Why do planets generally form into spheres?

Question

It seems that, at least in our solar system, planets form into mostly spherical shapes. Why is it that asteroids and most space rocks are not spherical?

Answer 1

A sphere is the most compact form that a mass can take, and the driving force for compaction is gravity. The gravity of the mass must overcome the internal friction of the mass in order to deform it.

Asteroids are so small in mass that their gravity is not enough to overcome the resistance to deformation, so they tend not to be spherical.

Answer 2

Gravity creates a spherical wave. Einstein explained gravity this way, as opposed to gravity acting as a "force" pulling things in. When enough gravity is present such as in massive objects like planets, the gravitational energy associated with their mass creats a spherical wave emanating outward from the center point of the planet. The object you are observing (the planet, sun or moon) is simply the physical expression of that spherical wave. Outside the physical dimensions of the planet you can't "see" it but it is still there affecting anything that comes within it's reach.

Answer 3

Planets generally form into spheres because when their mass collects together it curves the space around them. Time and space is like a four dimensional potter's wheel.

Asteroids are usually rocks that have broken off of some other planet. Many people believe that our moon was once another planet that collided with our earth. The collision caused much debris in our solar system and that debris gathered together in what is collectively known as the asteroid belt.

Answer 4

Because gravity pulls everything in to the middle, and with a circle all the sides are the same distance away from the middle.

Asteroids aren't circles because a planet has already formed into a sphere when molten then set solid. And then something hits it and a lump of any shape comes off and because its already set it doesn't change into a sphere.

Answer 5

Anything with the gravity of a planet has enough gravitation to force it's features to the lowest possible energy state which is a sphere. I can't imaging the earth with corners. The asteroids etc don't have strong enough gravity to do that and many of them can be results of collisions which makes them pieces of rubble

Answer 6

Gravitational forces in massive bodies overpower structural resistance of common materials, so that it behaves like a plastic or even a liquid, and "settles" into a ball, which is the shape of minimum gravitational potential. In other words, it can't get any more setlted than that.

For smaller space objects, like asteriods and rocks, they aren't massive enough for gravity to overcome the structural strength of the materials that make up them.

As an analogy, when the ancient Egyptians built pyramids, they found it easy to erect small ones with steep slopes. But when they tried building larger ones, they ran into trouble with pyramids collapsing disastrously during construction. They eventually learned to build pyramids with more moderate slopes as they went larger.

Answer 7

Well... The current theory on space is this: It is not endless. If you were to get in a spaceship and travel as fast as possible in one direction, eventually you would end up back where you started. That being said, we can assume that we are not on a huge planet, like in Men in Black, because when we look with our telescopes out beyond the quasars, there is nothing there.

Answer 8

The deffinition of a planet is that it has to be large enough for it's gravity to crush it into a sphere.

Answer 9

Gravity shaped them at the birth of the our star(sun). The rocks and such floating around are pieces that where broken off.