Pluto was dropped as a planet because of the fact that it did not pass one of the major criteria made by the General Assembly of the International Assembly of Astronomers Union. Discovered in the 1930s by Clyde Tombaugh, it has a diameter of 2,400 kilometers. Charon is classified as a moon of Pluto.  Pluto has 2 smaller moons, Nix and Hydra, discovered in 2005.

Pluto is found in the Kuiper Belt. In comparison to the Earth's moon, it only is a fifth of its mass and its volume, only a third of it. In addition, it has a very inclined orbit of 30 to 49 astronomical units that makes it come close to the sun more than Neptune can. Considered the smallest of all the planets before it was dropped in the list, its composition is made up of rock and ice.

Since it was first discovered in 1930, it was reclassified in 2006 because of criteria that were made by the International Astronomer's Union or AIU in August 24, 2006. This brought the whole union to define the name "planet" for the first time. There is a debate and the union has come up with the list of criteria that was responsible for dropping Pluto of the list.

• It has to be in orbit around the sun.
• it has to have a gravitational pull so it can maintain its spherical shape.
• It has to "clear the neighborhood" when in orbit.

Pluto passed the first and the second condition but failed the third. In comparison to Earth which has 1.7 million times of gravitational pull, Pluto only has a mass of 0.07 times of the other objects that fall in its orbit, making it a dwarf planet.

This reclassified Pluto's planet status. As a result, many protested its reclassification. The House of Representatives of New Mexico even proposed a bill to celebrate Pluto Planet Day in March 3, in commemoration of Tombaugh's discovery of the planet. There were also others that shared the sentiments of others stating that Pluto will remain a planet despite the IAU's decision.