions that arises in your mind is ‘Why is Pluto removed from the list of planets? And is it a right decision?’ Some of us think it's crap but some think the decision is absolutely right. And I'm one of them. In fact I was expecting something like this to happen for a year as Pluto is different from other planets in many ways.

Before discussing on why Pluto was removed from the list of planets let us know some of the details about Pluto...

Pluto was discovered by Clyde W. Tombaugh in 1930. It was known as the smallest planet. Its distance from Sun is 5870 x 10⁶ km. Its diameter is about 2,301 km. In fact Pluto is smaller than our satellite ‘Moon’ whose diameter is about 3,474 km. In 1978 Pluto was discovered with a satellite moving around it named Charon. And in 2003 astronomers discovered two more satellites moving around Pluto which was named Nix and Hydra.

Now let us see some of the details of Charon...

Charon was discovered in 1978 by James Christy. Its diameter is about 1,207 km which is more than half the size of Pluto. Its mass is about 1/7^th the mass of Pluto. It is the largest of the three satellites of Pluto. But since Pluto is no longer considered as a planet Charon is also not considered as a satellite. It was the discovery of Charon that began to change the fate of Pluto. The picture on the right is the artistic view of Charon from the surface of Pluto.

Since 2003 many more objects were discovered beyond the orbit of Neptune like Sedna, Quaoar, Orcus, Varuna, 2005 FY9, etc. and most of them were almost the same distance from Sun as Pluto. Some of them were almost the size of Pluto. In 2005 a new object was discovered ‘2003 UB313’ which was nicknamed as Xena and now officially called as Eris (in the left). Its diameter was found to be 2400 km which is slightly bigger than that of Pluto. And this discovery put an end to the journey of Pluto as a planet. The odds in the character of Pluto put together with these discoveries led to removal of Pluto from the list of planets.

Now let us see what are the odd characters found in Pluto.

1. Let us assume that the orbit of the Earth is horizontal. If we compare the inclination of the orbits of the other planets with that of Earth it is found that the planets other than Pluto were found to incline at an angle between 1° and 7°. But the inclination of Pluto was found to be 17.2°.

2. If we look at the orbit of Pluto it is found to draw within the orbit of Neptune for a time span of twenty years between 1979 and 1999 i.e. Pluto acts as the eighth planet for a time span of twenty years. This is clearly shown in the picture on the top. This type of behavior is not found in any other planet.

3. You can find huge gap between any two planets. For example the distance between Earth and Venus is 49.4 x 10⁶ km and the distance between Earth and Mars is 78.3 x 10⁶ km. All you find in between this gap is our satellite ‘Moon’. But as I said earlier many objects were discovered around the orbit of Pluto. These objects cannot be the satellites of Pluto as some of them were larger than Pluto itself.

4. A Satellite is an object that revolves around a planet just like a planet around a star. According to the Law of Gravitation the centre of gravity between a satellite and a planet should be approximately found in the centre of the planet which makes the satellite move around the planet in an orbit. If we compare the size of Pluto and Charon it is found that Charon is more than half the size of Pluto. By the Law of Gravitation the centre of gravity between these two masses will be approximately found in between the two objects. Which means that Charon does not revolve around Pluto but Pluto and Charon revolve around each other. Once again Pluto does not abide the rules of the Planet.

These are only few of the reasons that makes Pluto different from other planets and the astronomers had no choice but to remove Pluto from the list of Planets. All the objects which are beyond the orbit of Neptune are now considered as 'Trans-Neptunian Objects' (TNO) which include Pluto, Eris and other recently discovered objects. (The picture on the top is a comparison of the size of TNO's with that of the Earth and the Moon) The larger TNO's such as Pluto and Eris are considered as 'Dwarf Planets'. The eight largest TNO's are compared in the picture below.

And thus according to me removing Pluto from the list of Planets is the right decision. After all these there are still many unanswered questions put up about Pluto’s behavior and also about the Trans-Neptune Objects (TNO) which I believe may be found in the years to come.