Because it crosses paths with Neptune.
It is the 2nd largest. Ceres is the smallest Dwarf planet. Eris is the largest.
A Dwarf Planet
Pluto's orbital is elliptical. Its farthest planet from sun when it lies on two elliptical end. On the other hand Neptune's orbital is circular and become larger then Pluto's orbit when Pluto come in the middle of two elliptical end. For this reason Pluto is not always farthest planet from sun.
The IAU no longer regards Pluto as a planet so Neptunewill forever be our 8th planet even when it is farther from the sun than Pluto. However it will be another 230 years before Neptune is farther from the Sun than Pluto
Pluto was known as the last planet of our solar system as from when Clyde Tombaugh discovered it
Pluto
It is the 2nd largest. Ceres is the smallest Dwarf planet. Eris is the largest.
A Dwarf Planet
In order to be considered a planet, Pluto would have to clear its orbital path of debris. Pluto is not large enough to do this, so it was reclassified as a dwarf planet.
Pluto, it is now a dwarf planet or planetoid.
Pluto's orbital is elliptical. Its farthest planet from sun when it lies on two elliptical end. On the other hand Neptune's orbital is circular and become larger then Pluto's orbit when Pluto come in the middle of two elliptical end. For this reason Pluto is not always farthest planet from sun.
Since Pluto is no longer considered a planet, mercury has become the smallest planet.
Pluto may become a major planet again in a few million years, if it clears it's orbit of asteroids and other debris.
Pluto is not a planet its a dwarf planet
neptuneNeptune is the closest to Pluto. Uranus is the second closest planet to Pluto. Saturn is the third closest planet to Pluto. Jupiter is the forth closest planet to Pluto. Mars is the fifth closest planet to Pluto. Earth is the sixth closest planet to Pluto. Venus is the seventh closest planet to Pluto. Mercury is the most furthest away from Pluto. The Sun and the moon are not considered as planets. The planet Pluto is also not considered as a planet.
The IAU arrived at a new definition for "planet" which left Pluto out in the cold. It is now designated as a "Dwarf Planet". also it was called a planet when is was larger but now it has become smaller scientists no longer class it as a planet
Pluto is a rocky world. Pluto is now reclassified as a dwarf planet.