Why are all the planets everywhere round? Not oblong, not square, not triangular, but round?
Gravitational force. A sphere minimizes the ratio of the surface area to the volume.
Most planets (earth, included) are slightly oblong due to other planets, moons, suns, etc acting upon the planet.
Gravity pulls everything down into a rounded shape, for objects more massive than, say, 10% of earth’s mass, iirc.
Think of it as a giant spherical sucking machine, or vacuum cleaner, a very powerful one. Imagine what such a vacuum would do to a cloud of dust. The final clump of dust the vacuum cleaner created would be round, not having giant spiky tendrils of dust sticking out everywhere, because, if they even tried to form, they would be pulled down tight to the central mass, and wouldn’t stick out; it’d be a roundish ball of dust.
OTOH, something created by a less powerful vacuum cleaner, could be potato shaped, all lumpy, etc. Thus, planets are round. Asteroids, at least the smaller ones, have all kinds of shapes, potatoes, etc.
gravity pulls everything towards the center
if it is big enough, it forms a globe
Re “Why are all the planets everywhere round” and not “oblong, square, etc”.
Because their designer, GOD, is not a Democrat!!