Planets

[Henryn]

Why are planets always round?

[incitatus]

Gravity. Smaller objects (asteroids) are irregular in shape bacause the net effect of their gravity is not stong enough to deform them. As objects get larger the effect of gravity intensifies, and the moment of gravitational force comes from a notional centre of gravity, meaning that the equigrav is spherical. In point of fact planets are not true spheres, but oblate, as the spin tends to make them bulge at the equator.