In the end around 2700 astronomers agreed that the solar system be divided into two categories called 'Planet' and 'Dwarf Planet'. Pluto being put in the category of 'Dwarf Planet' that means it will no longer be placed in the company of eight planets viz. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. A new distinct class of objects called 'Dwarf planets was decided with Ceres, Pluto and 2003 UB313 (temporary name) being the first three members of this club.
When Pluto was discovered, in 1930 astronomers assumed that it had a mass comparable to Earth's. Only gradually, in the ensuing decades, did celestial mechanicals come to realize that this grossly overestimated. Pluto turned out to be less than 1% of Earth's size.
With the advent of powerful new telescopes on the ground and in space, planetary astronomy has gone though an exciting development over the past decade and we are bound to find many more dwarf planets in future, if we continue placing them all in the list of 'Planets', in the company of Earth moon then we'll doing injustice to this elite club members having such distinctive features as life, air, water, atmosphere etc.
Astronomy, the branch of physics studying celestial bodies, gives room for improvements and evolutions with newer discoveries. Since the time in 1930 when Clyde Tombaugh discovered Pluto, many similar objects were discovered in the outer solar system, most notably the Trans-Neptunian object Eris which is slightly larger than Pluto. If we continue to treat Pluto as a Planet, it is bound to give room for more debates for including some more names in the list.
Pluto is very unlike its inner neighbors, the gas giants Uranus and Neptune. This thought led to the exclusion of Pluto from the refurbished Hayden Planetarium in New York City when it unveiled its spiral planet walk. This goes on to prove that Pluto's place in the list was being doubted for long.
We now know of thousands of small icy bodies in a zone called the Kuiper Belt and at least 100 of them are like Pluto. Studies are still on to look for many more.
The article states that 'there are two fundamentally different ways to define planets. One is to treat the planets as dynamically interacting ensemble with bodies that perturb each other gravitationally. This approach is what led to Pluto originally being considered as massive as the Earth-to account for the perturbations on Neptune and Uranus that were supposedly the basis of Percival Lowell's prediction of a trans-Neptunian planet. But as the decade rolled by, astronomers realized that apparent irregularities in the motions of the outer planets were attribution to an erroneous mass assigned to Neptune. Pluto, discovered by coincidence roughly where Lowell said it should be, is actually an irrelevant lightweight compared to the main family of planets.'
Pluto, Eris and others require to be studied and analyzed further, before we arrive