## Why is Earth round?

If you look at our Solar system you will see that the planets made up of rocks, gas with rings without them some are small in size while others are big. But one thing is common is that they all are round shaped. Why that and what is the reason behind their round shape? When do we call a celestial body a planet? According to IAU for a celestial body to be called a Planet it needs to fulfill three essential criteria. First the object should revolve around the sun. Second the object should be spherical. And thirdly the area around its orbit should be clear and should not have any equivalent or a bigger celestial body that is with the help of its gravity the planet should clear asteroid and dwarf planets out of its way.

So, the point number 2 clearly states that the planet needs to be round or spherical. Most things we see are round or pretty close to it including asteroids. So, what’s going here? Earth and other planets are round because of the force of gravity that pulls equally from all sides. Gravity pulls from the center to the edges like the spokes of a bicycle wheel. This makes the overall shape of a planet round which is a three dimensional circle. But, planets are not exactly round but roughly spherical or oblate spheroids. If noticed carefully you will see that the equatorial diameter of the Earth is about 43 km larger than the polar diameter. This is because just like a spinning top our Earth spins on its axis with the speed of 1674.4 km/hr. And this much velocity causes the planet to bulge near the equator due to Centrifugal force as things near it tend to move away like the mud flying off a tire.

And it’s not just the Earth but Saturn bulges the most of all the planets in our solar system. If you compare the diameter from pole to pole to the diameter along the equator it’s not the same. Saturn is 10.7% thicker around the middle, while the Jupiter is 6.9% thicker around the middle. So, instead of being round like marbles, they are like basketballs squished down while someone sits on them.

Did you know, Earth and Mars are small and don’t spin around as fast as the gas giants like Jupiter, Saturn, Uranus and Neptune? Also Jupiter is also known as the fastest spinning planet in our solar system.