There is no doubt that most celestial bodies are spherical because of gravity. The obvious evidence is that asteroids and comets are not necessarily spherical because their mass is not in a certain order of magnitude. Once it reaches a certain level, its substance will inevitably collapse to the center of gravity under the action of gravity. In the hundreds of millions of years after the Big Bang, neutron protons began to combine to form nuclei, and electrons and nuclei together formed complete atoms. Atoms form molecules through chemical bonds, and then form macroscopic dust.

When the cosmic dust gets closer and closer under the action of gravity, it will combine to form gas, liquid and even rock. These newly formed macroscopic objects are further compressed under the action of gravity to form celestial bodies. The heavier sky will form stars and start nuclear fusion in the center. Planets have a small mass when they are formed. Whether it is a star or a planet, matter will be squeezed by gravity, which can keep the surface area of matter as small as possible, so that celestial bodies can naturally form spheres.

In fact, this is also a very simple math problem. For a given volume, the surface area of the ball is the smallest! Let's assume a rocky planet (Earth). Suppose that the rocky planet initially has a mountain height with a destructive spherical appearance (the mountain height exceeds one-fifth of the diameter of the planet). As we all know, the pressure at the foot of the mountain is p = ρ g h, ρ is the density of the mountain, g is the gravitational acceleration of the planet, and h is the height of the mountain.

At present, G is called the gravitational constant, the average density ρ, the radius r, g = GM/R 2 = 4π/3G P R. Since the density ρ is relatively stable, we assume that ρ is a constant. Therefore, the pressure at the bottom of the mountain is p = 4 π/3 g ρ 2 r h. In order to understand 4 π/3 g ρ 2 as a constant, we can temporarily ignore it. Therefore, the pressure limit that the foot of the mountain can bear is certain. We found that the height h of the mountain is proportional to 1/R, and the larger the object, the lower the mountain. This also means that if the radius r is small enough, H will be close to R, thus giving the maximum size of an irregularly shaped object.