Shape of Celestial Body - Spherical or Irregular

There are two major factors on which shape of the celestial body depends:

Gravitation Pull: The shape of a body is determined by the interaction between its gravity and solidity. It is simple Newton’s law of Gravitation, whenever we have huge mass close enough, each particle start experiencing the gravitational force towards the centre. This gravitation pull is equal in all directions, which results into a spherical shape.  

Gravity of the significantly larger moons and planets is so strong; by contrast, that it turns these celestial bodies into spheres. That is reason almost all the stars and big planets are spherical.

Planet Mars; Image Credit: NASA

Celestial objects that are too small for gravity to pull them into spherical shape can have a variety of shapes. Small asteroids and comets have little gravity, which is insufficient to force their larger rocks into a spherical distribution.

Comet; Image Credit: NASA

Asteroids; Image Credit: NASA

Rotation of Celestial Body: The spin around their own axis - also plays an important role with regard to the shape of celestial bodies. Spinning bodies are oblate--larger along the equatorial than along the polar axes because of the centrifugal force. The Earth is not complete sphere but oblate, it is around 0.3% larger across the equator than from pole to pole.

Shape of a celestial body may also depend on the Tidal forces and internal motions.

Written By: DMR