Topic: Gravity. Why are planets round? Because I commanded them. You wish. Planets are round because of the force of gravity. Gravity acts as if it originates from the center of a planet and pulls each point of the planet towards it. Hence, the only way for everything on the surface to be equally close to its center is to form a round shape. However, planets are not exactly round. They are roughly spherical. This is because planets spin on their axes. Just like a spinning top, right? Absolutely. When planets spin, things near the equator tend to move away from the center due to centrifugal force. Resulting in formation of an equatorial bulge. Because of this bulge, the equator of a planet becomes farther from its center than its poles. Creating a roughly spherical planet.