Why are all planets mostly irregular in shape?
Not all planets are irregular in shape, but many of them do have non-spherical shapes. This is primarily due to the forces that act on them during their formation and evolution.
During the early stages of a planet's formation, a disk of gas and dust known as a protoplanetary disk surrounds a young star. As planetesimals and dust particles within this disk come together due to gravitational forces, they collide and accrete, forming planets. However, these collisions are often not perfectly symmetric, resulting in irregular shapes.
Additionally, the gravitational forces exerted by nearby objects, such as other planets or moons, can also influence a planet's shape. These gravitational interactions can cause tidal forces that deform the planet over time.
Moreover, the rotation of a planet can also play a role in shaping it. As a planet spins, it experiences centrifugal forces that can cause its equator to bulge and its poles to flatten, resulting in an overall oblate shape.
While irregularities in shape are common, some planets, like Earth, exhibit a close-to-spherical shape due to a combination of factors such as their distance from the Sun, gravity, and other celestial bodies.