Almost all planets in our Solar System are not perfect spheres; they are "flattened" at the poles due to their rotation speed. Venus and Mercury are the closest to being perfect spheres, while Jupiter is the most flattened with its wider equator compared to its polar diameter by 9276 km, given its fast rotation of just under 10 hours.

However, the dwarf planet Haumea showcases extreme deviations from a spherical shape. With an axial rotation period of only 4 hours, centrifugal forces have significantly stretched it in various directions, making its shape highly irregular compared to the more rounded planets in our Solar System.