Why Spherical?

[Sasperilla]

This is probably going to sound really stupid to all you scientists / astrophysicists out there but it does puzzle me. Why are all the planets, moons etc. perfect spheres rather than just jaggedy lumps of rock?

[fo3nix]

They aren't perfect spheres.

But I suppose, many of them are close.

A few reasons though.

1) Gravity: it pulls everything together, in an anisotropic way. This means that it doesn't really depend on direction. A simple 3D shape that's the same in all directions is a sphere.

2) Hits from far smaller objects. If you took a big, odd-shaped rock, and threw lots of little stones at it for a long time, with the rock randomly moving about and spinning round, the stones will serve to gradually erode the sharper edges away.

3) Lowest energy configuration. All things like to be at the lowest energy they can be. Hot things go cold to reduce their energy, etc. A low-energy shape is a sphere. It's why rain drops are spherical. And why planets are spherical too -- it's easier to be this way than to be a cube, for example.

[Clanad]

While I certainly don't disagree with the previous, one has to realize that most, if not all asteroids are not spherical or anything approaching sphereicity ...Many asteroids are thought to be billions of years old (the universe being an estimated 13 to 14 billion years old (<i,bya) and still retain their odd shapes. Of the forces at play in the universe, the force of gravity is one of the weakest...and when objects have lower masses, such as that of an asteroid, there is not enough self created gravity for the pressure and the gravity to become balanced, so it never forms into a sphere, and instead they are very oddly shaped. Because gravity is a weak force, objects have to be very massive in order to obtain hydrostatic equilibrium producing sphereicity . Asteroids simply don't have enough matter to have a large enough gravitational pull.
Newton tells us that you, for example, have a gravitational attraction to other objects... weigh yourself in pounds, multiply it by 2.2 to get it in kilograms, and then multiple that by .000000000066726, which is your gravitational force in Newtons. (Thanks to Natural History)

I strongly suspect that you are not round either, perhaps a litle rotund, but not round, no?