PLUTO

                                                               

We all know that PLUTO was considered as the ninth planet of the solar system, but the theory changed and it is no longer considered as a planet of the solar system but a dwarf plant. To understand this we must know about a few terms. Whats is a planet?         

WHAT IS A PLANET?

A planet is a celestial body that 

(a) is in orbit around the sun

(b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round ) shape

(c) has cleared the neighbourhood around its orbit.

SELF-GRAVITY

Considering point 'b' Pluto have a respective mass of one-sixth times and one-third times of the volume od the moon. Due to which it possesses low self-gravity 

NEIGHBOURHOOD ORBIT 

its orbital path doesn't lie in the same plane as the eight planets, but it is inclined at an angle of 17 degrees. Its orbit is also more oval-shaped, or elliptical, than those planets. It means that sometimes Pluto is a lot near to the sun specially compared to Neptune. Pluto's orbit appearing to cross the orbit of the neptune when viewed from directly above. It means Neptune could alter pluto's orbit over millions of years so that a collision could be possible.