Question

Why pluto is not count in our solar system

Answer 1

Since its discovery in 1930, Pluto has been a bit of a puzzle:

It's smaller than any other planet -- even smaller than Earth's moon.
It's dense and rocky, like the terrestrial planets (Mercury, Venus, Earth and Mars). However, its nearest neighbors are the gaseous Jovian planets (Jupiter, Saturn, Uranus and Neptune). For this reason, many scientists believe that Pluto originated elsewhere in space and got caught in the sun's gravity. Some astronomers once theorized that Pluto used to be one of Neptune's moons.
Pluto's orbit is erratic. The planets in our solar system all orbit the sun in a relatively flat plane. Pluto, however, orbits the sun at a 17-degree angle to this plane. In addition, its orbit is exceptionally elliptical and crosses Neptune's orbit.
One of its moons, Charon, is about half Pluto's size. Some astronomers have recommended that the two objects be treated as a binary system rather than a planet and satellite.

Answer 2

Pluto is very small compared to the other planets.so it is considered as dwarf planet