Have you ever wondered why planets are shaped round? Why aren’t they shaped like pyramids, cubes, or discs? Well, if they were shaped like discs, it would surely be a paradise for flat earthers. 🤣😂 Jokes apart, let’s understand the reason why planets are spherical or oblate spheroid in shape.
When the solar system was formed, planets formed from the remnants of the protoplanetary disc that comprised of asteroids. These asteroids are large space rocks that bonded together to form the planets we see today. However, you may wonder, although each planet does not constitute just rocks but also gases, why do all elements bind together in the form of a sphere?
Why a Sphere?
Well, the simple answer is gravity. Around 4.5 to 5 billion years ago, space rocks from the protoplanetary disc that orbited around the Sun were the building blocks for planets. This protoplanetary disc was formed due to the aftermath of the birth of our star, the Sun. When large space rocks or space debris and gases bump on each other, they bind together to form large planet-size objects. Over a period of time, these large rocks gather enough mass to have gravity, the key force that holds elements together in space. Once the planet is big enough, it automatically begins to clear a path around the star it orbits.
Gravity works in one way; it pulls equally from all sides, specifically from the centre to the edges. When materials of large mass bind together, gravity starts acting on them in this manner, and they clump together to form a sphere. Whether it is just space rock or high-density gas and space debris, gravity acts in the same manner and pulls materials inward, giving them a spherical shape. Gravity holds planets together, it’s the universal glue.
Are all Planets a Perfect Sphere?
Not really; most planets are slightly bulged in the middle, similar to a basketball. For instance, our Earth is slightly flat at the poles but bulged along the equator, giving it the shape of an oblate spheroid. Some planets in our solar system, like Mercury and Venus, are the roundest among all, whereas others are thicker in the middle. For instance, Saturn and Jupiter are thicker in the middle.
Try this, soak a tennis ball in water and throw it in the air by giving it a little spin. What do you observe? The water on the ball would dissipate along the outer edges in a sprinkling manner. This is the same in the case of planets too, when large planets spin, materials on the outer edge move faster than the ones on the inside to keep up. This is because things along the edge have to travel the farthest and the fastest.
Saturn and Jupiter are large planets with a fast spin; this results in a large bulge along the middle like an extra width. This width is known as the equatorial bulge. Saturn is the planet that is thickest around the middle with a 10.7% bulge and Jupiter with a 6.9% bulge in our solar system.
Gravity, the binding force in the universe, always acts inward; that’s why all materials accumulate and bind together form as a sphere and not as a pyramid, cube, or disc. This law applies to not just the planets in our solar system but to all planets in the universe.
Space Age 