Alkina: There must be some way to get around this thing!
Station: What’s that young scientist? You would like to know how the planets get round?
Alkina: That’s not what I said!
Station: Planets become spherical once their own gravity becomes the dominant force in shaping them.
Jakar: This station sure is a know-it-all.
Alkina: I know someone who would get along with it really well. Epo, how is that interface coming?
Epo: 60% complete.
Station: Aside from being spherical and orbiting a star, do you know what else a planetesimal must do to become a planet?
Alkina: It must clear its orbit, of course.
Station: Correct young scientist! My, you’ll make a fine scientist someday!
In human speak please!
You may have wondered why the planets were fairly spherical and not some other shape like a cube or cylinder, or even potato shaped like the asteroids. It’s all because of gravity. A planet’s gravity pulls all the mass in that planet towards a single point; the center of gravity. If a planet has a strong enough pull, the planet becomes roughly spherical around that center of gravity. Of course, it’s not a perfect sphere, or we would have not features like mountains and canyons.
Is that all?
Dwarf Planets – What Defines a Planet, Dwarf Planet or Plutoid?