Why are all the planets so regularly shaped...?

Question

like the earth is an oval, etc. or do all the documentaries show the planets regularly shaped for the sake of simplicity?

Answer 1

A sphere is the shape that encloses the greatest volume with the smallest surface area. The planets (and the Sun) were formed by gravity pulling the material as close together as possible, so naturally the shape formed was a sphere. Now, since the Earth (and the other planets - and the Sun) rotate, the centrifugal force set up at their equators tends to bulge the surface out. At their poles there is no angular rotation and no centrifugal force. The planets (and the Sun) are thus not absolutely spherical, they bulge slightly at their equators. This shape is called an "oblate spheroid".

Answer 2

Consider a steep mountainside. Let α be the angle between the slope of the mountain and the radius to the center of gravity of the planet. Then the gravitational force tending to hold a particle, rock, or boulder in place on the mountain will be Wsinα, and the force trying to move the particle, rock, or boulder down the slope will be Wcosα.
The steeper the slope, the smaller the angle α. As α→0 Wsinα→0 and Wcosα→W. When Wcosα exceeds μWsinα the object starts moving down-slope, and continues until it reaches the bottom or encounters some obstacle. On the other hand, when α→90°, Wsinα→W and Wcosα→0, but when α = 90° you have a spherical surface.

Of course it takes eons for rock to erode, and other processes result in other upthrusts, but the smoothing process is inexorable. At interplanetary distances the surface variations are nearly negligible compared to the planetary radii.

Answer 3

A sphere is the most economical shape in the universe.
It has sod all to do with weathering, erosion, or ellipses.
Some planets (like the Earth,) are very, (very, very) slightly elliptical because of their spin.
The Earth is, to all intents and purposes, a sphere, as all true planets are.

Answer 4

The idea was that molten rock was thrown off of the sun after the big bang. The additional energy caused the masses to spin, which in zero gravity environments will force them into an elliptical shape. This is the reason that all planets (solid or made of gas) is elliptical in shape.

Answer 5

Conservation of Momentum: http://www.a2dvoices.com/realitycheck/Coriolis/

Answer 6

The simple answer is that it's all due to time, gravity and the forces involved in rotation.