Why the Planets are Round

Before explorers began sailing around the world, many people thought that the Earth was flat. Even scientists were ridiculed or killed because this, despite the fact that when looking up into the night’s sky, the round moon could be seen on numerous occasions. When the telescope was invented, however, it was confirmed that the planets, like the moon, were round. So, why are the planets round? Natural forces of the universe act on matter making up the plants.

We all learn about the earth’s gravity at some point in our educational careers; we are taught that it is the force that holds us on the ground and keeps us from floating into the atmosphere. In many science classes taught around the world, children initially learn that the Earth is the only planet with gravitational pull on the surface. Later, students are taught that gravity is not unique to our planet. In fact, the order in the universe is directly related to how gravity affects heavenly bodies. What does gravity have to do with why planets appear round?

The gravitational field of the planets places enormous pressure on their surfaces, pulling them toward their cores. Planets begin acting like viscous fluids because of their large sizes and internal radioactive heating systems; therefore, Scientific American states that they yield to this “gravitational pull from their center of gravity.” Nevertheless, this pull causes a spherical shape to form, which is why it seems as if a sphere is the ideal shape of a planet. A sphere, however, is not a perfect circle and depend on the shape and size of the planet as well as its rotational speed.

The planet forms a sphere in order to draw all of their mass to the center of gravity, a process known as isostatic adjustment. Sphere material moves close to the center without bumping into other material. This process is unique to larger heavenly bodies and does not occur in smaller objects in space, such as asteroids of less than 500 kilometers in diameter. That is why asteroids are odd, rocklike shapes floating through space.

Ironically, the strong gravitational pull seems counterintuitive when many planets, like Earth, have a variety of surface area types from high mountains to low valleys. It would seem logical to believe that every area should be smooth. So, what accounts for the combination of flat and lumpy land, such as mountains and hills? In actuality, gravity exerts itself on even the tallest mountains, keeping them within the atmosphere of the planets on which they are located. It’s amazing that, although gravity is an unseen force, it is stronger than solid rock.

So, next time you see a picture of any of the planets, remember that wonderful and strange force that makes them appear as they do to our eyes.


Live Science

Scientific American

UCSB Science Line