Many of us got emotional when we heard the news that Pluto is no more going to be called a Planet.

These used to be 9 planets but now only 8. But, why exactly Pluto was removed from the list of planets! Let us see.

The International Astronomical Union (IAU) has three criteria for a body to be defined as a full-sized planet. These 3 criteria are:

1.      It needs to be in orbit around the Sun – Yes, true for Pluto- check

2.      It needs to have enough gravity to pull itself into a spherical shape – Yes, true again for Pluto- check

3.      It needs to have “cleared the neighborhood” of its orbit – Uh oh. Here’s the rule breaker- Uncheck

According to this 3^rd point, Pluto is not a planet.

What does “cleared its neighborhood” mean? As planets form, they become the dominant gravitational body in their orbit in the Solar System. As they interact with other, smaller objects, they either consume them, or sling them away with their gravity. Pluto is only 0.07 times the mass of the other objects in its orbit. The Earth, in comparison, has 1.7 million times the mass of the other objects in its orbit.