Why Are Planets A Spherical Shape?

If you look around in our solar system and any other planet around, you might notice

that all plants are spheres. Perfect examples in our solar system, include Mars, Earth,

Mercury and Venus which are made out of rock and Jupiter, Saturn, Neptune and Uranus which

are made out of gasses. You'll notice that those eight planets in our solar system are

all spheres, so why it is that planets are spheres?

Well firstly the definition of a planet is something that "has sufficient mass for its

self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium

shape" -- which basically means it must be nearly round for it to be defined a planet.

So why are planets spheres in the first place? Planets are spherical shapes due to gravity.

The gravity on earth and other planets are trying to pull everything to the enter of

its mass and for the particles to be a equidistance from each other the planet must turn into

a sphere, as all outside points on a sphere are roughly the same distance away from the

centre. I say roughly because plants aren't complete spheres, with earth not even being

a complete sphere due to earth rotating on its axis which means earth is an oblate spheroid.

In our solar system Saturn has the biggest equatorial bulge at 11,808 km, while earth's

is 42.72 km.

Things such as asteroids aren't spheres because their gravitational pull is too weak to turn

the asteroid into a sphere. This means that because the gravitational pull is so weak,

things like asteroids can be all sorts of shapes.

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