Planets form into spherical shapes primarily due to the force of gravity, which pulls matter uniformly towards the center from all directions.
The natural shape of a sphere allows planets to minimize potential energy, leading gravity to mold them into this efficient, compact form.
Gravity's uniform pull from a planet's center ensures that any deviations from a spherical shape are corrected over time, resulting in a round form.
Planets and stars are large enough that gravity overcomes other forces, such as electromagnetic forces, leading to their spherical shapes.
While the force of gravity shapes planets into spheres, their rotation causes a slight bulging at the equator, making them oblate spheroids rather than perfect spheres.