Q Why are the Sun, the planets and their moons all spherical in shape? – Lionel
A Wait, what? The Earth is actually flat, haven’t you heard?
Kidding! We’ve actually known that the Earth is round for at least 2000 years, thanks to the ancient Greeks. In fact, the vast majority of objects in our solar system are spherical, from the Sun to planets to moons.
So why are planets spherical? Why don’t we live on a cylindrical or cube-shaped planet?
The main culprit is gravity. Every object in the universe with mass exerts a gravitational pull, which tugs towards the object’s centre of mass.
For a planet, everything is pulled towards its centre – that’s why things hit the ground when you drop them, and why you land back on Earth when you jump. When the Earth formed 4.6 billion years ago, it was composed of molten material that gravity pulled into a spherical shape, which solidified as the planet cooled.
Some objects in the solar system are too small to be forced into spherical shapes – Mars’ moons, for example, are potato-shaped, and asteroids are mostly irregular.
But not even the planets
