In the era where astronomers were in search of new planets within
the solar system, Clyde W. Tombaugh discovered a distant planet in the year
1930, which eventually got the name Pluto. An Oxford school girl gave the name
“Pluto” and it ideally suits the isolated planet. For decades, it was announced
and approved that the solar system consisted of nine  planets. However, with
the increase in power and technology in space observatories new confusions
started to arise.
After many decades, it is found out that Pluto is not the only mass
object floating in its region. There are numerous other objects some of them
which are nearly 80% of the size of Pluto. Therefore, scientists and astronomers
named the region as Kuiper Belt. More proof came to suggest that Pluto is just
another object of the Belt and it is not a planet. There are similar objects in
the region namely Eris, Ceres, etc. This led to the objections that Pluto
cannot be a planet.
What is the definition of a planet?
In the year 2006, the International Astronomical Union had a general
assembly to determine the fate of Pluto as a planet. Many ideas have come up
and many definitions of planet came to the forefront.
IAU considered the best definition possible to describe a planet
i.e. a planet should have a specific orbit around the sun with powerful gravity
so to maintain a spherical shape and with the capability of clearing the
neighborhood of the orbit in which the revolution takes place.
Pluto had a specific orbit and gravity that made it a spherical
object; however, it did not fulfil the last criterion i.e. clearing the
neighborhood. Pluto’s gravitational force is not strong enough to clear the
objects of Kuiper Belt of its orbit. Therefore, Pluto has been regarded as a “Dwarf Planet”
and excluded from the list of nine planets in the solar system.
So, our solar system has only eight  planets contrary to the
childhood education received. However, there is great chance that there are
still objects that could qualify as planets thus increasing the number of
planets in the solar system.