Question

Should Pluto be classified as a planet or not? If so, why, and would this open the classification of many objects in our solar system? If Pluto is not a planet, why not? explain briefly.

Answer 1

Pluto should not be classified as a planet. Because Pluto could not satisfy the criteria to considered as a planet. International Astronomical Union (IAU) is the authority for naming and designating the celestial bodies such as stars, planets, etc. According to IAU, there are three criteria that a full-sized planet should satisfy. They are:

1. It should be in an orbit around the star (in our solar system, star is 'Sun').
2. It should have an adequate mass for self-gravity and assumes a hydrostatic equilibrium shape.
3. It should clear its neighbourhood around its orbit.

Pluto has fulfilled criteria one and two but failed to meet the third criterion. 'Clearing the neighbourhood' means that the planet is gravitationally dominant and there should not be any other bodies of comparable size other than its own satellites in orbital zone. But it is identified that there exists a region similar to asteroid belt beyond the orbit of Neptune called 'Kuiper belt' and the celestial bodies in the Kuiper belt has comparable size with Pluto. This discovery led to the conclusion that the Pluto could not clear its neighbourhood and so IAU changed its status from Planet to 'Dwarf Planet'. Dwarf planet is a category of celestial bodies which satisfied only the first two of above mentioned criteria.